Leaves & Leaf Mold,
nature's mulch & top-coating
This November photo shows a Bunchberry groundcover, complete with an unexpectedly late blossom. For such short plants I have to be careful they don't get burried by autumn's falling leaves, which are otherwise left in place since the garden so wisely self-mulches in preparation for winter. The leaves that have accumulated here are from a Japanese Maple, & from a Choke Cherry.
Leaves break down through the winter into leaf mold for spring, one of the healthiest & best soil-toppings that can ever be had. Nature does know how to take care of herself given the chance! When all but the skeleton of the leaf has melted away, the dark residue is the leaf mold.
Commercially purchased composts are sterile, & that's a good thing for product purposes, but natural leaf mold increases & preserves every conceivable beneficial organism native to the soils: whiteworms, beneficial funguses, & healthful bacteria.
Before the days when people just went to the garden store to buy a few bales of peat or compost or manure, just about everyone would trundle their wheelbarrows into the nearest decidous woods & load up on autumn leaves with which to mulch. Unlike bark or shavings which break down slowly (or never breaks down if there is no nitrogen mixed with it), leaves break down into natural leaf mold very readily merely by being in contact with the ground, because the healthful organisms in the soil immediately recognize autumn leaves & begin breaking down. So leaving the leaves in the garden more or less where they fall results is protection against frost, keeps down weeds during the winter, & by spring it is all transformed into plant nutrient.
There are some mulches that literally have to be removed come spring (straw certainly, bark sometimes) because leaving it on the surface promotes explosive populations of harmful insect &am funguses, hence root diseases, & other problems resulting from leaving unbroken-down matter coating a spring & summer garden. But nature's leaves have largely broken down into wholesome leaf mold at winter's end so never causes a gardener to undertake the extra work of mulch removal.
There could be reasons, in certain situations, to prepare the leafmold artificially before it is added as a top coat in spring, as opposed to permitting the entire break-down process to occur directly in the garden for maximum number of benefits. Such situations occur in places where high winds will carry the leaves away from where they are needed; or in hot dry fire-prone regions where it may even be illegal to not remove leaves & needles from near houses; or just where there are so very many trees that the leaves pile up too high thus smother small plants, so that a percentage of the leaves at least must be removed.
Rapid break-down of leaves requires direct contact with the ground, so when removed to huge leaf piles, they lack sufficient nitrogen to break down rapidly. Breakdown of leaf piles can be fascilitated by the addition of nitrogen to wetted leaves. Leaves that are small (alder, beech, birch, acer japonica) can be put in garbage bags, wetted, a bit of nitrogen or compost-starter mixed in, the bag shoved in some crawlspace out of the way for six whole months. It comes out pure brown-black leafmold. Huge leaves however may take over a year to break down inside a bag, unless shredded beforehand.
Obviously leaves can also be used as the carbon ingredient in ordinary compost piles, but there's something to be said for pure leafmold per se. It has a crumbly attractive appearance that works well as a topcoating lending a dark loamy appearance to the ground. But leaf mold does not completely replace the need for other enrichments, again because of being low in nitrogen.
As some of our gardens' younger deciduous trees grow larger, we may eventually end up with so many leaves we'll have to bag a percentage of them to manufacture the leaf mold separate from the gardens. But presently we let it happen naturally right in the gardens. At most we shift autumn leaves from areas where there is too much leaf-fall to areas that are insufficiently mulched, & rake leaf-fall off lawn areas into gardened spots. In the majority of locations leaves don't need any attention, the trees naturally mulch the ground for themselves, & all we have to do is knock a few leaves off the heads of shrubs & perennials & make sure nothing short or with flat basal leaves gets buried.
People who regard fallen leaves as unappealing & discard them seem to me to have entirely the wrong idea. There's an aesthetic appeal to leaves in the process of decay. There is a decided beauty to the leaves themselves, which misnomered "beauty bark" simply never has, plus the familiar smell of "autumn decay" is one of the great smells in nature, no less appealing than spring's flowery perfumes.
So falling leaves left in place are a no-maintenance source of health & beauty for the garden. Part of the benefit fallen leaves provide is in the slow break-down process itself, which maximizes the presence of beneficial microscopic organisms & more visibly of whiteworms.
The whiteworm is sort of a miniature earthworm. It is one of the great under-appreciated garden friends, helping benificial fungus & bacteria create quality leafmold right there in the garden, not to mention the whiteworms' eency worm castings. Without fallen leaves in the garden, there will be no white worms to speak of, & their absence has a domino effect for the natural balance throughout the gardened areas, but especially in a woodland, shade, bog, or cottage gardens.
When you have a healthy quantity of whiteworms, this is evidence of a wholesome balance in your yard. The white worms have another use, too. You can lift up whole decaying leaves & collect white from the wet undersides of the leaves, & feed them to your goldfish or tropical fish. Whiteworms seem to thrive in cold autumn & even in winters that are only in the 20s, so its a cold-weather live food source for the fishies, not to mention for any winter birds that like to pick amidst garden rubble for bugs & worms.
Here in the northwest where winter is not so cold the ground rarely needs protection from freeze, but it certainly does need protection from being compacted & rinsed of nutrients by our hard rains. The hard rains on leaves help break down the leaves into nutrient particles, hence harsh weather seasons become slow-release fertilizing events rather than slow-leaching-of-nutrients events.
There is only one drawback to fresh large leaves as a mulch. Large leaves, or leaves piled too thickly as mulch, can under some conditions nearly function as a plastic barrier causing rainfall & waterings to run off before it soaks into the ground. This can be great to protect areas of bulbs at risk of winter rot, needing protection from too much rainfall in winter. But for plants other than bulbs, too much of a barrier can keep things from being sufficiently watered. This won't happen if there are unexpectedly summer-like "dog days" in autumn that make the leaves brittle for a few days, after which they crack & break up just enough to not form an intact waterproofing barrier. Or this small possibility of too much of a rain-barrier can be mitigated just by making sure there aren't too many layers of the leaves in one place, moving excess leaf-fall to other areas of a garden that get too little self-mulching from deciduous trees & shrubs.