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What Is Gypsum: Using Gypsum For Garden Tilth

Soil compaction can negatively affect percolation, tilth, root growth, moisture retention and soil composition. Clay soils in commercial agricultural sites are often treated with gypsum to help break up the clay and enhance calcium, which breaks up excess sodium. The effects are short lived but serve to soften the soil enough for plowing and sowing. In the home garden, however, it is not advantageous and regular additions of organic matter are preferred both for cost and side effect reasons.

What is Gypsum?

Gypsum is calcium sulfate, a naturally occurring mineral. It has been touted as beneficial for breaking up compact soil, especially clay soil. It is useful in changing the soil structure of excessively heavy soils which have been impacted by heavy traffic, flooding, overcropping, or simply overly weatherized.

One of the main uses of gypsum is to remove excess sodium from the soil and adding calcium. A soil analysis is helpful in determining if you need to apply gypsum as a soil amendment. Additional benefits are a reduction in crusting, improved water run-off and erosion control, assisting in seedling emergence, more workable soils, and better percolation. However, the effects will only last a couple of months before the soil reverts to its original state.

Is Gypsum Good for the Soil?

Now that we have ascertained what gypsum is, it’s natural to question, “Is gypsum good for the soil?” Because it reduces salt levels in soil, it is effective in coastal and arid regions. However, it doesn’t work in sandy soils and it can deposit an excess of calcium in regions where the mineral is already abundant.

Additionally, in areas with poor salinity, it pulls out too much sodium, leaving the location deficient in salt. Considering the cost of a few bags of the mineral, using gypsum for garden tilth is uneconomical.

Garden Gypsum Information

As a rule, using gypsum for garden tilth will probably not harm your plants, but it simply is not necessary. Using a little elbow grease and lovely organic goodies from fall clean up or compost worked into the soil to a depth of at least 8 inches will provide an excellent soil amendment.

Studies have shown that soils with at least 10 percent organic matter don’t benefit from the addition of gypsum. It also has no effect on soil fertility, permanent structure or pH, while generous amounts of compost will do all that and more.

In short, you can benefit new landscapes by application of gypsum on compacted soil if you have a need for calcium and have salt laden earth. But for the majority of gardeners, the mineral is not necessary and should be left for industrial agricultural use.

Growers, Turf and Ornamental

Beautiful Lawns and Gardens

Horticulture growers of fruits, vegetables and ornamentals along with professional turf and landscape managers have long used gypsum to improve soil structure resulting in better growth, yields, quality, nutritional value and resistance to insects, diseases, and environmental stresses Gypsum Is a Fertilizer, soil amendment and conditioner providing calcium and plant available sulfur in sulfate form without increasing pH. Gypsum can be spread on the surface and does not need to be incorporated since it is very soluble.

Reasons to use gypsum:

  • Supplies Calcium and Sulfate Fertilizer essential plant nutrients
  • Amend and remediate high salinity and sodium levels typically caused by de-icing or irrigation
  • Remediate subsoil acidity caused by excessive alum levels
  • Flocculate clay soils to improve water and oxygen infiltration reducing surface water run off thus reducing water use and retaining Nutrients

USA Gypsum Comes in Various Forms and Sizes to Meet Your Needs:

Pulverized Gypsum

  • Variable particle sizes deliver extended release
  • Broadcast with “vicon” style spreaders or drop spreaders designed for powder

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Granular Gypsum

  • Free flowing, low dust, slower release
  • Broadcast with any style fertilizer spreader

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Pelleted Gypsum

  • Fastest acting form of gypsum
  • Low dust, free flowing
  • Broadcast with any fertilizer spreader
  • Care must be taken to keep completely dry until applied

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Pulverized Organic Gypsum

  • Mined gypsum produced without heat or additives as required by USDA & OMRI
  • Broadcast with lime or fertilizer spreaders

Learn More Buy Now

Using Lawn and Garden Gypsum

It is recommended that you conduct a soil analysis to ensure lawn and garden gypsum will benefit you. If no soil test is available apply as follows:

Lawns

Established Lawns: Use 10 lbs. of gypsum per 150 square feet in the spring and in the fall. At these times of year, you can take advantage of seasonal moisture essential for the desired conditioning of the soil.
New Lawns: Use 10 lbs. of gypsum per 100 square feet, incorporating into the soil. Water thoroughly before seeding.

Gardens

Vegetables: Spade in 10 lbs. of gypsum for every 80 square feet. Mix well with soil.
For Roses & Flowers: Spade in 1/2 lb. of gypsum per plant and mix well with soil. Soak area with water.

Trees & Shrubs

Trees: Use 2–3 lbs. of gypsum per tree.
Shrubs: Use 1–2 lbs. of gypsum per shrub. Plant shrubs the day they are purchased. Make the hole twice the diameter needed.

In the late fall, apply generous quantities of gypsum to the soil around the base of trees and shrubs to stimulate root growth. This also helps to control insects that hibernate in the soil over the winter.

Salt Damage

Winter de-icing salt is toxic to most plants and grasses when it accumulates to certain levels. Use 1/2 lb. of gypsum per square foot to restore soil that has absorbed salt.

For all uses, when possible mix gypsum into the soil and water until gypsum dissolves.

Other sources, though, do recommend sand. , for instance, says that “clay soils… often require sand as well as organic matter for full amendment.”

As this quotation suggests, the cement problem appears to occur when sand is used by itself. Two guidelines emerge: first, don’t depend on sand alone as an amendment in clay soil. Use plenty of compost and other organic matter as well. Second, sources that do recommend sand warn against river sand, whose rounded particles, worn by erosion, allow clay particles to pack closely around it. Builder’s sand, however, or “sharp” sand, has more angular particles, which create a more porous soil with a better soil structure than that you’re likely to get with river sand.

The Special Case of Gypsum

Gypsum has several undisputed uses as an amendment, yet its value, like that of sand, is frequently debated or dismissed, and on-line discussion of its utility is both confusing and confused. This is in part because gypsum gets recommended for a wide variety of soil problems (including both raising and lowering pH) but its effectiveness for each is limited by very specific chemical conditions. It works in some cases, but not in others. Another source of confusion results from the fact that so many pages on it are written by university extension offices which are addressing the conditions of a particular state or region. It is difficult to find an overall discussion that’s accessible to the layperson. One of the best overviews I’ve encountered comes from the University of Minnesota, and is titled The Value of Gypsum. Though this page does address the applicability of gypsum in Minnesota, its authors also have the grace to list the various uses for which gypsum is recommended and to explain, in plain English no less, the action of each.

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Agricultural Gypsum is an excellent source of both calcium and sodium sulfate, it reduces or neutralizes aluminum in some soils (mostly in the South-West), and it can, in some cases, loosen or “flocculate” heavy, clayey soils. In addition, it helps restore some sodic, or alkali soils – this is the “lowering pH” part of the legend – and some forms of gypsum can act as liming agents – here’s the “raising pH” part.

At least some of the controversy and confusion arises because there are several types of gypsum (as there are lime), and the exact mineral composition of natural (mined) gypsum varies. Absolutely chemically pure calcitic gypsum (hydrated calcium sulfate (CaSO4•2H2O)) does not raise soil pH. However, a lot of mined gypsum contains dolomite, which does raise soil pH and which supplies magnesium, an important secondary nutrient, as well. This difference mirrors the distinction between calcitic and dolomitic limes, save that both limes will raise pH, while only the gypsum with dolomite will. Some gypsum may contain lime in one of its several forms, and that lime will raise pH.

Since pure gypsum is pH neutral and lime is not, gypsum is a better source of calcium for soils which lack that mineral but which have a balanced pH, as the University of Minnesota site mentioned above points out. However, if you are trying to raise your pH, pure gypsum is a non-starter.

By far the most common lawn and garden use for gypsum is to “loosen” or “lighten” clay soils, and it is here that the controversy rages. Gardening stores across the country sell gypsum, and homeowners and gardeners across the country trustingly purchase it to increase the porosity and improve drainage in their clay soils. Unfortunately, gypsum only works on some clays. The widespread but misguided use of gypsum may explain the terse tone of some sites, which declare categorically the uselessness of the stuff.

Why gypsum works to loosen some clays and not others involves some fairly complex chemistry that touches on clays, pH, soil structure, electrical charges, Van der Waals forces, sodicity (as measured by sodium adsorption ratio (SAR)), salinity (as measured by electrical conductivity (EC)) and probably other stuff I’ve never heard of.

Clay is a problem because it tends not to form the small clumps, or aggregates, that make soil porous, allowing air and water and roots to penetrate them easily. (You may think your clay soil has plenty of clumps, but technically speaking those are clods, much larger and harder than the aggregates considered desirable.) Good soil structure depends on aggregation and on the materials that promote it, called flocculants.

The short story on gypsum is that it flocculates only sodic soils that are not saline, in other words soils high in sodium and low in other salts such as magnesium and calcium. Sodium causes clays to disperse, while these other minerals actually help it aggregate. Gypsum’s high calcium content means that it can flocculate soils that are high in sodium.

Since gypsum can help restore sodic soils, which usually have a high pH, it has gained a more general and undeserved reputation for lowering pH. What actually happens is that the calcium in the gypsum replaces the sodium ions, which can then be washed or leached from the soil. On an agricultural scale, however, this requires hundreds of pounds of gypsum for an acre of land, and then a whole lot of rain or flooding with irrigation water that isn’t high in sodium.

How Gypsum Works: The Chemistry of Clay

This explanation leaves out a lot, but it does cover key aspects of the relevant chemistry.

Clay particles are very small and flat, so they usually lie in closely packed parallel layers that impede the free movement of air and water and the growth of roots. Since clay soils compact easily, it might seem that aggregates, in which the particles are drawn even closer together, would be the last thing one wants in clay.

But at the molecular level, the problem is not that the distance between clay particles is too small for good soil structure, but that it is often too uniform. These particles tend to distribute themselves evenly in space partly because they are negatively charged and therefore repel each other. In contrast, sand and silt are electrically neutral and have no particular tendency to pull together or push apart. Technically speaking, clay tends to disperse rather than to aggregate.

Calcium and magnesium help overcome clay’s dispersion because they are positively charged divalent ions, i.e. atoms missing two electrons. Their positive charge means that they are attracted to negatively charged particles such as clay. And because they have a double charge, these divalent ions can act as “bridges” between clay particles, forming an electrical attachment with two different particles. As a result, they help draw negatively charged clay particles together, aiding in soil aggregation. Since humus particles, like clay, are negatively charged, calcium and magnesium can also bridge the gap between a clay particle and a particle of humus, thus incorporating humus into soil aggregates.

Like magnesium and calcium, sodium is a positively charged ion (a cation), but unlike them it is monovalent, meaning that it has only a single electrical charge. (It is missing one electron.) Because it is monovalent, a sodium ion can only form a bond with one clay or humus particle. It has no second charge with which to bind to another particle. Sodium’s monovalence also means that more sodium cations than calcium or magnesium cations are required to fill the bonding sites on a clay particle. This results in a thicker layer of ions around the particle, “pushing” it further away from other particles.

Unlike magnesium and calcium, therefore, sodium does not aid aggregation, and when it builds up in soils, replacing divalent minerals at clay binding sites, it actually damages soil structure. It causes aggregates to break down and clay particles to disperse, clogging the remaining spaces in the soil. Furthermore, now that the magnesium and calcium cations are no longer bound to clay or humus, they leach from the soil, leaving it less fertile.

Gypsum acts on these soils by adding calcium, which competes with the sodium for binding sites on clay. Calcium, being divalent, draws soil particles together, beginning the process of soil aggregation. Now it is the sodium that leaches from the soil.

Soils in the eastern half of North America are unlikely to be sodic unless they have been heavily treated with synthetic fertilizers heavy in sodium. Western soils usually have higher concentrations of salts, including sodium, so they have a greater tendency to sodicity.

The action of gypsum is so complex and conditional that it makes sense to have your soil tested for salinity and sodicity and to discuss your situation with a county extension agent before using gypsum to flocculate clay soil. Nevertheless, here is a chart outlining various uses for gypsum and when it has what effect.

Will gypsum —
add calcium? Yes
add sulfur? Yes
raise pH? In normal soils, only if it contains magnesium. In some acidic soils of the US southwest, yes, because of complex chemistry of aluminum.
lower pH? No
reclaim alkali (sodic) soils? Yes, if those soils are also low in other salts, if sufficient quantity is applied, and if pure (non-saline) water then leaches out the sodium.
flocculate (loosen) clay soil? Yes, if the soil is sodic and all the conditions just above are satisfied. This is equivalent to reclaiming alkali soils.

Here are some guidelines for using gypsum:

  • As with sand, do not rely on gypsum alone as a flocculant. For one thing, gypsum is so fine a powder, it is hard to distribute effectively. Mix it with compost and either apply both as a top-dressing, or dig both in together.
  • Check on the source of your gypsum, and in general only use natural gypsum, not recycled or dry-wall gypsums, which can contain various impurities.
  • If your soil is low in magnesium, it’s a good idea to add some when you use gypsum, as the calcium in gypsum competes with magnesium and can cause it to leach out of the soil. Gypsum with dolomite in it may solve the problem, unless your pH is already high.
  • Do not overuse. Too much calcium can make important trace elements, as well as magnesium and potassium, unavailable to plants.
  • To determine whether gypsum will be effective in your soil, you can use the Emerson Dispersion Test, which you will be happy to hear is remarkably simple. Drop a small lump of soil (maybe half an inch or 6mm in diameter) into a glass of water, and then don’t move it for 24 hours. Check it after one day. If the clay is unchanged, don’t bother with gypsum. If, however, it has begun to dissolve, softening at the edges, or even flattening into a disk, then add gypsum. Since interpretations can vary, it’s still a good idea to talk to a knowledgeable local.
  • Above all, before you buy gypsum, check where it comes from, what other chemicals it contains, and what effect they may have on your garden. Remember that only gypsum that contains dolomite or some form of lime will raise pH levels.

Overseeding

To overseed means just what it says, to sow seed directly over other grass. This is a particularly effective method to improve a lawn when grasses are thin or patchy, but it can also be used to gradually replace a poorly suited grass with one better-suited to the region.

While overseeding your lawn can be effective anytime during the growing season, it’s far better to wait, and to do one’s seeding in spring or fall, not the middle of summer. September is ideal in most of North America, as the new grass has a chance to get established before the spring rush. For planting you want weather still warm enough for seeds to germinate (70 degrees F.), but cool enough so that they can’t dry out or get cooked where they lie.

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If you’ve got a standard-issue lawn, chances are good that the grass itself is not one best-suited to the region where you live, which makes all lawn care a challenge, organic or not. Overseeding lets you add a better-suited grass to your lawn without requiring that you start over from scratch.

Preparation

The goal here is to expose as much soil as possible without tearing up the grass you have, so that the new seed will be able to reach the dirt. The basic steps have asterisks. If you add in the others, you get what one pair of experts (Nancy Szerag and Jeff Ball) call the “Cadillac version.”

With that in mind, follow these steps:

Weed thoroughly. Once you’ve seeded, you won’t be able to do this for several weeks, so doing it beforehand is worth the time. Weeding will give the new grasses more space and less competition.

*Mow your grass as short as your mower will allow, even if you hit bottom from time to time, and collect the clippings. (Yes, here you get to do TWO things that are usually forbidden.) Short grass will give seeds better access to the soil below and more light once they sprout. It will also stress the old grass a bit, giving the new type a fighting chance to establish itself.

*Remove thatch; bare the soil. For seeds to take root in soil, they must touch it. A thick layer of thatch can be a major obstacle to successful overseeding, so if your thatch layer is thick, you’re going to need to get rid of it. If it’s light to non-existent, you may only need to rake briskly with a garden rake. Using a slice-seeder can eliminate this step, as the seeder actually cuts through thatch into the soil and deposits seed.

Aerate if you can. Both the loose soil plugs and the holes provide ideal sites for germinating seeds. Furthermore, since aerating helps improve soil, doing it will give grass seed an ideal start. When you’re done, you should have 6 to 12 holes per square foot. The easiest way to get this is by aerating in more than one direction. Move horizontally across your lawn, then vertically, then diagonally. The lawn will be a mess, but it’s all good. Those little plugs will simply disappear in a couple of weeks.

Amend the soil with a mixture of peat moss or coconut fiber and compost. Nancy Szerag and Jeff Ball, at the Yardening and Gardening blog post mentioned just above, suggest 3 bales of moss or fiber and 120 pounds of compost for every 1000 square feet. They also have suggestions about additional amendments.

Seeding

Seed thickly. A number of different sources recommend seeding much more thickly (up to one and a-half times) than recommended for whatever seed you’re using. This is particularly good advice if you’re trying to replace one type of grass with another. The undesired grass already has a serious head start, and over-seeding (seeding too much) can help to correct that discrepancy. Since most grass seeds will have instructions for both overseeding and for seeding a new lawn, one option is to seed at the new-lawn rate, rather than the recommended over-seeding rate.

Tip: Spreading seed alone can be a tricky proposition. Mix the seed with sphagnum peat moss, coconut fiber, sand, or compost, then seed.

Use a slice-seeder. As mentioned above, a slice seeder cuts through thatch, depositing seed directly into the cut. This mechanism ensures that seed comes into contact with soil and helps ensure that seed gets spread evenly.

Cover the lawn several times. To get an even distribution, divide the seeds into two to four packets and seed each while moving in a different direction or pattern across the lawn. If you’ve only got time or patience for two passes, divide the grass seed in two, and seed once moving back and forth in parallel paths across the lawn, and the rest moving at right angles to the first pass.

If you can, make three passes. Divide the seed in three and seed once vertically, once horizontally, and once diagonally.

Follow-Up

For best results, top dress lightly (about a quarter of an inch, not more) by sprinkling compost, topsoil, peat moss or coconut fiber over the newly seeded lawn. (A roller spreader makes this quite easy.) The soil amendments will give the seeds a boost and will help retain water over and around the seeds.

Alternatively, rake lightly to work the seed into the soil.

*Water thoroughly.

Roll the lawn if you want a perfectly level surface, but use a roller only half-full of water.

Care
Keep the soil surface damp while seeds are germinating (which may take as much as two weeks) and while seedlings are young and new. Most experts say this means watering twice a day until seeds sprout and once a day for at least a couple of weeks afterwards.

Mow when new grass is 2-3 inches high.

Stay off the grass! Give your seeds a chance.

Fertilizing

Organic lawn fertilizers are slow release, meaning that they work gradually. Quick-release synthetic fertilizers are chemically simple and become available to a plant easily and all at once, so they don’t last very long.

Think of the difference between popping popcorn and boiling water. When you boil water, unless you have a really weird stove or a very strange pot, all of it is at just about the same temperature, and it all starts to boil at the same time.

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Popcorn, however, does not all pop at the same time. Even if you’ve got only one layer of kernels and they’re evenly spread across the pan, some will pop before others. A graph of the popping cycle probably looks like some sort of bell curve: first just one pops, then a couple, then several, and more and more, and suddenly you’ve got a rush, and a lot popping all at once, and then the rate drops off, first pretty steeply and then more gradually. (Which is why some of us consistently burn our popcorn: we’re always waiting for that last kernel to pop.) This is like a slow-release fertilizer, though with a good one the rush and roar are somewhat diminished, and the whole process takes a couple of months, not a couple of minutes.

Quick release may sound like a good thing, but the problem is that it’s over quickly. A second analogy may make this clearer. Think of a light bulb, which releases energy, in the form of light, for quite a long time, at a steady rate. That’s your slow-release fertilizer. Quick release, however, is more like an explosion. There’s a sudden release of energy and light, but then it’s gone. If you’re trying to knit, read a book, or build a cabinet, the light bulb is a lot more useful.

Here’s how:

  1. Locate a SLOW-RELEASE organic fertilizer that’s easy to use and especially rich in nitrogen (rather than in phosphorus or potassium, the other key chemicals in fertilizer). Blood meal (12% nitrogen), corn gluten meal (8%), and cottonseed meal (6%) are all good choices. Liquid fish emulsion is an excellent plant food, high in nitrogen, but it isn’t slow-release. If you use it for your first stage, you will need to follow-up within a week or two with another dose.
  2. Follow the directions for your chosen product to determine the appropriate amount for your lawn. Apply it evenly over the grass in the late afternoon or evening, or in the morning just before you water.
  3. Sprinkle a quarter to a half-inch or so of coconut fiber or peat moss over the fertilizer.
  4. Water thoroughly, before sunlight reaches the treated areas.

CAUTION: Follow directions and do NOT over-apply nitrogen products, as they can “burn” your plants, leaving them brown and, well, dead.

Do NOT apply nitrogen fertilizers in the middle of the day, especially in the sun, as the sunlight will exacerbate the burn, making your grass, once again, vulnerable to death.

Reasons and Rational:

Why water? Watering will wash the nitrogen off the leaves of the plants and down towards the roots, thus protecting against burn (and death). Getting the stuff off the leaves doesn’t ensure that plants won’t be damaged, but it does help. Watering also keeps the layer on top (the coconut or peat moss) from just drifting away on the next breeze.

Why sprinkle coconut fiber or peat moss over the nitrogen product? You don’t have to. But there are a couple of good reasons for doing so. First, it shades any exposed areas, thus helping to prevent burn. Second, it’s good for your lawn anyway, as it adds organic matter (but not nutrients) and helps to hold water.

Why coconut rather than peat moss? Because peat moss, which comes largely from northern Canada, is harvested in vulnerable wetlands by large-scale machinery. Though not a non-renewable resource, it does take centuries to form, while coconut fiber, or coir, comes from a more renewable resource, the husks of coconuts.

Gypsum vs. Lime

Gypsum vs Lime

When it comes to lawn care and making sure your soil is healthy, you may hear the terms gypsum vs lime come up. Both are helpful amendments that can correct different nutrient levels that may harmful to your lawn and garden. But what are the differences? How do you know when to use gypsum, lime, or neither of them?

A good place to start is to know your soil and the problems you need to address. A soil test is always recommended to find out the nutrient levels in your yard. A key part of the soil test is measuring the pH of your soil. Soils with a pH below 7 are acidic while soils with a pH above 7 are alkaline. Both can affect the turf quality. Micronutrients tend to be less available in soils with high pH or alkaline soil while macronutrients tend to be less available in soils with low pH or acidic soils. Turf usually prefers a pH of around 6.5 – 7 on a scale of 0 to 14. It also helps to be aware of what else your soil is lacking or has an excess of based off of the soil test.

Educating our customers about pH, sulfur, calcium, lime & gypsum is a value offer we offer to our clients. A considerable amount of people believe that lime & gypsum can be interchanged for each other.

Lime

Lime, or calcium carbonate (CaCO3), is the naturally occurring mineral used to improve acidic soil. When the soil pH is less than 7, acidity exists as an accumulation of hydrogen (H), and aluminium (Al). Aluminium, which is toxic to turf growth, is soluble when the soil pH is less 5.5. When hydrogen accumulates on the outside of a soil particle, or exchange site, their presence is measured by a pH test.

When lime is applied to an acidic soil, the carbonate molecule (from lime) and hydrogen combine. The end products from this reaction are H2O (water) & CO2 (carbon dioxide). Calcium is now attached to the exchange site. Because the carbonate liberates the hydrogen, the soil pH will rise (become less acidic).

Gypsum

Gypsum, or calcium sulfate (CaSO4), is a naturally occurring mineral. It provides calcium & sulfur, both essential nutrients, but does not affect soil pH. Gypsum is a neutral salt (pH is ~6.7) and has a salt index, or osmotic potential, of 8. It typically has 20 to 22% calcium, and 16 to 18% sulfur. The sulfur is in a plant available, or sulfate (SO4) form. In addition to providing needed nutrients, the calcium in gypsum is soluble, even at a pH that is >7. This can be very helpful in improving soil tilth, reducing soil compaction, lowering sodium and improving aeration.

Gypsum is not the only way plants can get sulfur, but the sulfates in gypsum will not raise soil’s pH levels like elemental sulfur, the other commonly used additive. Elemental sulfur also has to steal calcium and oxygen from the soil in order to make its sulfur usable, something gypsum does not do.

The Takeaway

So, what’s the bottom line in the battle of gypsum vs lime? If your soil is acidic, gypsum won’t be able to help you. Lime can. Gypsum can add sulfur or take away sodium. Both can add calcium to the soil. Both are viable options depending on what your soil specifically needs, and it is important to know your lawn before jumping into the world of soil amendments. Always soil test!

While farmers have used gypsum (calcium sulfate dihydrate) for centuries, it has received renewed attention in recent years. This resurgence is due in large part to ongoing research and practical insights from leading experts that highlight the many benefits of gypsum.

Major Benefits Of Gypsum

1. Source of calcium and sulfur for plant nutrition. Plants are becoming more deficient for sulfur and the soil is not supplying enough it. Gypsum is an excellent source of sulfur for plant nutrition and improving crop yield. Meanwhile, calcium is essential for most nutrients to be absorbed by plants roots. Without adequate calcium, uptake mechanisms would fail. Calcium helps stimulate root growth.

2. Improves acid soils and treats aluminum toxicity. One of gypsum’s main advantages is its ability to reduce aluminum toxicity, which often accompanies soil acidity, particularly in subsoils. Gypsum can improve some acid soils even beyond what lime can do for them, which makes it possible to have deeper rooting with resulting benefits to the crops. Surface-applied gypsum leaches down to to the subsoil and results in increased root growth.

3. Improves soil structure. Flocculation, or aggregation, is needed to give favorable soil structure for root growth and air and water movement. Clay dispersion and collapse of structure at the soil-air interface is a major contributor to crust formation. Gypsum has been used for many years to improve aggregation and inhibit or overcome dispersion in sodic soils.

Soluble calcium enhances soil aggregation and porosity to improve water infiltration (see below). It’s important to manage the calcium status of the soil. It’s every bit as important as managing NPK.

In soils having unfavorable calcium-magnesium ratios, gypsum can create a more favorable ratio. Addition of soluble calcium can overcome the dispersion effects of magnesium or sodium ions and help promote flocculation and structure development in dispersed soils.

4. Improves water infiltration. Gypsum also improves the ability of soil to drain and not become waterlogged due to a combination of high sodium, swelling clay and excess water. When we apply gypsum to soil it allows water to move into the soil and allow the crop to grow well.

Increased water-use efficiency of crops is extremely important during a drought. The key to helping crops survive a drought is to capture all the water you can when it does rain. Better soil structure allows all the positive benefits of soil-water relations to occur and gypsum helps to create and support good soil structure properties.

5. Helps reduce runoff and erosion. Agriculture is considered to be one of the major contributors to water quality, with phosphorus runoff the biggest concern. Gypsum helps to keep phosphorus and other nutrients from leaving farm fields. Gypsum should be considered as a Best Management Practice for reducing soluble P losses.

Using gypsum as a soil amendment is the most economical way to cut the non-point run-off pollution of phosphorus.

Central Missouri Turf Management Incorporated

Gypsum – The Universal Soil Amendment

Gypsum is calcium sulfate. The most common form of it is the dehydrate which means that each molecule of calcium sulfate has two water molecules associated with it. It is expressed as CaSO42H20. The other form called gypsum anhydrite has no water.

Regular use of gypsum is essential to the sustainability of most irrigated soils. Irrigated land eventually leads to sodicity and salinity unless extreme care is taken. Gypsum is a key ingredient for the maintenance of agriculture on many types of soil and over a wide pH range, including sodicity.

Gypsum, in addition to prevention and correction of sodicity, include: greater stability of soil organic matter, more stable soil aggregates, improved water penetration into soil, and more rapid seed emergence.

For many reasons gypsum can be considered to be a farmer’s best friend. Some of the reasons are multiple and interrelated.

37 ADVANTAGES TO USING GYPSUM

Gypsum Improves Soil Structure
Gypsum provides calcium which is needed to flocculate clays in acid and alkaline soil.

Gypsum Helps Reclaim Sodic Soils
Where the exchangeable sodium percentage (ESP) of sodic soils is too high, it must be decreased for soil improvement and better crop growth. The most economical way is to add gypsum which supplies calcium. The calcium replaces the sodium held on the clay-binding sites. The sodium can then be leached from the soil as sodium sulfate to an appropriate sink. Without gypsum, the soil would not be leachable.

Gypsum Prevents Crusting of Soil and Aids Seed Emergence
Gypsum can decrease and prevent the crust formation on soil surfaces which result from rain drops or from sprinkler irrigation on unstable soil. It can prevent crusting that results when acid soils are lime& the gypsum is co-applied with the lime.

Gypsum Improves Low-Solute Irrigation Water
Gypsum is used to increase the solute concentration of low-solute water used for irrigation. Irrigation water from rivers that no longer have sources of leachable salts either penetrates poorly into soil or causes soil particles to degrade which results in low-water penetration. The problem can be corrected with surface-applied gypsum or application to the irrigation water.

Gypsum Improves Compacted Soil
Gypsum can help break up compacted soil and decrease penetrometer resistance. Combination with organic amendments also helps, especially in preventing return of the compaction.

Gypsum Makes Slightly Wet Soils Easier to Till
Soils that have been treated with gypsum have a wider range of soil moisture levels where it is safe to till without danger of compaction or deflocculation.

Gypsum Improves Water Runoff and Erosion
Gypsum improves water infiltration rates into soils and also the hydraulic conductivity of the soil.

Gypsum Decreases pH of Sodic Soils
Gypsum immediately decreases the pH of sodic soils or near sodic soils from values often over 9 but usually over 8 to values from 7.5 to 7.8. these values are in the range of acceptability for growth of most crop plants.

Gypsum Increases the pH of Acidic Soils
One mechanism in which gypsum can increase soil pH enough in some acid soils to sufficiently decrease the level of soluble aluminum to grow crops satisfactorily is replacement of hydroxyl ions from some clay lattices by sulfate ions.

Gypsum Improves Swelling Clays
Gypsum can decrease the swelling and cracking associated with high levels of exchangeable sodium on the montmorillonite-type clays. As sodium is replaced by calcium on these clays, they swell less and therefore do not easily clog the pore spaces through which air, water and roots move.

Gypsum Prevents Water Logging of Soil
Gypsum improves the ability of soil to drain and not become waterlogged due to a combination of high sodium, swelling clay, and excess water.

Gypsum Can Help Remove Excess Boron from Sodic Soil
More boron was leached from sodic soils when gypsum was applied than when the soil was leached without gypsum.

Gypsum Increases the Stability of Soil Organic Matter
Gypsum is a source of calcium which is a major mechanism that binds soil organic matter to clay in soil which gives stability to soil aggregates.

Gypsum Makes Water-Soluble Polymer Soil Conditioners More Effective
Gypsum complements or even magnifies the beneficial effects of water soluble polymers used as amendments to improve soil structure.

Gypsum Makes Excess Magnesium Non-Toxic
In soils having unfavorable calcium magnesium ratios, such as serpentine soils, gypsum can create a more favorable ratio.

Gypsum Corrects Subsoil Acidity
Gypsum can improve some acid soils even beyond what lime can do for them. Surface crusting can be prevented. Gypsum is now being widely used on acid soils.

Gypsum Can Enhance the Values of Liming
Addition to soil together with lime increased crop yields. The combination also decreased leaching losses of potassium and magnesium.

Gypsum Improves Water-Use Efficiency
Gypsum increases water-use efficiency of crops. In areas and times of drought, this is extremely important. Improved water infiltration rates, improved hydraulic conductivity of soil, better water storage in the soil all lead to deeper rooting and better water-use efficiency. From 25 to 100 percent more water is available in gypsum-treated soils than in nontreated soils.

Gypsum Creates Favorable Soil EC
Gypsum, being readily soluble, results in proper buffered solute concentration (EC) in soil to maintain soil in a flocculated state. It is better environmentally and cost wise to maintain the needed EC with gypsum than with excess application of fertilizers.

Gypsum Makes it Possible to Efficiently Use Low Quality Irrigation Water
Use of reclaimed municipal waste water is important for conservation of natural resources. Reclaimed water can be satisfactorily used if amendments, such as gypsum and water-soluble polymers, are also used.

Gypsum Decreases Dust Erosion
Use of gypsum can decrease wind and water erosion of soil. Severe dust problems can be decreased, especially when combined with use of water-soluble polymers.

Gypsum Helps Plants Absorb Plant Nutrients
Calcium, which is supplied in gypsum, is essential to the biochemical mechanisms by which most plants nutrients are absorbed by roots. Without adequate calcium, uptake mechanisms would fail.

Gypsum Decreases Heavy-Metal Toxicity
Calcium also acts as a regulator of the balance of particularly the micronutrients, such as iron, zinc, manganese and copper, in plants. It also regulates non-essential trace elements. Calcium prevents excess uptake of many of them; and once they are in the plant, calcium keeps them from having adverse effects when their levels get high. Calcium in liberal quantities helps to maintain a healthy balance of nutrients and non-nutrients within plants.

Gypsum Increases Value of Organics
Gypsum adds to the value of organic amendments.

Gypsum Improves Fruit Quality and Prevents Some Plant Diseases
Calcium is nearly always only marginally sufficient and often deficient in developing fruits. Good fruit quality requires an adequate amount of calcium. Calcium moves very slowly, if at all, from one plant part to another and fruits at the end of the transport system get too little. Calcium must be constantly available to the roots. In very high pH soils, calcium is not available enough; therefore, gypsum helps. Gypsum is used for peanuts, which develop below ground, to keep them disease free. Gypsum helps prevent blossom-end rot of watermelon and tomatoes and bitter pit in apples. Gypsum is preferred over lime for potatoes grown in acid soils so that scab may be controlled. Root rot of avocado trees cased by Phytophthora is partially corrected by gypsum and organics.

Gypsum is a Source of Sulfur
Gypsum is a source of fertilizer sulfur.

Gypsum Helps Prepare Soil for No-Till Management
A liberal application of gypsum is a good procedure for starting a piece of land into no-till soil management or pasture.

Gypsum Decreases Bulk Density of Soil
Gypsum-treated soil has a lower bulk density compared with untreated soil.

Gypsum Decreases the Toxic Effect of NaCI Salinity
Calcium from gypsum has a physiological role in inhibiting the uptake of sodium by plants.

Gypsum Multiplies the Value of Other Inputs
Gypsum can improve the response to all other inputs including fertilizers.

Gypsum Can Decrease pH of Rhizosphere
Increased calcium uptake by roots when gypsum is applied can decrease the pH of the rhizosphere.

Gypsum Keeps Clay Off Tuber and Root Crops
Gypsum can help keep clay particles from adhering to roots, bulbs and tubers of crops like potato, carrots, garlic and beets.

Gypsum Decreases Loss Of Fertilizer Nitrogen to the Air
Calcium from gypsum can help decrease volatilization loss of ammonium nitrogen from applications of ammonia, ammonium nitrate, urea, ammonium sulfate, or any of the ammonium phosphates.

Gypsum Can be a Source of Oxygen for Plants
The sulfate that is taken up by plants and metabolized releases the associated oxygen which is a source of oxygen to plant roots although a limited source.

Gypsum Helps Earthworms to Flourish
A continuous supply of calcium with organics is essential to earthworms that improve soil aeration, improve soil aggregation and mix the soil.

Gypsum Can Increase Water Retention in Soil
Gypsum when applied to sodic soil decreased levels of exchangeable sodium resulted in a large increase in water retention at a given tension compared with controls. Dry matter and seed yield were increased as a result.

Gypsum Can Increase Crop Yields
Gypsum for various combinations of the above effects can substantial increase crop yields from 10 to 50 percent.

**Information from the Diamond K company web site

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How to Use Gypsum in Clay Soil

Clay soil is high in minerals that plants need for growth, but it can also be high in acidity or contain more salts than plants prefer. To correct for this, additives can be put into the clay soil to balance acidity and remove salts. One of the most popular organic additives is gypsum, a light powder similar to lime. Just follow the simple steps outlined below for adding gypsum to the soil.

What are Clay Soils?

Clay soil is composed of tiny particles that are shaped so they fit together smoothly. This makes clay soils denser than most other soils and gives it some unique properties, including water retention. Many people think that objects slide on clay, but the truth is that clay particles coat other objects and then use their unique properties to slide against other clay particles. In short, clay particles bind to other particles, even other clay particles, causing it clump.

Why Gypsum is Used

Gypsum is a natural mineral and that makes it a preferred treatment for organic garden soils. Because gypsum is easily pulverized it can be converted to a powder that mixes easily in other soils, even clay. Gypsum, unlike lime, is able to neutralize salts as well as acids in the soil, which means better soil balance and healthier plants.

Step 1: Site Preparation

Before organic gypsum is used, the site needs to be prepared. To do this, mix the soil in the area to be treated. A motorized tiller may be used, but many organic gardeners believe these tillers dry out the soil and cause more damage than benefit. Even though it means a great deal more physical labor, the recommended method of turning the soil is to use a pitchfork or potato rake.

Step 2: Adding the Gypsum

Gypsum only needs to be applied sparsely. The usual application is about 1 pound of gypsum for every 100 square feet, or 1 pound for every 10 feet-by-10 feet section. The easiest way to spread gypsum is to wear a pair of gloves, and sow the gypsum in the same way that you might broadcast grass seed. Spread the powder well as you go, avoiding clumps and making sure that the whole section is covered uniformly.

Step 3: Mixing the Soil

Mix the soil well, using a potato rake or pitchfork. In order for gypsum to work properly, it must be well-distributed in the top 8 to 12 inches of the soil. If possible, water the soil after the first application, and then mix it well again. Allow several days for the gypsum to become active, and then test the soil. Repeat the process if necessary. Once you have successfully conditioned the soil, it won’t need to be treated the same way again for at least a year, perhaps longer.

Improving Soil With Gypsum

Gypsum is one of the best sources of calcium, the most important of the secondary plant nutrients. But calcium is more than a nutrient. It is the major balancing element in plants and soils. It protects, within limits, from nutrient excess and deficiency, problems caused by both high and low pH and heavy metal contamination. Along with organic matter, calcium improves soil structure.

Gypsum as Fertilizer

Pure gypsum is 23 percent calcium and 19 percent sulfate (CaSO4-2H2O). In the hierarchy of the 16 essential plant nutrients that begins with non-minerals hydrogen, oxygen and carbon, calcium is seventh and sulfur is ninth.

Calcium is the plant nutrient most likely to be unavailable to roots when needed. An essential nutrient itself, calcium also improves root uptake of other plant nutrients, especially ammonium nitrogen. Calcium does not move from old to new plant tissues, so a constant supply of soluble calcium is needed. The growing points of both roots and shoots are sensitive to insufficient calcium, but roots more so. The ratio of calcium to sodium is more critical than the actual concentration of calcium.

Symptoms of calcium deficiency include

  • Water-soaked, discolored areas on fruits, such as blossom end rot on tomatoes, peppers, melons and squash, or bitter pit or cork spot on apples and pears. Tip burn on young leaves of celery, lettuce and cabbage.
  • Death of terminal buds and root tips.
  • Abnormal dark green appearance of leaves.
  • Premature shedding of blossoms and buds.
  • Weakened stems.

Calcium is most often deficient in high-rainfall, acid-soil areas, such as the Pacific Northwest west of the Cascade Mountains, and east of the Mississippi River. These regions receive in excess of 40 inches of rainfall each year. Deficiency symptoms, such as tomato blossom end rot, often appear there after a period of heavy rainfall. Gardeners apply ground dolomite or limestone, primarily to raise soil pH, but also to replace lost calcium. But the calcium in limestone is not water soluble, however. It must be incorporated into the soil and brought into contact with soil acids before calcium ions (Ca++) are released.

Limestone does not migrate in the soil, and is effective only to the depth incorporated. In contrast, gypsum dissolves immediately in the moisture of the soil, allowing plant roots to absorb the calcium ions and the sulfate ions. Because it is dissolved in the soil solution, gypsum readily migrates into the lower depths in the soil.

Most western soils contain abundant calcium, but as very insoluble limestone in the form of calcium carbonate. Where pH is 7 or higher, the limestone is insoluble and the calcium it contains is not available to plant roots. Again, the calcium in applied gypsum is immediately available.

Sulfur

The other component of gypsum, sulfate, supplies plants with sulfur, which is essential to protein synthesis. Sulfur is a constituent of the amino acids cystine, methionine and cysteine. It is also essential for nodule formation on legume roots, and for the characteristic odors of plants such as garlic and onions. Sulfur deficiencies are less common than calcium deficiencies, but can occur throughout North America, particularly in high-rainfall areas.

If sulfur is applied as elemental sulfur, it is not available until the soil bacteria oxidize it to sulfuric acid. Surface-applied sulfur is oxidized faster than incorporated sulfur, but because the required bacteria are frequently not present in alkaline soils, the oxidation may be very slow. Gypsum supplies sulfur as sulfate, the form plant roots can absorb.

Symptoms of sulfur deficiency include

  • Light green to yellowish young leaves.
  • Small and spindly plants.
  • Retarded growth rate and delayed maturity.

Gypsum as Soil Conditioner

Gypsum can reclaim high-sodium or “sodic” soils. Soils with a high proportion of exchangeable sodium (Na+) lose structure. Once soil is tightly packed, water and air penetration is reduced and root growth suffers. Water often puddles on the surface of these soils.

To revitalize sodic soils, incorporate gypsum into the soil and then apply six or more inches of water. The calcium ions will replace sodium ions that are attached to the soil particles. The sodium (as sodium sulfate, NaSO4) washes away through the soil into the groundwater, and your topsoil is left more porous, so is more supportive of root growth.

Sodic soils occur almost exclusively in the arid and semiarid West. If you suspect your soil is sodic and would benefit from this gypsum-leaching treatment, order a laboratory soil test to confirm the presence of excess sodium. Applying gypsum to the surface of a compacted soil won’t work.

Compacted soils are potential problems anywhere, and organic matter–such as compost–is generally the best remedy. Gypsum helps you get the most benefit from organic matter added to the soil. Soil crumbs and aggregates that give structure to soil are cemented together with glues that include salts such as calcium. Leaching from salt-free rainwater increases acidity and decreases the salinity of soils, and this can cause soil to lose its physical structure despite the presence of adequate organic matter. Correcting acidity with limestone helps, but limestone does not contribute calcium ions to the soil. Gypsum also protects the soil from compaction and other types of degradation where irrigation water is reclaimed or of low quality.

Gypsum and pH

In most situations gypsum has little effect on soil pH. Use limestone to raise pH of acid soils, and elemental sulfur to lower pH of alkaline soils. However, if soil is alkaline because of high bicarbonate ions, or if irrigation water contains bicarbonate, the soluble calcium in gypsum reacts with the bicarbonate to form insoluble calcium carbonate. The pH of the soil is decreased to the range of 7.5 to 7.8 when bicarbonate is reduced. Also, limestone does not move through the soil to lower depths. Gypsum is the best way to supply calcium to soil and roots below cultivation depth.

Gypsum as Metals Protector

Heavy metals, such as cadmium, copper, lead and nickel, are toxic to plants in excess amounts, as well as to the people who eat the plants. Soils in or near some industrialized areas and soils very heavily amended with municipal sewage sludge might contain toxic amounts of heavy metals. Plants generally absorb less of the heavy metals from soil when gypsum is applied. Metals also become more toxic in highly acid soils. In those cases, use limestone to reduce acidity and metal toxicity. Some of the heavy metals plants absorb never move farther than the roots, the reason you should not grow root crops, such as carrots, in contaminated soil.

Using Gypsum

A calcium analysis of your garden’s soil or an assay of calcium uptake in your plants is the best way to gauge your garden’s gypsum needs. Most Cooperative Extension Service soil tests include calcium if you request it. Either very low (below about 5.5) or very high (above 8.2) pH values are also indicative of a need for calcium. If your soil pH is alkaline (above 7.0), make sure your lab doesn’t rely on an acidic testing agent, as many do. The results won’t accurately portray what goes on in your garden.

Natural-mined and finely milled gypsum costs $3 to $4 for a 10-pound bag, about the price of limestone. It’s also available in 50- and 80-pound bags. Apply 10 pounds per 1,000 square feet of garden area up to three times each growing season to correct calcium deficiencies. Over-application of gypsum is generally not a problem because it has low solubility and the increase in salinity is low. Look for high-purity, natural-mined gypsum. Although natural-mined gypsum is considered “organic” by the country’s organic certification programs, gypsum-based by-products and recycled materials are not.

Garn Wallace, Ph.D., operates Wallace Laboratories in El Segundo, California. Shelly Stiles is a writer living in Buskirk, New York.

Clay Soil

Angus Stewart

You know, clay is one of the most maligned substances in the garden. It can be your worst nightmare, as it is here, or it can be your best asset.

It all depends how you treat it. Clay can be a sticky mess, poorly drained and set like concrete. The traditional way to treat a large area of soil is powdered gypsum, which we sprinkle over and then dig it in.

But it does take a long time to dissolve and it’ll be a couple of months before you get the full effects. I’ve got a small planting hole today, so I’m going to use an alternative. This is a liquid clay breaker which is based on liquid organic matter. You could also use, say,

liquid from your worm farm or a liquid manure would have the same sort of effect – and cost a lot less, of course.

Now, once it’s taken effect, this is the sort of result that we’re looking for. So I’ve treated this with the liquid clay breaker and now, when that soil crumbles, we get these crumbs of clay.

So we still get water and nutrients stored inside them. But the water can run around the outside of them, giving us the drainage we really need.

So, I’m going to have two bob each way by sprinkling some gypsum in the bottom of the hole.

And then I’ve prepared this solution of the liquid clay breaker which we use to water in the gypsum, putting plenty of water in the hole for the plant that I’m going to put in there. I always like to give my plants a good soak before they go in the ground. This one’s a really good one for clay soil, but it’s had a few name changes.

It used to be known as Baeckea virgata, then it became Babingtonia virgata and I believe now they want to call it Sannantha virgata but I’m just going to call it ‘Becky’ because she loves the clay soil.

So, let’s just break that clay up a little bit more. Now we’re ready to go into the ground. Just tease those roots out a little bit.

..and of course we still need to water in, to make sure there’s great contact between the soil and the newly planted roots. But I’ve also got some of the liquid clay breaker in there as well, just to finish the job.

I reckon Becky will love that!

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