Though there are perennial wallflowers, many are biennial, meaning they have a two year life cycle, flowering in the second year.
When planting, choose a spot that is in full sun or partial shade with moist but well-drained soil. Add some horticultural grit to the planting hole which will improve drainage further.
In the right spot, sow perennial seeds from Feb to March, to plant out from May. If you are growing biennials, sow seeds in late spring, ready to be planted out in autumn.