Cerastium

cerastium

( ser - RASS - tee - um )

At-A-Glance Information

This genus includes both annual and perennial plants and is commonly called Snow-in-Summer, Mouse Ears or Mouse Ear Chickweeds. Species are native to most climates worldwide, with the greatest concentration in northern temperate regions. A number of species are considered weeds, and commonly colonize disturbed soils along roadsides, in fields, or in gardens. Use these small-scale groundcover plants to fill in difficult spaces in the garden, to front beds and border plantings, in containers or hanging baskets, or in crevices in rock walls or stone stairways. They are great perfect for the outskirts of the garden, where their spreading nature will not be bothersome to other plants.

cerastium species and varietals

The genus Cerastium includes 214 species and is a member of the plant family Caryophyllaceae. These plants are generally best in USDA hardiness zones 3-8 or Sunset growing zones A1, A2, and 1-24, though this varies somewhat depending on which species is grown. For more information, see the species descriptions below. To find your zone, click here: Zone Map.

Cerastium aleuticum (Aleutian Mouse-Ear Chickweed, Aleutian Chickweed)
This species is endemic to Alaska, where it grows on the islands off the coast. These plants prefer growing on mountainsides and rocky areas, and spread via underground rhizome. Branched stems are covered in soft hairs and flowers are white. These plants generally reach just 3 inches tall. This species does well in USDA hardiness zones 4a-7b.

Cerastium alpinum (Alpine Mouse-Ear, Alpine Chickweed)
These plants form mats of green, soft foliage and are native to Greenland, Canada, and northern areas in Europe. The species was first discovered in 1753 by Carl Linnaeus. At maturity, plants reach just a few inches tall, and produce white flowers with yellow centers. Foliage is silvery green and downy. Individual plants reach just 2-8 inches tall and have a spread of 6-12 inches.

Cerastium arcticum (Arctic Mouse-Ear Chickweed, Arctic Mouse-Ear, Arctic Chickweed)
These flowers form tufts of green, downy foliage and generally prefers to grow in damp areas and open gravel. Flowers are white and relatively large for the genus, and petals are deeply notched.

Cerastium arvense (Field Mouse-Ear, Field Chickweed, Meadow Chickweed)
This widespread species occurs in North America, South America and Europe, and its form is variable. These plants generally reach about 12-18 inches tall at maturity, and can grow from either a taproot or a tangled system of rhizomes. Flowers are singular or borne in clusters, and are white. These can serve as great groundcover plants in areas of the garden that are shady and difficult to grow in, though they can be a bit weedy.

Cerastium biebersteineii (Boreal Chickweed, Snow-In-Summer)
This ornamental species is endemic to Crimea, and named for German botanist Friedrich August Marschall von Bieberstein. It grows well in USDA hardiness zones 3-7. Flowers produced by these plants are white, and bloom from August through May in their native range. This species is considered invasive in Europe, Argentina, and North America.

Cerastium brachypetalum (Gray Chickweed, Gray Mouse-Ear, Gray Mouse-Ear Chickweed)
This annual species produces springtime shows of white flowers and is native to Eurasia. These plants are considered in need of protection from extinction in the wild. Individual plants reach up to 2-12 inches tall and have a spread of 1 to 2 feet. Stems are thin, flowers are small and white, and leaves are tiny and green.

Cerastium fontanum (Mouse-Ear Chickweed, Common Mouse-Ear, Starweed)
This mat forming plant can be used as an annual or perennial, and is native to Europe, though they have naturalized in many areas of the world. These plants reach between 4 and 8 inches tall at maturity and grow well in USDA hardiness zones 5-10. This species is considered invasive in every U.S. state and all Canadian provinces. It is also considered an invasive weed in the Falkland Islands, Macquarie Island, and South Africa.

Cerastium subtriflorum (Slovenian Mouse-Ear Chickweed, Subtriflorum Mouse-Ear Chickweed)
This perennial species is native to the Alps in Slovenia and Italy, and forms a low growing plant that reaches a foot tall at maturity. Leaves are green and flowers are white.

Cerastium tomentosum (Snow-In-Summer)
This perennial flowering plant grows in light shade in the warmest climates but can take full sun conditions elsewhere. They need moderate to regular water, and are native to Europe. Often used as a groundcover, it forms mats of silvery leaves in summer and gets to 6-8 inches tall and spreads 2-3 feet per year. This plant can also be used in rock gardens, to edge pathways, and for foliage between stepping stones. It is not a long-lived plant, so it shouldn't be used in prominent areas of the garden. Best in USDA hardiness zones 3-7. This species is considered invasive in the Pacific Northwest and northeastern North America as well as regions of Europe.

Cerastium utriense (Mouse-Ear Chickweed)
First formally described in 1988, this species is endemic to Italy. These plants are perennials, and form clumps of foliage from which thin flowering stems emerge. Individual plants top out at 8 inches tall at maturity, and produce white flowers and green leaves.

Caring for cerastum

Grow these plants in full sun; ideally, they should be receiving between 6 and 8 hours of direct sun each day for best performance. Plant 1-1.5 feet apart for best coverage as a groundcover. They prefer very well-draining soil, with a pH of between 5.0 and 5.8. These plants can be quite sensitive to high salt content in soil, and are not recommended for coastal gardens or soils that have had non-organic fertilizers added to them. If local soils are particularly poor in nutrients or do not drain well, make sure to amend the planting area with plenty of organic compost before installing. After planting, mulch around the base with organic mulching material to help retain soil moisture and suppress weed growth. Keep mulch away from the plant stems, as this can encourage an environment for root rot issues to take hold.

These plants are considered easy to care for, and can thrive even when neglected. Water newly planted Cerastium regularly as they develop a strong root system in their new home. Regular waterings will encourage speedy growth, but at maturity these plants are very drought tolerant. Fertilize yearly with an application of organic compost; Pull back mulch before applying compost, and replace after working it into the soil and watering. After the bloom period has finished, shear or mow plants. Cerastium can look a little shabby in wintertime but will revive in springtime, especially if they get a nice haircut at the beginning of the growing season. Sometimes, these plants can develop 'bald spots'. Dig clumps from healthy areas to fill in any patches that do not return the following spring. These plants are considered perennials, though they will only survive for 3-5 years in the garden before needing to be replaced. They will freely re-seed, however, providing new plants in the landscape indefinitely.

Caring for Cerastium in Containers
Cerastium, or Snow-In-Summer, are great choices for containers, and have a spilling effect when in front of upright plants. They can be installed in any size container. Ensure that soil is well-draining and there are adequate drainage holes on the bottom of the pot to allow for excess water to drain away. Water new plantings regularly. At maturity, Cerastium is drought tolerant, getting by on rainwater alone for much of the year with supplemental waterings needed during extended periods of drought. In general, they will need more frequent irrigation than their in-ground counterparts. Prune to remove leggy, damaged, or diseased growth in early springtime. Move containers into a sheltered, frost-free location over the winter months to help them overwinter. Alternatively, they can be treated as annual color; pulled and replaced each spring.

Propagation

Cerastium can be propagated by using cuttings, division, volunteers or from seed. To ensure that your propagated plant will have the exact same qualities and characteristics as the parent plant, use the volunteer, division or cutting method. If you would like to experiment and see what plant you can grow from seed, just keep in mind that the resulting plant may not necessarily be the same as the parent plant the seeds are harvested from. To propagate your Snow in Summer, follow the instructions below:

Propagating Cerastium 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. A good substrate for propagation of cuttings is a light blend of 1/3 pasteurized soil or compost, 1/3 sand, vermiculite or perlite, and 1/3 coconut coir or peat moss.
In early summertime, 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. Cut one or more 3-4 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 flower.

Propagating Cerastium 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, a pot or tray filled with well-draining compost or other organic material, a spray bottle and a fork. The best potting medium for seed germination is a light blend of 1/3 pasteurized soil or compost, 1/3 sand, vermiculite or perlite, and 1/3 coconut coir or peat moss.
Harvest your seeds. The seed heads ripen in late spring to summer, and can be simply cut off of the plant and placed into a paper bag for temporary storage. Store the seeds over the winter in cool (but not frosty), dark conditions.
In early spring of the next year, water your prepared seed tray or 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 with your spray bottle. Place your tray 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 is usually pretty quick for these plants, occurring within 10-14 days after sowing.
Keep the seedling's potting medium moist, but not wet, by spraying the soil with your spray bottle. 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 seedlings reach a few inches tall. Young seedlings are best stored in a shaded area of a greenhouse; direct sun can scorch the developing leaves.

Propagating Cerastium by Volunteer

Volunteer seedlings are likely to pop up around your existing Cerastium plants if you do not deadhead or cut off runners. If you see these small new plants appearing, you can remove them and repot or replant them wherever you'd like. To propagate your plant via volunteer seedlings, you'll need a garden shovel, potting soil, and a pot (if you won't be replanting it immediately in your garden).
Dig up your volunteer plant using your garden shovel, being careful to not damage the roots. For volunteers that have propagated via runners, disconnect the stem that runs between the new and old plants. Then, either in your prepared pot or a prepared spot in your garden, replant it. Water it in, and continue providing regular waterings until it has established itself in its new home.

Propagating Cerastium by Division
This type of propagation is relatively simple; you will need a clean shovel, mulch, fresh soil, compost, and pots (only necessary if you will be saving divided plants for transporting elsewhere). Division is best done in spring or fall. To propagate by division, follow these steps:

Gather your materials. Using a shovel, dig up your existing plant. Start from the outside and work your way in to avoid damaging the roots. Once you have worked it up out of the ground, lay it out.
Start to tease apart the roots with your fingers. Once the roots are untangled, separate your plant into segments, ensuring that each one has at least one thick root section to grow from.
Prepare your pot(s) or new planting site(s) with amended, well-draining soil. You can either bring in new soil or simply amend your existing soil with compost to complete this task. Then, plant your divisions and water them in thoroughly.
Apply a thick layer of mulch over the new planting to protect it from cold weather as it acclimates to its new home. Then, enjoy watching it sprout.

Cerastium seed heads are brown-tan and dry when mature.

Cerastium seeds are small, light brown and have bumpy surfaces.

Problems and Pests

Cerastium, or Mouse Ears, can itself be a weed in some gardens, and is even considered invasive in certain regions around the world. Check with local authorities before planting. These flowers can be susceptible to developing problems with the following pests and diseases in the landscape: