You can start some now if their germinating temperatures are warm enough. You will have to look at the packets or look on line for each variety. Many perennials germinate in cooler temperatures and that is why they are started in the spring. Start them when it is hot and fewer will germinate.

That having been said--if you can give them what they require to sprout then go ahead.

The reason you put a humidity hood on plants has nothing to do with temperature. It is there to keep the seeds moist until they sprout. Once they sprout then you remove the hood. DO NOT put these in the sun with the hood on or you will fry your plants and or seed

This is going to be challenging, I think, unless you start them indoors under lights. I plan to start several types of perennials in late summer, indoors under lights, say around July/August. They'll be big enough to plant out just as the summer heat is breaking (September or so), and hopefully develop nice root systems before the ground freezes. I've had success doing this in years past. The issue with starting anything outdoors now is that it's just too darn hot, and you're in a tough spot because seedlings need light to grow, but direct summer sun is too much for them; hence why seedlings sprout in spring when it's cool. Just some thoughts.

Sleepy, I'm glad to read this since this is what I was thinking of doing. I never have enough room under lights in the early spring to start all the perennials I want - too many vegetable starts! I'm going to start a bunch more now that the veggies are all outside.

I know, my lights are sitting there all lonely, they need some seedlings! We just found out that we're going to move in to a friend's house while she goes to live overseas indefinitely, and she has given me permission to do whatever I want with the yard. It's in sad shape now, but it has a lot of potential, and I get to start from scratch, so I'm going to start some perennials; we've been moving around too much for me to enjoy any long-term flowers, so I'm very happy to settle in for awhile. Now to decide on seeds!

Have you visited Swallowtail Garden Seeds? They have a really good assortment of perennials. I went to the site for bellflowers and ended up with a whole lot more.

Here is a link that might be useful: Swallowtail

Oh, I love them. Also, hardyplants.com, hazzardsgreenhouse.com and geoseed.com are some of my favorites.