Do you have any images of this happening? I suspect something else other then rain is at the root of the problem.

It might be that dahlia growing is not for you, if this problem has you looking at 'throwing in the towel.' Perhaps easy to care for perennials is more to your taste. I don't say this to be 'mean,' but dahlia growing does take dedication and time. Great results rarely come from tossing the tubers into the ground and walking away.

Oh, I didn't find your reply mean, just patronizing. At age 70, I've grown many unusual and labor intensive plants.

What type of Dahlia are you growing? The really big ones should have their flowers far above any watering. Mine blooms at above 5ft.

Also, I do find that rain shortens the bloom life. They get kinda"soggy' when they are approaching past prime. However, they open just fine for me. I also find that rain will significantly weigh down the blooms. Next year I might construct heavier gauge supports.

Not really an expert, just trying to expand the conversation.