Erysimums in cultivation
Successful erysimum growing really depends on understanding the sorts of conditions in which they thrive in the wild, and the sorts of conditions they hate! They are not woodland, moorland nor marshland plants and will not tolerate wet, boggy or acidic soils. Rather, we need to think Mediterranean garrigue – with rosemary, thyme and cistus on thin, sun-baked soils, or alpine pastures and limestone scree slopes – with campanulas, phlox and saxifrages. And, archetypically, think of ‘wild’ wallflowers growing in the lime mortar of the walls of an abandoned medieval castle or priory. So, generally speaking, erysimums prefer poor soils, which are neutral to alkaline and are well drained. They prefer full sun or only light or partial shade.
Erysimums do vary in their tolerance of cold. In my experience most of the commonly available sub-shrubby cultivars and the alpines will tolerate several degrees of frost, though not necessarily for long periods. What they seem to dislike more are winter wet and strong winds (which can result in wind-rock and consequent neck-rot). For alpines grown in beds or rockeries, a cloche with open ends is a good option. For sub-shrubby erysimums in an exposed site, wind netting or staking is helpful. Alpine erysimums also do well in containers, which can be brought into a well ventilated, unheated greenhouse over winter.Like most of the brassica family, erysimums are prone to various pests and diseases, including flea beetle, downy mildew, club root and mosaic virus. The remedies are similar to those you would use in other members of the family.
To summarise: erysimums are fairly exacting in terms of soil type, site characteristics and winter protection, as well as being prone to various pests and diseases. And if you can get them to thrive, they have a short lifespan anyway. But fortunately, there is some good news! First of all, they are very easy to propagate. The species grow easily from seed and in good conditions they will readily self-seed around. The mat-forming alpines can easily be propagated by division once they have reached a decent spread. Just about all erysimums grow well from cuttings (I use tip cuttings in spring and autumn), and plunging also works well.