What is Kief? When a marijuana plant reaches maturity in its growth cycle trichomes are formed on the leaves and buds of the plant. These trichomes are kief and they contain a higher concentration of THC than any other part of the plant. The buds and the leaves of the plant also contain THC, but trichomes are by far the most potent part of the plant. What can you do with Kief? You can use kief to make THC infused butter or oil