Cerastium tomentosum aka Snow In Summer

Cerastium tomentosum also goes by the name snow-in-summer. It belongs to the pink family. This low plant creeps along the ground and is a perennial. It comes from Italy, Sicily, and Corsica. Gardeners grow it for its silver leaves and white flowers. It has spread beyond gardens in parts of the United States. Plants form dense mats but often live just a few years. Runners below the soil help them spread across open ground.

The leaf mat stands about 0.5 feet [0.15 metres] tall. Flower stems bring the height to 1 foot [0.3 metres]. RHS gives a wider height range, reaching 1.6 feet [0.5 metres]. Sources give different widths. Missouri Botanical Garden gives about 1 foot [0.3 metres]. NC State lists up to 1.5 feet [0.46 metres]. RHS allows 3.3–4.9 feet [1–1.5 metres] for well-grown mats. Narrow leaves grow in pairs on opposite sides of stems. Soft white hairs give them a silver-grey look. Sources differ on whether plants keep their leaves through winter.

Thin stems branch and bear groups of white, star-shaped flowers. Each flower has five petals with notched tips. Plants bloom from May into June, based on local conditions. The flowers draw bees. Chicago Botanic Garden also lists butterflies. Small, dark seed cases, called capsules, follow the blooms. They ripen in autumn. These fruits are long, with a slight curve. Plants can seed themselves unless gardeners remove the spent flowers.

Full sun and soil that drains well give the best results. Plants suit dry, sandy ground but accept other soil types. They grow in acid, neutral, and alkaline soils that drain well. Cool summers suit them better than hot, humid weather. The usual USDA range is 3–7. Missouri notes that plants can survive in zone 2. RHS gives the plant a cold hardiness rating of H7. Use it along borders, on sunny banks, or among rocks. It also suits gravel beds and gaps in stone walls. Deer tend to leave it alone, but foot traffic harms it.

Most plants have few serious problems with pests or disease. Wet soil can cause root rot. Shade and high humidity can also lead to damping off. Summer heat may spoil the leaves. Older mats grow bare patches. Plants can become weedy where cool summers help them grow well. Cutting back spent flower stems curbs seeding and tidies the mat. Grow new plants from seeds or stem-tip cuttings, or divide them. The supplied sources give no clear evidence about food use or toxicity.