How to Improve Heavy Clay Soil

If there’s one kind of soil that every gardener and farmer fears, it has to be clay. Any soil that’s high in clay will be very hard to work with, draining very slowly, compacting into a solid mass that will stifle and strangle roots, and being too alkaline for many vegetables (aside from the typical problem of lacking the ability to support needed life in the soil).

In short, it makes growing anything a whole lot harder, and very few plants of any kind grow well in high clay soils. But, all is not lost…

With the right approach, the right materials, and plenty of elbow grease it is possible to improve clay soil and make it nearly as good as any other. But I warn you, it’s a lot more work than some folks will lead you to believe, but I can assure you that it is possible.

If you’re tired of the stranglehold that clay has on your property, keep reading and I’ll tell you what to do.

What is Clay Soil, Exactly?

Clay soil is exactly what it sounds like: soil that has a high percentage of clay in it. But to get more specific, any soil that contains at least 25% clay, by volume, is considered clay soil.

Obviously, clay soil that consists of a higher ratio of clay to soil will be even more difficult to work with and even more deleterious for plants as mentioned above.

How Can You Tell if You Have Clay Soil?

The best and most decisive way to determine if you have clay soil, and how bad that clay content is, is to do a soil test. They don’t cost very much, and scientific data is always best. Good soil tests can also give you a plan of action for addressing the soil with the right amendments.

However, an ad hoc method, one that’s been employed basically forever and still works, is to interact with the soil directly, physically.

First, moisten the soil just a little bit if it’s not already. You don’t want it sopping wet and dissolving, just good and damp. Try to pack it into a ball. If it doesn’t fall apart, poke it. If you can shove your finger into it without the ball breaking open, it’s definitely clay.

Also, test it under your feet: When the soil is wet, if it has a sticky, heavy, and glue-like consistency it’s almost certainly clay. Pay attention to bare soil when it dries out again; if it cracks significantly, it is certainly clay.

Once you know you’re dealing with clay for sure, it’s time to get a plan together for dealing with it if you want to plant in it without hating your life.

What is Clay Soil Amendment?

The way to fix clay soil for planting is to amend it. Amendments for clay typically consist of different kinds of organic matter that will help to fortify the soil with nutrients and other things needed to support plant life and other kinds of life that will sustain favorable soil conditions.

It does this by adding in compounds and elements that plants need, and also lowering the overall ratio of clay.

In time, as these amendments break down, more are added. It is a lengthy process, no doubt, but if you approach it diligently in time and with certainty, your clay soil can be improved.

How Can You Break Down Clay Soil Fast?

There’s no great way to break down clay soil quickly for amending it, not if you want to do the job right.

Yes, you can hit it with a tiller to grind it up and that can save your back, but it also has a tendency to pulverize the clay and make the subsequent amendments that you put in there less effective.

A better way to go about things is simply, sadly, to just use a shovel to break it up manually and gently mix in the amendments when required. Some amendments you can actually lay down directly on top of the soil and let time and nature do the rest.

Ultimately, no matter how you want to go about things, it’s going to be a long process though it’s possible to meaningfully improve your clay soil with just an afternoon or two of work.

Ways to Improve Clay Soil

The following ways are all proven methods for improving clay soil through various techniques and amendments, oftentimes in conjunction.

Terrace Your Beds

One of the best, and most labor intensive, ways to improve your clay soil is simply to build terraces over your beds.

Simple terraces are nothing but raised areas of other, better soil over the clay. It sounds a little bit like you’re just sweeping the problem under the rug, and in a way you are, but this is also highly effective for a host of reasons…

When you place good, suitable soil directly over the clay and plant in that you can kill two birds with one stone: For starters, your upper, better soil will drain more readily and prevent the roots of your plants from getting waterlogged or root-bound because they can’t penetrate the clay.

But then the clay layer beneath, which will be far more impermeable, will actually trap nutrients that drain away, allowing you to easily fortify that soil over time and, slowly, improve the clay itself.

It might seem a bit odd to recommend the nuclear option like this straight away, but I’ve done it before myself and, if you’ve got the resources and the gumption to do it, I highly recommend it.

The Golden Rule: Till and Mix at the Right Time

For all of the other amendments on our list, we will be mixing them into the clay soil directly. And with this approach, there is one golden rule: till and mix in these amendments at the right time.

The right time to till is when the soil is properly moist. How moist is properly moist? Remember that test I taught you of above about forming a ball with the soil? Not as moist as that; meaning that when you form the ball and prod it with your finger, it should still crumble.

Next, using your tiller or shovel, don’t overwork the soil. You only want to go down between 6 and 12 inches, and it’s much better to make a series of shallow passes to reach the desired depth versus going all at once. Especially if you’re using a tiller on high speed and set deep, this will pulverize the soil and work against you.

In short, go deep gradually, and only amend your clay when the soil is slightly moist, not dry and not soaking wet.

Add Compost

Compost is every gardener’s best friend, and for a good reason. It’s a great way to supercharge soils with concentrated, diverse organic matter that all plants need, simultaneously providing nutrients and improving structure.

Compost is also especially good for amending clay soil because it will rapidly add nutrients and also create a suitable environment for all the microorganisms, and insects and worms, that we need in there too.

In fact, certain fungal organisms that are invariably found in it start to bind clay particles together into larger and larger arrangements, reducing the likelihood that the soil gets compacted.

Basically, if you’ve got a lot of compost to spare, now is the time to use it as you can’t really add too much compost when you’re trying to amend clay. If a neighbor owes you a favor, and they’ve got compost, now’s the time to call it in!

Add Manure

Manure is very much like compost when it comes to adding nutrients and some structure to clay soil, but unlike compost, it has some major drawbacks. If you add too much, you can wind up damaging the roots of plants, and also turning the clay into a disgusting, mucky slime.

Add a little bit, give it time to break down, and then come back later on to add more in a couple of weeks. Do not overdo it!

Mix in Bark and Other Organic Matter

Bark, leaf litter, and other detritus are some of my go-tos for amending clay soil. It loosens it up, adds in a good amount of nutrients, and improves overall soil structure.

If you shredded or chipped this litter, so much the better, as it’ll be easier to add, distribute, and mix compared to the whole stuff that you’ve just gathered up.

It’s a lot more forgiving than using manure, but unlike compost, you should add a good amount of this work it in, and then give it time to break down before reassessing and retesting the soil as necessary.

Aerate, Aerate, Aerate!

One of the simplest, most time-consuming, and still most important ways you can improve clay soil is to aerate it. And I mean aerate the heck out of it! Aeration is your best bet for immediately improving drainage and reducing the ongoing effects of impaction.

If you have a small garden or other area that you’re working with, it’s possible. Aerate it using a handheld fork or other tool for the purpose.

Larger parcels that are mired by clay are better serviced by power equipment. In both cases, don’t drive or walk over the soil that you have aerated because you’ll close up the holes.

And, as mentioned above, timing is important here. You don’t want to aerate all the time or do it randomly because you can do more harm than good.

I recommend that you aerate twice a year, in the spring before you plant and in the fall when you’re breaking down old plants and getting your garden ready for winter.

Plant the Right Plants

I mentioned earlier that most plants simply don’t do well in clay soil, and that’s true. But believe it or not, some plants do, in fact, love it!

Typically, these plans, whatever they are, all have a few things in common, namely that they have strong, persistent, and pervasive roots that can bust up even firmly compacted clay.

Some of the best, clay-loving plants that you might try are sunflowers and radishes, the latter being an especially good choice because leaving them in the ground to decompose will help to break up soil and start amending it.

All these approaches have merit, and you can try one or several of them to good effect.

Should You Add Sand to Clay Soil?

No! Although sometimes it is recommended by the inexperienced, or by people who are working with clay soils that were very little clay in the end, sand is one of the worst things you can do.

That’s because sand will mix with the clay to make something that is very much like all-natural cement, turning the clay incredibly hard and difficult to work once it has been compacted.

It’s very easy for this to go wrong, and once that happens you’ve got almost no choice except to excavate it and put in fresh soil.

Remember this diddy: Put the sand away if you’re trying to fix your clay!

How About Gypsum? Is it Good for Clay?

Gypsum, like sand, is often purported as an amendment for clay soil but in my experience, it’s rarely the right solution. More often, it just makes things worse in a different way.

First, yes, it is true that gypsum can work to soften clay, especially in preparation for intensive tilling. It’s often used for serious excavation and new construction for this reason.

The problem is that gypsum adds a ton, and I mean a ton, of calcium into the soil. It is also antagonistic to salt, reducing levels in the soil.

In short, it will readily and seriously throw your soil levels completely out of whack. However, if you know that your soil is very low in calcium and very high in salt, and also high in clay, gypsum can work well to amend soil levels during or after tilling or aeration.

However, what you don’t want to do is continually add the gypsum as you continue to work over the clay throughout the year: you’ll have less and less salt and more and more calcium.

Use the gypsum in the beginning if your soil levels meet the profile, and once that’s done switch over to the other amendments as detailed above to improve structure.