A growing number of experts say annual tilling is unnecessary—maybe even harmful. Here’s why.
Garden wisdom has long held that preparing a vegetable garden means yearly tilling: digging to mix up the top 6 or 8 inches of soil and incorporate new organic matter such as compost to increase its fertility.
“Turning the soil loosens the soil particles and folds in air, creating fluffy, loose soil that’s easier to plant and maintain—and which will sustain healthy plants with strong roots,” is the fairly standard advice that tiller maker Troy-Bilt offers on its Web site.
Mechanical tillers have made the job easier, but traditional tools such as the wide broadfork and techniques such as double-digging show that the general idea is ancient. It’s also the basis of conventional agriculture. Every fall, Illinois farmers till in millions of acres of cornstalks to prepare their fields for the next spring’s planting.
But in recent decades, dissenting voices have been raised. As scientists have come to understand more about how soil works—about the complex web of living things that, over seasons and years, digest plant matter to release nutrients and create good soil texture—some gardeners and farmers have come to question whether disturbing the soil is necessary or wise.
Leave your tiller in the garage (or a garage sale), they say, and leave your soil alone. Spread compost, leaves and other plant matter on top and let the earthworms, fungi, bacteria, nematodes and other soil organisms work it in over time, as they have evolved to do over millions of years. Disturb this soil layer cake only enough to make a planting hole in spring, so you don’t mess up the elaborate structure that makes this community work most efficiently.
Not only does this approach spare your aching back, it more closely mimics the way nature works. Recall the phenomenally dark and rich soil that attracted so many farmers to settle the Midwestern plains in the 19th Century. It was rich because it hadn’t been disturbed for some 10,000 years, since the glaciers melted.
During all that time, underground organisms had been digesting plant roots and material on the surface and releasing their nutrients. The roots had been tunneling, breaking up dirt chunks, and dying to leave air spaces and perfect texture 10 feet down. Every fall for all those centuries, dead stalks and leaves decomposed to create a natural mulch that made it hard for weed seeds to take root and also conserved water in hot, dry summers. That soil was a wonderland for plants.
But once farmers stripped off the protective mat and started tilling, it took only a few decades to exhaust the soil’s fertility. Today, Midwestern farming depends heavily on added fertilizer.
It also depends heavily on weed killers, because tilling brings buried weed seeds to the surface where they can germinate in the sun. Wind-blown weed seeds find a welcome in the exposed soil—unless the wind blows it away.
You may well already practice no-till gardening, whether you know it or not. Do you till established perennial beds? Probably not. You most likely spread mulch between the plants and add compost to a new planting hole, but otherwise you leave the soil alone for the earthworms to improve.
In recent years there has been an increased understanding of how soil “works.” In healthy soil, countless organisms and microorganisms interact to create the foundation in which plants thrive, as this drawing from Secrets to Great Soil by Elizabeth P. Stell illustrates. Digging and tilling can destroy that balance.
For vegetable gardens, the no-till idea was widely popularized in 1981 in Mel Bartholomew’s book Square Foot Gardening. Its fundamental idea is that if you start with good, rich soil and don’t mess it up, you can plant much more densely in enclosed raised beds than in a conventional, tilled, long-row vegetable plot.
In 1998, Patricia Lanza published Lasagna Gardening: A New Layering System for Bountiful Gardens: No Digging, No Tilling, No Weeding, No Kidding! Her pitch: create raised beds with layers of compost, mulch and other organic matter. Keep mulching and let each year’s garden debris accumulate. Over time, those beds will only get more fertile. And since you won’t be walking on those beds, the soil won’t get compacted.
Lee Reich leaned on the labor-saving aspects of the no-till idea in 2001’s Weedless Gardening. If you grow in boxy raised beds, as do most city gardeners and an increasing number of suburban ones, you almost certainly practice no-till. It’s just not easy to get into those boxes with a shovel or fork, much less a mechanical tiller, so you rarely bother. And your soil is probably the better for it.
Under this approach, pretty much the only time to till is when establishing a new garden bed, preferably about 4 feet wide so you can reach into it from either side. To start, you want to thoroughly work in lots of organic matter— compost, composted manure, leaves—so the bugs and microorganisms have ample material to digest as they settle in. Fall is a good time so that the critters have a head start before spring. You can do this with a garden fork or perhaps borrow your neighbor’s tiller.
But then give it back. Spread another layer of mulch on top of your new bed; perhaps apply a soak of compost tea in order to inject the new raised bed with a starter army of beneficial bacteria and fungi.
Come spring, plant your seeds or seedlings through the mulch into your developing soil. At season’s end, leave the mulch alone and compost the spent plants. As you spread compost and mulch on the surface year by year, your raised bed will rise a bit, improving the drainage. The mulch will mean you have to water less and weed rarely.
For years, my mother has raised all her lettuce, onions, garlic, tomatoes and herbs in raised bed boxes without tilling, a labor that she could never manage. She just adds layers of homemade compost, oak leaves from her trees and occasionally well-composted horse manure. And until you’ve eaten one of my mother’s ‘Cherokee Purple’ tomatoes, you don’t know what a tomato is.