seeds
"Seeds might seem still, quiet, passive. But in them all is a forceful
dynamism not to be underestimated."
- Jennifer Jewell
dynamism not to be underestimated."
- Jennifer Jewell
introduction
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Botanically speaking, a seed is a plant embryo and food reserve enclosed in a protective outer covering. The seeds produced by plant species are as unique as the plants themselves, and have differing qualities in regards to shape, size, color, makeup, and germination requirements. Seeds are relatively small in size compared to other plant parts, but are well-suited to handle many environmental stressors. Seeds hold the key to the continuance of most plant species in the world, making them some of the most important living (albeit dormant) beings on the planet. Carpology is the study and science of seeds and their dispersal methods.
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Quick Question: Which Came First, the Plant or the Seed?
The first land plants, which resembled the modern-day liverworts (simple moss-like plants) reproduced using spores, as most aquatic plants do. Spores contain a single cell, whereas seeds contain multi-cellular embryos protected by a tough seed coat. These extra features took a long time (about 150 million years) to evolve. So, in short, the plant came first because the first plants had to evolutionarily develop the ability to produce seeds. The gymnosperms (the first true seed-producing plants) evolved between 416 and 358 million years ago, and produce 'naked' seeds, or seeds without coverings. Angiosperms, or flowering plants, evolved later on, and produce seeds inside of protective structures.
The first land plants, which resembled the modern-day liverworts (simple moss-like plants) reproduced using spores, as most aquatic plants do. Spores contain a single cell, whereas seeds contain multi-cellular embryos protected by a tough seed coat. These extra features took a long time (about 150 million years) to evolve. So, in short, the plant came first because the first plants had to evolutionarily develop the ability to produce seeds. The gymnosperms (the first true seed-producing plants) evolved between 416 and 358 million years ago, and produce 'naked' seeds, or seeds without coverings. Angiosperms, or flowering plants, evolved later on, and produce seeds inside of protective structures.
seed makeup
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Seed-producing plants (also known as spermatophytes) make up the largest group of plants in the world, and include angiosperms and gymnosperms. Sexual reproduction in seed-producing plants begins with pollen reaching female cones (in gymnosperms) or flowers (in angiosperms). A pollen tube is then formed, extending into the ovule, which eventually matures into a viable seed. In gymnosperms, seeds develop atop cone scales, and in angiosperms, seeds develop inside a structure that provides sustenance for the growing embryo (the endosperm).
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Seeds, once they are disseminated from the parent plant, consist of a miniature undeveloped plant (the embryo) and a protective coat called a testa. The embryo, or fertilized ovule, inside the seed is the part of the seed that will grow into a new plant. This embryo develops to a certain point through a process known as embryogenesis, and then enters a dormant stage, in which the seed cannot develop further until certain environmental or temporal conditions are met. Within seeds, the store of nutrients to be used by the developing embryo is called the endosperm. This material is rich in oil or starch and protein. The coating, or testa, on the exterior of seeds can be paper thin or more substantial, and can also be fleshy. Seed coats help to protect the developing embryo from mechanical injury, predators, and drying out.
Dormancy and Germination
Seed germination will begin when certain conditions are met, and only then. To be viable, seeds must have a mature embryo, contain a large enough endosperm to sustain the embryo, and have sufficient hormones to trigger the growth process. In general, germination rates for most species is between 65% and 80%, meaning that a great number of seeds do not get a chance to become fully-grown plants. There are four main factors that affect germination.
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Water
The first step to germination for most seeds is the absorption of water. Due to the nature of the seed coat, most seeds have great absorption power. The most critical ingredient in the germination process is moisture. If there is no moisture in the substrate surrounding a seed, it will not germinate. Once water is present and the germination process has begun, a dry period can cause the death of an embryo. |
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Light
The quantity of light available to seeds can stimulate or inhibit growth. Some plants are more sensitive to light than others. For example, the seeds of some species do well on the surface of soil, and others do better when covered by soil. Starting seeds indoors requires fluorescent light fixtures or placement in a south-facing window to assist germination. |
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Oxygen All viable seeds respirate, for which oxygen is required. Respiration rates increase during germination, and the substrate in which the seeds are placed should therefore be loose and well-aerated. If the oxygen supply during this time is limited or reduced, germination can be severely retarded or inhibited. |
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Temperature
Favorable temperatures are another aspect of seed germination. The seeds of some species are pickier than others about the required temperature range, and many seeds have minimum, maximum, and ideal temperatures at which germination can occur. Generally, somewhere between 65 and 75 degrees Fahrenheit is best for most plants, and these temperatures must stay relatively stable throughout the 24-hour day. |
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Dormancy serves to prevent a seed from germinating unless these varying requirements are met, assuring that a plant will not grow where it will not survive. In some plants, dormancy is particularly difficult to break, even when the environment is otherwise ideal. Various treatments are performed on seeds to assist dormancy breakage, falling into the categories of either scarification or stratification.
Scarification
This process involves damaging the seed so that water can enter and begin the germination process. Seeds are carefully broken, scratched, or softened during this process through chemical or mechanical means. There are a few main ways that seeds are scarified prior to sowing.
This process involves damaging the seed so that water can enter and begin the germination process. Seeds are carefully broken, scratched, or softened during this process through chemical or mechanical means. There are a few main ways that seeds are scarified prior to sowing.
Scarification using sandpaper.
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Warm water soak.
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Chemical scarification.
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Scarification with sandpaper is a method of mechanical scarification in which part of the seed is repeatedly rubbed against a sheet of sandpaper to damage the seed coat. Seeds can also be filed with a metal file or cracked with a hammer (only for the hardest seeds) to allow moisture to enter the seed. Alternatively, seeds can have their coats softened through prolonged exposure to warm water or a chemical bath. In the first technique, seeds are placed in a bowl or other container and hot water (about 170 to 212 degrees Fahrenheit) is poured over them. The seeds then soak in the water as it cools for 12 to 24 hours. Chemical scarification involves placing seeds in a glass container and adding concentrated sulfuric acid to the container until they are covered. Seeds are gently stirred and allowed to soak for between 10 minutes and a few hours, and are then removed and rinsed.
Stratification
Seed stratification refers to exposing seeds to cool temperatures for an extended period of time to mimic the natural environment in which they germinate. Seeds of some fall-ripening trees and shrubs in temperate zones will flat out refuse to germinate unless chilled. Stratification, also called 'after ripening', involves placing sand, vermiculite, or a special mix of substrates in a container or sealable plastic bag and wetting the medium thoroughly, allowing excess water to drain off completely. The seeds are then placed in the container and covered with more substrate. Cool temperatures are attained through placement in a refrigerator or other cool, controlled environment. The ideal temperature range for successful cold-stratification is between 35 and 45 degrees Fahrenheit. After about 10 to 12 weeks (for most seeds, though this timing varies greatly in some situations), seeds can be removed and sown. Sometimes, seeds are planted within the stratification medium inside of a nursery pot, which is then placed in a plastic bag in the refrigerator. Once the seeds are removed from the refrigerator, they do not need to be replanted; the container simply needs to be placed in an area where the seeds will germinate.
Seed stratification refers to exposing seeds to cool temperatures for an extended period of time to mimic the natural environment in which they germinate. Seeds of some fall-ripening trees and shrubs in temperate zones will flat out refuse to germinate unless chilled. Stratification, also called 'after ripening', involves placing sand, vermiculite, or a special mix of substrates in a container or sealable plastic bag and wetting the medium thoroughly, allowing excess water to drain off completely. The seeds are then placed in the container and covered with more substrate. Cool temperatures are attained through placement in a refrigerator or other cool, controlled environment. The ideal temperature range for successful cold-stratification is between 35 and 45 degrees Fahrenheit. After about 10 to 12 weeks (for most seeds, though this timing varies greatly in some situations), seeds can be removed and sown. Sometimes, seeds are planted within the stratification medium inside of a nursery pot, which is then placed in a plastic bag in the refrigerator. Once the seeds are removed from the refrigerator, they do not need to be replanted; the container simply needs to be placed in an area where the seeds will germinate.
Seeds are commonly cold-stratified in refrigerators.
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Various media that can be used for cold stratification.
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Seedlings may begin to sprout while undergoing cold-stratification .
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Another similar procedure that works well for cold stratifying seeds is to use sphagnum moss or peat moss. The moss is wetted thoroughly and then excess water is squeezed out. It is then placed inside of a plastic sealable bag and seeds are mixed in, and the bag is placed in a refrigerator or similarly cool space and left for 10 to 12 weeks. Moisture needs to be maintained during this time. Adding moisture is not always necessary; a good way to check for moisture is to see if there is condensation on the interior of the bag. After the stratification period has passed, the bag is removed from the refrigerator, seeds are carefully removed, and then they are planted in their growing medium.
Each species has its own unique requirements for dormancy to be broken and germination to occur. From temperature fluctuations to soil variables to moisture requirements, it is no wonder why germination rates vary so widely from year to year and species to species. It is a horticulturalist's job to promote successful germination by controlling the seed environment as much as possible and providing the ideal materials required.
From Seed to Seedling
The most important step in starting seeds is ensuring that all materials are available from the start, and that the right materials are used throughout the process, depending on the conditions and planting situation. The two most important seed-starting materials are substrates (or planting media) and containers. A wide range of materials can be used as substrate, from pre-mixed seed starting soil purchased at garden centers to home-made substrates fine-tuned for each seed species. The 'right' substrate depends on the type of seed being sown, but in general, good substrates for seed germination are light, aerated, well-draining, and uniform. The planting medium should be free of insects and their eggs, any diseases or fungi, and weed seeds. The soil should not be overly fertile and also capable of holding moisture. A solid, basic home-made seed starting mixture is 1/3 sterilized soil, 1/3 sand/vermiculite/perlite, and 1/3 peat moss. Garden soil on its own is not an ideal substrate for starting seeds; it tends to be unsterile, too fertile, and does not drain quickly enough.
Seed starting mix (left) and regular potting soil (right). The seed mix is more uniform, lighter, and contains more perlite than normal potting soil.
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Peat moss is a product made from decomposing materials found in bogs and other wetland areas.
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Seed starting mix must be light enough to support healthy growth and have good drainage.
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Choosing the correct container is critical to successfully germinating as many seeds as possible. Flats and trays are commonly used for germinating seeds, and can be purchased from garden centers or online with or without covers. Seed starting trays are simple to make, as well, using recycled household containers like pie pans, milk jugs, or large household cleaner containers. These materials will need to have holes punched in their bottoms to allow for adequate drainage. There are many companies that have developed trays made of recycled materials like newspaper and scrap lumber, as well. A convenient size for germination trays is between 12 and 18 inches long, 12 inches wide, with a depth of 2 inches. A few things to look for in a good seed starting tray include:
Cell Size
The purpose of seed starting is to allow plants to grow as much as possible before being planted out in the garden. The larger the cell size, the better. Generally, trays with more cells have a smaller cell size than those with less cells. |
Tray Size
The tray chosen should be able to securely fit in a space that will be undisturbed as seeds germinate. The ideal area should have adequate lighting for germination. |
Drainage
The key to healthy seedlings is keeping a moist but well-draining substrate for them to thrive in. Trays need to have drainage holes in the bottom to allow excess moisture to exit. If there is a tray underneath the seed starting flat, it will need emptying regularly. |
One of the most important requirements of any container used to germinate seeds is that it be clean; this lessens the chances that damping off will occur. This issue is caused by fungus or mold, and can wipe out sections of sown seeds or even entire trays of seedlings. Cleaning trays helps to prevent damping off, and can be achieved by following a few simple steps:
- After trays have been used, shake out residual soil. If soil is dried on, the trays may need to be soaked in water and then wiped out.
- Scrub containers and any water catchment trays with warm, soapy water. Dish soap works well, or a biodegradable cleaning concentrate like Simple Green.
- As an added precaution, a 3% hydrogen solution can be used as a final wipe down. This will sterilize the trays and prevent mold and mildew from building up.
Pregerminated Seeds
Sometimes, horticulturalists will sprout seeds before sowing them. This reduces the time to germination, as temperatures and moisture are easy to control throughout the process. A higher percentage of germination is achieved due to optimal environmental factors. To complete this process, lay seeds between the folds of a cotton cloth or on top of a layer of vermiculite in a shallow pan. Keep the cloth or container in a warm place and ensure that it stays moist. When roots begin to show, pull the seeds and place them in growing trays or directly into the garden. While transplanting, make sure not to break off any of the tender roots. There are some companies that sell pregerminated seeds, though this method is not as popular due to the short shelf life of pregerminated seeds (about a month) and increased cost, but it is a convenient way to ensure a higher production rate for the seeds being sown.
Sometimes, horticulturalists will sprout seeds before sowing them. This reduces the time to germination, as temperatures and moisture are easy to control throughout the process. A higher percentage of germination is achieved due to optimal environmental factors. To complete this process, lay seeds between the folds of a cotton cloth or on top of a layer of vermiculite in a shallow pan. Keep the cloth or container in a warm place and ensure that it stays moist. When roots begin to show, pull the seeds and place them in growing trays or directly into the garden. While transplanting, make sure not to break off any of the tender roots. There are some companies that sell pregerminated seeds, though this method is not as popular due to the short shelf life of pregerminated seeds (about a month) and increased cost, but it is a convenient way to ensure a higher production rate for the seeds being sown.
Sowing Seeds
As with most aspects of gardening, the ideal time to sow seeds depends on the species. Generally, this planting time is expressed in terms of weeks prior to transplanting and typically varies from 4 to 12 weeks. Planting time information can be found on seed packets and through online sources like local Master Gardener programs. The idea behind this system is that seedlings should not be set out before the last frost of springtime has passed to avoid losing them (frost will kill most tender seedlings). There are many online resources that have data on frost dates for various locations, including a handy one run by the National Gardening Association. A common mistake made in the early steps of growing from seed is sowing them too early. This leads to the seedlings being held back at a point when they should be putting on growth outdoors, and usually results in tall, weak, spindly plants that don't end up doing well in the garden. Planning out and marking down sowing dates ahead of time ensures a more straightforward process.
As with most aspects of gardening, the ideal time to sow seeds depends on the species. Generally, this planting time is expressed in terms of weeks prior to transplanting and typically varies from 4 to 12 weeks. Planting time information can be found on seed packets and through online sources like local Master Gardener programs. The idea behind this system is that seedlings should not be set out before the last frost of springtime has passed to avoid losing them (frost will kill most tender seedlings). There are many online resources that have data on frost dates for various locations, including a handy one run by the National Gardening Association. A common mistake made in the early steps of growing from seed is sowing them too early. This leads to the seedlings being held back at a point when they should be putting on growth outdoors, and usually results in tall, weak, spindly plants that don't end up doing well in the garden. Planning out and marking down sowing dates ahead of time ensures a more straightforward process.
Once the sowing date comes around, prepare the seed tray. If you haven't already, mix your substrate together and fill all cells evenly, without pressing down the soil too much. Aeration is key to seed germination. Fill to within 3/4 inch from the top of the container. For large and medium-sized seeds, a hole should be made in the middle of each cell in the substrate with a pencil. Drop a seed in each hole. More than one seed can be sown in each cell if desired, and those that sprout can be thinned later on so that the hardiest seedlings are chosen from the bunch. The number of seeds sown per cell depends on the germination rate of the seeds being planted. For seeds with a germination rate of 40% or below, sow three seeds per cell. For germination rates of between 40% and 80%, sow two seeds per cell. For germination rates of 80% or over (or for pregerminated seeds), one seed per cell can be sown. Hole depth varies depending on the size of the seed; the general rule is to plant a seed at a depth equal to 2-3 times its width. Fill in the holes with dirt and then water in the seeds, ensuring that good drainage is occurring. For small seeds, simply drop them on the surface of each cell and then lightly cover them with a layer of substrate. Water in smaller seeds using a spray bottle instead of a heavier stream of water, which can dislodge them from their placements in the cell.
Holes should be made for medium to large-sized seeds.
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Smaller seeds can be placed on top of soil and be covered with a light dusting of substrate.
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Small seeds and delicate seedlings should be watered using a spray bottle.
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Starting seeds in an indoor, controlled environment certainly has its benefits, including providing more predictable results and earlier blooms (and therefore, somewhat earlier harvests). Plants that are typically transplanted include peppers and tomatoes, because they take a bit longer than others to reach a productive stage, and growing them from seed indoors gives them a jump-start. Seeds can alternatively be planted outdoors in a process called direct sowing. This is a simpler, less expensive method than sowing seeds indoors because it requires fewer materials. It is better for crops that have larger seeds or those with hard seed coats. Common direct-sow plants include beans, peas, carrots, beets, chard, corn, watermelon, cantaloupe, and squash. When seeds are sown outdoors, they are exposed to the elements, and will need to be watered more frequently than seeds grown indoors. Weeds will also need to be dealt with in a timely manner to avoid them becoming competitive with the intentionally-planted crops.
To direct sow seeds in a garden bed, follow these instructions:
- Prepare your soil. Soil should be loose, level, and weed-free. Larger sticks and rocks should be removed. Break up large clumps of dirt.
- Loosen the top few inches of the soil with the tines of a fork or a trowel. Add a top dressing of an inch or two of compost mixed with peat moss and work it into the loosened soil.
- Plant the seeds at the correct depth and spacing. It can help to make straight trenches in the dirt and drop the seeds in at varying intervals. In general, seeds should be planted at a depth 2-3 times as deep as their diameter. Very small seeds can be placed on the surface of the soil and be covered by a light dusting of substrate. Labeling seeds is recommended, because it will be very difficult to see where the seeds have been planted once they are covered.
- Water in the seeds after planting, and ensure that water is not pooling at the surface. Using the shower setting or the mist setting on a multi-function watering nozzle is ideal, but any irrigation system will work, including a watering can (with a head on it) or a drip system.
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Quick Question: What is Seed Tape?
Seed tape is a pre-sown product of a single or multiple species of seeds that are already spaced between tissue layers at the correct distance for growing. It is a simple way to lay out rows of crops quickly and easily, and the tissue breaks down into the soil, leaving the seeds to grow free. Seed tape is commonly used in direct sowing situations, where plants will be spaced evenly in long rows. It is also very useful for sowing small seeds, ensuring that they stay in place as they develop. |
Seedling Care
The time it takes for a germinated seed to put on enough growth to break the soil surface varies depending on the species being grown. Some seeds will take a few weeks to show above-ground greenery, others will take months - or even years. Research the plant you are growing from seed to make note of its schedule. If it is taking a little longer than expected for a plant to sprout, it may just be that a variable like lighting, temperature, seed depth, moisture, or soil quality is off a little. The most common culprit for seeds not sprouting on time is too little or too much water. To ensure this problem is sidestepped, make sure that soil is well-draining, and keep it relatively moist at all times. Soil should at the very least be checked for moisture, if not watered, daily. Always use room temperature - not cold or hot - water to irrigate seeds and seedlings.
Temperatures should be kept between 72 degrees and 75 degrees Fahrenheit while seeds germinate and sprout. This temperature range will vary, but generally this range is sufficient for most species' seeds. Check growing information for the species (which should be included on the packet) for more specific temperature requirements. If the range of temperatures is difficult to keep steady, it may be good idea to invest in a heating mat. These products can be placed underneath seed trays, and help to keep soil temperature in the ideal range. Another aspect of growing seedlings to think about is providing light. Most of the time, a south-facing window will do just the trick, but if space is limited or lighting is not sufficient, it may be prudent to purchase a grow light that can replace or supplement the natural rays of the sun. Although it may seem silly to provide light to seeds because they don't have leaves yet, it is necessary; the seeds will use the light source to figure out the direction in which to send out roots and stems.
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Sown seeds will absorb water, causing them to swell and break open from their protective coat. Oxygen exposure allows for metabolic activity to resume, and the radicle (the first plant part that emerges from the seed) begins to form a basic root system. The shoot that contains the leaves and stem emerges next, and once above ground, cotyledons (the first leaves, or seed leaves) will open. Continue providing the same amount of water during this time, and ensure that good drainage is occurring. Make sure that temperatures stay steady, as well.
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Once the cotyledons are fully opened and plants have formed their first true leaves (the second set of leaves), they are ready to be thinned. This process is only necessary if more than one seed per cell was sown. Removing the weaker seedlings will allow the healthier ones to have more space for root and above-ground growth, and increase the chances that they will transplant well out into the garden when the time comes. This process also ensures that good air circulation is occurring. Poor air circulation can cause fungal issues to develop, and damping off can occur. This issue affects many vegetable and flower seeds and seedlings, and is caused by a fungus or mold that thrives in cool, wet conditions. Keeping temperatures in the ideal range, watering with room-temperature water, and thinning the herd to increase air circulation are all steps horticulturalists take to lessen the chances damping off issues will occur.
The Hardening Process
Hardening is the technique used to alter the quality of plant growth to withstand the change in environmental conditions between indoor and outdoor spaces. This process goes a long way in lessening transplant shock, and allows seedlings to continue a pattern of strong growth. Hardening is most critical for early crops, when adverse climatic conditions are more frequent after transplanting. Hardening should begin about 2 weeks before plants are put out into the garden. If possible, move young seedlings to an area that stays between 45 degrees and 55 degrees Fahrenheit. When put outdoors, plants should be shaded, and then gradually moved into sunlight. Each day, increase the length of exposure to cooler temperatures and direct sunlight. If it is particularly cold or windy outside, skip a day. During the hardening process, plants should be receiving a bit less water in order to slow growth, but should not be allowed to wilt or completely dry out. Once seedlings are hardened off and transplanted into their forever homes, regular care instructions can be followed.
Hardening is the technique used to alter the quality of plant growth to withstand the change in environmental conditions between indoor and outdoor spaces. This process goes a long way in lessening transplant shock, and allows seedlings to continue a pattern of strong growth. Hardening is most critical for early crops, when adverse climatic conditions are more frequent after transplanting. Hardening should begin about 2 weeks before plants are put out into the garden. If possible, move young seedlings to an area that stays between 45 degrees and 55 degrees Fahrenheit. When put outdoors, plants should be shaded, and then gradually moved into sunlight. Each day, increase the length of exposure to cooler temperatures and direct sunlight. If it is particularly cold or windy outside, skip a day. During the hardening process, plants should be receiving a bit less water in order to slow growth, but should not be allowed to wilt or completely dry out. Once seedlings are hardened off and transplanted into their forever homes, regular care instructions can be followed.
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Transplanting and Handling Seedlings
A very common mistake made when growing from seed is that seedlings are left in the seed flat for too long. The ideal time to transplant younger seedlings is when they are still relatively small, but have their first true leaves established. Try to transplant seedlings within a week from when these true leaves emerge. To transplant, carefully extract the root systems with a fork or butter knife and raise the soil out of the cell. Seedlings should never be handled by their delicate stems; if they need to be handled from the top to be moved around, grab them by the leaves and gently lift. |
Seedlings can be planted out in the garden once the last frost of the season has passed, or they can be kept inside in larger containers as they out on more growth if it is still to chilly outdoors. A sufficient container size for a transplanted seedling is a three-inch pot. As you plant your seedling in its new home, take care to not damage the root system or any above-ground plant parts. Undergoing mechanical damage at this point can be a death sentence for a seedling that is already experiencing transplant stress. If planting in a bed or vegetable garden, ensure that spacing is correct. Newly planted seedlings should be protected from direct sun, wind, and other harsh environmental conditions as much as possible as they get acclimated to their new surroundings. Continue to provide water so that the soil is kept moist, but is not waterlogged. If keeping the seedlings indoors, keep them in a sunny window. The heat mat can probably be removed at this point unless you are dealing with particularly sensitive seedlings.
Seed collecting
Harvesting and storing seed from the garden is a time-sensitive, work-intensive process that takes a bit of understanding and planning to carry out successfully. It is a process that can reward gardeners with their own unique cultivars of flowers, fruits, or vegetable crops. In fact, there are many astoundingly beautiful cultivars of flowers that have undergone artificial selection in private gardens over decades that rival the beauty of commercially-sold seed cultivars. Starting out in seed collection can be a fun process, and goes a long way in connecting the dots between gardening concepts and building a stronger relationship between the gardener and their outdoor space.
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If seeds are saved each year from healthy plants, each following year, those same plants can be grown that are then better adapted to your specific garden growing conditions. Freshly and responsibly saved and stored seeds also commonly have higher germination rates than purchased seeds. Choosing to grow and cultivate heirloom varieties is a great choice, because these cultivars have already been selected for flavor, flowering, or hardiness qualities over time.
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Quick Question: What's an Heirloom?
Heirloom seeds are those that have been passed down from generation to generation without breeding, and are often open-pollinated, meaning that genetic crosses happen often. The fruits and flowers of heirloom cultivars are known for their resiliencies (especially locally-known heirloom varieties), unique flavors and colors, and interesting histories. Heirlooms are exciting varieties to grow, and seed-saving heirloom varieties goes a long way in maintaining desirable qualities. |
Cross-Pollination and Seed Saving
Cross-pollination occurs naturally, and is the mechanism by which plants diversify the genetic pool of their species. It is desirable in the natural world, but when seed saving, it can become problematic. Most gardeners when saving seeds want to grow plants the next year that are true to type, or that have the same characteristics as the mother plant. This requires some extra work, but it does pay off. If preserving the unique qualities of a plant is not important, or if experimentation is desired to see what variations will occur in the next planting, preventing cross-pollination is not important. In order to lessen cross-pollination, follow these guidelines:
Cross-pollination occurs naturally, and is the mechanism by which plants diversify the genetic pool of their species. It is desirable in the natural world, but when seed saving, it can become problematic. Most gardeners when saving seeds want to grow plants the next year that are true to type, or that have the same characteristics as the mother plant. This requires some extra work, but it does pay off. If preserving the unique qualities of a plant is not important, or if experimentation is desired to see what variations will occur in the next planting, preventing cross-pollination is not important. In order to lessen cross-pollination, follow these guidelines:
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Familiarize Yourself with Your Varieties.
Knowing when cross-pollination has occurred is an important skill in seed-saving. The more familiar a gardener is with the variety of plant they are trying to save seeds from, the easier it will be to identify plants that are growing true-to-type. Saving a few of the original seeds for as long as possible can provide plants for comparison after a few seasons, to make sure that those being cultivated are maintaining the same qualities year over year. |
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Choose Self-Pollinating Cultivars. Planting self-pollinating varieties can go a long way in lessening cross-pollination, because these plants so easily pollinate themselves without the actions of bees or other insects. Some vegetables that have typically will have self-pollinating varieties are tomatoes, peas, and beans. |
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One at a Time. Growing one variety per plant family is the most foolproof way to ensure cross-pollination is lessened. This does mean that not as many varieties will be grown in the garden, and cross pollination may still be possible if a neighbor is growing a different variety. Plants in the same family can also be separated by distance in the garden. This may not be possible if the landscape is small, but larger gardens can accommodate this tactic. |
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Exclusionary Practices. Another option for gardeners who are concerned about cross-pollination is to hand-pollinate individual flowers and then cover them with a mesh bag that is tied at the base. These bags are relatively inexpensive, and reduce cross-pollination by not allowing insects, animals or pollen carried by wind to access the flowers. Hand-pollinating can be completed with a Q-tip or small paintbrush. Intentional crosses can be carried out in this way as well, if the goal is to create a hybrid between two specific plants. |
Harvesting and Collecting Seeds
Saving seeds really begins with growing and nurturing plants that are healthy enough to produce seeds. This will ensure that the seeds are ripe, mature, and viable during harvesting time. The next steps include harvesting the seeds, drying and processing them, and placing them in storage. Great choices for seed collecting for beginners are plants such as:
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Knowing when to harvest is the first step in the process, and is quite the balancing act. Harvesting should happen when the seeds are as fully mature as possible. This can be difficult, especially towards the end of the growing season when summer or fall rains come around. Seeds should be kept as dry as possible after they have matured, so provide cover during rainy times and avoid overhead watering. It is common to harvest some dry seed heads before all seed is sufficiently dried and matured to avoid losses and damage from moisture, wind, or animal activity, and these seeds will need extra time to cure before they can be processed. Individual plant species each have unique times when their seeds are ready for harvesting; knowing when this time is for the plants you are cultivating is key. Harvested seeds must be hard and dry enough to withstand processing, and the plant material that the seed is attached to needs to be brittle enough to shatter and break away from the seed with ease.
In practice, it is usually required to make a few harvests from a crop of plants, as seeds on individual flower inflorescences will mature at different times. If multiple harvesting events are not possible due to time constraints, a general rule to follow when timing a harvest is to collect when between 60 and 80 percent of seeds are ripe. All vegetable, herb, and flower crops have unique clues as to when seeds and fruits are ready for harvesting, and it takes some practice to identify when this is for each plant in the landscape. Knowing the difference between dry seeded and wet seeded crops is critical for successful harvests.
Dry Fruit Seed Collection
Dry fruits refer to plants whose seeds do not have a fleshy covering, and include most annual flowers, edible greens, legumes, and herbs. This group of seed-bearing plants is divided into dehiscent and indehiscent. Dehiscent plant seeds are released from fruits or seedpods which shatter or split open when mature and release the seeds directly into the environment. Examples of plants with dehiscent seeds are peas, beans, poppies, and milkweeds.
Dry fruits refer to plants whose seeds do not have a fleshy covering, and include most annual flowers, edible greens, legumes, and herbs. This group of seed-bearing plants is divided into dehiscent and indehiscent. Dehiscent plant seeds are released from fruits or seedpods which shatter or split open when mature and release the seeds directly into the environment. Examples of plants with dehiscent seeds are peas, beans, poppies, and milkweeds.
Legumes like beans have pods that split along two seams.
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Poppies have capsules that open through pores or slits.
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Peas, when allowed to mature, will be released from pods.
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Milkweed plants have fruits called follicles that split along one side.
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When working with dehiscent plants, it is best to collect seeds by cutting off fruiting stems from the plant before they completely dry out and split open. Seeds can then ripen on screens or in paper bags in a dark, dry, cool environment. The seeds will be released from the pods, a process sped up through shaking them in a bag after pods have partially opened. Alternatively, mesh baggies can be tied around maturing flower heads that will catch the seeds before they fall to the ground, or the entire plant can be pulled up, hung upside down, and covered with a bag to catch seeds. After they have been released, the seeds can then be separated from the chaff, or husk. Store seeds in a cool, dark, dry place until they are ready to be used.
Indehiscent plant seeds, by contrast, are contained inside of a released dry fruit that does not have a seam that splits open to release the seed. In a natural environment, these fruits are dependent on animals and water for seed dispersal, because they can't open on their own. For indehiscent plants, seed collecting and processing begins, like that of dehiscent plants, with the harvest of fruiting plant stems that are placed in a paper bag. The difference in this case is that seeds need to be threshed to break the seed free from its fruit. A very state-of-the-art way to do this is to place the fruits in an old pillowcase and whack it against a hard surface. Fruits can also be crushed with a rolling pin or underfoot. Particularly hard-to-open fruits can be hit with hammers or meat tenderizers, with frequent checks for released seeds to avoid damaging them. After this process is complete, remove seeds from the pillowcase (or other container), and set them out so that the chaff can be removed.
Seeds can be picked out by hand, run through a sieve that allows seeds to fall through, or winnowed. Winnowing refers to the process of removing chaff from seed using wind, either natural or generated. All products of the threshing process are poured out of their container in front of a fan (or outside in the wind). Heavier materials (the seeds) will fall into a container placed on the ground in front of the fan, and the lighter material (the chaff) gets taken by the wind. Seeds should be stored in a cool, dry, dark place until they are ready to be sown. Examples of plants with indehiscent seeds are sunflower, oak, corn, and dandelion.
Sunflower
Sunflower seeds are enclosed within a fruit that must be crushed to release their contents. |
Oak
Acorns have a hard shell around seeds that does not open easily. |
Corn
Seeds are enclosed within a tightly formed fruit. |
Dandelion
Dandelion seeds are small but mighty, with a hard protective coating. |
Dry seeded crops are ready for harvest when a few characteristics have been achieved. As seeds mature and ripen, the color can change from white or green to dark yellow, light brown, or almost black. Pods or seeds will also start to feel crispy and dry. If harvesting is put off for much longer after this happens, the chances that the pod will break open and spill seeds before they can be collected increases. Finally, the seed or seed pod will be easily removable from the plant. The purpose of seeds are to travel before finding a nice spot to settle in, and plants will commonly shed seeds and their pods at the peak of maturity to give them the best chance for survival.
Fleshy Fruit Seed Collection
There are a few indications that seeds are mature in fleshy-fruited plants. Fruiting crops that contain seeds inside of pulp, such as tomatoes and eggplant, are best harvested when the fruit is over-ripe, just past the point of being edible. Cucumber, Zucchini, Okra, and Sweetcorn are commonly harvested before they are ripe in order to be eaten, but for seeds to mature, they will need to stay on the plant for about three weeks past normal harvesting time. Pumpkin and pepper fruits are harvested for seed collection at the same time they are ready for eating. In general for this group of plants, after the fruits become edible, seeds will continue to increase in size and quality for days or weeks. It is sometimes necessary to pick fruits to protect against disease or damage and allow them to ripen in storage before removing and processing seeds.
There are a few indications that seeds are mature in fleshy-fruited plants. Fruiting crops that contain seeds inside of pulp, such as tomatoes and eggplant, are best harvested when the fruit is over-ripe, just past the point of being edible. Cucumber, Zucchini, Okra, and Sweetcorn are commonly harvested before they are ripe in order to be eaten, but for seeds to mature, they will need to stay on the plant for about three weeks past normal harvesting time. Pumpkin and pepper fruits are harvested for seed collection at the same time they are ready for eating. In general for this group of plants, after the fruits become edible, seeds will continue to increase in size and quality for days or weeks. It is sometimes necessary to pick fruits to protect against disease or damage and allow them to ripen in storage before removing and processing seeds.
There are two types of fleshy fruit seeds, non-gelatinous and gelatinous. Non-gelatinous seeds are found in plants like peppers, eggplants, and tomatillos. In these plants, seeds can be removed by threshing or mechanical means. They are then washed until they are clean, and poured out onto a dry, clean, non-porous surface to dry out, and stored. Gelatinous seeds are found in plants like tomatoes and cucumbers, and need to be fermented to be released. This process mimics the experience of the seed in a natural environment, either staying within rotting fruit and germinating in place, or being consumed by an animal and passed through their digestive system. Place these types of seeds in a container and add hot water. Shake or stir several times a day. Allow the seeds to ferment in the water until a white scum is formed on the surface and most of the seeds have sunk to the bottom. The scum and any seeds that float can be scooped off with a spoon and discarded. Take a seed out as a test to see if it has shed its gel, and if it has, pour the fermentation container through a sieve to remove the seeds, and then rinse them repeatedly until they are all clean. Put the seeds out onto a clean surface and allow them to dry. They can then be stored in a cool, dark, dry place until they are needed.
Seed Storage
Seed saving is the ancient practice of collecting and preserving seeds from plants to replant in future seasons. It has been a fundamental part of agricultural practices around the world for thousands of years, ensuring food security, biodiversity, and sustainability. In recent times, seed saving has enjoyed a resurgence in interest and popularity. It is an essential tool for farmers and backyard gardeners alike, who seek to maintain control over their own seeds, grow heirloom varieties, and cultivate plants adapted to local environments. Responsibly storing seeds is critical to the long-term success of a seed library. While our home operations may not be as sophisticated as those of the Svalbard Global Seed Vault, we can try to create an ideal environment for seed storage. The following tips and tricks can help to determine where and how seeds will best be stored for home gardening operations.
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Maintain Cool Temperatures Seeds should be kept out of direct sunlight in a consistently cool place. Closets, basements, and rooms on the northern sides of homes are ideal. For short-term storage needs, freezing is not necessary. Seeds can be refrigerated, provided that they stay relatively dry. |
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In the Dark When seeds are dormant, one of the ways they are triggered to sprout is the presence of sunlight. When seeds are in storage, it is important to keep conditions as dark as possible to prevent this from happening. Seeds stored in a refrigerator or freezer will be safe from the rays of our sun, but other storage options may not be so dark. If it is not possible to store seeds in a closed location, they can be stored in opaque containers that block light from entering. |
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All Dry All the Time To combat mold and seeds germinating while in storage, keep them in a place that does not have excess moisture. Using a dehumidifier in a seed storage closet can work, as can using silica gel packets in individual seed containers. Make sure seeds are completely dry before being put into storage. This is especially important if seeds will be frozen or refrigerated; make sure that seeds are in an air-tight plastic or glass container. |
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Keep them Safe There are many insects and other critters who love eating seeds due to their high energy content. Storage spots should be pest-free and closely monitored for activity. Keeping seeds in containers like glass or metal jars can protect seeds quite well, as can plastic pill bottles. For storage spots that are cool and dry year-round, seeds can be stored inside paper bags or envelopes or mesh. Any moisture and heat that is released by the seed while in storage will have a way to escape the container, keeping them fresh and ready for sowing. For the most part, seeds can be kept in the envelopes they come in from the retailer they were purchased from. |
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Materials for seed collecting and storage
If you'd like to begin collecting seeds and storing them, you'll need to gather some materials together. For collecting seeds, you'll need a variety of tools, containers and materials, listed and described below. Many of these materials and containers can be thrifted or may be even sitting unused in a drawer in your house. Although it seems like a complicated undertaking, seed collecting and saving is actually a very low-cost, do-it-yourself practice.
Snips or Pruners
These tools are handy for harvesting seed-filled dried flower heads and fruits. |
Containers
Buckets, trays, plates, pans, and other containers are great to have on hand for collecting and winnowing. |
Drop Cloths
These materials are helpful when harvesting fruits from trees, drying seed heads, and when winnowing. |
Sieves or Fine Mesh
Having different mesh sizes can serve different purposes, such as separating chaff from seed and straining water from wet seeds of various sizes. |
Rolling Pin
Rolling pins are very handy for cracking open seeds with hard seed coats, like those from Sunflower plants. |
Brushes
Pastry brushes, small paintbrushes or makeup brushes can help with pollination, cleaning, and other seed-saving related tasks. |
Mesh Bags
Sometimes called pollination bags, these helpful protective covers assist in seed collecting and storage, and also prevent cross-pollination. |
Air-Tight Glass Containers
These are a must-have (or a must-save) for storage purposes. These jars and bottles are designed to keep moisture out, and typically stay cooler than plastic containers. |
Envelopes or Paper Bags
These containers for seeds allow air and moisture to pass out of the bag away from the seed environment. |
resources and references
UCANR Garden Notes: Soil Temperature Conditions for Vegetable Seed Germination
Books
Seed to Seed: Saving Our Vegetable Heritage (Suzanne Ashworth, 1991)
Seed Sowing and Saving (Carole B. Turner, 1998)
What we Sow (Jennifer Jewell)
Collecting, Processing, and Germinating Seeds of Wildland Plants (Young, 1986)
The Seed Garden: The Art and Practice of Seed Saving
Seed to Seed: Saving Our Vegetable Heritage (Suzanne Ashworth, 1991)
Seed Sowing and Saving (Carole B. Turner, 1998)
What we Sow (Jennifer Jewell)
Collecting, Processing, and Germinating Seeds of Wildland Plants (Young, 1986)
The Seed Garden: The Art and Practice of Seed Saving
