Adding sand to clay soil, in any amount, has been proven by the University of California Agricultural Extension and the U.S. Department of Agriculture to be about the worst thing anyone can do for their garden soil. Adding organic soil amendment, such as horse manure, to name just one possible amendment, is a worthy suggestion, especially if the manure has been aged or composted for three months by layering it with rotted alfalfa hay. However, if the manure is salty this can be a negative factor in clay soil since it’s difficult to wash out the salts. In general, the safest method for amending alkaline clay soil is to work in all the pre-nitrolized or fully composted organic amendments one can get one’s hands on or, when impossible to dig them in, then use them as mulch on top of the ground. Plant roots will also eventually help break up soils.
Southwest gardeners need to know that when poor drainage in clay soil is caused by alkalinity, one of the best things one can do is to apply soluble gypsum according to package directions. Organic gardeners prefer using rock gypsum which has not been altered by chemical processing. However, the honest truth is the soluble type works best. Gypsum breaks up clay soils that are alkaline by releasing soluble calcium which replaces some of the sodium on the clay particles and thereby produces a more open soil structure. Work approximately half a coffee can full of gypsum into the earth on the bottom of each planting hole and also broadcast gypsum on the ground surrounding plants in the established landscape so it looks as if a light snow had fallen. Do this at least once every three years and water it into the ground. The action of gypsum does not last forever, so repeated applications are necessary. Gypsum is a relatively inexpensive amendment. It will not hurt your garden soil and may help a great deal.
All soil experts will tell you one of the first rules of amending soil is “never tamper with the structure of your soil.” A soil’s “structure” means the arrangement of the sizes of particles in it and their relationship to one another. All soils are categorized according to their texture and the 4 basic soil types are clay, sand, silt, and loam. Clay is a firm, fine-grained earth containing a large amount of tiny mineral particles less than 0.002 millimeters in size that have negatively charged surfaces. Clay feels slippery and sticky when wet. Sand is a loose earth mainly composed of tiny particles of rock between 0.05 and 2 millimeters in size. It feels scratchy or gritty to the touch. Silt is a fine-grained earth made up of rounded, weathered particles. Loam is a combination of the other three (clay, sand, and silt) in varying ratios, the optimum being equal quantities.
Since loam is a naturally occurring mixture of clay, silt, and sand and is widely considered the best garden or agricultural soil, many people, sadly including some misinformed garden writers, have erroneously supposed that all you need to do to get loam is to mix the other three together, or perhaps only clay and sand, and that—Voila!— you will end up with loam. Unfortunately, this doesn’t work. The fact is that adding sand to clay soil in any amount is an extremely dangerous thing to do. You end up with something akin to concrete. The same is true of adding clay to sand. In either case, the fine clay particles will fill in the larger spaces between the sand particles, thus permanently destroying drainage. In a garden of clay soil, it would be impossible to add sand in sufficient quantities to approximate a natural soil made up of a mixture with a ratio that is more sand than clay.
Gardeners often confuse lack of drainage due to clay soil with the word hardpan, but actually these are different condition. Clay is a type of soil, but hardpan is a condition in which a layer of soil that does not drain lies on top of the soil or is buried under topsoil that drains. Hardpan is a layer of hard, compacted soil of any type cemented together by minerals and almost impenetrable to roots or water. Hardpan is often made of clay but it is not the same as clay soil.
Caliche is yet another type of soil sometimes referred to as hardpan by gardeners. Caliche is a crust of calcium carbonate, usually white or gray in color that forms on the stony soils of arid regions such as found in the Southwest. Hardpan and caliche may be buried under the ground, as in housing developments where it is sometimes covered with a layer of topsoil, or it may lie on top of the ground. In some cases the hardpan may be only be a foot thick in which case one can use a crow bar to break through it to a lower layer that drains, thus creating drainage in the bottom of planting holes. In other cases hardpan may be many feet thick. The best way to combat a clay-based hardpan is to plant in raised beds and terraces filled with amended topsoil, or to make frequent additions of soluble gypsum and a variety of organic soil amendments as explained above.
Related Articles:
- Clay soil in Kensington area of San Diego
- Categories Of Soil
- How Gypsum Improves Drainage
- Vegetables, Eucalyptus, Clay Soil, and Fruit Trees
- Dealing with Clay Soil
This is funny since there is a book called ‘Build Your Own Earth Oven’ by Kiko Denzer that specifies mixing sand and clay or clay, sand and manure/sawdust, to make a clay oven for baking artisan breads, pizzas and other good things. The mixture of clay and sand – hard as ‘brick’ for an oven that lasts and holds together with a large baking area inside.
Thanks for your amusing comment. I just returned from a trip through New Mexico and Arizona where the walls and buttresses of churches that have stood for hundreds of years are built of clay, sand, and straw. In order to keep these sun-baked buildings standing to this very day, dedicated locals apply a layer of this muddy mix (sand, clay, and straw) to the exterior walls annually. While in Taos, New Mexico, I saw a video of Maria Martinez gathering clay and then mixing into it about 20% of volcanic-based sand before shaping it into pots and firing it in an outdoor open fire of dry cow pats to create her distinctive black Santa Clara pueblo pottery. I guess my heading should have been: “Be Sure to Mix Sand into Your Clay Soil if Your Aim is to Make Pottery or Adobe Bricks Instead of Growing Vegetables and Flowers.” Do you think that would finally teach people?
This is Ben Cole,I want to order some CLAY SAND,that you have in your shop.I want you to get back to me with the price including taxes and I want to know do you accept Credit cards as your payment.Hope to hear from you soon.
Hello Ben:
Once you select the product of interest you’ll see the prices. Shipping and taxes are then calculated based on the products you order and the ship to address.
Please contact us with any additional questions!
-Pat Welsh Gardening
I was so pleased to find your blog. I am researching for a science activity with 3-6th graders, and this is exactly the information I was looking for. We will actually be doing exactly what you advise NOT to do, but the purpose is to show why taking our clay soil in Texas and mixing in sand would actually be detrimental to the soil.
However, I would like to give them something to think about as positive alternatives for soil enrichment that can be done in their yards. Many of us have yards that are likely placed over thick, compacted layers of clay. (I can tell by the runoff when the sprinklers run in our neighborhood.) How do we add organics to the yard without tearing up the grass that is there?
Thank you for your question and for the work you are doing with kids. I think it’s a great idea to replicate experiments that were done years ago by the UC Extension and Department of Agriculture in California. These experiments could be done in 1-gallon nursery cans, I would think, though the University of California might have used larger containers. I am not sure. Presumably one could mix various measured percentages of sand with clay and then fill the nursery cans to about 2 inches from the top with the mixtures and subsequently apply measured amounts of water to the soil in the cans and then measure how much comes out the bottom of the cans and at what rate.
The important thing to impress on the kids is that in a garden it would be impossible to add an equal amount of sand to clay. In a practical example, years ago I knew of a garden in Fallbrook California where the soil was heavy clay. Instead of adding organics to improve his soil, the gardener added wheelbarrows full of sand to the clay because an English garden book gave that advice. He kept adding more sand every year to a long flower bed filled with perennials. Eventually the soil was so ruined that drainage was nil and many plants died from root rot.
To answer your question: There are a couple of ways that organic materials can be added to existing lawns. One way is to rent an aereating machine that goes all over the lawn and makes round holes in it. The next step is to rake up and throw away or compost the plugs that the machine pulls out of the lawn. After that spread ground bark onto the lawn and rake it into the holes. Follow up by fertilizing and watering the lawn. The best time to do this job is fall. September or October would be ideal. This will help increase drainage.
Please note that while answering the first gardener who wrote to me on this subject I recommended adding soluble gypsum to help break up clay soil. When clay soil fails to drain due to its alkalinity, applying gypsum according to package directions can aid drainage. One can mix it with the ground bark recommended above and rake it into the holes along with the bark or apply it separately once or twice a year on top of the ground and water it in.
Another idea for adding organics to lawns is to top the lawn with dry cow manure in fall or early spring. Back in the years when I had a lawn I did this job every fall but my lawn was growing on sandy soil, so it was okay. First I would cut the lawn short, then top with manure and follow up with water and the grass soon bounced back greener than before. The problem with using this technique on clay soil is that bagged cow manure is often salty and clay soil can retain salts. A better way is to use any fine-textured mulch recommended for topping lawns. By topping the lawn annually or bi-annually in spring and fall you can gradually add to the organic structure of the soil under a lawn, but not as much as if you aereated first and then raked the organics into the holes.
Hello,
I have been searching for a solution to gardening in clay soil since last year when I moved to Arlington, Texas. Almost everything says to add sand to amend the clay. I am wanting to plant a couple of fruit trees and had I not found your article I would have used sand (in fact I was already figuring out how many bags I needed). I am planning on putting my trees(miniature peach and apple grafted onto M-111)in a raised bed. Do you have any recommendations?
Thank God you did not add sand to your clay soil! I am certainly glad you looked at my blog first. Adding sand to clay soil or clay to sand results in something akin to concrete, stopping drainage completely and the problem can never be fixed. I once knew someone who did this to his perennial flower beds and drainage became ever worse as he added more sand annually. Eventually the guy, an avid gardener, died so I never heard what happened to that garden later. The opening chapter in my current organic book, and also the (conventional gardening) edition published in year 2000 and now out of print and out of date also, but still obtainable on the Internet, explain soil problems and solutions more fully. These books go into soil problems and drainage problems in detail. But it’s best now to be an organic gardener, so if you spring for one of these books, buy the current organic one.
Clay soil is nutritious. Plants will grow in it, but you are right a raised bed can be a great help when first planting. Luckily it does not need to be very high. For a deciduous fruit tree you could build a raised bed that measures 5×5 and is at least 4 inches high and fill it with a good grade of top soil.
What is important here however is that you must dig up the clay beneath the raised bed to about a foot deep and mix gypsum into that and also mix some of your top soil into the top layer of the native soil below the raised bed. This is so you do not create a hard horizon between two soils which will stop roots from penetrating.
If you create a hard horizon between friable soil above and hard clay below you are making hardpan, which happens when builders in housing schemes throw a layer of top soil on top of bulldozed ground. Plant roots tend to stay up in the top layer and never penetrate the lower layer, and then the hard lower layer stops drainage. This is a genuine problem for many gardeners in new homes.
Despite having explained the system above which will help prevent rotting roots in clay soil by use of a raised bed, my belief is that you can garden in clay soil and plant straight into it, just as it is since I have seen it done many times. The surprising thing is once you begin digging into clay soil and mulching the top of it, eventually the very act of gardening in it and the roots getting into it will help break it up and plants will grow. Clay is minerally rich and plants will often thrive in it better than poor sandy soils that drain well but do not retain nutrients.
The wrong thing to do is to dig planting holes and fill them with organic soil amendment since that creates pockets of soggy ground that fill up with water and rot roots. Also roots will think they are in a container and go around and around inside the amended plant hole and never get out into the surrounding soil.
Many scientific experiments have been done to show that the best way to deal with clay soil is to plant directly into the native soil, though plant a little high, and then continually mulch the top of it. The roots of plants have to get out there eventually so the sooner the better. Rough up the sides of planting holes, instead of making a smooth hard edge. Even clean unsalty horse manure can help break up clay when laid on top like mulch before the rains, but I strongly emphasize must not be salty. Manure brings earthworms and they also help break up the ground and make it drain. (When using horse manure, be sure your tetanus booster is up to date.)
One important factor is that if the clay is compacted due to alkalinity, adding gypsum can aid in breaking it up and making it drain, but you should add the gypsum every two years and a half-coffee can full of it dug into the bottom of every planting hole. Gypsum will not correct drainage problems caused by compaction from walking on the ground or heavy equipment but it will greatly help soil to drain when the compaction is caused by alkalinity.
I have known a few gardeners who have hauled away truckloads of pure sandy or clay soil in gardens built on sand or clay and replaced with top soil but this is not necessary and is very expensive. (Again, one must be sure not to create a hardpan layer beneath the top soil. More details on all this are in my book.)
Hello
I read your article after a number of others that reccommend mixing in sand to clay soil to achieve better quality.
You specifically warn against that. Does that apply to the Northeast as well?
I was about to buy additives . . .
Thank you.
Karen in Montpelier VT
Dear Karen:
It is unfortunate that some websites, books, and TV shows give the wrong advice about adding sand to clay soil in a futile attempt to lighten it up and make it drain. Adding sand to clay soil is one of the most dangerous practices imaginable since you will end up with something akin to cement. This advice applies nationwide.
The natural arrangement of particles in soil is called “soil structure.” Never monkey with the natural structure of your soil. (See pages 21 of my organic book for a full explanation.) The only safe way to make clay soil drain better is to increase its humus content by adding organic materials, such as well-rotted bagged, trucked, or homemade compost or aged manure. In the west we also add soluble gypsum to our clay soils to make them drain better, but this technique only works when the cause of bad drainage in clay soil is it’s alkalinity and this is unlikely to be the case in your east coast garden. See page 20 for full explanation of pH.)
In the days of my youth I lived on a Bucks County Pennsylvania organic farm. We had hard red clay soil, but clay soil is nutritious and full of minerals. We amended our garden and agricultural soils with chicken, cow, and sheep manure from our own animals, and our red clay soil became amazingly productive. In our pastures the soil became black with organic matter.
If you were to add sand to clay or clay to sandy soil the process is similar to filling a room with basket balls. Then you add tennis balls and shake it down. This fills all the space between the basket balls, then you add ping-pong balls, and shake it down again and this fills up all the spaces between the tennis balls. Finally you add marbles and once again shake. By then all the spaces between the original balls are filled up and you have less drainage than before.
Experiments done by Agricultural Scientists at the University of California many years ago demonstrated conclusively that adding sand to native clay soil in the attempt to make it drain or adding clay to sand with the hope of making it more water-retentive does not work and harms soils in a devastating way. It is a drastic mistake because it is irreversible, and this is true nationwide. It is impossible to add enough sand to clay to create a natural soil that drains well, as occurs in nature. (The textures of soils and types of soils are discussed in detail on pages 21 and 22 of my book.) The only safe substances to add to clay soil are organics. Adding organic matter to soil is your path to a highly productive garden. I can promise you it works.
Hi, Thanks very much for this information. A local man here in montpelier vermont named Ray Hickory stated that I needed to buy a truckload of sand to add to my yard’s soil because of the clay soil conditions, he told me. I didn’t go along with his trucking in sand because he was not willing to write up an estimate for a job here (a bulkhead) and also I wondered about the safety of importing sand — how does one know what’s in it, for example. But I did not know that the effect of adding sand to clay soil makes for diminished drainage (cement). I wonder who else this Hickory guy has given such poor “information” to. He’s been in bizniz around here for a long time, so I can’t help wondering if he doesn’t know better about trucking in sand.
Good points all around. Truly aprpaecited.