Leaves- natures (almost) perfect mulch

31 Oct

Every year, as the trees start to drop their leaves, my neighbor rakes them up, or at least has his gardener do it for him. And every year, I have his gardener pile them up here so I can use them.

They are particularly useful this year since I have so many beds that are more or less starting from scratch. Leaves are great for putting over the top of compost and soils you think (or know, lol) are full of weed seeds. They are a great way to smother most seed growth, though if your careful not to go too deep, most perennials can grow through most leaves no problem. Evergreen stuff you may have to carefully pull the leaves through the mulch back into the sun, such as it is this time of year, but other than that leaves are pretty easy to deal with, and as they break down they are the perfect organic matter to add to soils.

At this point I can recognize different leaves for different purposes:

Oak and chestnut take longer to break down, and have more tannins in them, which act as a chemical weed suppressant as much as the physical leaves deter the weeds from coming up. Oak especially stays while and amazingly “fluffy” for often at least two years, so is a good choice for putting around trees and shrubs where you are building up the soil, but don’t want to bury the trunk too much all at once. Eventually they do create a beautiful composted mulch to soil, but it takes a while.

Chestnut on the other hand tends to collapse fairly quickly, and between the dense mat of sodden leaves and the allelopathic chemicals, is a great mulch for patches of stubborn perennial weeds like creeping buttercup (Ranunculus repens) and grasses. It simply smothers them and prevents seedling growth for a good year or two.

Big-leaf Maple are big and whole, work good in areas where you want to cover a lot of ground quickly. They tend to mat down by the end of winter, and smother seeds well but usually break down by the end of the next summer. They make a terrific mulch for newly created beds you make in the fall to plant in spring, and other existing shrubs where you basically just want to discourage weeds. If you grind them up into a finer leaf mulch, they work great for perennial borders where you can feather them in between perennial stems for eventual soil building and weed control in one. They also work great stuffed wet in have to make leaf mild for potting soil and such.

Alder is one of the best soil building leaves you can get, since it breaks down quickly and contains more nitrogen than most leaves. Dry, they almost fall apart just moving them around. They are some of the best for using in perennial beds and areas where you want to give a quick boost, and added to compost piles as the “brown” component usually make quick easy compost. Oak by contrast takes ten times as long, even in hot composting.

If your lucky enough to have locust or mimosa leaves available, these break down even faster, and are even better for soil building. Usually these break down so fast that most gardeners don’t even need to do much with them.

Camellia and most other evergreens have tough leaves that take a long time to break down. Like oak, they work well in areas where you can let them take their time to break down. Dried and shredded, they will break down faster, but still tend to smother more delicate perennials, so work best under shrubs where there aren’t as many perennials growing.

Fir, Hemlock and to some extent pine and cedar needles make a great very distinctive soil as they break down. If you like native woodland plants, there are things that grow beautifully in this “needle duff” that won’t grow anywhere else. If you don’t have the trees that produce this leaf litter, importing it can take time to build a suitable base, but can be lots of fun finding the plants that like it, and weeds typically don’t.

For the most part, leaves are one of the cleanest mulches you can put down. Few diseases are spread by leaves, though there are some. If you have black spot on your roses, rake those up and throw them in the trash. Same if you have anthracnose on you dogwoods and other susceptible plants, or rust on the backs of the leaves on anything. I’ve even read you shouldn’t burn these, as the pathogens may be able to ride the smoke and reinfect anything nearby susceptible.

You also want to be careful not to go too deep, or you can actually create a moisture barrier. Whole leaves should at least cover the ground, but no more than 4-6 inches depending on the size of the leaves. The bigger leaves can go a little deeper, as they usually compact more over the winter months. Shredded leaves usually can make a good mulch at an inch depth, two to three should be ok so long as they aren’t covering and evergreen perennials or shrubs, but more than that is pretty much overkill unless you want more soil building and don’t have much in the way of plants in the bed.

If nothing else, disease free leaves can be bagged up to make a really nice potting soil ingredient called leaf mold. After the first rains, just fill big bargains bags, tie them off and let them sit, preferably in a little sun to warm them up, but that’s not essential. Usually by spring, the leaves will have broken down into a soil like mulch, which can be used with sand, perlite, etc in place of or in addition to peat moss as the organic component in potting soil mixes. I prefer using leaf mood when I can, since the peat moss is mined from ancient peat bogs, whereas leaves are a free renewable resource. I just have to remember to do it in fall when I have the leaves.

You can also directly compost leaves of course, mixing them with weed tops, grass clippings etc. If you “hot compost” you know dry leaves are one of the best and easiest sources of brown material in the fall. Even if you just pile stuff, layer leaves with lawn clippings, green leaves of whatever kind (an old trick is to have something like comfrey planted near your compost bins, which can be harvested when needed to add leafy green matter to your compost). Get the right ratio of green to brown, and things will hear up quickly an create compost fast for use in the garden.

So next time your raking leaves, consider carefully what to do with them. I know I can always use more!


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