Leaves offer great benefits to wildlife and your garden’s soil. Don’t throw them away!
In another post I extol the virtues of letting leaves do their thing. By that I mean allowing them to do what nature intended: Protect and enrich the soil, offer food for ground-feeding birds, provide a nursery for butterfly larvae/pupae and cover for overwintering queen bumblebees and other beneficial insects and microbes, afford animals like frogs and salamanders places to hunt and hide, and myriad other ingenious things. Leaf litter breaks down with the help of mycorrhizal fungi that move carbon into soil, extract nutrients for plants and protect them from disease, lessen soil erosion, and play a very important role in storing the gigantic pool of carbon within soil.
I’m not sure how leaves got such a bad reputation—I constantly see and hear people blowing them and raking them not only from hardscape and lawn (which is understandable), but also from bare soil. I’m not sure what the aversion is, unless it’s another kind of “biophobia,” in this case a fear of organic materials. Another no-no is putting leaves in the trash, which ends up in landfills. The US EPA says that nationwide, 13 percent, or 33 million tons of municipal solid waste is from leaves and grass and tree/shrub trimmings. Here in Portland, as well as some other cities, there is curbside pickup for green waste for those who don’t compost, and the city picks up leaves from the streets of leafy neighborhoods every autumn to make leaf compost that residents can purchase for a modest fee. But using them in your yard is even better!
How to do it: For areas like driveways, walks, sewer grates and drainage pathways, rake them up (but please don’t use noisy, polluting leaf blowers), and use them as follows:
Mulch your beds.Take raked leaves from hardscape and lawn and place them in your planted beds, a couple of inches thick to protect the soil and provide insulation from the cold (if you live in a very cold climate, add more). Keep them off of tree and shrub trunks and perennial crowns to prevent rot. Try to do your raking on a non-windy day and consider moistening them after you apply them if it’s a dry day. Don’t shred leaves before applying—it won’t help the wildlife described above.
If you must have lawn, leave small amounts of leaves on it and mulch them in situ. Use your mower to shred leaves on grass to improve lawn health by naturally fertilizing the soil. Freshly fallen leaves are high in minerals, and don’t kill soil organisms like synthetic fertilizers do.
Make leaf compost. Collect leaves to compost separately to make leaf compost (also known as leaf mold), a great soil conditioner. If you have a lot of space, simply round them up into piles and let nature break them down with fungus and microscopic creatures. Shredding large leaves will speed up the process. If space is lacking or you want more control, create round chicken wire enclosures and fill them with leaves. You can also dig large depressions and fill them with leaves. Keep piles moist (but not completely saturated) and add more leaves as they sink down. During excessively rainy periods, consider covering the pile. In a year or more (depending on the type of leaves used), after the leaves have broken down, you will have some very dark, crumbly humus to add to your veggie beds and other places that need high quality soil.
Add leaves to your mixed compost bins, heaps, or cages. In your mixed compost bin, add collected leaves—which are mostly carbon—to help balance the “greens” (compost should be roughly half “greens” and half “browns”). Consider storing extra leaves and adding them to your compost bin throughout future months.
Save some for spring. If you have a large amount of leaves, put some aside—or just take some from your leaf compost heap—to use as mulch next year. Mulch applied in spring, after the soil warms, helps maintain soil moisture and protects the soil from oxidation. Be sure to leave some soil bare though, because the majority of native bees nest in the ground and cannot get through thick layers of mulch.
One word of caution: Leaf compost generally makes the soil slightly more acidic. This won’t be a problem for most Pacific Northwest native species, which evolved in slightly acidic soil. But when using leaf compost in vegetable beds, test your soil’s pH—it may need a bit of lime to keep the soil neutral or slightly alkaline, which many cultivated vegetable plants need.