--If you have horse farms nearby, these homeowners may let you pick up truckloads of that rich manure/straw combination for free. Once this breaks down, this is a rich compost material -- a great natural lawn fertilizer. --Earthworms are one of nature’s best soil builders. They aerate, leave castings that increase microbial activity, reduce compaction, and help churn the soil, to name a few. While it is not recommended, in some cases, to purchase earthworms, organic matter is a food source for them (including manure). The adage “If you build it, they will come,” applies. Another benefit of using organic methods on the lawn is that you are not using pesticides, which can be toxic to earthworm populations.