Wallflowers set their seeds the same way do: in little tubes that line the
spent flower stalk.

When is a good time to collect the seeds? Can I cut the stalks now and
hang them to dry or do they have to come to a certain state of ripeness
while still on the living stalk?

I was wondering if I should collect them now before it rains today. (At
least I hope it's going to rain today.)