kill them, they are about as potent as the reallly reallly brown swaagy brick weed with tons of seeds, the stuff that tastes like wet grass and makes your fillings fall out. and the pollen is nasty in your nose, makes it drip like a faucet, the best place for them is cut at the stem and tossed in a creek or pond, to ensure the polen wont become airborn as the plant dries out. but i usually just toss them in a pile by my plots.