Making leaf mould

Judith Adam

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Gather fallen leaves to make leaf mould: your soil will thank you.
Gather fallen leaves to make leaf mould: your soil will thank you.
Gather fallen leaves to make leaf mould: your soil will thank you.

This is almost too easy. If leaves are left in a pile and exposed to moisture, they will compost into a dark crumbly mass that is perfect for improving soil texture and moisture retention. Leaf mould is an effective conditioning material for mulching the lawn, and a nutritious soil amendment for planting holes. (Tree leaves contain about twice the mineral nutrients found in composted animal manures.) Mature trees pull minerals from deep soil lying just above the rock underbase. Most of these rock minerals are used in the leaves, in the process of photosynthesis. When tree leaves degrade, they return minerals to the soil. For example, sugar maple leaves are about 5 per cent mineral content, while pine needles are about 2.5 per cent mineral. Both contain calcium, magnesium, nitrogen, phosphorus and trace elements. Using a mix of different leaves results in a broader range of minerals in the finished leaf mulch.

The simplest method for producing leaf mould is to rake fallen leaves into a loose, low pile, somewhere out of the main flow of wind. I gather drifts of leaves under the low branches of large conifer trees, and let them sit there to compost until needed. For a pile out in the open, a long piece of chicken wire  laid over the top and anchored with bricks or rocks on the corners would prevent wind from scattering the leaves.

The leaves on the bottom of the pile will be the first to degrade and produce crumbly material. In summer, be sure to frequently spray water from the hose over the piles to replenish evaporated moisture (fungi and bacteria need a moist environment to work effectively). I usually leave the pile alone for a year, and then fork it into a wheelbarrow for use in the garden. Adding a nitrogen source to the pile of leaves speeds up the process. A few sprinklings of lawn fertilizer mixed into the leaves is sufficient. Bloodmeal also works, but it will attract animals.

It’s also possible to produce leaf mould in large plastic garbage bags. Be sure the leaves are moderately moist before putting them into bags, along with a sprinkling of lawn fertilizer. When the bags are filled (and don’t pack them too tightly, the leaves should be able to move around inside), leave the tops open and poke holes in the sides to allow air passage. Store the bags outdoors, perhaps along a fence or behind a garage and out of sight. Check them in early summer; you’ll probably find partly decomposed leaf mould. The material is certainly usable at any point in the process; it’s not necessary to wait for the leaves to entirely break down.

And did I mention that this most perfect soil amendment is entirely free?

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6 thoughts on “Making leaf mould”

  1. I live in Cobourg Ontario and have a very large Black Walnut tree on our property line. One Clematis that does well next to this tree is the Sweet Autumn Clematis. The Rouge Cardinal clematis does so-so. Also the Hardy Kiwi Vine – Actinida Kolmirta thrives.. Every other vine seems to struggle, although I have one honeysuckle- Dropmore Scarlet that is thriving . With the rest of my smallish garden, I have stuck to the recommended list of Juglone tolerant plants but even they can be a hit or miss for me.

  2. I am very interested in the article on making leaf mould. Almost all the trees around my yard are black walnut so I am aware of the issues of juglone and try to graden accordingly. I have searched around on line and have found the following: you cannot use black walnut leave for leaf mould because of the juglone content of the leaves; walnut makes great leaf mould because the juglone discipates as the leaves break down; there is not much if any juglone in the leaves of black walnut, it’s mainly in the roots; you can make leaf mould from walnut leaves but don’t put it on your vegetable garden.

    Do you have any information or can you recommend a definitive source of information on the juglone content of black walnut leaves?

  3. Hi Sharon,

    Thanks for all the information about growing near black walnut trees (Juglans nigra). When considering this problem, it’s best to also include two other well-known and loved walnut trees, butternut (J. cinerea) and English walnut (J. regia). Walnut trees are allelopathic plants, meaning they produce a chemical (juglone) to inhibit the growth of other nearby plants and eliminate competition for moisture and nutrients. The black walnut is known to produce copious amounts of juglone, and it’s uncertain how much is produced by other walnut species. Hardiness zone, soil character and growing conditions also affect the amount of juglone produced and how effectively it’s absorbed by other plants.

    Although the roots of walnut trees exude the greatest amount of juglone, all parts of the trees contain the chemical. It seems a shame to waste the fallen leaves, and rather than dispose of them, they can be used as mulch under the tree, all the way out to the drip line.

    If walnut leaves are mixed with other tree leaves in the preparation of leaf mulch, plant scientists suggest that the composting process degrades the juglone. That makes sense to me, and I wouldn’t hesitate to use walnut leaves as one component in a compost pile. However, it would be wise to wait until the full pile degrades to finished compost before spreading it.

    I wouldn’t consider using lime on garden soil, unless you already know your soil is strongly acidic, and below 6.0 pH. Adding lime to slightly acidic soil (6.3 to 6.5 pH) or neutral soil (7.0 pH), or alkaline soil (above 7.0) will inhibit plant growth.

    — Judith

  4. What about the leaves from walnut trees? Very little grows in the close proximity of these toxic trees in city gardens. Do the leaves have to be raked up and disposed of, or can they be left on the lawn overwinter?


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