Adopt-a-Genus: Draba
by Sue Leduc

Draba, which is the Greek word for 'acrid', is the largest genus in the mustard family (Brassicaceae, formerly Cruciferae). There are about 350 species that are primarily native to the northern hemisphere in arctic, sub-arctic, alpine and sub-alpine regions. Because their natural habitat is so harsh, they are very good candidates to withstand our extremes of climate.

Members of the Brassicaceae family feature flowers that are bisexual and whose 4 petals form a cross (+). They have six stamens, usually 4 longer and 2 shorter. The fruit, called siliques or silicles, breaks open at maturity to release the seeds (dihiscent).

Draba is a diverse genus of annuals and perennials. Their forms include cushion, tuft, rosette, carpet, lax carpet, sub-shrub and erect shrub. Most require a fairly deep root-run, so are not well suited to growing in a shallow trough.

Generally, they bloom in early spring and their flower colour is most commonly shades of yellow (D. hispanica (bottom of page photo), D. rigida (photo above), D. aizoides, D. paysonii, D. haynaldii). White flowers are not rare but they are uncommon (D. glabella, D. loiseleurii, D. norvegica, D. sakuraii (photo on the left), D. dedeana). Some are orange-red (D. matthioloides).

There is a Draba for every imaginable combination of growing conditions in a rock garden: hot, dry and sunny; humousy, moist and semi-shady; Ca rich and Ca poor soils; and anything in between. You name it - there is a Draba that will do well. About the only absolute in cultivating Drabas is that they must be protected from winter wet.

The most frustrating thing about Drabas is that it is very difficult to identify their individual species correctly. I have a collection of plants the seeds of which were acquired from entirely reputable sources that simply are not the species they are supposed to be. I have labels in the garden that say things like 'not Draba dedeana' (photo on the right). To compound the frustration, there is very little written about Drabas. Otto Eugene Schultz wrote a monograph of the genus in 1927, but I have been unable to find anything more than passing reference to it in my research. On his excellent website, www.kadel.cz/flora, Dr. Pavel Slaby has a list of 168 species, most of which have synonyms. Very few have pictures to help in identification, but all are well described.

All of the Drabas that I have tried have been the cushion, tuft or rosette forms. They are tiny little evergreen cuties that bloom from mid-April (the tufts) through to late May (the rosettes). Some will self-sow quite plentifully (such as D. paysonii) while others are far more modest. I have found though, that most Drabas are very easy from seed. The trick is not to sow them so early that you have to tend the seedlings indoors for too long. They form a large root mass very early so should not spend too much time confined to a pot. Many only need 2 to 3 weeks at 20°C to germinate. I have yet to find any that need any kind of special handling such as cold treatment.

Drabas are widely available through rock garden society seed exchanges, though rather uncommon in the nursery trade. When requesting seed from an exchange or purchasing seed from a commercial source, be prepared to receive something other than what you have requested. When your plant has grown to blooming size and has flowered for you, you will be better able to determine if it is in fact the species it was purported to be. Better yet, search out a nursery that offers Draba plants so you can be sure that it is the form you want. The nursery owner will also be absolutely certain of the flower colour.

Even the misnamed species are worth having in your garden. Very few plants bloom as early or as brightly and require so very little care as Drabas.