An ode to clay soil

Everyone in Colorado has clay soil. Okay, fine, maybe not the whole state, but most of the front range, particularly the Denver Metro area, is clay. I’ve lived all over this town and never have I dealt with anything else. It’s clay, clay, clay everywhere you go.

No one ever has anything nice to say about clay soil. It is hard to work with, that’s true. It’s prone to compaction and it’s hard to get water into it. I get where the complaints come from. But there’s also a lot of good things about clay soil, and after years of gardening in it, I’ve got to say I don’t think it’s so bad.

Clay soil holds water like nobody’s business, due to it’s incredible surface area. Sure, it’s hard to get in there, but just apply it slowly and it will soak in and stay there! Clay soil allows you to do deeper watering less frequently, which is great for helping plants to grow deep, healthy roots, and for making your water use efficient.

Clay soil also tends to be very high in soil nutrients. It has a high cation exchange capacity, which allows it to hold on to more nutrients than sand or silt does. In other soil textures, vital nutrients for plants can easily be washed away, sandy soil can barely hold on to nutrients at all, but it takes a ridiculous amount of water and time to wash stuff out of clay soil. So much so that it’s not even really practical. This can be a problem too, because pollutants, salts, and toxins can also accumulate in clay soil, but the flip side of that is that clay soil filters our water run off, making it cleaner when it enters our streams and ground water. To avoid buildups of substances that can make growing plants tougher, it’s best to minimize inputs like fertilizers, pesticides, and herbicides, which means clay soil encourages people to reduce their use of polluting inputs in their soil, which is a good thing for everyone!

Here is a cool video for better understanding cation exchange capacity, and here is a good article on cation exchange capacity!

Clay soil is the least prone to erosion of any of the soils. If you have clay soil, odds are that you are going to keep your soil. It doesn’t really wash or blow away. Clay soil also resists acidification, again meaning it needs fewer amendments and inputs than other soil textures do. In fact, clay soil more often than not tends to be very alkaline. In Colorado, the soil is so alkaline that if you pour vinegar on it it will bubble up. You could probably use Colorado soil instead of baking soda in an erupting papermache volcano for your kid’s school science fair project (if anyone actually tries that, you have to come back here and tell us about it). That also means that all that stuff you hear about not being able to grow anything under or around pine trees because pine trees acidify the soil too much, that doesn’t apply most places with clay soil. I grew tomatoes under my pine tree last year. I didn’t even try, they just grew out of the compost I spread under there. Also, from what I can tell, using pine trees in hugelkultur when you have clay soil is not only okay, but may actually be beneficial.

When people are complaining about clay soil, it’s usually not actually the clay that’s the problem. Its the structure. There are different ways to judge a soil’s attributes. One of them is texture, that’s your soil’s compilation of either sand, silt, or clay. But you can also evaluate a soil by it’s structure, which is how the particles in your soil stick together, forming peds (chunks of dirt). Some structures are better than others. When people complain about clay soil, most often what they are dealing with is massive or platy peds. But clay doesn’t have to be massive or platy. The good news is that while there is no real way to change a soil’s texture, we can, with time and effort, change a soil’s structure to get that good, granular structure you want to grow healthy roots on plants. Even with clay soil!

So how do we care for our clay soil to ensure that we encourage good structure? Check out the following tips (most of which, by the way, are good advice for other soil types as well).

Add organic material!

Make sure your soil gets regular applications of compost and/or manure. Mulch your lawn clippings (no, this doesn’t create thatch, thatch is part of grass, like your hair is part of you, only grass needs thatch to be healthy more than we need hair). Use organic mulches like wood chips, leaves, straw, etc. Organic material (that is, material that came from living beings, such as plants, fungi, or animals, not as in USDA Organic, meaning meeting certain standards of production by a certifying agency) helps to break up peds and adds more air and glomalin to soil, as well as beneficial fungi, microbes, and all kinds of other things that keeps the clay particles from sticking together too much. This allows water and roots to more easily penetrate the soil, which also encourages better structure.

Avoid anything that will compact your soil.

Don’t drive on it, put heavy things on it for long periods of time, or run laps on it. Especially don’t do any of this stuff when wet! Don’t even mow your grass when it’s wet! Wet soil compacts more than dry soil does.

Actually, just don’t even touch it when it’s very wet.

Don’t dig when it’s wet, don’t till when it’s wet. All of that compacts the soil and jacks up your peds.

Don’t bother it when it’s very dry either.

Especially don’t till when it’s dry. You’ll turn it into dust and end up with your own personal dustbowl situation. You want the soil to be damp when you are working with it, but not sopping wet.

Avoid over watering.

Especially your lawn, where you are likely to get a lot of foot traffic. Too much water makes soil prone to compaction, but evaporation of too much water from your soil can also bring up salts causing new problems. Get an irrigation audit done on your irrigation system, and stick to the scheduling recommended.

Always keep soil covered.

Mulch, mulch, mulch, mulch, mulch. Mulch absorbs some of the weight when you walk on an area, and it helps regulate moisture at those optimum levels that encourage good structure. It also protects against erosion and keeps plants protected from weather extremes.

Grow deep rooting, aggressive cover crops.

Soil should always be covered, and plants are an excellent way to do that. If you choose to grow a cover crop/living mulch, on parts of your soil (yes, turf grass is a living mulch), choose deep rooting varieties, and depending on your needs, very aggressive varieties. For example, people with pet dogs often have trouble keeping a traditional bluegrass lawn, considering all the foot traffic the dogs cause. A better choice would be a deep rooting, aggressive grass variety, such as bermuda grass, or better yet, DogTuff grass which is resistant to dog urine. You might also consider non grass cover crops, like clover or even dandelion. A blend of those would probably be lovely, keep your soil healthy, and keep your dog cleaner when they are out in your yard.

Minimize fertilizer use.

Commercial fertilizers, even Organic ones, can cause salt buildups in the soil, which can negatively impact soil structure (as well as make it harder for your plants to absorb nutrients and water from the soil). Clay is more prone to this due to it’s cation exchange capacity, so it’s best to minimize the amount of fertilizer you put on it. Luckily, clay soil doesn’t need as much fertilizer anyway, because it holds on to more nutrients. You can find out what (if anything) your soil needs, and exactly how much, by getting a soil test done. Then you can make sure you aren’t adding any more than you need. Our clay soil in Colorado most often needs nitrogen, and you can utilize methods such as growing nitrogen fixing crops (like my plan to grow clover in with my grass) to get that into the soil, which adds organic material to the soil at the same time. Two birds with one stone! Yes!

Encourage biodiversity in your soil

You want a lot of stuff living in your soil. Worms and other creepy crawly bugs dig tunnels through your soil, creating spaces for air and water and roots, while at the same time pooping beneficial manure into your soil. Fungi and bacteria all break down organic material further, releasing nutrients for your plants and creating substances like glomalin, which improves texture and sequesters carbon. When all of them die (hopefully not all at once in a mass extinction, but gradually, over time, as part of a lifecycle) their little dead bodies are organic material in your soil. And the more varieties of creatures you have in your yard, the harder it is for any one variety to grow out of control and start causing problems, thereby minimizing your need for pesticides and herbicides.

Core aerate in high traffic areas/turf grass

Core aeration is really essential for turf grass. You should get it done once a year, in the spring or fall if you have cool season grass, or in early summer if you have warm season grass. What it does is take plugs of soil out of your grass, allowing air, water, roots, and organic material to penetrate further into the soil. Eventually it fills back in, but the soil in those holes is looser, has more organic material, and more roots in it. Basically, it undoes compaction. It has to be core aeration, because if it doesn’t remove a plug of soil, then all it’s really doing is compacting the soil around where the spike poked a hole. Leave your plugs on the top of the grass, they disappear quickly and help move around organizisms in the soil to make sure your biodiversity is well distributed in your soil.

Take care of your thatch

Say it with me, thatch is a normal function of healthy grass. Okay. Most sod forming grasses have a tendency to produce thatch. Thatch is the dead roots, rhyzomes, stolons, and crowns of old grass plants, all knit together to form a mulch that helps keep grass healthy. You want about 1/2″ of thatch in your turf grass, it will help with water retention and protecting the roots from weather extremes, while feeding the soil life that helps keep your soil and grass healthy and adding organic material to the soil. Too much thatch can be a problem, and likely indicates that your soil structure is lacking. You can reduce an overgrowth of thatch by encouraging biodiversity, reducing traffic, core aeration, and if you really need to, dethatching. Dethatching will tear up your grass and look messy for a while though, and open up a lot of soil space to weed seeds, so if a conventional, nice looking lawn is your goal, I would save that as a last resort. Or you can use a dethatching rake, which is a lot of manual labor, but much gentler on your turf. I’m dethatching my lawn in order to kill some of the bluegrass and reseed with tall fescue and other plants.

Clay soil is not nearly as bad as everyone makes it out to be. It has a lot of positive attributes that I have come to appreciate over the years, even if I can’t grow blueberries (sadness). If you take good care of your clay soil, your clay soil will take good care of you!

What kind of soil texture are you working with? What do you love or hate about it? Tell us what you think in the comments!

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