They have a name for everything! I few months ago I was reading the book “Let It Rot!” and I found out that a practice I’ve been observing for years had a name - sheet composting.
Sheet composting is one of the easiest ways to add organic matter to your soil. There’s no compost pile needed, no turning, no layering… in other words, none of the things that can make composting difficult. It’s the most passive of all composting methods but it really works and fall is a great time to do it.
So what is sheet composting? It’s the process of spreading a layer of organic material on the surface of the garden and working it into the soil. That’s it! The major material that I use for sheet composting is leaves. Instead of raking them up and bagging them, I add them to the garden. Over the years I’ve learned a few tricks to make the sheet composting process work well for me.
The first thing that I do is shred the leaves. A whole leaf can take a long time to break down. Shredding the leaves provides more surface area for microorganisms to perform their work of turning vegetable matter into hummus. I have a lawn vacuum that shreds the leaves but you could also shred them by running a lawn mower over them.
I then spread the shredded leaves on the garden soil. The leaves are often in a layer 4-6 inches deep… it seems to get deeper every year as the trees grow larger. To have a good sheet composting experience, be sure to work the leaves into the soil. I made the mistake one year of not doing this. I left the leaves on the surface of the garden. The leaf layer provided a thick mulch that didn’t break down very much over the winter. But worse than that, the leaves prevented the spring garden from drying out and kept the soil too wet and cool. Now I always till the leaves into the soil.
The other thing I do is add nitrogen to the soil when I’m tilling in the leaves. The organisms that break down organic matter need nitrogen to thrive. Tree leaves are very high in carbon and low in nitrogen, so the incorporation of some additional nitrogen to the soil will help break them down. Phosphorus and potassium aren’t necessary for this process, so look for a fertilizer with high nitrogen (the first number on a bag of fertilizer) and little or no phosphorus and potassium (the second and third number on the bag.) I use blood meal as an organic source of nitrogen (12-0-0). Fresh manure, if you have a means of obtaining it, would provide the needed nitrogen. You could also use a lawn fertilizer (like 29-2-4) - just make sure that there isn’t any herbicide or insecticide in the lawn fertilizer that you choose! A light coating of fertilizer mixed into the soil with the leaves will provide the nitrogen needed to break them down into hummus.
That, in a nutshell, is sheet composting. Throughout the winter, as long as the soil isn’t frozen, the soil microorganisms will continue breaking down the leaves. Come spring, while some leaf pieces will still be present, the sheet composting process will certainly have helped increased your soil’s organic matter content and improved its tilth. Plus, it keeps all of those leaves out of the landfill!
Marc Baase is a contributing writer for Mike the Gardener Enterprises, LLC the exclusive home for the Seeds of the Month Club.