Mulching in Winter

Keep Veggie Garden Soil Covered: Add Leaves Now

By Jane Shellenberger:

Excerpts from Jane's book: Organic Gardeners Companion: Growing Vegetables in the West Dry winters are the norm on the eastern plains of the Front Range. Our higher elevation and thinner atmosphere allows greater solar penetration so winters are more pleasant, even when snow is on the ground. Strong chinook winds blow down from the mountains to the high plains, sometimes reaching 100 miles per hour in the foothills, where the transition is especially abrupt. These roof-ripping warm dry winds can occur in any season, but they’re most common during the winter. Dry, windy western winters desiccate and erode uncovered soil.

Forking in a layer of wetted down leaves in the fall will add nutrients and build humus in veggie garden beds and some perennial beds too. They will break down faster if you shred the leaves. Avoid cottonwood unless they are well shredded and mixed with other types.

Added protection in the form of mulch is essential to building and maintaining a healthy environment year-round for the worms and other helpful soil creatures in a food garden. Mulch reduces evaporation and modulates the soil temperature. Whether you live in the mountains or on the plains, the simple step of covering bare garden soil with a thick layer of mulch, especially in the winter, will save you a lot of work and do more for the health of the soil life than anything else.

Healthy soil is bustling with life, movement, energy, even electricity. Often described as a living, breathing organism, soil is in a constant state of transformation as the dead are continually reprocessed for the benefit of the living.

Western soils are typically lean, with very little organic material compared to more-humid woodland climates - just right for the native plants that have evolved here and others from similar climates. To grow food plants, however, our soils need added organic matter like compost. This provides the crumbly texture that allows crop roots to get a good foothold and grow, the right porosity so that the soil drains but also holds some moisture, plus the air spaces that roots need and the nutrients that support growth and fruit and vegetable formation.

Earthworms drag food (plant debris) down from the ground’s surface into the soil and deposit castings (worm poop) loaded with nutrients that are especially beneficial for plants. Tireless tillers, earthworms continually aerate and mix the soil while creating channels for plant roots as they tunnel deeply and extensively underground. They move forward by secreting a nitrogen-rich slime, which stays in the soil for plants and helps soil particles cluster together. A healthy earthworm population greatly decreases soil-borne diseases and indicates that a healthy herd of microbes also inhabits the soil.

Begin building your garden in the fall when so many leaves are available and free for the taking. If you set up your garden six or seven months ahead of the growing season, the organic materials you add now will have time to break down and change into humus, helped by the freeze-thaw cycle of winter. Your soil will be more alive if you can give it plenty of organic matter, plus enough time to weather, coalesce, activate, and come into balance through the unfailing help of the microorganisms. Once spring arrives, your seeds and seedlings will have a nicely prepared bed ready to call home, with a healthy population of active soil critters, including worms. Fall is also a great time to apply a soil drench of compost tea to introduce microbes that will spark the decomposition and transformation process.

Since we usually have plenty of warm spells throughout the winter, you will have other opportunities to get started if you didn’t get to it in October; but don’t procrastinate much longer and do save or gather bags of leaves when they’re available. Leaves are one of the best materials for humus building in the garden and provide nutrients that soil microbes and worms convert into food for plants. You can also use them as mulch throughout the growing season.

You don’t have to chop up leaves if you’re using them as mulch or for compost, but they will decompose a lot faster if you do. Leathery cottonwood leaves, especially, can take a long time to break down and, like grass clippings, they mat and clump together when they get wet, so air can’t circulate through them. The microbes that break them down need air.

I like to use an electric leaf vac to suck up and shred the leaves into an attached cloth bag with a zipper. I dump the shredded leaves into a plastic garbage can with wheels so they’re easy to move around. It takes about four big bags of leaves to fill one garbage can. 

Wood chips are another readily available material for your garden, but they need much more time and moisture than leaves to break down. Dug into soil fresh or even somewhat aged, and to a lesser extent when used as mulch, wood chips will temporarily rob the soil of nitrogen, because the microorganisms consume it while decomposing the wood.  But given enough time, wood chips can be a great soil builder. It’s best to dump them in a spot where you eventually want a garden bed and spread them out so the pile isn’t too deep – no more than a foot or two high.  Soak the pile periodically to speed up decomposition, and cover it, especially during the heat of summer. In a year or two the volume will be greatly reduced and the soil underneath will be fantastic.

After trying many different digging and tilling methods over the years, I became a convert to the no-till sheet mulching (or sheet composting) approach because the results are spectacular. Though I also grow some vegetables and herbs in containers I think sheet mulching is by far the least strenuous way to create healthy garden soil on top of grass or in raised beds. It does take time, eight months to a year or longer, for everything to break down completely and mix together. It effectively smothers grass and weeds without any herbicides or digging, while building, conditioning, and holding moisture in the soil.

During one particularly warm, dry, windy winter I was able to create loamy chocolate-cake soil loaded with worms in three large dried out and neglected raised beds simply by spreading a thick (six-inch) layer of chopped-up leaves on top, watering well, and covering with flakes of hay. All winter I dumped my kitchen scrap compost under the hay flakes.

Mulching the garden with thick hay was originally Ruth Stout’s method, which she popularized in the 1950s in How to Have a Green Thumb Without an Aching Back and later in Gardening Without Work. Both are great reads (she was also a proponent of gardening in the nude), though pricey since they’re out of print. Decades later, Patricia Lanza, who told me she had never heard of Ruth Stout, refined the mulch layering method for urban gardeners in her book Lasagna Gardening. There are also lots of videos you can watch that will show you exactly how people are creating layered, no-till sheet-mulched gardens, step by step.

I use musty old hay flakes on top of the moist leaf layer. They will suppress weeds, hold moisture in the soil and eventually break down too. Straw can work but make sure your source is herbicide-free.

Before I understood how to apply hay mulch thickly enough, I used a lighter, thinner layer and ended up growing a new green crop of hay in the garden. Straw is not supposed to contain seeds but it often does too. The trick with sheet mulching is to use the hay (or straw) thickly enough so that any grass and weed seeds in the ground, as well as any hayseeds that may drop down onto the soil, won’t be able to germinate and grow up through the mulch. My hay layers are six inches thick or more -  thicker than the usual recommendations for mulch. I find that hay holds together better in flakes, whereas straw flakes are usually thinner, lighter, and they tend to fall apart and blow away more easily. But straw is better for digging directly into soil to lighten and loosen it up, especially for growing potatoes, corn, and squash.

You need roughly one bale of hay or straw to cover eighteen to twenty square feet of garden space. Leave the flakes intact but fill in any gaps or holes with loose handfuls.

It’s amazing how fast uncovered soil dries out in our climate, causing worms and other soil critters to vanish; they just go deeper. It’s important to keep soil from drying out during our typically dry winters as well as during the growing season. I keep my vegetable beds thickly covered with leaves (shredded, ideally) and a top layer of intact hay flakes over the winter every year. I water each layer well at the beginning. Don’t worry about growing a new crop of hay from the mulch as long as you mulch thickly enough. The few sprouts that pop up will be easy to pull.  Second cutting hay has few, if any, seedheads.

Move mulch aside to plant starts in the spring, then tuck them back in.

During your first growing season, simply pull the mulch away enough to dig holes for planting plant vegetable starts. For sowing seeds, remove the mulch and scatter some finished compost, scratching it in lightly with a fork to blend with the top layer of soil. This creates a better texture (if you need it) for sprouting, rooting seeds.

When they have two true leaves (these come after the initial two seed leaves) you can tuck the mulch back in around the plants. Leave the surrounding mulch in place. Each year as your soil gets darker, crumblier, and more full of soil critters it will be easier to plant.