It is not valid to train a vine, gourd, or ivy to cover a sukkah and then cover it with sukkah covering ("s'chach"). If, however, the sukkah-covering exceeds the vine, gourd, or ivy in quantity, or if the vine, gourd, or ivy is detached, it is valid. The general rule is that one may not use for sukkah-covering anything that is susceptible to ritual impurity ("tumah") or that does not grow from the soil. But one may use for sukkah-covering anything not susceptible to ritual impurity that grows from the soil.