Whether you are growing in a home garden, or working on a commercial growing site such as a farm or market garden, compacted soil can be a complex issue that can be challenging to overcome.
What Is Compacted Soil?
Healthy soil requires aeration. When there is no longer adequate air space within the soil, and all the particles within it are close together, this is known as compaction. Compacted soil is soil that has been degraded in such a way that it no longer provides optimal conditions for plant growth.
Why is Compacted Soil a Problem?
When there is not adequate air space within the soil structure, that soil fails to function as it should. Water cannot filter through it sufficiently and it can become either very dry or waterlogged. Plant roots often cannot make their way through the structure to obtain the water and nutrients that they need.
Most crucially, without adequate aeration, and without sufficient oxygen, the micro-organisms that we depend on for healthy soil cannot continue their important work. Soil life degrades, and the complex web of life upon which plant growth depends fails to function as it should.
What Causes Compacted Soil?
Some soil types are more prone to compaction than others. Soil types which contain higher proportions of clay tend to be more likely to suffer this problem. Clay soil has smaller particles than silts or sands, and those particles can clump together more easily. Heavy clay soils can be particularly prone to developing this issue.
Compacted soil can be caused by:
- Compression from above, from cars, heavy machinery, or even foot traffic.
- Soil that has been tilled or dug too frequently, or when the soil was too wet or dry.
- Degradation of the soil by rain and water, when it has been left bare.
Compaction can be worse where there is a shortage of organic matter in the soil.
Is My Soil Compacted?
It is very easy to identify compacted soil. Most obviously, if you try to dig or work in the soil and have trouble breaking through, the soil is likely compacted. Trying to work with compacted soil to make holes or prepare an area can be back breaking work, and nigh on impossible in extreme cases.
If your soil is compacted, water may pool on the surface. Water that falls may well fail to drain away, or will do so only very slowly. And in dry weather, you may well see that the surface becomes very hard and cracked.
If you attempt to plant into compacted soil, the growth of the plants that you grow may well be stunted. Foliage may be discoloured – a sign that the plants are not getting the nutrients they need.
When trying to identify soil problems, the weeds that grow in an area can often give us some clues. If soil is compacted, certain plants will do rather well and tend to colonise the area.
Weeds often found thriving in compacted soil where other plants struggle include bindweed, chicory and plantain, for example.
Preventing Compacted Soil In the First Place
As with any challenge in the garden, prevention is better than cure. Especially if you feel you have a soil type that may be prone to compaction, it is important to take whatever steps you can to prevent this problem from occurring in the first place.
To prevent soil compaction:
- Avoid the use of heavy machinery or other vehicles on the area if possible.
- Don’t walk or step on beds or growing areas – shaping and sizing these so that you can easily reach all parts of them without having to do so.
- Adopt a low or no till approach, or a no dig approach in a garden. Keep the soil as undisturbed as possible to let nature function as it should.
- Create systems that replenish organic matter in the soil and keep organic matter in the soil sufficiently high over time.
- Keep a living root in the ground over as much of the year as possible.
- Cover bare soil either with ground cover plants, or with organic mulches.
- Where necessary, prevent waterlogging or flooding, or drought, by creating earthworks to manage the flow of water effectively on your property.
How To Fix Compacted Soil
One important step when trying to deal with compacted soil is ceasing the problems that caused this issue in the first place. Of course, you cannot set about trying to solve an issue until you tackle its root causes.
So think about what has caused the compaction and make sure that any practices or environmental issues that have caused it will no longer continue. The tips above to prevent this issue should also help you to identity ways to prevent the perpetuation of an existing issue.
Those with compacted soil often believe that digging or tilling is the answer. But nature, and a little time can often do the job with far less damage and far greater success.
This story, of a parking area turned into a food forest, is just one example that shows the possibility of taking a more holistic, earth-centric approach to fix even badly compacted soil.
Adding Organic Matter
Many gardeners or smaller-scale growers faced with soil compaction will heavily dig the soil laboriously to work on more organic matter to improve the soil structure and amend the soil.
But digging (or tilling on a larger scale) can take a lot of work. And the best policy in any space is to work with nature rather than fighting it.
By spreading plenty of organic material on the surface of the soil, rather than digging it in, then simply waiting, you won’t need to undertake the work of incorporating that material into the soil below yourself, but can instead wait for an army of hidden helpers to do the work for you.
In a no dig or no till approach, to deal with soil compaction in a particular growing area, you can layer cardboard over the soil to suppress weed growth.
Next, you can layer any organic materials that you have on hand – anything that you might add to a garden or farm composting system can be included. It is best, where possible, to source the materials from the site itself, or from the nearby area.
As in a composting system, add organic materials in layers of ‘brown’ (carbon rich) and ‘green’ (nitrogen rich) materials. Essentially, you are composting in place, rather than in a dedicated heap or bin.
Over the top of these materials, you can add branches or other heavier biomass to hold everything down. Or you can top the mixture with a layer of good quality peat-free compost if you are dealing with a smaller growing area.
Creating No Dig Raised Beds to Get Growing Right Away
If you would like to get growing straight away, you can create raised beds above the compacted soil – layering materials to at least 35cm – 45cm deep in order to give space for root growth above the compacted layer, and top these with a material like compost or leaf mould into which you can plant or sow.
While the soil below will remain compacted for the first year or so, over time, the soil below the bed will begin to improve. And in the meantime, you should be able to grow a range of annual crops and companion plants in the raised bed areas.
Improving Compacted Soil Over a Larger Area
Adding organic matter to the surface of the soil, and waiting, is the best way to improve compacted soil over a larger area.
However, finding sufficient organic matter for this may sometimes be a challenge if you are dealing with a much larger space. You may wish to start by sheet mulching an area, spreading organic matter over the surface as above.
When left for a year or so, the organic matter should begin to be incorporated into the soil below through natural processes and you should find it easier to begin to revegetate a site.
Boosting Microbial Life & Earthworms in the Soil
Remember, when we seek to redress issues with compacted soil, we are not working alone. When we spread organic matter over the surface of the soil, we are ‘feeding’ the soil life that will slowly incorporate that material into the soil below, make channels through the soil, improving aeration, and gradually improving its structure and composition over time.
In smaller areas, we can also do more to boost the microbial life and other life within the soil by adding compost tea or other organic liquid feeds. If we take care of the life below our feet, the will continue to toil away and take care of us.
Planting To Loosen Compacted Soil
However, beyond simply adding organic matter, it is also worth considering how you can plant to loosen and improve compacted soil and create conditions that allow other plants to thrive.
On a smaller scale, perennial, deep rooted plants can be useful in helping to break up areas of compacted soil. Planting brassicas, Daikon radishes etc. can help to improve an area of compacted soil sufficiently to allow for crop plantation.
It can also be extremely beneficial to think about how you can add dense and ecologically functioning planting on a compacted site – to plant areas of native woodland, forest gardens, or an agroforestry system, for example.
The impact of soil compaction on trees is a complex topic. And a severely compacted soil is not easily fully recovered. But when a tree-based system can be established on a site, the trees themselves can provide organic matter over time, natural cycles can be re-established on a degraded site, and the soil can slowly improve over time.
Some trees respond far better to compaction than others. Pioneer trees like alders, for example, are sometimes used to colonise degraded soil areas and begin to improve conditions for other species of tree, shrubs and other plants. So choosing the right tree species can be key to recovering compacted areas and creating sustainable growing systems over time.
References:
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/improving-compacted-soil.htm
Elizabeth Waddington is a writer and green living consultant living in Scotland. Permaculture and sustainability are at the heart of everything she does, from designing gardens and farms around the world, to inspiring and facilitating positive change for small companies and individuals.
She also works on her own property, where she grows fruit and vegetables, keeps chickens and is working on the eco-renovation of an old stone barn.
To get in touch, visit https://ewspconsultancy.com.