Hi,

Thanks for your question.

I would plant your dahlia bulbs as soon as possible. It's true that dahlias prefer a well-drained soil and won't tolerate boggy conditions. However, once established you'll need to check the soil frequently to make sure they're getting enough moisture (at least 1" of rain or water through irrigation/week).

The Minnesota Dahlia Society has some good information. Their "Growing Guide Handout" states that spring soil is naturally moist and that plants "are not watered until they sprout above ground." However, unless you have heavy clay soil I wouldn't worry about the possibility of more rain. Next year you could consider starting the dahlias indoors where you can control the moisture and to give them an early start.