Hardy annuals are plants that complete their life-cycle in one year - they are sown, flower, and ultimately die. They are capable of surviving a frost without the need for protection. Hardy annuals can tolerate a frost that damages their foliage, however do need some protection if a heavy frost is predicted. This is because any damage done to their roots, such as from a heavy ground frost, can ultimately kill the plant. You can protect hardy annuals using cloches or by covering them with fleece.