About draba (whitlow grass)
Draba is a genus of over 350 species in the cabbage family Brassicaceae, almost all of them small cushion-forming alpines native to mountain ranges across the northern hemisphere. In the UK they are specialist plants for rock garden and alpine enthusiasts rather than everyday garden choices. Most grow to just 5 to 15 centimetres tall, forming dense mats or tight bun-shaped cushions covered in tiny leaves. The foliage is often clothed in star-shaped (stellate) trichomes, giving the plants a silvery or woolly appearance depending on species.
What makes draba unmissable in late winter is the flowers. Each plant produces masses of tiny four-petalled blooms in yellow or white from February through April, often when little else is awake in the garden. Key species to know include Draba aizoides (yellow whitlow grass, the UK native on limestone cliffs in the Gower Peninsula in Wales, bright yellow flowers from March to April), Draba rigida (a stiff tight yellow cushion, very hardy), Draba mollissima (an intensely woolly high-alpine cushion considered one of the most challenging species to grow well), and Draba dedeana (white flowers, compact, more tolerant of outdoor conditions). On the alpine show bench, well-grown draba cushions smothered in flower are considered showstoppers.
Cause 1: Wet crown rot (the number one killer)
If your draba cushion is turning brown from the centre outward, with individual rosettes going soft and mushy before the whole plant collapses, wet crown rot is almost certainly responsible. This is the single biggest cause of draba death in the UK, and it claims plants that looked completely healthy going into autumn.
The problem is structural. Draba evolved on exposed scree slopes and cliff faces where rain falls hard and drains instantly. The hairy star-shaped trichomes on the leaves are partly there to channel water away from the growing points. In a typical UK garden border, or even a well-intentioned rockery, winter rain sits around the crown of the plant for hours or days. That persistent moisture at low temperatures is lethal. The central growing rosette turns to brown mush first. Within days or weeks the infection spreads outward and the entire cushion can collapse before spring.
The fix is perfect drainage, and for the more challenging species this means growing under glass. Serious draba growers in the UK keep their prize specimens in an alpine house: an unheated or frost-free greenhouse with maximum ventilation and zero overhead watering from October through to March. Under glass the plants get the cold they need to flower reliably, but the cushions stay dry. A sand-based compost (see the FAQ on compost below) ensures any water that does reach the roots drains straight through.
For outdoor growing, the principle is the same: place draba somewhere rain cannot reach it persistently. A rain-shadow position against a south-facing wall, under a stone overhang, or in a deep gritty trough under a clear polycarbonate sheet in winter are all workable solutions for the hardier species like D. aizoides and D. rigida. Avoid planting in any spot where water pools even briefly after heavy rain.
Cause 2: Pests attacking the tight cushion
A second major cause of draba decline, often mistaken for disease, is pest damage. Three culprits are worth checking for.
Vine weevil grubs are the most destructive. The adult weevils are active at night in summer and lay eggs at the base of plants. The grubs hatch and feed on roots through autumn and winter. Because draba forms such tight cushions, the grub damage is invisible from above. The first visible sign is often the cushion lifting cleanly off the soil with no roots attached at all, by which point it is too late to save the plant. If your draba tilts or lifts more easily than it should, scrape back the top layer of compost and look for fat cream grubs with a brown head capsule. Treat preventatively with Steinernema kraussei nematodes in September to October when soil temperature is still above 5 degrees Celsius.
Birds, particularly sparrows and tits, are an unexpected problem for outdoor draba. The woolly or hairy cushions are irresistible as nesting material in late winter and early spring, exactly when draba is coming into bud. Birds will peck circular holes in the cushion to extract the silvery trichomes. If you notice circular bald patches appearing in late February or March, bird damage is the likely cause. Growing under glass eliminates this entirely. Outdoors, fine netting or a cloche during the nesting season offers protection.
Aphids and slugs are lower-level concerns. Aphids occasionally colonise the emerging flower stems in spring. Slugs rarely bother the tough hairy rosettes but may damage emerging flower stems in mild wet springs. Both are easily controlled with standard measures.
Other causes of curling and decline
Red spider mite becomes a serious problem for draba grown in an alpine house during warm summer months. The mites thrive in hot, dry, poorly ventilated conditions and produce fine webbing between the rosette leaves, causing the foliage to look dusty and then bleached before curling and dying back. Maximum ventilation and a slight increase in humidity counteract the conditions mites prefer. Biological controls work well under glass.
Overwatering in summer is another common mistake. Draba is semi-dormant from late spring through to autumn and requires very little water during this period. Even plants in free-draining compost can develop root rot if they are watered heavily through July and August. In the UK, rainfall alone is usually sufficient for outdoor plants. Under glass, water sparingly from June to August and allow the compost to dry almost completely between waterings.
Wrong compost underpins many of the problems above. Peat-based or multi-purpose composts stay wet, compact over time, and fail to replicate the free-draining mineral soils draba needs. A lime-based gritty mix is not optional for this genus; it is the baseline.
Frequently asked questions
Can I grow draba outdoors in the UK without an alpine house?
Yes, but you need to engineer conditions that mimic an alpine house as closely as possible. Plant in a deep grit trough or raised scree bed with at least 50% horticultural grit in the compost mix. Position in a rain-shadow spot such as under a south-facing overhang, against a dry stone wall, or wedged between paving slabs where roof or wall overhang keeps persistent winter rain off the cushion. Avoid clay soils and any position where water pools even briefly. The easier species like Draba aizoides and Draba rigida cope well outdoors with good drainage; the woolly high-alpine types like Draba mollissima really do need glass protection.
What is the UK native draba and where does it grow?
Draba aizoides, yellow whitlow grass, is the UK's only native draba. It grows on limestone sea-cliffs on the Gower Peninsula in south Wales, one of its very few natural sites in Britain. In the wild it tucks itself into rock crevices where drainage is perfect and winter wet runs straight off the cliff face. In gardens it is the most adaptable of the drabas, producing cheerful bright yellow four-petalled flowers from late February through April. Its near-native toughness makes it a good starting point if you are new to growing draba.
Why does my draba cushion lift cleanly off the soil in one piece?
A cushion that lifts cleanly with no roots attached is a classic sign of vine weevil grub damage. The fat, cream-coloured grubs feed on roots through autumn and winter, leaving the above-ground cushion apparently healthy right up until it simply detaches. Check the soil at the base of the plant for grubs and treat with Steinernema kraussei nematodes, applied when soil temperature is above 5 degrees Celsius, usually September to November. Water the nematodes in thoroughly and keep the compost moist for two weeks.
My draba flowered beautifully in spring but now looks grey and limp. What happened?
Draba is semi-dormant through summer and looks less vibrant at that time of year, but greyness combined with limp or curling growth after spring usually points to one of two things. If the summer has been warm and you are growing under glass, red spider mite is likely. The mites thrive in hot dry conditions and produce a fine webbing between rosette leaves. Improve ventilation, raise humidity slightly, and treat with a biological control such as Phytoseiulus persimilis. If the plant is outdoors and the summer has been wet, overwatering or poor drainage is the cause. Ease off watering completely in July and August; draba in free-draining soil rarely needs supplemental watering in the UK.
What compost should I use for draba?
Use a lime-based, gritty, free-draining mix. A standard alpine house mix is one part John Innes No. 2, one part horticultural grit, and one part limestone chippings or pea gravel by volume. Avoid peat-based or multi-purpose composts, which retain too much moisture and compact over time. Top-dress the collar of the plant with coarse grit or limestone chippings to keep the hairy rosettes clear of wet soil. Draba aizoides and D. rigida will tolerate slightly richer mixes; the high-alpine cushion types like D. mollissima need the leanest, grittiest compost you can provide.