Ranunculus have fine roots that would, if they could, spread out and down for at least 12 inches.

They require excellent drainage. They are NOT like buttercups. (Though buttercups can go mad in silty shingle if there's enough water...)

If it were me: I'd mix up a gritty brew - chunky small grit say 2 parts grit to one part potting medium.
I'd use bigger pots to get the width I'm wanting and I'd plant deep in the pot - with about an inch of mix only, under the plant's existing root ball, then fill in until the fresh mix is level with the original level of the plant. If there are three inches in depth between there and the rim of the new pot - fine.

Then I'd put the plant/s where there's morning sun only. I'd protect from excess rain. And I'd water only when the top has dried out down to about first finger joint level.

I'd feed weakly only - and I'd be looking for roots escaping from the bottom. At which point I'd heave a small sigh of relief - and repot with less grit but still into a very free-draining mix. This time with plenty of depth and room for those roots to really get on with their work.

I'd also remember that the side buds are never going to be as lush in flower as the main buds but slightly stronger feeding could be useful - along with more sun.

PS ensure excellent air circulation at all times to prevent mildew.

Thanks for the advice! I will save it for future reference...but I think I've figured out what the problem was. They're in terra cotta pots, which I know wicks water away...but we had 2 days of hard rain so I was sure that they didn't need watered. But when I finally went outside and started feeling around, the soil was really dry. I watered well and they perked back up overnight. I'm still new to container plants so I guess I'll need to be more careful about watering!

You have received good advice above. I can only add for future reference When you repot any plant, keep it out of the full sun for a couple of weeks at least. That 85 degree sun with roots not yet established was too much. Al

Oh, that makes sense. Taking note! :)

Sometimes growers will ship plants in a peat-based mix because it's lightweight and cheaper to ship. If it dries out it can be seriously difficult to re-wet.

Sounds like that may have happened for you.

If you use tepid water and a drop (not a squirt!) of dishwash liquid in a container big enough to take your plant pot totally, then plunge your plants until the bubbles stop and let them drain well, you can probably re-wet.

However - if the mix is seriously dry - expect to see HUGE bubbles, and even potting mix, hurl themselves to the surface of your dunking pot. Drain - and add fresh mix as a 'band-aid' until you can repot properly. Don't dunk for any longer than thirty minutes max.

(The dishwash liquid helps to break the 'skin' on the water surface so it penetrates a bit better.)

Around here people buy Ranunculus asiaticus (there are lots of different types of Ranunculus) as cool weather seasonal interest flowers - ones that are thrown away after a week or so when they start to look ratty. Not sure if that's what you have.

Oh, they could've been...I got them out of the clearance bin for a dollar. Grrrr! I'm going to try the re-wetting method, too, and see if it revives them. Fingers crossed!