Characteristics of the Plants
Snow-in-summer plants get their common name from their blooming habit. They bloom profusely in the early summer, and the flowers are a pristine white -- suggesting a fresh snowfall -- with little notches cut into them. But their name does not tell the whole story. This ground cover is just as admired for its delicate, woolly, silver leaves as for its charming flowers. The plants grow to be 6-12 inches tall, with a width 12-18 inches. They spread quickly by reseeding themselves and by producing runners when grown in conditions favorable to them (see below).
Planting Zones, Sun and Soil Requirements
Indigenous to western Asia and to Europe, snow-in-summer plants are commonly grown in USDA plant hardiness zones 3-7. They can be grown in zones 8-10, but they are short-lived in such warm regions. In fact, even in zones 3-7, they will be short-lived where summers are hot and humid.
Snow-in-summer plants prefer sun and thrive in well-drained, poor soil. Having a site with good drainage is a must for growing them successfully. These perennial flowers perform superbly well along the coast of Maine (United States). This fact suggests that they are reasonably salt-tolerant. It also suggests that they enjoy the cooling breezes coming off the Atlantic, thus moderating summertime temperatures.
Care for the Plants and a Warning
After they have dumped their "snowfall" of white blooms in early summer, trim away the faded blooms and some of the foliage to keep snow-in-summer plants looking attractive all summer. Remember, they are grown as much for the silvery carpet that their foliage can provide as for their attractive flowers. Divide these perennials to keep them vigorous and/or to propagate them. The University of Vermont Extension recommends the period just after they have finished flowering as the best time for division.
Snow-in-summer is considered an invasive plant in some areas. This is quite ironic, because, in other areas, trying to grow them is very problematic; they can be rather fussy plants. It seems that, when they like the local conditions, they really like them -- to the point of spreading where they are unwelcome and even becoming naturalized plants. But when they do not like the climate where they are growing, they simply refuse to grow there for very long. Nor do you have to travel many miles to see this difference played out: while snow-in-summer thrives in coastal Maine, it struggles in some of the interior portions of the neighboring state of Massachusetts, where summers can be hot and humid.
Uses in Landscaping
Snow-in-summer plants are a popular choice for perennial flowers in rock gardens and border plantings. They are similar in some respects to another rock garden favorite, yellow alyssum (Aurinia saxatilis), but they stay shorter and are fussier to grow. These perennials form a dense mat, making them useful as flowering ground covers.