Is it possible for wallflowers to get clubroot?
All members of the cabbage family, cruciferae, can suffer from clubroot which is caused by a slime mould, Plasmodiophora brassicae. Liming the ground will help to keep it at bay in future and if you raise your wallflowers in pots before planting them out, that will help too. It will make a lot of extra work, though.