We all know that the cardinal sin of gardening is stepping in the bed, but why? As long as you don’t step on the plants, it shouldn’t be a problem, right? Actually, soil compaction is one of the worst fates that could happen to your garden – even worse than pests or drought – because it takes years to reverse compacted soil.
Soil compaction is a result of increased pressure on soil, resulting in reduced space between soil particles that make it harder for water, air, and nutrients to be taken up by plant roots. Usually the result of over-tilled soil or human and animal traffic in the garden, you can slowly reverse soil compaction over time by cover cropping and amending the soil with compost.
Keep reading to understand what soil compaction is, its effects on the environment, and how to prevent and repair compacted soil in your garden.
What Is Soil Compaction?
Soil compaction is a serious problem for many gardeners and farmers. However, the problem often goes unnoticed at first, since the warning signs aren’t easy to recognize.
Soil compaction occurs when external pressure compresses soil particles tightly together. The University of Minnesota Extension Office defines soil compaction as:
“When soil particles are pressed together, reducing pore space between them. Heavily compacted soils contain few large pores, less total pore volume, and consequently, a greater density. Compacted soil has a reduced rate of both water infiltration and drainage.” (DeJong)https://extension.umn.edu/soil-management-and-health/soil-compaction#soil-structure-1147260
The reason that soil compaction is such a pervasive issue is because soil compaction impedes healthy root development in plants. Compacted soil makes it harder for plants to force roots, and as a result, plants form underdeveloped and weak root systems.
Plants use their roots to absorb water, nutrients, and air – all essential ingredients to healthy growth. Less space between soil particles means that water and nutrients are exchanged more slowly since liquid particles don’t move as quickly through compressed soil.
The Main Contributing Causes Of Soil Compaction
Heavy machinery and over-tilling are directly tied to the disintegration of healthy soil structure. While soil compaction is much more of an issue on commercial farms, small-scale growers should still be mindful of how our habits affect the overall health of the land.
Human Causes Of Soil Compaction
Machinery & Vehicles
Use of heavy machinery and vehicles are the major contributing factor to soil compaction.
If you must drive, be sure to only drive on established roads – never through a field where you are growing or intend to grow. You can also lessen the negative impact of a tractor or truck by reducing axle weight and lowering air pressure in the tires.
If you can, haul smaller and lighter loads when you drive across the field – it might make your trips a little less efficient, but your soil will be healthier in the long run (and it might extend the life of your farm use vehicle, too).
Many farmers swear by tilling, and they have reason to. Tilling is the most efficient and fastest way to prep the earth for planting (and to knock back weeds).
Even though tillers loosen the ground to a certain point, years of tilling the same stretch of land will create a hardpan, or an impermeable layer of soil just underneath the reach of the tiller.
Due to the detrimental effects of tilling on soil health, it might be worth transitioning to no-till if you have time and the patience to play the long game. Studies have found that no-till gardens with permanent raised beds actually produce healthier, more vigorous plants that are often far more productive than traditionally-grown crops.
On a smaller scale, human foot traffic is the most common culprit of soil compaction. While stepping in garden beds doesn’t have the same long-term effects as using a tractor, this season’s crops can certainly be affected by trampled soil.
Create permanent walking paths in your garden, and if you need to aerate a bed use a broad fork or a shuffle hoe to disturb the soil, rather than resorting to a tiller.
Livestock (especially larger livestock like cattle and horses) can do a number on the landscape. Mitigate this problem by rotational grazing between pastures, so that one pasture is never overworked.
If you do opt to use livestock to prep your fields before you plant, use smaller animals like pigs, goats, and poultry. Poultry will fertilize the area, goats will eat weeds, and pigs will actually turn the earth as they root around for food.
Natural Causes Of Soil Compaction
Sometimes soil compaction is no one’s fault but Mother Nature herself. Rain, sleet, and hail can occasionally fall with such force that the surface soil is compacted.
Smooth, flat soil broken up by cracks is usually the result of raindrop impact. Fortunately, natural soil compaction is usually less than an inch deep, and hoeing or raking the crusted soil is enough to reinvigorate the soil.
Factors That Affect Soil Structure Degradation
Some soils are a little more susceptible to soil structure degradation than others. Wet soils are far more likely to be damaged by applied pressure than dry soils because water weakens relationships between soil particles.
Finer-textured soils that are high in clay are more likely to compress than loamy soils. Dense soils and soils rich in organic matter are better able to withstand soil compaction, as the particles are larger and more rigid.
Environmental Impacts Of Soil Compaction
Not only does soil compaction affect the health of your crops in the short term, but it has lasting effects on the well-being of the surrounding environment.
Compacted soil has devastating effects on crop root development and growth. Plants are designed to grow vertical roots, but when the roots are met with an impermeable layer like a hardpan, the roots are forced to grow horizontally or not at all.
Weak root systems result in weak plants that are more susceptible to disease and are not nearly as productive as plants that are anchored securely in the soil. While compacted soil certainly obstructs root growth, severely compacted soil might even inhibit seed germination and seedling development.
Movement Of Water
Compacted soil is more likely to retain water than healthy soil, hindering transpiration – the movement of water through the soil – and potentially dehydrating plants.
Plants depend on their subterranean networks for water, nutrients, and even air. Roots are responsible for moving water and nutrients through the plant, and plants that have compromised channels suffer.
Crops grown in compacted soil are more likely to get detrimental diseases like root rot, since compacted soil retains water. When compacted soil does dry up in periods of drought, shallow-rooted plants are unable to survive.
Decreased Biological Diversity
Healthy soil is a living medium enriched with billions of microorganisms. Bacteria, insects, fungi, and many other life forms make their home in the soil.
Plants depend on these organisms to thrive – a prime example of this is mycorrhizal fungi. Mycorrhizae have a symbiotic relationship with plants – the fungi take up residence on plant roots, and help the plants extend their reach to absorb more water and nutrients.
Microorganisms live in the spaces between soil particles, and so they cannot exist in compacted soil. Plants that don’t have access to these beneficial organisms won’t be as strong as plants that do.
Soil Erosion & Surface Runoff
Compacted soil is less efficient than uncompressed soil at filtering water. Groundwater is slower to recharge when the soil is damaged, resulting in more surface runoff.
Gray water is more likely to contaminate water sources and contribute to the process of eutrophication, or the greening of bodies of water due to increased nutrient intake.
Microorganisms in the soil, just like organisms above the surface, need air to respirate. When oxygen isn’t available – like in heavily compacted soils – these organisms use nitrogen in its place.
This reduces the supply of soil-borne nitrogen available for plants to use, resulting in a nutrient deficiency that manifests itself in stunted plants that produce less.
How To Prevent Soil Compaction
The old adage says that an ounce of prevention is worth a pound of cure, and that saying has never been more true than with soil compaction. Use the following techniques to avoid compacting your soil in the first place.
Go No-till (Or Reduce Tillage)
The best way to prevent soil compaction in your garden or on your farm is to till as little as possible, or better yet, avoid tilling altogether. Maintaining a garden is a lot of work, and too many of us will reach for a rototiller to knock back a section of weeds, sacrificing longevity for efficiency.
Never till wet ground, as wet soil is much more likely to become compacted than dry soil. If you can ball up a handful of soil, it’s too wet to till. When the soil is so dry that it won’t hold a shape, you can till if necessary.
Use a broadfork instead of a rototiller to turn the soil in small spaces. Broadforking is a workout, but it doesn’t damage the soil or harm the microorganisms that exist in living soil.
Create Permanent Paths
The number-one rule of gardening is to never walk in your beds. Soil compaction explains why properly laid out walking paths is so essential to a garden.
Obviously, you need to move in between beds to weed and harvest, so make sure you have designated walking paths to avoid unintentionally creating one in the garden bed.
If you need a move a truck or tractor between different quadrants of your garden, establish permanent roads. It might not be as fast or as easy as driving through the garden, but your soil (and your crops) will thank you in the long run.
Stepping stones are a great way to add an aesthetic to your garden and protect the soil from compaction. Stepping stones aren’t terribly expensive, and when properly placed they can create a path that distributes weight more evenly than walking on bare earth. Stepping stones also very clearly mark where you (and visitors to your garden) should walk.
Mulch your paths with woodchips or landscape fabric to suppress weeds, or cultivate grass paths. Make a clear differentiation between garden and path so that there are no questions and your crops don’t accidentally get trampled.
Build Beds Just Wide Enough
You want to build your garden beds just wide enough that you can reach the middle from either side – for most adults, that’s no more than four feet across. If you build a bed any larger you’ll have to step in the bed to weed and harvest the crops in the middle of the bed.
Whether or not you have a problem with deer, you might want to build a fence around your garden to keep animals and human traffic alike out of the beds. Raised beds are another easy way to signal that this is sacred ground that shouldn’t be trampled on.
How To Correct Soil Structure Degradation
Don’t till more or till more deeply as a temporary fix – you’ll just cause more damage in the long run. The following solutions aren’t quick fixes, but if you put in the effort you will see improved results in the long run.
Cover Crop With Deeply Rooted Plants
Use the off-season as an opportunity to heal damaged soil. Plant daikon radishes, rye, and other cover crops with long taproots to break through the hardpan.
These cover crops will keep soil from eroding over the winter, as well as incorporate air and nutrients back into the soil.
Rather than disk in the cover crop in spring, harvest the radishes for food or “chop and drop” by cutting the cover crop and letting it fall where it lands. The organic material will break down and continue to enrich the soil.
Amend Your Native Soil With Coarse Sand & Compost
The quickest way to improve compacted soil is to add textural amendments like compost and coarse sand.
There’s no end to the ways that compost benefits the garden. Organic compost acidifies the soil – which most fruits and vegetables love – and adds essential nutrients to the soil.
Due to its chunky nature, compost also improves the texture of native soil by adding aeration and increasing drainage.
Coarse sand also improves soil porosity, but be careful how much sand you add and to what kinds of soils – sand is only really effective when added with pure compost or loamy soils. Adding sand to clay soils will exasperate the problem and create a concrete-like mixture.
The pitfalls of modern farming equipment and the dangers of soil compaction should be on every mindful gardener’s mind. Preventing and reversing soil compaction isn’t always easy, but it is doable and very much worth the effort in the long run.
I hope you found this article helpful. If so, please share it with someone who can use the information.
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DeJong, Jodi. “Soil compaction | UMN Extension.” University of Minnesota Extension, https://extension.umn.edu/soil-management-and-health/soil-compaction#soil-structure-1147260. Accessed 1 June 2022.
About the author:
When not writing content or growing flowers in her native Virginia, you can find Sarah hiking a long-distance trail deep in the woods. Follow along with Sarah’s adventures at http://sarahcolliecreative.com.