Heavy clay soil can frustrate even the most optimistic gardener. Follow this 6-step plan to improve soil structure and drainage so you can garden with ease and grow crops that thrive.
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The compacted, hardpan dirt in my first yard was a despicable pass for soil. The builders scraped off the topsoil when they built the home in 1955, and after the clay subsoil was nice and compacted by construction machinery, they placed sod right on top of it.
During a rain, water hit the hardpan clay soil like pavement and quickly sheeted away, unable to soak in and irrigate the lawn or hydrate the soil organisms below.
In the backyard, previous homeowners filled in the swimming pool with low-quality, heavy clay construction fill. Not only did I find blue-painted chunks of concrete when I tried to dig, the thought of trying to put a shovel into the clay sent shivers down my spine!
I wasn’t sure how to create a healthy, productive garden without back-breaking labor to improve my situation. It seemed hopeless. I added organic matter in large amounts, but the clay soil just seemed to swallow it up without showing any signs of improvement.
I figured there had to be a better way, so I started researching how to transform my hardpan dirt into rich, loamy-clay soil the way nature might do it. My research led me to a combination of steps that totally worked, and I’m excited to share them.
They’ll have you feeling optimistic about your garden again! But first, let’s look at what’s good and not so good about clay soil.
The Good and the Bad of Clay Soil
Of all the different soil types (sand, clay, silt), clay soil is made up of the smallest and densest particles. These small and dense particles can cause drainage problems and become compacted easily. However, clay can also hold onto nutrients.
So, all is not lost, we just need to manage it properly!
Let’s look at how to transform that solid, waterlogged soil into a rich, loamy clay that is just right for planting.
Correcting Clay Soil Problems
Following are a number of things you can do to make your clay soil amazing. The more of these steps you can take, the more amazing your soil — and garden crops — will be.
1: Contour the Land
Add contours to your garden terrain by creating a gentle undulation of alternating high peaks and low valleys. Contours of raised planting berms, terraces, raised beds, or even permaculture swales help slow and manage water.
As water undulates and slowly filters through the high and low points, it is oxygenated, which reduces waterlogging.
Organic matter naturally builds up in low spots where water collects, while high spots provide planting areas that dry out faster.
If you plan to build raised beds, follow steps two and three below before constructing the beds so that you have a well-drained foundation. Read more:
Contour the land before all other steps. The ideal time to build contours is when the soil is moist but not waterlogged. Working clay soil when it’s soggy can make matters worse.
In summary, gardens with heavy, clay soil can become compacted very easily, so it’s essential to think about contours (peaks and valleys) to combat gravity and drainage problems.
Would you like to learn more about improving the quality of your soil, reducing maintenance, and increasing yield?
You’ll find loads of information just like this in my award-winning book, The Suburban Micro-Farm.
2: Aerate Clay Soil
Injecting air pockets into clay soil is essential for improving drainage, breaking up compaction, and inviting in soil microorganisms. When clay soil isn’t prepared properly, a solid sheet of clay can be found underneath a layer of loosened/amended soil.
Here are three tools that I love to use for this work:
- Broadfork
- Digging fork
- Plug coring aerator
>>> Browse my favorite tools for the job in my Improving Clay Soil Amazon Shop.
Use your tool of choice to aerate garden soil twice a year — in the fall as the season ends, and in the spring before planting. Fall aeration is especially important because it counters any acts of gravity/compaction that occurred throughout the season.
To use these tools, simply start at one end of the garden and work backwards (so you don’t step on loosened soil) poking holes throughout as deep as you can.
Or let clay-busting plants do the work for you. 🙂
A Note on Tilling: Are you wondering about tilling to improve clay soil? In many cases, tilling can contribute to more compaction.
However, as long as the soil is moist (but not waterlogged), a one-time tilling can be a decent aerator, after which, the other suggestions in this section will likely produce better long-term results (less compaction, lighter and richer soil, fewer weeds).
Learn more about transitioning to a no-till garden.
The digging fork pulls double duty as I add homemade compost to an aerated garden bed.
3: Add Soil Amendments to Clay Soil
Add soil amendments immediately following aeration so that the rain can wash them into the holes and soften the clay. You’ll need lots of organic matter at first to really change the structure of the soil.
The following types of organic matter attract microorganisms that speed up soil improvement by developing tunnels (more aeration) and pooping a lot (more organic matter to break up the tightly wound clay particles).
Some Amendments to Consider for Clay Soil
Compost:
Homemade compost is an excellent soil conditioner that improves drainage. Learn how to build a compost bin that’s right for you.
Green manure:
Cut green plant matter from other areas of the garden and spread it evenly over the soil for a nutrient-rich amendment. (I like to use herbs of all kinds, but comfrey is a favorite.) Herbal compost teas can also be used.
Leaf Mold:
Leaves that have decomposed for a year or two are considered to be leaf mold, a rich and crumbly “black gold” for garden soil.
Livestock Manures:
All kinds of garden-approved, composted manures are excellent soil conditioners. The only modern challenge is the potential for it to be contaminated with herbicide. Learn more about herbicide in manure.
A Note on Manure Application Etiquette: Do not spread manure on frozen or waterlogged soil, or before a heavy rain. This will help to keep your local waterways clean and ensure valuable nutrients don’t wash away.
Worm Castings:
This is one of my favorite homemade sources of organic matter, which is high in minerals, nitrogen, and humus. Learn how to make your own worm castings in this article about building a worm bin. Check out these worm bin problems for beginners before getting started!
>>> Browse my favorite soil amendments in my Improving Clay Soil Amazon Shop.
Leaves composting into leaf mold, a rich garden amendment.
Once you’ve dispensed soil amendments evenly over aerated garden beds and allowed a rain to wash it in, what’s next? You’ll either plant a cover crop (if it’s the right time of year) or mulch appropriately, which I discuss in the next steps.
4: Plant a Cover Crop
Cover crops help incorporate soil amendments deeper into clay soil by rooting thickly and downward. They reduce erosion and enrich soil. You can plant either fall or summer cover crops.
There are a lot of cover crops to choose from, and which is right for you will depend on your climate. Cold winter temperatures kill some cover crops so you can plant in the spring without a lot of prep work. Other cover crops require tilling or cutting before planting crops.
Your local extension office will be a huge (free!) help in selecting a cover crop that is appropriate for your climate/soil/region and gardening style.
The Rodale Institute discusses cover crop options for the no-till garden, and Anna Hess covers the topic thoroughly in her book, Homegrown Humus: Cover Crops in a No-till Garden.
Plant fall cover crops in late summer or early fall. They’ll provide overwintering habitat for beneficial insects.
Plant summer cover crops in late spring. They’ll fill empty spaces in the garden and provide flowers for pollinators.
>>> Browse my favorite cover crops in my Improving Clay Soil Amazon Shop.
Chop cover crops back (I use a weedeater) about three weeks before planting, if they haven’t died back on their own. A few days after cutting, use one of the aerating tools mentioned above to poke holes into the root mass to incorporate some of the plant matter as well.
Plant directly into the plant matter.
This garden bed is mulched with shredded leaves.
5: Mulch Appropriately
Once you’ve aerated and added soil amendments, add mulch if you won’t be sowing a cover crop. Bare soil is a recipe for compaction. Shredded leaves are my favorite mulch. I get to recycle free matter that I find in my own yard! Leaves feed the soil quite well.
Straw used to be a very appropriate and age-old mulch material, but it’s possible that modern straw is contaminated by herbicide. Always know your farmer, always ask.
An alternative is alfalfa hay (Find one of my sources in my Improving Clay Soil Amazon Shop). While herbicides typically target broadleaf weeds, alfalfa is a legume, and therefore not typically sprayed with herbicides.
During rainy periods, mulch lightly so that the soil can breathe and won’t become susceptible to fungal issues. Mulch heavily in dry and hot conditions to protect soil. To learn more about mulching in the permaculture garden, see this article.
6: Avoid Walking in the Beds
After all the work you’ve done to improve your clay soil, the last thing you should do is walk in the garden bed and cause compaction all over again.
Garden soil is very expensive when you think about all of the time you’ve taken to improve it, purchase soil amendments, and collect and disperse organic material.
Create garden beds narrow enough that you don’t have to walk in them to manage all sides.
When I started gardening, 4-foot-wide beds were a great size for making the best use of space in my small garden. But I quickly learned how frustrating it was to not be able to reach all areas easily. I’ve settled on three feet wide as my favorite bed size for my personal reach.
Whichever size bed you decide on, be sure you don’t have to step on your rich, pampered soil.
As you can see, even though heavy clay soil can be frustrating, there are a lot of ways to improve it so you can garden with ease and grow crops that thrive.
Read next:
- 6 Flowers to Grow in the Vegetable Garden
- 7 Ways to Improve Soil Quality
- Clay Busting Plants That Fight Compaction
>>> Get my free 19-page Guide to Organic Soil Amendments for more ideas:
What are your favorite ways to improve clay soil?
Luis says
Hi,
Would the addition of earthworms help in aerating clay soil?
Thanks for all the information you provide.
Sincerely,
Luis
Amy says
Earthworms are part of the “micro-herds” of soil organisms that help to improve clay soil over time. Personally, I would not add imported earthworms to your soil. If they aren’t present, then it may be because the soil environment isn’t hospitable enough for them yet. Rather, by adding organic matter and following these other steps, you create a habitat that should naturally attract worms that are native to your soil.
Tony Griffin says
I dug a root cellar and had 20 yards of caliche as a result of this dig. Using huglekulture as a means to improve this mess I now have four hugle beds in the process of becoming garden soil. Building soil from the bottom up takes a lot less time than building soil from the top down.
Amy says
Great idea to build hugels. This is an excellent idea if you have woody debris on hand.
Valori says
Hi Amy! Thanks for all the info you give here.
I planted a dense cover of crimson and white clovers in my garden and now that I’m chopping it down, there are a lot of baby slugs and also in a lot of spots there are very strong above ground spreading of the plants that seem impossible to cut through to plant in. (I’m sorry I don’t really know how to describe that!) My best guess is that they are trying to hold the soil in place, which is probably good, but how am I going to plant in that? I’m transitioning to no-till – last year my neighbor (we share a garden) dug it all out and turned it over and we put a lot of compost on top and had a very productive season, I grew clovers, vetch and fava in that spot over the winter and am trying to build the soil up with limited financial resources. Because of Covid 19 I want to plant right away but I don’t have access to garden stores. I’m not sure what the best course of action is. If I had the resources, I’d do sheet mulching over this, but cardboard and newspaper are out and getting more soil or compost to put on top is also out. Not wholly sure what to do. Any recommendations? I do have some straw (not enough for a thick cover). I have some leaves that were covering ground from winter that I can collect and put over. I’m guessing I need to cover them so that they will die and decompose, right? Or do you think those heavily rooted clovers should be pulled all the way out because it will be very hard to cut through to plant starts into? I don’t have a lot of space in my garden as is, and food scarcity is a real issue right now so I can’t afford to let it sit and work magic on its own for the year. Thanks for your advice! I hope that all makes sense.
Amy says
You’ve made some excellent decisions for building healthy soil. Unfortunately, many of the cover crops you mentioned are either perennials that come back every year, or annuals that are cold-hardy and often survive the winter. This isn’t a problem in gardens that are tilled, but in a no-till garden, your best bet is sheet mulching. Otherwise, you could try using a broadfork or digging fork to break up the plant matter. If you pull the clovers, definitely use them as a green mulch.
TAMMY SHODA says
I HAVE HAD THE SAME GARDEN FOR 20 YEARS. THE PAST 5 YEARS IT HAS NOT GROWN OR PRODUCED. IT IS ALL CLAY AND HAVE NEVER HAD WATER PROBLEMS. THERE IS A CROP FIELD 4′ FROM THE GARDEN. DO YOU THINK OVERSPRAY FROM CROP FIELD COULD CAUSE PROBLEMS?
Amy says
If the crop field is sprayed, then that would certainly affect your garden.
Lauren says
Hi Amy, thanks so much for all the info in your site! Question about leaf mulching- do you find it’s much more beneficial to shred your leaves, or do they work just as well whole? I’m not sure if I should invest in a little mulcher for leaves and twigs; do you find it to be worth the extra steps?
Amy says
Shredded leaves tend to break down faster from mulch to rich soil, increasing soil health. They also tend to allow rainwater and air to better reach the soil. Non-shredded leaves tend to form an almost impenetrable mat for a time until they start to compost down.
On the flip side, non-shredded leaves host many overwintering native and beneficial insects, so it’s important to leave some leaves non-shredded. I allow those that have naturally fallen in my perennial landscaping areas to remain in place, un-shredded.
However, if I gain access to leaf bags that I’ve collected from neighbors, then I like to shred those to make mulch and to compost it into a rich soil amendment. A mulcher is nice, but I think a lawn mower is almost just as effective. I like our mulcher, but it tends to clog easily.
John Hack says
I personnaly like “alfalfa Pellets or cubes” the carbon to nitrogen is optimal as compared to straw or wood chips, i put a 3-6 inch layer down and cover with tree chips, in less that a year we have earth worms and mushrooms, and no salts from what manure brings and the other nasty stuff fed cattle etc.
I am lucky I have a pellet plant close by, but they are reatively cheap in a feed store, some pet stores also carry them.
We are in the arid part of Arizona, and no native organics, the use of the pellets has changed quite a few wanna be gardeners here to having success, also the 1st ingredient in most compost staters is “Alfalfa meal'” and the pellets or cubes (use whichever is more economical) , as for clay I till in “decomposed granite” as a source of minerals and assist drainage, I get it at a aggregate supply place, my biggest issue is drainage, and root rots, so I build hills so to speak, I find the work worth it, done once and done for ever.
Amy says
For those with alkaline soil, I recommend caution with this strategy, especially alfalfa in concentrated forms like pellets/cubes/meal, as it can make soil even more alkaline. If soil leans toward the acidic, then great. If root rot is an issue, then tilling has likely moved the hardpan layer to just below your efforts. The steps in this article can help.
Joshua Awome says
Hi Amy,
I came across your website today and have read a lot of the articles and appreciate your advice. I am a young father working full-time and trying to learn as much as I can now to be self-sufficient and I am keen to find other gardeners who have advice to share that can make a difference to my daily life, so thank you!
I have three questions I would really like to ask.
1: Is it too late to add organic matter, leaves, manure etc to my garden? I live in Sweden, and right now we have snow on the ground still but according to the forecast it will melt before the weekend is over.
I live next to a big forest, so there are plenty of leaves lying around to collect, and there are some shetland ponies living very close to me that I could potentially collect manure from. I am, however, unsure if its too late and if there is another method I should turn to to give life and love to my soil?
2. If I was to embrace the no dig method on ‘a normal’ grass patch, would I then just first put mulch down on the grass, as you mention, cardboard and then put new soil on top of that and sow the seeds directly into that?
3. Is sea weed a good addition to the soil? The sea isn’t either far from me and there is an abundance of seaweed and I have heard that it is an excellent addition to garden soil?
Thank you for your time.
Joshua
Verner says
Sea weeds are an excellent addition, of not only nitrogen, but over 60 micronutrients. You can’t use it directly in the garden though, because of salt. You have to first let the rain wash it over winter. Put it on the terrace, and turn it over a couple of times during the winter as rain washes away the salt. A nice side effect is that the salt kills the weeds between the tiles.
David W Elliott says
I’m getting started with backyard gardening in the PNW, and I’m done some of these. In addition to the lasagna method, I’m planting comfrey and perennial sunflowers for their deep roots, to take it all deeper. What do you think?
Amy says
Comfrey and perennial sunflowers are well adapted to clay soil, but it depends on your goal. If your aim is to improve soil in order to plant crops, then I would select annual cover crops for temporary cover. See my article about clay busting plants for more ideas.
Mike Arrowood says
We just planted our garden because cold nights (below 45 degrees) are past till fall, we hope. My friend gave us a pickup truck load of fresh grass clippings and we mulched our whole garden with it. It covered the garden well. By the way, the clippings had no type of chemical spray applied during growth. May I ask your opinion using grass clipping for mulch during summer garden growth, then tilling it back into the soil for building up richer soil for next years garden?