Back Yard Gardener: Leaf mold compost

Hello Mid-Ohio Valley farmers and gardeners! As we move into the third week of September the lack of rainfall is beginning to show up.

The dry weather has caused some of our lawns to turn brown and go dormant. Don’t worry, in most cases the lawn will regain its green color as soon as adequate moisture returns. A healthy lawn only requires about one-quarter of an inch of water every three weeks to stay alive.

Lack of rain has stressed some of our trees and shrubs, causing marginal scorching of leaves and plant wilting. Evergreens may experience yellowing of interior needles. Most plants will recover with rainfall.

However, drought stress can cause damage to already weakened trees and shrubs which may have more disease and insect problems down the road next year.

This week I want to discuss composting leaves to make leaf mold, otherwise known as black gold. I have noticed many trees are already turning color or dropping from trees in our area from the dry weather. As fall approaches many homeowners will be dealing with leaves in the yard. Why not gather these leaves to make leaf mold, a valuable compost?

Leaves are a natural soil builder, can reduce the need for fertilizer on lawns and gardens and can offer excellent winter insulation for plants. Leaf mold is a nutrient rich soil amendment produced through fungal decomposition of tree leaves.

However, unlike traditional compost that undergoes a heat generating, bacterially driven process, leaf mold is produced through a cooler and much slower fungal driven process. The resulting decomposed material is an excellent additive to soil. It can be mixed in during tillage, or used as a surface mulch for no till gardening.

Leaf mold is different than other compost. Tree leaves are high in carbon and low in nitrogen compared to other compostable materials. Because of this, tree leaves cannot be conventionally composted without adding a nitrogen rich material to increase the carbon to nitrogen ratio.

The high carbon to nitrogen ratio is also the reason that tilling leaves directly into soil is not recommended. The soil microorganisms will use up the soil nitrogen in an effort to break down the leaves, which leads to nitrogen deficiency in plants. However, given adequate time and moisture, separate fungal decomposition of leaves results in an excellent material that can be added to the soil.

The simplest way to take advantage of all the nutrients leaves have to offer is to just gather them up and let them sit to create leaf compost or leaf mold. If you already have a compost bin but have more leaves in autumn than your bin can handle, store leftover leaves in bags or bins. Shredding first can save a lot of space. Depending on how finely shredded the leaves are, they can take as little as one-sixteenth the space of whole leaves.

A simple pile is effective or a wire compost bin can be used to better contain the leaves. The leaves should be moist, but not wet, to provide adequate moisture for the fungi. Let the pile compost or “mold” for two years before using. As a rule, a healthy dose of the fungus to create leaf mold is already present in fall leaves. This is what gets the decomposition process started.

You can speed up the process by chopping the leaves with a lawnmower before piling, and/or occasionally turn the pile. This will increase the speed and uniformity of the leaf molding process and the leaf mold will be ready in about a year. Properly maintained, a compost pile does not smell.

Leaf mold adds valuable organic matter to the soil. This natural soil conditioner improves water holding capacity and enhances soil structure. Research has shown that leaf mold and other composts can increase crop yield, improve plant health, and even enhance a plant’s resistance to disease. As a mulch, leaf mold moderates soil temperature and reduces evaporation. Use the compost when you install new plants, or you can spread it on your flower gardens in spring.

There are a few types of leaves that homeowners do not want to compost into leaf mold. Because of allergic reactions, discard poison ivy, poison oak, and poison sumac leaves rather than risk the adverse effects of handling them. Do not use black walnut leaves which contain juglone and may inhibit plant growth.

It is also good to know that beech, birch, hornbeam, sweet chestnut, magnolia and holly leaves all contain high amounts of lignin and should be shredded before composting to speed up their breakdown in leaf mold. When finished, the leaf mold should be dark and have an earthy smell and be ready to enrich the soil.

Contact me at the Wood County WVU Extension Office, 304-424-1960, or email me at jj.barrett@mail.wvu.edu with questions. Good Luck and Happy Gardening!