Yes, an old sheet laid over them will work nicely. Or paper bags upside down. If you have a small number of small plants, little "hats" of crumpled newspaper work well. Anything that will stand between them and a light frost, basically.

I've often "put my garden to bed" by laying old sheets over my veggie garden when frost is expected! I'm always too anxious to wait for my no-frost date, so I run into a few frosty nights each spring. I've used lightweight blankets to wrap around garden planters and hanging baskets too. Just use a clothespin to prevent the blankets from shifting around. Don't worry if the sheets/blankets touch your plants...just as long as they don't add too much weight, they won't harm anything.
Great gardening to you, Justine

Thanks to you both for the great tips.

I got some kind of fleece to protect my lettuce from the heat a few years ago and now I can't find it anywhere. Nobody knows what I'm talking about. Does anyone here know about this. In one of my garden books it was called "Agricultural Fleece" but it was called something else when I bought it at canadian Tire . Sure would love to get some again with this hot spell we've been getting.

I just bought one the other day at a larger garden centre (Hole's) to protect my brussel sprouts from cabbage butterflies. They are also referred to as "row covers". I haven't seen them at CT or Home Depot/Rona type stores, but then I probably wasn't looking for them. LOL! Probably a bit cheaper at those stores than at the garden centre.

Shauna