In the fall when many municipalities accept or collect leaves for making mulch and compost, which they sell at low cost, I make a point of driving my old truck around to pick up some bagged leaves placed out by the curb. Other gardeners I know manage to amass a mountain of delivered leaves to share with friends by putting out “Leaves Wanted” signs.
We do this because leaves are one of the best ingredients for healthy veggie garden soil. The fall gold you gather can fuel the transformation of soil into black gold. The valuable nutrients & micronutrients in leaves become available to plants through decomposition by soil microbes.
Earthworms pull leaf pieces down from the surface, eating them as they tunnel through soil, aerating and fertilizing it with their castings (poop), making nutrients available to smaller soil critters and microbes including the beneficial bacteria and fungi that play a major role in decomposition and growth processes.
As long as trees aren’t treated with common systemic “neonic” pesticides like imidacloprid, the organic matter and nutrients in leaves nourish the biology of the soil, creating conditions for plants to thrive.
If you start building healthy soil now, using leaves to feed the worms and microbes, they will do the heavy lifting for you. By the time spring arrives you’ll be ready to plant without rototilling, which rips up the tapestry of soil life, or back-breaking digging.
To speed up the alchemy in your soil it’s best to shred leaves for veggie gardens. You can use a mower or better yet, a leaf-shredding mower, and then rake. Some people use weed whackers inside a trashcan full of leaves. You and the kids might have fun jumping up and down on bags of dry leaves to break them up. But I find the easiest way to transform big piles of leaves into trashcans full of nicely shredded leaves is to use a leaf vac/shredder, usually the reverse setting on those obnoxiously loud leaf blowers. It’s not a very heavy or expensive tool; I paid about $100 and mine lasted 10 years.
Unshredded leaves take much longer to break down when forked in, which means nutrients won’t be readily available, and they can form an unwieldy wet mat on the bed’s surface. If they’re not too big or leathery (like cottonwood leaves), whole leaves can be used effectively as mulch on vegetable and perennial beds, and under shrubs and trees, but if the site is exposed they may blow away. I sometimes mix them with wood chips for mulch around trees, always keeping a 6-inch radius away from the trunk to prevent decay.
I fork or hand dig a lot of shredded leaves into already soft beds each fall along with herbicide-free grass clippings, compost, or whatever I’ve got, depending on what I plan to plant, and water them in well. (Many dryland plants prefer gravel mulches. Wood and leaf based mulches that hold moisture can cause their crowns to rot, especially in winter.) Some gardeners dig trenches in the beds, fill them with shredded leaves and cover with soil. I cover my beds with flakes of hay as organic gardening pioneer Ruth Stout once did in Connecticut and as many permaculturists now do wherever they may be. Spoiled, moldy hay works fine and is cheapest. This creates a moister environment for the soil critters, and wonderfully dark, crumbly soil, full of worms come spring.
Though I’ve heard some say that thick hay or straw mulch “doesn’t work” I have to wonder, (as Ruth Stout did), if they’ve ever tried it. The trick is to use it thickly enough (intact 4-6” thick flakes) so that any seeds won’t sprout. Second cuttings of hay have few if any seeds, but any hay flakes used thickly enough will prevent the light-deprived seeds from sprouting. Thick mulch also smothers weeds; if a few straggle up through cracks between the flakes they’re easy to pull.
Leaves contain all three major plant nutrients (NPK) plus mineral micronutrients that plants need, but potassium is the first to become available through decomposition. If you shred leaves, fork them in to your veggie and perennials beds, water well in the fall, and, if you live in a dry place, mulch the beds with hay or straw the nutrients should be available the following spring. Do this every year and your vegetable garden soil just gets better and better.
To create a new bed, mow any grass short and put down cardboard (a good use in this era of internet purchasing). Wet it, then alternate several layers of compost and shredded leaves on top, wetting down each one. Top with more leaves and flakes of hay or straw if you have it. The volume will decrease a lot over time. Wetting the leaves periodically or placing scrap branches on top will stop them from blowing away. The breakdown process will take a few months longer but you should be able to plant through the cardboard by early next summer. Many Youtube videos show this “lasagna gardening” method.