- How to Improve Heavy Clay Soil
- Clay soil can provide an excellent foundation for healthy plant growth
- Checking Soil Drainage: Tips For Making Sure Soil Drains Well
- How to Tell if Soil is Draining Well
- Making Sure Soil Drains Well
- Importance of Well-Drained Soil
- The Good and the Bad of Clay Soil
- Correcting Clay Soil Problems
- Urban Farming: How to Check Soil Drainage
- How to perform a percolation test in your garden soil
- How to perform a metal rod test in your garden soil
- Soil Drainage Test
How to Improve Heavy Clay Soil
When you wrestle with heavy, compacted clay in your lawn and garden, your body and your plants can show the strain. But don’t despair. Clay soil offers many benefits, but it can need a hand to reach its potential. Healthy, well-maintained clay soil translates to less work for you and less stress on your lawn and garden. With these insights and a little effort, you can fix your heavy clay soil and reap its rewards:
- Clay soil can provide an excellent foundation for healthy plant growth
- Compacted clay inhibits healthy growth for grass and other plants
- Soil amendments such as organic matter and gypsum improve heavy clay and relieve compaction
- Gypsum enhances your soil and delivers extra benefits to your garden
Clay soil can provide an excellent foundation for healthy plant growth
Clay’s potential as one of the best soil types for plant growth lies in its unique properties. The individual particles that make up your clay are extremely small compared to other soil types such as sand, silt or loam.1 Thanks to the surface area of all those small particles, clay soil has a greater capacity to hold water and nutrients your lawn and garden needs. Managed well, clay soil typically requires less irrigation and less fertilizer, and leads to healthier plants all around.
Even if you’re certain you have heavy clay—and have the clods on your boots and tools to prove it—take time to test your soil before you make changes. A soil test takes the guesswork out of your starting point, so well-intentioned soil work doesn’t backfire and make things worse. If you’re new to soil sampling, your local county extension agent can help with advice and soil testing kits.
Your test results and recommendations can include ways to improve your clay soil, along with helpful information about your soil’s organic matter, pH and nutrients. In areas with heavy clay, it’s a good idea to test your soil every three to four years.1
Checking Soil Drainage: Tips For Making Sure Soil Drains Well
When you read a plant tag or seed packet, you might see instructions to plant in “well-drained soil.” But how do you know if your soil is well-drained? Find out about checking soil drainage and correcting problems in this article.
How to Tell if Soil is Draining Well
Most plants won’t survive if their roots are sitting in water. You may not be able to tell by looking because the problem lies under the surface of the soil. Here’s a simple test to check the soil drainage. Try this test in different parts of your landscape to get an idea of where plants will thrive.
- Dig a hole about 12 inches wide and at least 12 to 18 inches deep. It doesn’t have to be measured precisely for the test to work.
- Fill the hole with water and let it drain completely.
- Fill the hole again and measure the depth of the water.
- Measure the depth every hour for two or three hours. The water level of well-draining soil will drop at least an inch per hour.
Making Sure Soil Drains Well
Working in organic matter, such as compost or leaf mold, is a great way to improve soil drainage. It’s impossible to overdo it, so go ahead and work in as much as you can, and dig as deeply as possible.
The organic matter you add to the soil improves the soil structure. It also attracts earthworms, which process the organic matter and make nutrients readily available to plants. Organic matter helps solve problems such as heavy clay soil or compaction from construction equipment and heavy foot traffic.
If the land has a high water table, you need to raise the level of the soil. If hauling truckloads of soil isn’t an option, you can build raised beds. A bed six or eight inches above the surrounding soil allows you to grow a wide variety of plants. Fill in low-lying areas where water stands.
Importance of Well-Drained Soil
Plant roots need air to survive. When soil doesn’t drain well, the space between the soil particles that would normally be filled with air is filled with water. This causes the roots to rot. You can see evidence of root rot by lifting a plant out of the ground and examining the roots. Healthy roots are firm and white. Rotting roots are dark-colored and feel slimy to touch.
Well-drained soil is more likely to have an abundance of earthworms and microorganisms that keep the soil healthy and nutrient-rich. As earthworms consume organic matter, they leave behind waste material that is much higher in nutrients, like nitrogen, than the surrounding soil. They also loosen the soil and create deep tunnels that allow roots to reach further into the soil for the minerals they need.
The next time you find that the plants you’ve chosen for your garden need well-drained soil, take the time to make sure your soil drains freely. It’s easy, and your plants will thank you by thriving in their new home.
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. Are raised beds right for you?
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:
- 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.
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
Homemade compost is an excellent soil conditioner that improves drainage. Learn how to build a compost bin that’s right for you.
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.
Leaves that have decomposed for a year or two are considered to be leaf mold, a rich and crumbly “black gold” for garden soil.
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.
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.
- 6 Flowers to Grow in the Vegetable Garden
- 7 Ways to Improve Soil Quality
- How to Build a Fruit Tree Guild
What are your favorite ways to improve clay soil?
>>> Get my free 19-page Guide to Organic Soil Amendments for more ideas:
Urban Farming: How to Check Soil Drainage
By The National Gardening Association, Paul Simon, Charlie Nardozzi
The soil particle size determines how well your urban garden will drain water. The microbes and plant roots need a balance of air and water in the soil to thrive, which is why proper soil water drainage is essential.
While some plants, such as cactuses, can survive on dry soil that drains water fast, and other plants, such as willows, can survive in temporary standing water, most plants need a well-drained soil to grow their best.
Brown patches on your lawn in midsummer while the rest of the lawn is green may be a sign that the soil under the grass is predominantly sand. If, after a rain, you have puddles of water in certain spots in your yard that last longer than in other sections of the yard, the soil in those spots is likely to be mostly clay.
If you want to be a little more exact about how well your soil drains, particularly where you want to place your garden, you can conduct a percolation test or a metal rod test. Read on for more.
How to perform a percolation test in your garden soil
To find out whether the spot where you plan to grow a garden or plant a tree is adequately drained, you can do a percolation test. Here are the steps to follow:
Dig 1-foot by 1-foot holes in several places on your planting site.
Let the soil dry out for a few days.
Cover the holes to keep water out (and to make sure no one — human or beast — falls in).
After the holes dry out, fill them with water and determine how long the holes take to drain completely.
Use a timer so you don’t forget what time you started. Then use the following list to determine you soil’s likely drainage pattern:
If the water drains out within 10 minutes of filling it, the soil drains too well. It will probably dry out too fast for most plants.
If the water drains out within 30 minutes of filling it, the soil is still draining fast, but it’s probably okay for plants that like well-drained soils.
If the water drains within 30 minutes to 4 hours of filling it, you have ideal drainage. Most plants thrive in this type of drainage situation.
If the water takes longer than 4 hours to drain, the soil is poorly drained and probably won’t be good for most plants. It’s best suited to plants that are adapted to wet soils, such as cattails and certain irises.
You can improve whatever drainage conditions you have by adding organic matter. Adding organic matter to the soil helps fast-draining soils retain more water and poorly drained ones to dry out faster. Organic matter really is the miracle additive for soil. And, of course, selecting plants that are adapted to your existing drainage conditions makes it more likely that they will grow and thrive.
How to perform a metal rod test in your garden soil
The metal-rod test, which helps you determine how well your soil drains, is particularly important in urban areas because you never know what’s been buried under the soil you’re trying to grow in.
Some garden areas have an impervious layer of soil called a hardpan, which is made of solid materials like asphalt, packed clay, or concrete. This layer can prevent soil water from draining, creating a wet environment for plants to grow in.
Knowing whether you have these materials under your garden and how deep down they are can help you decide whether to move your garden to a different spot or build raised beds on top of the soil instead.
The metal rod test couldn’t be simpler. Just take a 1/2-inch-diameter metal rod and push it into the soil in different places around your garden. If you can push the rod down 6 to 8 inches without meeting any firm resistance, your soil doesn’t have an impervious layer and it’s okay to garden or plant in.
If you do find an impervious layer, you can dig down to see what it is, or you can simply build your garden up.
Soil Drainage Test
Soil is a crucial consideration for in-ground gardening. However, not all types of soils are created equal. In addition to the level of the various minerals and nutrients found in soil naturally, you also need to consider how much water the soil can retain. Well-drained soil will not hold standing water for long, while poorly-drained soil can hold standing water for long periods.
Ideally, garden soil should hold no standing water, but should be able to retain sufficient moisture to support healthy plant growth. To determine your soil water retention rate, you can perform a simple soil drainage test, or percolation test. This requires nothing more than some basic tools and a shovel.
Dig a hole in the soil that is at least 12 inches by 12 inches. The sides should be straight up and down, not angled. Fill the hole with water and let it sit and drain overnight to saturate the soil. The next day, refill the hole with water and measure the level. You’ll need a straight edge over the top of the hole (you can use a yardstick, pipe or even a stick here), and a tape measure. Continue measuring the level of water in the hole every hour until all of it is gone.
In an ideal situation, water should drain at a rate of two inches per hour. Slightly faster or slower than this is ok, but if it is too much different, you will need to amend the soil using organic matter.
Even a novice gardener knows that soil needs to drain well for plants to thrive. What most of us don’t know is how to measure the drainage rate of our soil – or what that rate should be. You can assess the drainage rate of your soil quickly and easily with nothing more than a large can and spade.
- Remove the top and bottom of a 46-ounce aluminum can. You can typically find these cans in the juice aisle of your grocery store.
- Did a hole to a depth of four inches in the area where you wish to assess the drainage rate.
- Insert the can in the hole. Back fill around the can with fresh soil, pressing it against the can to secure the can in place.
- Fill the can to the rim with fresh water.
- Measure the amount of water that has drained through the bottom of the can in one hour.
The water level should drop approximately two inches in well-drained soil. If it drops less than an inch, your soil is likely to become waterlogged after rains. If the water drops more than four to five inches, your soil drains too quickly.
To correct soil that drains poorly, dig and loosen the soil to a depth of eight to ten inches. Dense, compact soil does not allow water to penetrate and cannot drain properly. This is often the result of soil compaction or high clay content. Adding organic matter improves the texture and promotes good soil drainage. If the area is sunken, build the soil up to a slighted raised mound to prevent water from collecting in the area after rains.
Ironically, the solution to soil that drains too quickly is also adding organic matter. This improves the water-holding capacity of gravely or sandy soil. Good sources of organic matter include compost, aged manure or leaf mold. Work it in well with the existing soil with a garden spade or garden tiller.
Test the soil in all areas of your yard for drainage before planting as considerable variations can exist within your yard. For severe problems with drainage, add organic matter to the soil in the fall and allow it to work its magic as microbes go to work improving the soil.