echnically speaking, all wallflowers are perennial; that is, they live for more than one or two years.
However, they are not long-lived plants, which is why the spring-flowering hybrids, like ‘Cloth of Gold’, are usually treated as biennial (sown one year, flowering the next), then discarded, as the best flowers are produced in the spring after sowing.
There are, however, other forms of erysimum (wallflower) which do survive well from year to year, many of which flower continuously from early spring to late autumn.
The best known of these is ‘Bowles Mauve’, a shrubby form with blue-green foliage and a profusion of typical wallflower-like flowers, which can reach as much as 80cm in height eventually.
It’s a good idea to keep taking cuttings, as, in my experience, even a plant that looks to be bursting with health can suddenly fold up and die. It’s rather late for this as I find they strike most successfully earlier in the spring, but I would still be prepared to have a go.
They root best as small side shoots, pulled off the plant with a ‘heel’, and preferably without flowers, although with ‘Bowles Mauve’ it’s difficult to find flowerless side shoots.
Trim up the heel so there aren’t any bits of bark hanging off, pull off the lower leaves, and insert a third to half the cutting in an open, damp compost of about half and half multi-purpose compost and sharp sand, fine perlite or vermiculite.
Remove any flower buds and place the cuttings in a cold frame with the lid open or a well-ventilated, unheated greenhouse.
Watering is critical – too much and the slips will rot, too little and they won’t form roots.
The rooted plants can be planted out in the garden next spring and summer.
It’s a good idea to take plenty of cuttings, although well over half should strike, even as late as this in the season.