The greatest threat of frost usually occurs overnight when the temperature drops enough to freeze the moisture on plant leaves and buds. The signs of frost damage are usually visible within two to three days and are included blackened leaves or mushy leaves and buds. To protect plants from frost, you will need to cover them to keep the moisture from freezing.
Use sheets, light blankets or burlap to protect your plants and trees from frost damage. Hardware stores actually sell large sheets of light, porous cloth for this purpose. Don't have extra sheets and new ones are too expensive? Try buying sheets at a thrift store. Don't remove plant and tree frost covers if it is still dark, and preferably not until late in the morning the next day. Some of the coldest temperatures are just after sunrise.