What happens when you add sand to clay soil? Many people claim that this will make concrete and others say that it results in soil that is easier to dig. How can there be such large discrepancies about something that is so easy to test?
Why is this a problem? Gardeners with heavy clay find it difficult to dig, so they want to loosen it up. Sand is very easy to dig and it makes a lot of common sense to add it, to create a looser soil.
Sand and Clay Makes Concrete
This myth, as stated, is simple to debunk. Concrete is a mixture of sand, gravel and cement. Since neither clay soil nor sand contains cement, it can’t form concrete.
Maybe when people say concrete they really mean hard soil? Does clay become harder when you add sand to it?
Making Adobe
Some people claim that sand and clay forms adobe, a strong material used in the Southwest US and Central America for making bricks. Adobe is made from soil that has approximately 70% sand and 30% clay. Too much clay will not make hard bricks. Heavy clay soil is around 60% clay, not 30%. Adding a bit of sand will not create soil with 70% sand, so it does not make adobe.
Regional Opinions
Most gardeners who believe the myth are from the Southwestern US. There are enough reports that I am starting to think that there might be something to their claims. People tell the story of adding some sand and ending up with soil so hard they can’t dig at all. Maybe they used the wrong sand?
On the other hand, people in Europe recommend adding sand on a regular basis. Many top gardeners like Beth Chatto use this method to loosen their clay soil. A Google search for UK websites will give you a long list of recommendations for adding sand to clay. They do caution that it should be rough builder’s sand and not smooth playground sand.
Australians also recommends adding sand to clay soil, but their problem is mostly sandy soil, in which case they add clay to it.
These regional differences suggest that the clay, sand or climate in these regions affects the results people see.
Scientific Evidence
There are numerous references to a California study, but nobody ever gives the details of the reference. I have been asking for and looking for it for several years without success. None of the people who claim it exists have produced it. If you have a reference, please post it in the comments.
Personal Experience
My first garden had very heavy clay that could be used for making sculptures. Digging in 3-4 inches of sand resulted in soil that was friable enough to dig and plants started to grow better. The soil did not get harder after adding sand.
My next two gardens had 50% and 40% clay. Adding sand in both cases produced soil that was more friable.
All of these gardens are in Southern Ontario.
Some claim that you can’t mix the sand into the clay properly and that is quite true. What I found is that the sand coats the clay clumps and prevents the clumps from joining back together. This soil now has sand channels running through it that allow more air and water into the soil. Even after 5 years, I can still see the channels when I plant something. Keep in mind that I disturb my soil as little as possible.
Soil Texture Triangle
The soil texture triangle pictured above shows the amounts of clay, silt, and sand in various types of soil. The triangle is useful for classifying soil, but I think it has led to the myth that you need to add 30 – 40% of sand, before you will have any effect on the soil. Looking at the triangle, this seems to be the case. If your soil is in the middle of the clay section you have to add a lot of sand before it becomes sandy clay or clay loam. But this is just a convenient way to label soil; it does not mean that a small amount of sand can’t make a difference. Not all of the soil in the yellow clay area has the same properties. A soil with 80% clay and one with 45% are very different, but both are still classified as clay.
You do not need large amounts of sand to change the properties of soil.
Logical Extrapolation
Since we have no science data, let’s look at this logically. Let’s say that you have clay soil and after adding some sand, it gets harder. What happens if you add more sand? If the myth is true, the resulting soil will be harder still. Add more sand and it gets even harder. At some point you will have soil that is almost pure sand, and as hard as a diamond. Does this make logical sense?
Even if there is some critical point at which adding sand makes the soil harder, most gardeners will not have soil at the critical point. Logic clearly shows that, at best, the myth is only true for some clay soils.
Clay Soil Does Not Make Clay Harder
Without some scientific evidence, it is most likely that sand does not make most clay harder. Perhaps the clay in the Southwest is different and reacts with sand differently. After all, there are many types of clay soil.
Sand Does Not Create Good Soil
Sand may loosen soil for digging, and it might even open it up and allow more air into the soil, but it can’t make good soil and it won’t improve soil structure. Clay soil needs to have more organic matter added. This will increase microbe activity, and only then will the structure of the soil improve.
Looking for Comments
If you have experience adding sand to clay, please let me know about your results. Be sure to include some information about where you live.
Hello good sir, I live in the US South West. Another thing to consider with our soils here is that while the majority of other locales must contend with acidic soils out here ours are more alkaline. Cement to make concrete is an alkali compound. Another thing I have heard but not directly tested or studied is that concrete used in homes leeches into our soils further altering the soil’s PH… A condition that while likely desirable/unnoticed in other locales of the US where acidic soil is a larger concern could very well likely, if true, allow for conditions to create a semi natural concrete. This is of course just theory crafting as I haven’t tested any of this myself but it doesn’t sound like an absurd thing to look into. What is more however any person worth their salt trying to grow anything non-native here would likely be adding sulfur to their soils (while natives should need minimal such efforts) in an attempt to reach a more neutral PH which would, again in theory, remedy the situation by reacting with the alkali in the soil preventing a concrete.
This sounds like something that should be asked of one of the universities in Southern California who may of already looked into such things, or might consider it worthy of investigation.
Much of our soil in S. Ontario is alkaline.
Living on a farm with abundant aged manure, which is plowed into the blue clay garden every fall for over 60 years along with numerous bales of rained on straw, I can say that the soil produces superior produce, if you can jackhammer it out of the clay.
The most effective solution to date is a truck load of decidiuos chips. The soil is workable for several years, the down side is it takes a lot of nitrogen to break it down and you will need commercial fertilizer for at least the first year.
Where I have also added sharp landscape sand from the pit, the soil initially feels harder but in the end adds to the longevity of the mix.
I’ve read through your book several times now (and loving it), and I am trying to figure out if there is anything I should do to prepare my soil before starting my new landscape.
I’ve read from your book and posts that: amending a small bit of soil before planting causes rooting problems, that tilling soil is terrible for the soil structure, and that the soil structure should be disturbed as little as possible.
I’ve also read from this post and the replies that you’ve left that: ‘digging in’ sand can aerate and improve drainage in clay soil in a permanent fashion, and that adding organic matter to the soil is necessary to improve the soil structure.
I felt confused and conflicted by these two points, so I went out and measured the drainage in my clay soil. I’m finding that I’m getting an OK 30~60 minutes per inch of water drainage. The majority of the plants that I’ve chosen to grow are reported to be tolerant of clay soils, provided that no waterlogged conditions occur. I’m therefore concluding that no improvements to the soil structure or drainage need to be made.
That said, I’m still tempted to buy a lot of sand and a tiller…but I don’t know if that would hurt or help.
Adding sand and organic matter will improve the soil. Tilling damages soil structure. Which should you do?
I think it depends on how bad your soil is. My current garden is 40% clay, but 40% sand with some organic matter. It is not too bad and my current practice is to kill the grass, and plant. I don’t amend or till.
My previous garden was probably 70% clay. It was gray, and smelled. Digging produced hard clumps of clay. It really needed some amending before it could be used. Was I worried about destroying soil structure? No – it did not have any.
Robert,
Regarding your April 19th reply to martinwelbank you state,
“I have discussed this very point with Linda, who I have known for several years, on The Garden Professors Facebook Group. She was not able to provide any scientific evidence to support her statement “To significantly alter a clay soil, sand must be incorporated to about 50% of the total soil volume.” As far as I have been able to tell, this statement is a complete myth.”
In fact, Art Spomer in a classic Journal of Environmental Horticulture article, “Physical Amendment of Landscape Soils” (http://www.hrijournal.org/doi/pdf/10.24266/0738-2898-1.3.77) explains and illustrates precisely why adding coarse sand to clay reduces soil pore space. (Versions of this article appeared in many professional turf, landscape and arboriculture publications in the early 1980s.)
Interestingly it is possible for a 100% sandy soil to have less total pore space than a clay soil! However, because the pore spaces in sandy soil are much large (macro versus micro pores), the sandy soil is much “looser” and drains much more readily.
These diagrams have been published a lot. However, they are theoretical diagrams – they are not actually measuring soil properties.
They also assume that ‘soil” consists of uniform, equally spaced small particles. Clay is actually a much different structure. There is no reason to think that these diagrams apply to clay soils.
The property of making the soil more friable is never discussed. Nor do the diagrams imply that adding sand to clay will harden it.
There’s a very old saying “Clay to sand – money in hand. Sand to clay – throw money away”.
Adding sand to clay would have to be one of the most expensive, labour intensive and impractical ways to break up clay imaginable. It simply creates a very expensive clay/sand mixture
By far the best method is to use gypsum or a water-based clay breaking polymer. These change the electrical charge on the clay particles causing them to clump. You can then add organic material to create a friable soil.
Sand is very cheap, easy to spread and works. The sand stays put for ever.
Gypsum should only be used in sodic soils.
from a review by Dr. Linda Chalker-scott:
This myth falls into the category of agricultural practices misapplied to ornamental landscapes.
Gypsum effectively changes the structure and fertility of heavy clay soils, especially those that are heavily
weathered or subject to intensive crop production. Gypsum also improves sodic (saline) soils by
removing sodium from the soil and replacing it with calcium. Therefore, one can see improvement in
clay soil structure and fertility, and desalinization of sodium-rich soils, by using gypsum.
What other effects will gypsum have on soil and plant health? There are a number of scientific studies
on gypsum usage both in the literature and on websites. Briefly, researchers have found:
• Gypsum does not usually change soil acidity, though occasional reports of both increasing and
decreasing pH exist;
• Gypsum can increase leaching of aluminum, which can detoxify soils but also contaminates
nearby watersheds;
• Gypsum can increase leaching of iron and manganese, leading to deficiencies of these nutrients;
• Gypsum applied to acid soils can induce magnesium deficiency in plants on site;
• Gypsum applied to sandy soils can depress phosphorus, copper and zinc transport;
• Gypsum can have negative effects on mycorrhizal inoculation of roots, which may account for
several reports of negative effects of gypsum on tree seedling establishment and survival;
• Gypsum is variable in its effects on mature trees;
• Gypsum will not improve fertility of acid or sandy soils;
• Gypsum will not improve water holding capacity of sandy soils; and
• Gypsum’s effects are short-lived (often a matter of months)
With all due respect to you Mr. Vegas, your poem is in an alternate reality here in Chicago Near Suburbs soil.
At no time in the past ten years did adding #1 “Bank Sand” and #2 “Masonry Sand” to the 90% black-as-the-Ace of Spades clumping to 4-inches every not result in a more friable soil. Sure, I added the dehydrated cow manure and orange peat moss also, an in gardens I added Perolite and Vermiculite.
Where the lawn is still 80+% Clay, My 250# can stomp on a regular garden spade and not dig in one-half inch. Is there any wonder I cannot get the cheap sod to root despite plenty of fertilizer and water? In order to stick in my plastic rain gauges, I must put the multi-nozzler to “Jet” where I am placing the gauge, multiple times, to seat the gauge all the way in.
Also, I have tried the “Gypsum the hell out of it” for the lawn in frustration with the clay, which as far as I can tell, is as hard as the concrete walk this 2021 drought year. I saw no difference in any subsequent days after applying the Gypsum. I now have to worry that the extreme excess Gypsum is tying up what was available phosphorus. I do see the sodded lawn getting completely replaced every 4-7 years.
Meanwhile, the “seeded” parkway is going on its 18th year, but is looking tired. I am taking a 4’x4′ section of the sod which died out in this drought, and dumping sand into it, tilling it, peat-mossing it, dyhydrated cow manuering it, and Kentucky “Midnight” Bluegrass from an Oregon seed company.
I am only talking about 600 sq-ft of lawn, so adding the sand in 5-gallon buckets cost only my back. Three to four dollars gets a bucket of sand from the quarry by me or $5.00 for a sand-tube which fills a bucket at Menards.
BOTTOM LINE:
My poem is: “Clay will make you lose your religion in a every way, while sand amendmending will save the day in a heavenly way.”
– Sodfather
Thank you Sodfather, for giving your experience.
I live in Melbourne, Australia and have similar soil problems. Can you please tell me how much sand, peat-moss, dry cow manure, perlite and vermiculite you would use for garden beds?
One of the links on your site took me to Linda Chalker-Scott’s site, where she has the following article :
https://puyallup.wsu.edu/wp-content/uploads/sites/403/2015/03/soil-amendments-2.pdf
It contains an interesting juxtaposition of ‘sand’, ‘clay’ and ‘concrete’
I have discussed this very point with Linda, who I have known for several years, on The Garden Professors Facebook Group. She was not able to provide any scientific evidence to support her statement “To significantly alter a clay soil, sand must be incorporated to about 50% of the total soil volume.” As far as I have been able to tell, this statement is a complete myth.
Lady’s slipper orchid growers have said to watch out for sodium salt in sand. So, if sodium salt can be a contamination issue with sand and rinsing is needed it would be a good tip to mention.
I’m pretty sure I know why some people are reporting the addition of sand causing their soil to harden. The big retailers and landscape supply stores carry a line of products called “paver sand” or something to that extent. It is meant to be spread over the ground that pavers or flag stone will be placed to provide a level, stable base. It looks like sand, feels like sand, is called sand on the label, and it IS sand, the kicker is that it is not just sand. The product is intended to act like grout for outdoor “tiles”, spread it, lay the pavers and wet the whole area. When the sand dries it hardens. I’m not sure but the paver sand may contain cement, so in essence these people are mixing a low grade concrete into their soils. Again this is just a theory, but the myth seems so outside of logic that I would guess there is some hidden player involved.
Interesting suggestion – I had not thought of that.
Yes, I almost bought this paver sand by mistake!
As pertains to “Paver Locking Sand”: My understanding is that amounts of Portland Cement are mixed in with the fine sand. This wetting this sand while in the gaps between pavers is what “locks” them.
Too much water will dilute the Porland similar to when I over-watered the parkway last week evidently causing all the fertilizer applied to be washed below the root zone, to the chagrin of the grass.
Lightly mist the locker-sand and let it sit to get hard is how I found the best way to use it. Oh year, do not forget to sweep off the locker-sand from the pavers before misting them lest you want to scrape off the material from each paver at a future day.
-Sodfather
Paver sand is pit sand, that is, it has sharp edges unlike beach or river sand. Paver sand indeed compacts and locks together, the way crushed gravel does, but pebbles don’t. It does not contain Portland cement, which is not needed. I have installed hundreds of pavers using only sand. The sand under pavers, used for leveling on top of a permeable membrane, can be of any variety, typically less expensive.
An interesting theory though most likely not accurate. You are referring to polymeric sand which has a glue additive added to it and is only bagged. Moisture instantly starts the process for the glue to activate and harden. This is used professionally in landscaping to fit between paver joints and lock things together. The base underneath the pavers sometimes is sand though much better if 1/4 minus gravel over the top of a compacted base of 3/4 minus gravel prior to pavers. You can obtain fine or plaster sand in bulk which sometimes is used as a final base layer and this would be much finer sand than coarse or builders sand. Generally speaking after reading all of the comments my current theory is the actual over working and filling of the soil when sand is added that than when compacted becomes very hard especially when the soils dry out in summer. WA glacial till soil experience. Key is perhaps some sand lots of organic matter added. Get the soil right at first which might involve loosening the soil to begin. Then stick to no till and add organic matter each year on the top never tilling for the rest of your life. Watch the plants and food grow. Wood chips on top for perennial woody plants. Compost on top for veggie beds and annual food crops. Tilling wood chips into soil is one of the worst ideas you will have practically experience.
“What I found is that the sand coats the clay clumps and prevents the clumps from joining back together. This soil now has sand channels running through it that allow more air and water into the soil. Even after 5 years, I can still see the channels when I plant something. Keep in mind that I disturb my soil as little as possible.”
I think what you’ve said here is the key to the beneficial use of sand. Although I would still seriously question the wisdom of using sand over using compost in the same way. Sand doesn’t facilitate the formation of soil aggregates like organic matter does. Nor does it increase fertility, soil life, or water-holding capacity.
Clay soils are not the curse that many home gardeners consider them to be. Here in Vermont, a large proportion of agricultural production (much of it corn for silage for dairy operations) comes from soils (Vergennes series) that have clay percentages of around 75%.
In any case, following guidelines for managing soil health (https://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/health/mgnt/) is important for clay soils just as it is for any other soil texture: 1) minimize disturbance (plowing, cultivation, etc.), 2) diversify your crops, 3) keep living roots in the soil all year (perennials or winter cover crops for us in the North), and 4) keep the soil covered (mulched or fully-vegetated).
And if you do have to disturb clay soils, pick your time wisely. You may spend years recovering soil structure after digging or tilling a clay soil when it was too wet.
I agree organic matter works better than sand for all the reasons you mention. The one benefit of sand is that it is long lasting. Organic matter is used up and needs to be added regularly or the effect is lost.
A few years ago, I saw a presentation by Professor Nina Bassuk (Cornell Univ.) on amending soils to combat compaction. One method she used was referred to as “scoop-and-dump” where about 1/3 by volume of compost was worked deeply into the soil. Bulk density and soil carbon were monitored over the following 12 years and it was found that soils continued to improve over that period of time; that is, bulk density continued to decrease and carbon increased. The only input of organic matter, other than what was produced by plant roots, was maintaining a mulch of 2 to 3 inches of shredded bark. Here’s the slideshow: http://www.hort.cornell.edu/uhi/outreach/pdfs/StrategiesCompromisedSoil.pdf. There’s also a video of the operation: https://www.youtube.com/watch?list=PLHPXm2Es8aQC-A4BA87YhFLPvxKK76qpm&v=1sX5c97Mju8
From the video, it looks like the soil is a fine sandy loam or silt loam, but I don’t know of any reason that results would be different for a more clayey texture.
I live on Long Island, NY….On the n. shore it is clay like, on the S. shore it is sandy….I learned through Cornell Cooperative Extension that if your soil is to clay-like, add organic matter. If your soil is to sandy, add organic matter. Makes sense. Organic matter feeds plants and loosens up clay for more air into the soil, and sandy soil will benefit without question…the soil needs food……
You get no argument from me – makes perfect sense.