The best way I've found to deal with a lot of potted plants during the summer is to put them in a baby pool in the shade. Then put a couple of inches of water in the pool, and leave it for a few days. Three or four days later, the water should be gone, and the plants starting to look a bit droopy, so the process is repeated. A bit more water starting out, and they can be left a week.

The only problem I've ever had with this was when it started raining, and I forgot to get the plants out of the pool. Weeks and weeks of sitting in water isn't good, but if the pool dries out between fillings, it works well.

Thanks, that's a good idea!

If they don't all fit, do you think the basement idea would be bad as a backup?

I find that my closed garage stays cooler than the outside. It also has windows so the plants get some light. I water them really well and can leave them in the garage for a week. They need to be reintroduced to the outside slowly so they don't burn, put in a shaded area for a few days. Your basement should also work if they get light.

Great, thanks! My basement does get light and is usually quite a bit cooler than the outside, and since I've got many pots it's good to have two possibities.

^Just make sure you aren't bringing in bugs as well...

I keep many pots of perennials outside till they are a good flowering size - I make a long windbreak using poles and green shade netting and line the pots (at least 5inches, 1litre size) along the length of it. I can keep a few hundred pots going as long as they are both out of strong winds and direct sun. I water by hand, just running along the rows a few times with a 10litre can.