The prospect of gardening in thick, back-breaking clay soil is enough to turn away even the most enthusiastic of gardeners.
But that’s because they don’t know clay soil’s unique potential. Trapped in the clumpy layers and dough-like consistency rests the most beneficial nutrients for thriving plants, trees, veggies, shrubs, and so much more.
This silver lining of hidden fertility is well-worth amending and improving clay soils for thriving growth. In fact, there are several methods you can use to improve clay soils and tap into this locked-away potential.
In this article, we’ll show you how to test your soil for clay content, how to work with heavy clay soil, and how you can improve clay soil structure for growing the best garden around.
What is Clay Soil?
Many people look at their soil and see a layer of dark, moist dirt sitting over their planting beds. They assume that this type of soil extends all the way down. But this is just the humus, and maybe even the topsoil layer.
It’s when you dig a little deeper that you will hit your soil structure’s true make-up. That’s the subsoil layer, where levels of sand, silt, and clay lie. This is also the layer you’ll test to determine whether you have clay soil or not and in what concentrations.
The science of soil deserves a deeper look. It’s made up of just two materials: organic matter and minerals. Organic matter is either dead, like decayed leaves and roots, or living, like earthworms, fungi, and important bacteria.
Minerals, however, are the primary way we “classify” soil. There are three main types of minerals:
- Sand (the biggest particle)
- Silt (a more-refined version of sand)
- Clay (even finer silt)
Geologists classify soils based on the mineral ratio make-up. The ideal soil — one that’s easy to work with, has excellent drainage, and supports various plants with more delicate roots like perennials — is loamy soil. It’s 40% sand, 40% silt, and 20% clay.
It’s when you shift these percentages — for example, increasing the concentration of clay in the soil structure — that you get a more clayey soil.
When people hear that loam soils are the most ideal, they instantly see the other soil types as less desirable offshoots of this preferred type. But that’s not the case at all — each of the six types of soil has its own advantages and disadvantages. They’ll each support different kinds of plants.
Sandy soil, for example, drains very quickly, so you’re not likely to get hit with water puddles and bloating. Silt in soil holds water much better. And, of course, clay in soil holds water the best, as the molecules get trapped both between the clay particles and within the clay particles through absorption.
Why Does Clay Soil Have Such a Bad Reputation?
When people encounter clay soils in their gardens, they usually approach the situation with much trepidation.
Heavy clay particles tend to stay moist, which is great if you’re ever hit with drought conditions. But their fine structure becomes compacted very easily and quickly. These soil particles also don’t provide very little air space to reach roots, which is part of the reason why they’re hard on certain plant species.
Here are some of the disadvantages of clay soils:
- If you gather some of these particles in your hand and rub them together, they’ll feel more slick than grainy.
- In fact, the “slippery” nature of heavy clay soil is what makes it so hard to till and work with.
- Because heavy clay soil compacts down so quickly, plant roots and microorganisms won’t be able to receive the oxygen they need
- They don’t drain very quickly or very well, so if you get too much rainfall, your lawn and garden beds are likely to become bloated and full of puddles.
- Finally, it’s undoubtedly challenging to carry and work with these soils, which can be an issue when you’re trying to plant a garden patch.
All these “side-effects” of clay soils come from one prominent feature: the particles’ density. Heavy clay soils are dense. This means before improving and amending soils, you have to actually dig it out.
The Hidden Benefits of Clay Soil
The beauty of soil with clay matter is that its “weakness” also happens to be its strength. Its density means that soil clay holds onto both moisture and nutrients far better than any other type of soil.
To improve the make-up of soil clay, you’ll need to use particular amendments to transform it into garden soil capable of supporting plants season after season.
For example, the nutrients with clay soil need to be tapped into. So you can take advantage of these nutrients by using slow-release mineral fertilizers, including rock phosphate and calcium sulfate, to build soil fertility. Furthermore, calcium sulfate helps to loosen up clay’s tight texture.
Clay, Silt, Sand, Or Loam: A Simple, Homemade Test for Evaluating Soil Type
There are quite a few ways to test your garden soil for clay. An easy soil test is to dig a bit after rainfall and check the texture yourself.
When you ball up the soil and then knead it between your fingers, a flat ribbon of more than two inches long is a clear sign that you have clay in your soils.
You can also use a homemade soil test to check for clay matter in your soil.
- Step 1: Take a 1-cup sample of soil, remove any rocks or roots, and then break apart any lumps.
- Step 2: Find a clean mason jar and put the soil in with a teaspoon of powdered dishwashing detergent. Fill the rest of the jar with clean water, leaving half-and-inch of air space at the top.
- Step 3: Put the lid on tight and shake the jar well for three minutes.
- Step 4: Set the jar on a flat surface and let the mixture settle. After a day, measure the depth of each layer.
A ratio of 55% (or greater) clay and anywhere between 10% to 40% silt indicates that you have clay soil.
Where in the United States Can You Find Clay Soil?
Altogether, the six soil types are spread across each region in the United States. You can expect a combination of these in various regions. Clay soil, for example, makes a significant appearance in Northeastern states, but it’s not limited to this region.
Weather plays a role in a soil’s make-up. In desert-like, southwestern states, for example, you can expect primarily sandy soils. These are great for supporting cacti (and other plants made for dry and arid conditions), but moisture-hungry perennial flowers are harder to support.
Another key thing to note is that each state in the United States has its own soil representative.
In New York state, for example, the selected soil is Honeoye (pronounced Ho-nay-o-yay). It includes a subsoil of a significant amount of clay content, but the topsoil has a silt loam texture.
This combination of well-draining loam coupled with the fertility of the soils clay makes the state’s soil structure ideal for planting crops.
What is Clay Soil Good For?
People think that clay soils are a death sentence for all plants and gardens. But some plants that don’t just “tolerate” clay soil, they thrive on it. Clay soils are suitable for a wide variety of plants, including:
- Alders, oaks, hickories, black and green ash, butternuts, willows, aspens, elms, and lindens, to name a few
- Roses, Japanese irises, black-eyed daisies,
- Perennials like hardy cranesbill, dahlias, geraniums, and salvia
- Switchgrasses and Eulalia grass
- Shrubs like chokeberry, dogwoods, forsythia, and currants
- Veggies like broccoli, Brussel sprouts, cabbage, cauliflower, squashes, pumpkins, onions, leeks
These trees, shrubs, flowers, and vegetable varieties have exceptionally strong roots that can push through the compaction of clay soils. On the other hand, they absolutely need the water and nutrients that sit in clay soils.
Can You Fix Clay Soils?
Fixing clay soils requires a mix of short-term and long-term strategies. You’ll need to focus on some of the most significant issues with clay soils to balance out the “obstacles.”
Here are a few issues that you can fix in the “short-term”:
- Promoting ventilation — You can mix coarse forms of organic matter into clay soil, right between the plants. These particles of organic matter also help microorganisms that need ventilation to survive.
- Improving drainage — Adding garden compost (rather than finer amendments like peat moss) can help transform the soil’s ability to store and drain excess water properly. You’ll find that it dries faster and cracks less during dry weather. You also won’t need as much aeration to break up compaction.
You should aim to use these amendment and improvement methods to increase available organic carbon and humus in the long term. You also want to promote nutrient cycling through regular applications of compost and manure. You can also incorporate cover crops and plan for rotations that include grasses and legumes.
How to Amend and Improve Clay Soils for Gardening
With a consistent strategy for improving the “tilth” or texture of clay soils, you can enjoy the best of both worlds. You’ll be able to work the soil much easier and still tap into its natural moisture and nutrient content.
Here’s the trick: While clay soil responds well to methods of conditioning (which we’ll cover more below), the texture works best when you leave it alone. This might seem like a catch-22: How can you amend and improve clay soils if you can’t frequently work organic matter in?
The answer is to implement a minimum tillage system.
Excessive tillage results in significant losses of the soil’s organic matter content. Instead, minimum- or no-till practices can help increase:
- Soil organic matter
- Soil organic carbon
- Total nitrogen
- Soil microbial biomass
- Organic carbon
Meanwhile, the soil remains undisturbed, and a plant’s feeder roots thrive in the top two inches of fertile topsoil.
Step #1: Contour the Land
Your first step is to contour your property’s natural terrains. If you’re not on a sloping hill, use raised beds (planting berms), terraces, and even permaculture swales to help distribute water more evenly and promote better overall drainage.
The combination of high and low points will help promote organic matter (in low spots where water collects) and provide areas for planting that dry faster (high spots).
Addressing water first will help you reduce the amount of tillage you have to do later on. Gardens with these strategic “peaks and valleys” will help combat gravity and drain out easily, which, in turn, reduces compaction.
Step #2: Aerate the Soil On a Regular Basis
Once you’ve set up a contoured garden, your next plan of action is aeration. Over time, soil naturally compacts. With clay soil, however, compaction is a certainty and an inevitability. And tillage simply exacerbates the issue.
This is why you need to plan to aerate your property twice a year — especially in the fall. Tools like a broadfork, digging fork, or plug coring aerator can help you inject air pockets into your soil.
Step #3: Use Soil Amendments
There are several “additions,” also known as soil amendments, that you can incorporate and work into your soil.
1) Using Green Manure
“Green” manure is green plant matter that you can cut from other areas of your garden and spread it evenly over the soil.
You can also use “farmyard” manure, which is animal manure. These garden-approved amendments deeply condition clay soil and make it far more pliable and easy to work with.
2) Using Cover Crops
Cover crops are a fantastic way to add organic matter without stirring up the soil too deep. They also help suppress weed seed germination and pathogenic nematodes that can harm your attempts at improving your soil’s health and structure.
Both leguminous and non-leguminous cover crops can help subsequent crops as well. While leguminous crops like hairy vetch, clover, cereal rye, and borage can help convert atmospheric nitrogen (nitrogen fixation). Non-leguminous crops, on the other hand, can help recycle residual soil nitrogen.
3) Using Compost
You can build your own compost bin and then use the contents to work into your soil. Compost adds organic matter to your soil. Continue to do this for about three years and you’ll see a significant improvement in your soil’s drainage.
4) Mulch, Leaf Mould, and Rotted Bark Chips
Amendments to soil can help tackle poor drainage. It can also prevent wind and water erosion. However, bear in mind that too much wood content depletes the soil of nitrogen because the soil’s bacteria will also require nitrogen to break down the wood.
5) Use a Liming Agent
Some soils respond very well to liming agents like calcium. However, you need to make sure that your soil’s pH runs more acidic. Since clay soils generally tend to be more alkaline, it’s a good idea to test your soil’s pH first.
Improving Clay Soils On Established Beds
Sometimes, you already have plants in an established garden, and you can’t afford to dig too deep. You’ll have to be a little more strategic to improve clay soil. It’s tricky but doable.
Here’s how it works:
- Add thick layers of mulch, compost, and leaf mould over the soil surface during the summer.
- Don’t dig this in — insects, worms, and microorganisms will naturally break these down and transfer it into the ground.
- Make sure to keep off the soil when it’s wet. If you have to walk around, consider putting boards down to distribute your weight.
- During the autumn, dig over and incorporate organic matter.
- Over the winter, leave the soil in ridges. The settling frost will work its way in and break up the natural clumps of clay soil.
Getting clay soil into shape is really just a matter of being consistent and using proven strategies to unlock the numerous benefits of this soil type. Organic matter is the key to most improvements you’ll make as these incorporations help increase plant root growth, boost water holding capacity, distribute nutrients, and smooth out drainage issues.
At Nature’s Seed, we’re all about taking advantage of these kinds of natural and sustainable methods for improving your land. Our grass seeds and planting aids are designed specifically for innovative uses such as soil improvement, pollinator population increase, habitat restoration, and more. Contact us to learn more about our projects and products at work in your community.