Most gardener associate wallflowers with the late spring and early summer when their perfume fills the warming air. It is a very evocative scent.
Unfortunately very few of the 80 species, plus cultivars, are scented. It is restricted to those that are treated as biennial bedding plants. These produce their leaves during the first year, then flower and die in the second year.
In fact most of the wallflowers grown in their garden are perennials, but they are all short-lived and it is often more practical to treat them as biennials, sowing the in spring, planting out in autumn and then removing them after flowering in the following early summer.
If you want, cuttings can be taken and so the plants can be kept going indefinitely. This is what happens to the border wallflowers. These are treated more as perennials, but are rarely long lived unless they have very free-draining positions (such as on cliffs or walls hence the name).
Cuttings should be taken every summer in case plants are lost during the winter. They are hardy but do not like wet conditions. Wallflowers will grow in most soils as long as they are free-draining. They need a sunny position, preferably sheltered from the wind.