Aesculus
( ESS - kew - luss )
At-A-Glance InformationAesculus is a genus of deciduous trees or shrubs that are commonly referred to as Horsechestnut, Conker, or Buckeye. These plants need full sun and regular water, and they will attract hummingbirds and butterflies to your garden. Take care when planting these in your yard, as all parts of the plant are moderately toxic if ingested. Horsechestnuts can give an almost tropical look to your yard, and have flowers that appear in dense clusters at the ends of the branches. Leathery fruit capsules will appear in fall, and are called 'Conkers'.
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Fun Fact: The game of 'Conkers' is played using the seeds of Horse Chestnut Trees.
This fun, nature-centric, two-player childrens game uses Horse Chestnut tree seeds (called 'conkers') threaded onto strings. Players take turns, one dangling their conker on their string, and the other trying to smash it with their conker. A point is scored when a conker survives a hit, regardless of whether the conker is the attacking or dangling one. Some conkers will break at the first hit, others will survive multiple or all hits in the game. |
There are various names for conkers that belie their strength. A none-er is a conker that does not have a score; it has not yet engaged in a round of the game. As each hit progresses, the conker gains points, and is called a one-er, two-er, three-er and so on as it continues to take hits without breaking. The conker that can take the most hits without breaking wins. This simple game became so popular that championships have been held since 1965.
Aesculus Species and Varietals
The genus Aesculus includes between 13 and 19 species, and is a member of the plant family Sapindaceae (Soapberry). This genus was named by Carl Linnaeus and the moniker is derived from the Roman word for 'edible acorn'. Although these trees are commonly called Horsechestnuts, they are not related to actual Chestnut trees (which are in the plant genus Castanea). The best growing zones for Horsechestnut trees vary by species. For more information, see the species descriptions below. To find your zone, click here: Zone Map.
Aesculus x arnoldiana 'Autumn Splendor' This tree grows best in zones A2, A3, 1-9, and 14-16. This hybrid species is attractive and cold-hardy. Gets to 35-40 feet tall and just as wide, with glossy dark green leaves that turn a brilliant maroon color in fall. Leaves are resistant to leaf scorch. Flowers are yellow with an orange-red blotch and bloom in clusters 8 inches long. These do best with some shade. |
Aesculus californica (California Buckeye) This can be grown as a shrub or a tree, and is native to the dry slopes and canyons below 4,000 feet in elevation in coast ranges and sierra foothills. Grows best in zones 3-10 and 14-24. This plant has a graceful habit and spreads to 10-20 feet tall and 30 feet wide, though it can get larger if given room. New foliage is apple-green and matures to rich green. This plant often has multiple trunks supporting its width. Cream-colored plumes of fragrant flowers appear in spring, though the pollen and nectar is poisonous to honeybees. Pear-shaped fruits form and split open revealing shiny brown seeds. Seedlings make unusual bonsai subjects. If given moderate water, the tree will hold its leaves until fall, and after they drop, the silvery trunk and branches make a great silhouette. |
Aesculus x carnea (Red Horsechestnut) This tree grows best in zones 1-10, 12, and 14-17 and grows to reach 40 feet tall and 30 feet wide. This tree has large dark green leaves that forms a dense canopy that provides ample shade. Flowers are soft pink to red. Varieties include 'Briotii' (with rosy crimson blossoms), 'Fort McNair' (with pink flowers that have yellow throats), and 'O'Neill Red' (with single bright red flowers). |
Aesculus hippocastanum (Common Horsechestnut) This tree grows best in zones 1-10, 12 and 14-17. This is native to European and gets to 60 feet tall with a 40 foot spread. Has a great, shade-heavy canopy area. Roots are strong and can break up paved surfaces, so plant away from walkways, driveways and other paved areas. Flowers bloom spectacularly in ivory with pink markings on one foot long plumes. Variety 'Baumannii' has double-blooms and doesn't set seed. |
Aesculus pavia (Red Buckeye) This shrub or tree grows best in zones 2-9 and 14-24. It is native to the eastern United States. This is a bulky tree that gets 12-20 feet tall and almost as wide. Leaves are glossy green and flowers bloom in narrow clusters and are bright red or orange-red. This is the best choice of Buckeye for humid climates. |
Caring for and pruning Aesculus Trees
Horse Chestnut trees are considered to be pretty simple to care for. Choose a sunny location with well-draining soil and plant your tree in fall or early springtime. Water new plantings regularly, especially if your area is experiencing any dry spells. When mature, these trees are relatively drought-tolerant, but will benefit from deep waterings every few months, especially during the warmer times of the year. Apply a layer of mulch after planting around the base of the tree, taking care not to come up too close to the trunk itself. Horsechestnut trees do not need much in the way of fertilizing, but if your soil is particularly poor, it may be beneficial to apply a slow-release balanced fertilizer in the springtime.
Pruning established Horsechestnuts should only be done to eliminate dead or damaged wood and any awkward-looking branches. Do not over-prune; these trees have a beautiful, natural shape. When these trees are getting established, they will benefit from some support from staking, especially if they are in a high-wind area. Make sure to remove stakes as the tree grows to avoid choking issues.
Pruning established Horsechestnuts should only be done to eliminate dead or damaged wood and any awkward-looking branches. Do not over-prune; these trees have a beautiful, natural shape. When these trees are getting established, they will benefit from some support from staking, especially if they are in a high-wind area. Make sure to remove stakes as the tree grows to avoid choking issues.
Propagation
Aesculus can be propagated either by using cuttings or from seed. To ensure that your propagated plant will have the exact same qualities and characteristics as the parent plant, use the cutting method. If you would like to experiment and see what plant you can grow from seed, just keep in mind that it will not necessarily be the same as the parent plant. To propagate your Horse Chestnut, follow the instructions below:
Propagating Aesculus by Cutting
Propagating Aesculus by Seed
Propagating Aesculus by Cutting
- Gather your materials. You'll need a clean, sanitized, sharp pair of garden shears, rooting hormone, a pencil, and a 3-inch pot filled with well-draining compost or other organic material. If you don't have any potting medium on hand, you can make some. Just mix together equal parts (by volume) moss peat and horticultural-grade sand or grit sand.
- Choose the plant that you'd like to propagate. Ensure that this plant has had a good watering the night before, as this will improve the chances your cutting will take root. Cuttings can be taken either in spring (for softwood cuttings) or fall (for hardwood cuttings). Cut one or more 4-6 inch portion(s) of the end of a non-blooming branch and strip the leaves off of the lower half. Make a hole in your planting medium by pushing your pencil into the soil. Dip the end of the stem in rooting hormone, and plant it in your pot. Fill in soil around the cutting to support it, but do not pack it down too much.
- Moisten with water, and ensure that the pot has good drainage. Your pot should be kept in warm, sunny conditions indoors (and not in direct sunlight). Water whenever your soil is dry under the top layer. After about four to six weeks have passed, your cutting should be rooted. When you notice new growth, you'll know you have roots.
- Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring, when you can transplant it to its new home. Ensure that the last frost of the year has occurred before doing this, as it can seriously damage your new shrub.
Propagating Aesculus by Seed
- Keep in mind that the plant you get from seed will not necessarily mimic all of the characteristics of the parent plant. To propagate by seed, you will need a paper bag, and a pot filled with well-draining compost or other organic material. If you don't have any potting medium on hand, you can make some. Just mix together equal parts (by volume) moss peat and horticultural-grade sand or grit sand. You will also, after a few weeks, need individual 3-inch pots for each seedling that grows.
- Harvest your seeds. The seed pods on these trees are pretty easy to spot, they're large, green-yellow and dangle from the branches, left behind after flowers have faded. Once they have dried out and begun to split open, you can harvest the seeds inside. Cut them off of the plant, placing them in a paper bag. Harvest as many as you can, and place the paper bag in a dry, cool, dark area. They will begin to split open and release the seeds contained inside. Once they have been released, take them out of the bag and put them in a container so you can work with them. Ensure that you use your seeds soon after they are harvested; if they are left out too long to dry, they develop a wrinkly texture and lose viability. To check to see if a seed is viable, place it in a glass of water. If it sinks, it is viable, and if it floats, it is not. In nature, most seeds will germinate in early springtime, though California Buckeye seeds germinate just after winter rains have begun (which is usually in November).
- Buckeye seeds have a hard coating that protects them, but this coating also makes it a little difficult to get them to germinate. We can help the process along by scarifying them with sandpaper (or simply rubbing them against an abrasive surface). Do this with as many seeds as you can; they will probably not all sow, and the ones that do will be of varying characteristics. The more seeds you plant, the more chances you will have to get the resulting shrub you want. Place your seeds in lukewarm water for 48 hours.
- Water your prepared pot filled with soil, and ensure that good drainage is occurring. Place your seeds in your prepared pot or seed tray about a quarter inch to a half-inch under the soil surface. Cover them with soil and water. Place your pot of seeds in a warm area that receives bright, indirect light. A greenhouse is the most ideal climate, but a planting tray inside a window will do as well. Germination usually takes 21-28 days from sowing. Once you begin to see seedlings sprout and they are able to be handled, transplant them to their own individual pots, filled with the same potting medium as described in Step 1. Loosen the seedlings from the potting medium by digging down, gently working the seedling up until it is out. Then, replant the seedling in its individual pot.
- Keep the seedling's potting medium moist, but not wet, as it develops. Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring (after the danger of frost has passed), when you can transplant it to its new home.
Problems and Pests
Horse Chestnut trees are susceptible to the following pests and issues:
- Aphids
- Leaf Spot
Gallery
The seeds are called 'Conkers'.
Use these trees in areas that need shade.
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The 'Anne Frank Tree', which gained notoriety for being the tree mentioned in The Diary of a Young Girl, was a Horsechestnut. Sadly, the tree fell in 2010 during a storm.
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Horse Chestnut trees come in a variety of flower colors.
Horse Chestnuts are beautiful trees to add to any type of landscape.
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Videos
Learn about these amazing trees.
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How to grow Horsechestnut trees from Conkers.
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Differentiating between Chestnuts and Horse Chestnuts.
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Caring for a Horse Chestnut tree from seedling to full-sized tree.
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Experience a year in the life of a Horse Chestnut tree, right from where you are right now.
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All about the Conker Tree.
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Why should you grow a Horse Chestnut in your garden?
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How to grow a Horse Chestnut tree from seed.
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Resources
The New Sunset Western Garden Book: The Ultimate Gardening Guide (2012) - Page 136, Aesculus (Horsechestnut)
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