Various kinds of mats are used to protect plants in hotbeds and cold frames. In some sections lath crates about 3 inches thick, stuffed with fine hay or sea weeds, are used for this purpose. They furnish excellent protection, but are heavy and inconvenient to handle. Burlap mats stuffed with cotton waste are on the market, but they are difficult to keep on the frames in windy weather; they furnish poor protection when wet and are lacking in durability. Canvas mats are satisfactory, but are too expensive for general use. When all points are considered, rye-straw mats are most serviceable; they are inexpensive, are not easily displaced by even hard winds and furnish thorough protection. Machine-sewed mats of this type, as illustrated by Figure 40, are on the market, or they can be made by hand. The mats made by machine are uniform in thickness and are much neater than can possibly be made at home, unless an unusual amount of time is spent on each mat. When not in use, mats should be stored under cover where rats and mice will not damage them. With good care they will last several years. A mat is generally large enough to cover two sash, 6 x 6 1/2 feet being the popular size.
Shutters are sometimes used instead of mats in covering frames. They may be made of light lumber and may be of any convenient size. When used alone on frames they do not protect the plants nearly as well as mats. Sometimes shutters are used over the mats, which they protect from rain and snow.