Q. Is it safe to use toxic plants in compost or mulch? I have a lot of pokeweed, and I understand only the young leaves are safe to eat, so I had been putting the mature leaves and stems in my compost pile. Then I heard that rhubarb leaves should be added only to a very hot compost pile. I don’t want to make poisonous compost, but I hate to waste all this green matter!
A. Unless you plan to eat your compost—which we do not recommend!—there is no harm in putting leaves and stems of plants such as pokeweed (Phytolacca americana) or rhubarb (Rheum rhabarbarum) in your compost pile—whether it’s hot or not. The compounds that make some plants unsafe for human consumption are not a concern in the biology of a compost pile, and they are unlikely to have an effect on the quality of the finished compost or on plants or soil to which the compost is applied.
A far greater concern of putting pokeweed in your compost is the risk of spreading that vigorous weed throughout your garden by way of seeds or pieces of roots that readily grow into new poke plants whenever conditions suit them. Even a hot (160°F) compost pile may not guarantee the roots’ demise. Let the plants dry out in the sun for several days—until the fleshy roots are dry and shriveled—before adding them to the compost pile.