I don't know what the absolute minimum distance between plants would be in order for them to still grow and bloom like they're suppose to. But I'm sure the more room, the better. I've read articles about the dahlia clumps grown by the Dutch that are imported here and sold in garden centers and big box stores. It sounds like they're planted in very tight rows with the plants practically touching each other. Blooming is probably minimal but not a concern anyway. Crowding them close together produces smaller clumps that are easier to package. Anyone who has dug dahlias in the fall knows 3 of those clumps would never fit into a bag like those sold at Walmart, Home Depot, etc.
I agree about the rain and have considered growing rice. Only half of my dahlias are planted and none of the tomatoes. We had a brief heavy t'storm this morning and another warning has been issued for tonight for heavy rain and possibly hail. Definitely don't need either!
One good thing about later blooms around here is it sometimes allows you to miss part of the Japanese Beetle invasion. Early blooms are great but mine usually get eaten anyway.
