Purchasing plastic sheets, pricey "tents", or "walls of water" really isn't necessary. Bricks work well, if you have or can find them easily and cheaply. If not, other recycled products, such as opaque gallon milk jugs, also work very well in spring for a wide variety of plants. Just cut out the bottom and mound up the soil around the sides of the jugs so that they do not blow away. These jugs and their lids can be saved, stored, and reused for many years. The caps allow gardeners to keep seedlings warm on cold nights and can be removed during warm days.