Use Compost in Place of Fertilizer

Sudan grass without compost (above) and with compost applied (below) growing in Amargosa Valley, Nevada. Composts can provide alot of benefits to plants including much needed nutrients that improve color and growth.

Q. If I make my own compost, can I use it instead of commercial fertilizers for grass, plants, trees, shrubs?

A. Yes you can. But please be aware that homemade compost is not consistent in fertilizer content and quality. This is because of variability of different ingredients used to make the compost. The ingredients used to make compost directly impact the nutrients found in compost made from it. However, compost is universally good, whether it’s commercial or homemade, when added to soils as a soil amendment.

Spreading compost on vegetable plots between palm trees for soil improvement and fertilizer content.

            When using compost as a substitute for fertilizer, it is important to know its carbon to nitrogen ratio (C:N), in other words how much nitrogen fertilizer it contains. The nitrogen content of a compost is critical. High nitrogen content (low carbon to nitrogen ratio) makes compost “hot” and less of it should be used. If compost has a high carbon to nitrogen ratio (low nitrogen content), then more of it should be applied when substituting it for fertilizer.

When applying compost to lawns a compost drum spreader is used to apply it evenly.

            Commercial composts aim for a carbon to nitrogen ratio close to 20:1 or twenty times more carbon than nitrogen. As this ratio increases to 40:1, the nitrogen fertilizer content decreases. At a ratio more than 40:1, the compost is still valuable but it’s value is greater as a soil amendment rather than fertilizer.

When applied to fruit or landscape trees, compost can be applied in a circle around the trunk so that it doesn't damage the tree. It is then watered in.

            The carbon to nitrogen ratio in homemade compost is managed through what is added to the compost mix before composting. “Woody” additions to compost like wood chips, sawdust and shredded newspaper (sometimes referred to as the “brown” component) increase the carbon to nitrogen ratio.

Compost piles have ingredients that are shredded, water is added to help it all "rot" and  the pile is turned when the temperature inside the pile gets hot, around 160F. Manures are usually used to get the nitrogen content high enough for rotting to begin.

            Additions of grass clippings, leaves of trees and shrubs, and vegetable scraps (referred to as the “green” component) lowers the carbon to nitrogen ratio and make it more valuable as a fertilizer.

            Animal manure (think of it as a concentrated “green” component) is high in nitrogen and added to get the carbon to nitrogen ratio low and improve fertilizer content. If lots of different components are mixed together in the right proportions, green components are balanced with brown components, homemade compost has all the nutrients needed by plants.

            The short answer is “yes”. But substituting a homemade compost for a fertilizer application varies from batch to batch depending on what was used to make the compost.