Fertilizer for Your Lawn Mulch is a great way to help your grass stay green and healthy year round. The best time to fertilize lawns is in the spring as they are actively growing. Give them a dose of composted manure, pine needles or wood chips from trees that have been cut down recently. Make sure the material you use has not been treated with chemicals so it won’t burn your grass! Also make sure you don’t overdo it on this step; too much fertilizer can burn the roots of your plants and cause them to die off early which can really hurt their overall health (especially if they were heavily seeded).