Snow In Summer
(Cerastium tomentosum)

Snow-in-Summer is the common name of an Italian wildflower, Cerastium tomentosum — an often overlooked but garden-worthy perennial. Snow-in-Summer is a reference to the pure white flowers that cover the plant in late spring and early Summer (mid-April – May, in my garden.) The specific name ‘tomentosum‘ indicates that the silvery leaves are covered in fine hairs, having a texture like felt. Plants of the genus Cerastium are known as Mouse ears, hence another common name for the plant is ‘woolly mouse ear’.

I have grown Snow-in-summer for over a decade on my Green roof, where it stands out in summer as a bright patch of silvery-white against the surrounding foliage. Somehow, I’d got the idea that it was a rather invasive plant, spreading aggressively at the roots, but on my roof, it only spread slowly. It may be that I have one of the better-behaved cultivars (‘Olympia’, ‘Silver Carpet’ or ‘Yoyo’) but I can’t be sure.

A few years ago, as part of my Pond Garden replanting, I decided to try planting Snow-in-summer in the perennial border, setting out two clumps in my free-draining raised beds. They have worked splendidly, frequently impressing me with their ease and beauty and out-surviving both Artemisia ludoviciana ‘nana’ and Rhodanthemeum ‘Casablanca’ which were planted at the same time close by, but succumbed to winter cold. The photo above was taken in early May, one year after planting, just before they reached peak flowering.

Once flowering is over, Snow-in-summer can be trimmed back hard to create a tidy clump. If left, the seed heads dry to an unattractive light brown, and may cause a nuisance with seeding. The cut-back shoots can look a bit bare for a week or two, but they soon sprout new leaves, creating a beautiful silvery mound of foliage which continues to spread outwards for the remainder of the summer… Like this…

Although the clumps grow increasingly wide over the season, most of this is from trailing stems spreading out over the surface. These will tumble down banks or over the edge of walls or beds. Planted at the base of taller perennials, these shoots will weave their way between their neighbour’s stems. This propensity to ‘flow’ is very appealing, but easy to control if they wander too far. They can easily be cut back (even quite savagely) with scissors or shears. They recover quickly and soon look good again.

The two clumps in my garden have spread at the base, but not aggressively or excessively. Where the spread has been in a direction that I do not want, I have simply dug up the extraneous part and planted the division elsewhere. If I wanted to ensure they didn’t wander, I’m sure a root-barrier, such as a bottomless plastic pot, would keep them in bounds.

FLOWERS The flowers of Cerastium tomentosum consist of five heart-shaped petals of pure silky white, with fine grey lines in the throat and yellow-green centres. From mid-April to late May, flowers open in succession from slender grey buds atop narrow silver stems which rise some 6 inches (15cm) above the foliage. Their brightness is striking from quite a distance and they remain a-glow long into the evening, the reflective petals shining in moonlight.

PLANTING Although fully hardy, Snow-in-summer does not tolerate high humidity or soggy feet. Give it a free-drained soil that is not too rich, in an open sunny spot and it should do well. I have kept it in a small terracotta pot for several years where it hangs on rather than thrives. It might do better in a large terracotta bowl with plenty of drainage.

FOLIAGE After flowering, the foliage of Snow-in-summer continues to provide an effective silvery foil for adjacent plants, and remains looking good right up until the first frosts. It typically grows 6-9 inches high (15-20cm). As a foliage plant it is as effective as the silver mugworts (Artemisia sp), cotton-lavender (Santolina chamaecyparissus), curry plant (Helichrysum italicum) or lambs ear (Stachys byzantina) — all of which would make good companions. Under grey-skies, the leaves of Snow-in-summer often take on a bluish hue, similar to the colour of the Myrtle spurge (Euphorbia myrsinites).

CARE Snow-in-summer needs little care once established, and although cutting back after flowering isn’t essential, it makes the plant much neater for the remainder of the year.

USES Snow-in-summer’s low-growing habit makes it ideal for the front of border or as an edging to a path. It also combines well with alpines in a rock garden or rockery, or with small to medium perennials, as long as it isn’t too crowded. The silver foliage works well with other silver plants, or in contrast to dark green or purple foliage.

DIVISION Snow-in-summer can be easily divided by lifting and splitting the root ball into smaller pieces. An ideal time is straight after flowering (i.e. early June). Replant each chunk and keep watered until established.

PROBLEMS
• Can be invasive — use a root barrier or plant less aggressive cultivars.
• May be short-lived — plant in poor soil. Don’t fertilise.
• May die off in centre — probably reduced if regularly pruned after flowering. If it happens, lift, divide and replant.

Planting Combinations

PLANTING IDEA #1

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PLANTING IDEA #4