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As a founding employee of Gardener's Supply, I wore many different hats over the years. Currently, I have my own company called Johnnie Brook Creative. The gardens around my home in Richmond, VT, include a large vegetable garden, seasonal greenhouse, cutting garden, perennial gardens, rock garden, shade garden, berry plantings, lots of container plants and a meadow garden. There's no place I'd rather be than in the garden.
In Britain, leaf mold is the connoisseur's choice for mulching perennial gardens. It's easy to see why this cocoa brown, sweet-smelling, moisture-retentive mulch is so popular. In the U.S., few gardeners even know what it is. That's probably because the only way to get leaf mold is to make it yourself.
Leaf mold is nothing more than partially decomposed leaves that are somewhere along the continuum between shredded leaves and humus. If you wonder what it looks like, next time you're in the woods, just kneel down and push away a small area of dry leaves. Underneath, you'll reveal a layer of leaf mold — a crumbly brown material with a pleasant, earthy scent.
Leaf mold has several great attributes. The first is that it can hold up to 500 percent of its own weight in water. Besides helping retain moisture in the soil by reducing evaporation, leaf mold also absorbs rainwater to reduce runoff, and in hot weather, it helps cool roots and foliage.
Most leaves are slightly acidic when they fall, with a pH below 6. However, as the leaves break down into leaf mold, the pH goes up into more a neutral range. Leaf mold will not correct pH problems, but will have a moderating effect.
Over time, yearly applications of leaf mold mulch can significantly improve the quality of your soil. The result will be better water-holding capacity, a more friable texture, and an increase in beneficial soil life. Though leaves are not high in nitrogen, phosphorus and potassium, tree roots mine calcium, magnesium and many other trace minerals from the soil and your garden will also benefit from these nutrients.
Unlike making regular compost, making leaf mold is a "cold" composting process. The decomposition is done primarily by fungi, rather than bacteria, and it is considerably slower. The rate of decomposition is largely determined by four key factors.
The simplest way to shred leaves is to run over them with the lawn mower a few times and then rake them up. You can also rake the leaves and run them through a leaf shredder. Or use a hand-held leaf vacuum with a shredding capability.
A leaf pile needs to be fairly substantial in size, in order to retain enough moisture and heat to get finished leaf mold within 12 months. Six feet square and five feet high seems to be an ideal size. It takes about 25 trash bags full of leaves to make a pile this large.
A second option is to pile the leaves into a wood or wire enclosure. Again, 4 or 5 feet square is ideal. Wet the pile thoroughly and cover it with a tarp. Check the moisture level several times during the year. It should be like a well-wrung sponge. If you live in a dry climate, you might want to line the enclosure with cardboard or plastic to help retain moisture. If you have a minute when you're checking the moisture content, use a fork to stir the leaves and incorporate a little fresh oxygen.
Another easy, yet very effective way to make leaf mold, is to pack the leaves into black trash bags. If the leaves are fresh and shredded, just moisten them, close up the bag, and poke a few holes in the sides of the bag. If the leaves are whole or dry, moisten them well and add a shovelful of garden soil, compost or manure. Then just stash the bags out of the way for a year or two.
Leaf mold is ready to use when it's soft and crumbly. Distribute it around your perennials, vegetable plants (shrubs, too if you have a lot of it), no more than about 3 inches thick. Because leaf mold retains so much moisture, be sure to keep it several inches back from the crown or base of the plant. This will help prevent pest and disease problems.
You can also incorporate leaf mold right into the soil. Unlike raw leaves, it will not steal nitrogen from the plants around it, so it’s safe to use in vegetable gardens and around annual flowers. You can also add it to new garden beds, use it instead of peat moss to lighten the soil in containers, use it to enhance the soil in a shade garden, or to improve any soil that’s too sandy or too heavy.
Someday, gardeners here in the States may catch on to the value of leaf mold. Leaves are certainly an abundant natural resource in most parts of the country. For now, they’re still free for the taking, so don't delay. Grab a rake and start making your own super-premium, extra-fancy leaf-mold mulch.
Last updated: 2/13/19
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