WHY WE SHOULDN’T TILL
Posted 1/8/2024
Nature has its own ways of “turning the soil” — through the processes of a group of members of the edaphon (the soil’s living community) called “bioturbators,” the microscopic, the tiny and the not-so-tiny organisms that move about in the soil, moving mineral, organic, and gaseous bits from place to place. Although the balances of nature are sustained over the long haul in this manner, it is a mostly crude and messy process, certainly not a “gardening” method and not for short-term expectations.
Tilling garden soil should be a thing of the past. Among the issues caused:
disrupts/kills the edaphon (the soil’s community of life)
degrades soil structure
brings up weed seeds
damages roots of nearby plants
speeds decomposition, releasing needed nitrogen and carbon into the air.
The gardening routine of repeatedly turning the soil (tilling, double trenching, “prepping the garden,” etc.) almost always has the opposite effect of what we expect. Even the innocent conventional acts of amending the soil and pulling weeds do more damage than any expected benefits. There are ways to streamline nature’s effects, some require a bit of patience and others are faster yet worthwhile.
Gardeners have practiced rototilling or otherwise turning up the soil for many centuries. Farmers have probably done it, as a routine practice, much longer. It’s a widespread practice but not universal.
For almost as long as gardeners and farmers have been whipping up the soil, there’s been a smaller band of growers, amateur and professional, who have followed an approach that has become known as “no-till.” The no-tillers found benefits in doing so and knew some reasons why it worked but most hadn’t (haven’t?) yet discovered the bigger picture of why tilling is “bad” and why not tilling is “good.”
The most important reason why tilling is no longer recommended is because it damages the edaphon – that living component of the soil, the thousands of species of very visible, barely-visible, and microscopic entities that make soil “work.” In a natural ecosystem, it’s this living "machine" that allows plants to grow without the help of farmers or gardeners. Yes, including the messy bioturbators (among the not-so-messy bioturbators).
In properly nurtured garden soils, this underground multitude performs the most amazing array of tasks: they decompose organic matter; they aerate the soil; they make nutrients from organic and mineral matter available to plants; they create one specific key nutrient, nitrogen, “from thin air;” they prevent nutrients from leaching away; they detoxify pollutants; they produce essential plant hormones; they induce drought- and stress-tolerance; they put carbon into the ground (sequestration); they increase plants’ water and nutrient absorbing capacities; they build soil structure; they kill pests; they suppress diseases; and they just might allow plants to “talk” to each other. And, yes, more.
The edaphon occurs in several layers (or “levels”) and in several “modules” (or volumes) of the soil. Each layer or module has its own distinct community of species. Starting with directly on the soil surface, possibly the most important layer as far as gardeners are concerned, these are the species that focus on decomposing any organic matter that falls onto the soil either naturally or by human practice. This is why mulching is so important and why it must be done correctly. This is the “mulch-soil interface.”
In this uppermost subsurface layer of the edaphon are mostly “seasonal” types, doing the jobs of further decomposition, processing mineral and organic nutrients, and making connections among the shallow-rooted plant species. Various mycorrhizal fungi species make their connections all the way down into the deepest layers of actual soil. Many biologists consider this zone the archetypical, true biological “topsoil,” also called the “A-Horizon.” [“Topsoil” is natural and is not to be confused with what a gardener can buy from a “soil” making company.]
While biological activity is greatest at this subsurface level, the edaphon extends at least as deep into the soil profile as do the plant roots. With the commonly occurring variation in soil strata, there are wide ranges of moisture and oxygen levels, pH, and organic and mineral nutrient levels. These differences support soil microbial diversity that may be upwards of 1,000-fold greater than in any aboveground or aquatic ecosystems. Scientists have even found microorganisms deeper than plant roots, sometimes much deeper.
These layers take time developing the right population formula. The edaphon works in a balance, with different species, different types working together and toward a synergy that best suits the entire soil community, which includes the plants that grow on top of the soil. Such a balance takes time, often many years from a damaged soil. As with all of nature, when the edaphon is diverse and complex, it is healthier and it will do more to benefit the garden.
Turning the soil disrupts this layering, balance, and diversity. It has a serious impact on the fungal populations and, when frequently repeated, it can drop the bacterial population. Tilling particularly dislocates and damages those very important top two layers — the mulch-soil interface and the topsoil just below that.
Beyond this biological demolition, tilling has other undesirable effects on the soil.
Repeated tilling degrades the soil structure — the “crumb,” the “tilth” — the critical piece that provides enhanced moisture retention and movement, an arrangement conducive to best root growth and the all-important environment that best suits the edaphon. When farmers constantly till the soil, especially when the tilling or digging is to the same depth, they often create an area of serious compaction known in farmers' parlance as “plow pan.” Soil structure, by the way, is much more important to plant life than loads of organic matter. (Something to think about.)
Tilling also brings up buried weed seeds — the ones you thought couldn’t possibly germinate after ten or more years of being six inches down. These seeds now come to the disturbed (an essential environmental factor for weed seeds) surface where it’s also warmer and usually moister and, boom, off they go.
There’s often collateral damage, too, to the roots of permanent/perennial, desired plants nearby.
Regular tillage stimulates the growth of decomposing bacteria, hence speeding decomposition and mineralization which releases some of the soil’s valuable stores of nitrogen and carbon (as CO2) into the air. While at the same time, tilling exposes and kills other microorganisms leading to even more carbon and nitrogen release.
When the tilling is done to incorporate organic matter into the soil ("amending"), there are additional problems. A surprise to most gardeners: adding organic matter INTO the soil isn’t necessary to get the benefits of organic matter. Bulk quantities of organic matter buried in the soil can lead to water movement issues; in some conditions, the burial of organics can develop into a restricted biolayer limiting drainage. When green leaves (or fresh kitchen waste) with waxy leaf coatings are added, this wax coats individual soil particles and restrict or, in some cases, completely impede water movement. The waxes particularly attach to sands and other coarse-grained soils, causeing affected soils to become “hydrophobic” (water repellent) at the soil surface.
When an abundance of organic matter is incorporated into the soil, including too much compost that still contains a lot of un-composted organic matter, the resulting population explosion of decomposers will rapidly use up the oxygen and the soil will go anaerobic for at least a short time. With reduced oxygen, anaerobic species take over and this then becomes anaerobic decomposition or, more properly, fermentation. Fermentation is usually accompanied by disagreeable odors of hydrogen sulfide and reduced organic compounds that contain sulfur, such as mercaptans (any sulfur-containing organic compound). Also included is lactic acid and alcohol, two chemicals that are toxic to plant roots. During fermentation (“anaerobic decomposition”), much less heat is generated than in aerobic decomposition and this lack of heat means a slower process. It’s more efficient and effective to use such organic matters to make compost (another blog post to come), which has its own array of special, beneficial by-products.
These various issues, from the serious reduction in edaphon and the increased release of CO2 to the maybe-minor stinkiness, almost always lead gardeners to rely more on fertilizers, additional water, pesticides, herbicides, and special potions to help their plants survive in a diminished soil. All of it becomes a treadmill, including tilling itself — the more one tills, the more one needs to till, and water, and fertilize, and....
Despite these problems associated with tilling the soil and amending the soil, these two very common practices remain the biggest sacred cows of the gardening world.
Of course, there are times when we must disturb the soil. We must plant a plant, remove a plant, transplant a plant. We must dig up our potatoes and carrots and turnips (raise your hand if you love turnips). We are committed to raking in preparation for a new seedbed. In a sense, the whole of “gardening” is a disturbance of the soil and the natural environment. But it all can and should be minimized. Gardeners can encourage, conserve, and take advantage of the natural and more subtle bioturbators in home garden soils, the native earthworms, the native ants, and even plant roots.
We don’t need to “till” the soil and we shouldn’t till the soil. In the garden, we can get the many benefits of organic matter and in a much more efficient and effective way by using a coarse mulch for the large spaces of the landscape and by making compost and using that compost as a mulch (in this case, better called “topdressing”) between plants and in hard-working gardens such as vegetable beds. Additionally, there’s the structure-fixing benefits of putting plant roots into the ground and leaving them there. The roots will help pull the soil particles into clusters to further develop structure (versus the un-clustering result from tilling) and the roots will help feed the mycorrhizal fungi (instead of breaking up this fungal network by tilling). If not a mulch, cover with seasonal cover crops for cover and for the roots.
Tilling doesn’t work and yet it is fervently defended by many, particularly those who preface it with “We do it this way because we’ve always done it this way, and I’m comfortable with that” or, its more popular incarnation, “It works for me.” That comfort zone is important. And I suspect my myth demystifying has caused many a reader to dig in heels even further.
Those who insist “they’ve done it this way for 50 years and it’s always worked for them,” have probably never made side-by-side comparisons with a control entity. The insistent gardener has no idea if it’s doing any better with it versus without it, especially in the long term. These claims of success are strictly anecdotal and generally pretty hard to prove. And because it’s “worked” for them, these gardeners assume it does or will work for others (which, of course, it doesn’t).
In the home garden, the area most commonly tilled on a regular basis is the vegetable plot. Farmers tilled (and most still till) their vegetable acreages for many reasons, most having nothing to do with why gardeners till their small plots. Many farmers till to turn under excessive crop residue, to level out rutted soil, for weed control, for getting the soil thawed and warmed up in earliest spring, for economic reasons, and/or because it’s easier than sowing a cover crop. Most, if not all, of these reasons, by the way, can be replaced with more earth-friendly practices.
This constant cultivation and tillage of the veggie plot physically severs the hyphae of important fungi within the edaphon and exposes much of it to the drying sun. Although the fungal network (“mycorrhizae”) can rebuild itself, continual tilling prevents it from allowing the whole system to function. When the fungi decline, bacteria become dominant and although they have their own way of managing soil functions, they do not do it as extensively or as thoroughly as fungi do. Frequent or deep tilling suppresses even the bacteria.
To compensate for this loss of natural functionality, the gardener resorts to more water, more fertilize, etc., as mentioned earlier. THIS added effort and expense is the reason behind the “success” of a tilled plot, not the tilling. (Another complexity: the added water, fertilizer, pesticides, et al, also degrade the edaphon.)
When gardeners consider one season of good growth or abundant yield, they don’t know (or care?) about the damage they may have caused to obtain the growth or yield. When a gardener asks “If it can’t hurt, why not?,” sometimes only the gardener can answer. Most often the hurt isn’t so obvious, at least not immediately. Gardeners are prone to judge only what they can see. If something is damaged in the process of their bad practice(s) and they can't see it, it doesn’t concern them. But tilling does hurt, as delineated herein. The big hurt in this case is the edaphon. This then becomes a long-term issue and not just for the garden and gardener.
In addition to this greater damage, in almost every case, the answer may be that it’s probably a waste of money, it’s probably a waste of time, and a gardener’s time and money could be better spent on practices that do work. There are so very many productive and rewarding things that can be done in the garden. If you’re already planting posies for the bees, butterflies, and pollinators, why not create a garden that benefits the edaphon?
© Copyright Joe Seals, 2024