I usually describe the so called perennial wallflowers as “short-lived shrubs” they like a well-drained soil in a sunny position. Cold wet conditions on heavy soil in winter spells death. The ever popular Erysimum ‘Bowles Mauve’ is the best known and most widely planted. I find this lasts for a couple of years and then needs replacing: almost an extended-life biennial. Some gardeners look surprised when I say this and tell me they have had theirs for several years. My soil is light and sandy and it certainly doesn’t last long with me, but it doesn’t stop me planting it and recommending it. Its great value and blooms from early spring to late fall.
I think the first perennial wallflower I came across was the low growing Erysimum ‘Constant Cheer’. This has dark green leaves and forms a low sprawling plant up to 20cm (8”) high. The heads of fragrant flowers are in shades of soft copper, mauve with hints of orange and gold; faded silk shades that are a delight against paving or gravel.
I imagine the more recently introduced Erysimum ‘Monet’s moment’ is derived from ‘Constant Cheer’; the character and colour is similar. In both cases the name is enough to make you want to buy it.
The narrow leaved forms of Erysimum linifolium seem to be more hardy and longer lived with me. You will never find these in garden centres because of their loose, habit and curious spikes with a few flowers at the top of a long spike of seed heads. However they are great garden plants and have a wonderful transparency. I have one that grows amidst a golden-leaved hedera on the edge of a wall. It has bloomed reliably and grown happily for the past fifteen years. I suppose the ivy starves it and protects it from the winter wet from the soil. Soil splash onto the base of plants like these is not desirable.
The biennial wallflowers are the ones used for seasonal bedding. Grow the plants in a nursery bed and transplant to flowering position in autumn. Then dig them out after flowering and replace with summer seasonal plants. If left alone plants often go on from year to year. A new variety ‘Sugar Rush’ is becoming popular, especially for containers. This flowers in autumn and in spring/summer. It is fragrant and compact and closer in character to the perennial varieties.
Most wallflowers hail from Europe but there are species from South West Asia and North America. They like warmth; the common name comes from their affinity with stone and gravel, rather than soil. You will find them hanging on to stone walls, their roots finding anchorage and some water and nutrition in the tiniest crevices. Where they are happy they will seed and practically naturalise on the walls in village lanes and near the sea. Coastal garden suit them: plenty of light, good air circulation and mild winters.
They are members of the cabbage family, brassicas. Their single, four-petalled flowers are easily accessible by pollinating insects and you will find them very attractive to bees and butterflies.
So what are the secrets of success with wall flowers?
Good drainage and a sunny position. If you’ve got heavy, soil grow your perennial wallflower in a terracotta pot on the terrace.
Although perennial wallflowers seem to grow on neutral to acid soils they prefer more alkaline conditions. It may pay to apply lime before planting on acid soils, particularly neutral to acid clay
Covering the soil surface with grit or gravel under perennial wallflowers helps to keep wet and soil splash off the plants. This is particularly useful on heavy clay soils
Take a few cuttings each year. Perennial wallflowers root easily from cuttings and these will provide you with replacements.
Grow perennial wallflowers with lavender and silver foliage shrubs that like the same conditions. However, do not crowd the plants or give them excess competition.