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Mulches tend to be an aesthetic tool for many gardeners, creating pretty coverings for the empty spots between plants. So it’s not surprising that most mulching happens during spring and summer when gardens are at their aesthetic peak. But organic mulches are hard-working garden helpers that benefit your plants, your soil and the environment all year long. Spreading a nice, thick layer of organic mulch in fall can bring many benefits to your plants, because mulch plays many roles in managing the soil environment:
Insulator: A thick, insulating blanket of mulch lessens the effects of freeze/thaw cycles in spring by keeping the ground frozen during an unexpectedly early thaw, preventing plants from starting to grow prematurely.
Weed Blocker: A layer of mulch around your garden plants blocks sunlight to the surrounding weeds, keeping them from growing or even germinating in the first place.
Water Manger: Using mulch keeps heavy rains or snow melt from compacting your soil, and slows the evaporation of moisture in your soil.
Soil Organism Supporter: Mulch also helps attract and feed beneficial organisms in your garden.
That last one may be one of the most important benefits. For instance, worms are mulch-shredding machines in their underground in dens, making more soil-aerating tunnels as they drag home the mulch to their dens. Several different types of arthropods find mulch a welcoming place to live. The decay they enable adds more organic material in the soil, which in turn attracts other important soil microbes.
In terms of the best mulch material for your garden, it depends on what plants you are growing, and what kind of diverse population of soil organisms those plants need. Some of our favorite mulch materials include:
Green grass clippings make great mulch for supporting a robust bacteria population, beneficial for annuals, vegetables and grass. Just be sure to avoid clippings from lawns that have been treated with herbicides or pesticides, or where dogs are prone to “do their business.”
Brown leaves saved from last fall help fungi populations thrive, which is perfect for perennials, trees & shrubs. Don’t grind the leaves up to finely, or bacteria may get to them first.
Aged pine needles make great brown mulch to support fungi, but the “aged” part is particularly important. Fresh pine needles contain terpenes, which are toxic to some plants.
Wood chips or shavings are another fungi-friendly brown mulch option, but steer clear of cedar, which also contains terpenes.
If your focus is building a beneficial ecosystem in your soil, how you apply the mulch is as important as what kind of mulch you use. A few tips:
Add or replace mulch every 12 to 18 months. Natural mulches should have decomposed in that time, or at least be greatly reduced, if you have good microbial activity in the soil underneath.
Apply a layer of corn gluten meal before you mulch. This nitrogen-rich fertilizer provides food for worms and microbes and helps prevents weeds from germinating.
To help bacteria to really thrive, pre-shred your compost into tiny pieces and keep it nice and moist. Mix the mulch into the topsoil where the bacteria can easily access it.
To allow fungi to be more dominant, keep the pieces large and dry, and spread them over the surface of the soil.
Apply mulch no more than 3 inches thick, or you risk blocking moisture and air that soil microbes need.
Introduce a “starter population” of microbes to your soil by applying a layer of organic compost before spreading mulch on top.
Finally, be sure you’re not laying down more garden problems when you lay down mulch.
Leave a few inches of no-mulch zone around tree trunks to avoid inviting critters to burrow into the bark.
Lightweight mulches like buckwheat hulls and cocoa hulls can blow away, making a mess and leaving bare spots in the soil.
Make sure wood chips are not made from construction waste or treated wood that will introduce harmful chemicals to your soil.
Use caution when mulching with straw or hay, which often carry the unwanted “gift” of weed seeds – the gift that unfortunately keeps on giving!