Ever wonder what to do with the shells of nuts from walnuts, pecans and pistachios? One idea is to save them and scatter them as mulch in the garden. If there is any residual salt on the shells, it will help deter slugs from attacking your plants. Use the shells for indoor houseplants, too. If there is residual salt on the shells, simply soak them in water first to remove it. Line the bottom of a planter with shells and fill it with soil. This will help provide draining for the plant, and the shells will eventually decompose.