How to add calcium to soil

All plants need calcium rich soil to grow. The calcium is used by the plant in developing the plant cell walls and membranes. Furthermore, it is a non-leaching mineral (it will stay in the soil) and will improve water penetrability and reduce soil salinity. It is thus helpful to determine the amount of calcium contained in soil. Generally, Atomic Absorption Instruments (AA) or Inductivity Coupled Plasma-Optical Emission Spectrometry Instruments (ICP-OES) are used to measure the amount of calcium ions present in soil. An easier method involves extracting the calcium ion from sample soils with 1 mol/L ammonium acetate (CH3CO2NH4), and then by using the handy and affordable LAQUAtwin calcium ion meter B-751.

The LAQUAtwin Ca2+ meter is used as a quick check to determine the Calcium content of soil.

How to add calcium to soil


1.Dry the soil for about a week, and sift it using a 2mm diameter sieve.

2. Place 1g of test soil in 100 mL glass beaker and add the 20 mL of 1mol/L CH3CO2NH4 to the beakers.

3. Shake the beakers (amplitude 40m/min, speed 250 rpm) for 1 hour to extract Ca2+ from the soil using a laboratory reciprocating shaker.

4. Filter the liquid through Whatman No.6 filter paper.

5. Calibrate LAQUAtwin B-751 with 150mg/L and 2000mg/L Ca2+ standard solutions which contain the same concentration of CH3CO2NH4 as in the filtered samples. (Do not use the standard solutions packed with the instrument)

6. A small sample of the filtered solution is placed on the sensor of the LAQUAtwin Ca2+ and measured. To repeat sampling, wash with tap water and pat dry with a paper tissue.

Results and Benefits

The use of accurate Calcium ion testing in controlling the calcium content of soil ensures that the plants which are grown in the soil are given the necessary minerals and can easily absorb water. The table below shows that the results given by the LAQUAtwin Ca2+ pocket meter are comparable to those from Inductivity Coupled Plasma-Optical Emission Spectrometry Instruments (ICP-OES). The LAQUAtwin Ca2+ pocket meter is small and compact; convenient to carry around in your pocket for quick on-site testing. Its easy-to-use interface is simple for anyone to use the LAQUATwin Ca2+ pocket meter.

How to add calcium to soil

The LAQUATwin Calcium pocket meter is small and compact and convenient to carry around.

How to add calcium to soil

Calcium is one of the secondary macronutrients in soil. While not required in the quantities of nitrogen, phosphorus, and potassium, calcium is crucial for plant growth and makes plants less susceptible to diseases and pests. But when it comes to calcium, more is not always better. Too much calcium in your garden soil can go hand in hand with a high pH, which means the soil is too alkaline, which then affects the absorption of the macronutrients contained in other fertilizers.

The way to determine whether you need to add calcium to your soil is a professional soil test. It is different from a simple pH test that you can do at home. A professional soil test analyses both the calcium level and the pH of your soil. Professional soil tests such as those offered by a state Cooperative Extension also will tell you exactly what to add to the soil, and in which amounts.

Keep in mind that in a living plant, calcium moves from the root tips upwards throughout the plant with water via transpiration. That’s why sufficient watering is always important. Once calcium has reached its destination, such as new, young tissue or tips, it will stay put.

When to Add Calcium to Soil

The calcium level in your soil does not say anything about how much of it can actually get absorbed by plants.

A key term for the calcium absorption of soil is Cation Exchange Capacity (CEC). Imagine the soil like a storage tank of plant nutrients for calcium and magnesium. CCEC is the relative ability of the soil to absorb and hold a particular nutrient in the form of cations or positively charged ions. Knowing this, the questions whether your plants are getting enough calcium, and what you can do if they aren't, are directly connected to the CEC level. It is also linked to the pH of your soil; soils with a higher pH level usually contain more available calcium.

A professional soil test will determine the CEC of your soil. The higher the CEC, the more organic matter and clay is in your soil, which is good, because that’s a soil that holds water and nutrients such as calcium better than sandy soil. A low CEC indicates a sandy soil which is more likely to lack nutrients because they leach out of the soil quicker.

Based on the CEC, the soil test might tell you to add organic matter to the soil. It also indicates whether you need to make your soil less acidic by adding lime, or make it more acidic by adding sulfur. The combination of increasing the CEC and adjusting the pH will increase the availability of calcium to your garden crops.

How to add calcium to soil

Signs of Calcium Deficiency

While the soil test is the surest way to determine if you need to amend your soil, there are also some telltale signs of calcium deficiency in plants.

Stunted or weak growth, curling of young leaves or shoots, scorching or spotting on young leaves, inhibited bud growth, stunted or dead root tips, cupping of mature leaves, chlorosis (yellowing of leaves), burnt leaf tips, and fruit damage such as blossom end rot on tomatoes, and bitter pits in apples can all be signs of calcium deficiency.

Calcium Fertilizers

There are numerous calcium sources. Which one is right for you, how much to apply and when depends on the pH level of your garden soil, the timing, and also the crops you are growing.

The Spruce / Almar Creative

Foliar Spray

(Calcium acetate, calcium nitrate, calcium chloride)

Commercial foliar calcium sprays are the quickest remedy for acute calcium deficiency, as plants absorb nutrients more efficiently through leaves than through roots. It is often used as a remedy for container plant issues especially for seedlings and transplants. Foliar sprays do not amend the soil and should be considered a supplement to proper soil nutrition management.

(Calcium carbonate and other forms of mined limestone)

Adding lime to your soil is the biggest calcium booster you can give your soil but it also raises your soil pH, making it less acidic.

How to add calcium to soil

Dolomite Lime (Calcium carbonate)

In addition to adding a good amount of calcium to your soil, dolomitic lime also contains magnesium carbonate and it’s therefore used for raising pH on low-magnesium soils. If a soil test shows that magnesium levels are already high, choose another calcium product.

Gypsum (Calcium sulfate)

This is a fast-acting calcium supplement with low CEC that does not lower nor raise the pH.

Ground Oyster/Clam Shell Flour (Calcium carbonate)

While it is a good source of calcium, the shells have a low solubility and take several years to be effective. They will also slightly raise soil pH over time.

Wood Ashes (Calcium carbonate)

Hardwood ashes – unlike softwood ashes, which are not recommended – add a good amount of calcium to your soil but they also raise its pH. If you need to raise your soil pH, keep in mind that hardwood ashes are half as effective as lime.

Soft Rock or Colloidal Phosphate (Calcium oxide)

Also called rock phosphate, it releases calcium to the soil slower than lime and is less soluble. It moderately raises the pH.

Bone Meal

This high-phosphate fertilizer is slower released than lime and less soluble. Use it for soil where you want to moderately raise the pH. Bone meal is especially beneficial for bulbs and root crops.

Egg Shells

It’s a myth that ground eggshells prevent blossom end rot. While they decompose too slowly to be effective as a calcium fertilizer, they are still a welcome addition to compost as organic matter.

How to add calcium to soil

By Ken Scharabok – Ensuring your soils have an adequate level of available calcium should be an essential part of your field fertilization practices for several reasons. Here’s why and how to add calcium to soil on your homestead.

• Calcium improves tilth and friability by reducing the stickiness and clinging ability of soils containing clay.

• Calcium, by breaking up clay particles and improving clay soil, increases the surface area of soils so more nutrients can be held by each particle.

• Calcium, by loosening up soil, increases water penetration ability, water-holding capacity and aeration ability. Oxygen is required by soil life, thus the more oxygen available, the more soil life which can be supported.

• Calcium is a direct nutrient to growing plants and soil life. Among other benefits, it is essential to healthy cell walls, affecting both permeability and strength. For a grain crop, adequate calcium can help to prevent lodging as the plants reach their full height.

• Calcium acts as a buffer/carrier for some other nutrients and enhances uptake of water.

• Calcium promotes root and leaf development in plants.

• Calcium can up to double the effectiveness of other fertilizers applied, such as nitrogen, phosphorus, potassium and other essential nutrients. For example, at a low pH, phosphorus is precipitated as iron and aluminum phosphates which are relatively insoluble and unavailable. With liming, phosphorus compounds in the soil become more soluble and can reduce the amount of phosphorus fertilizer needed.

• Calcium is a relatively immobile element within a plant. Thus, a continuous supply is essential for growing plants.

• Calcium encourages the growth of symbiotic nitrogen-fixing bacteria on legumes, and thus makes more nitrogen available to the legumes and other plants.

• Calcium can extend the life of legume plantings. Legumes are heavy users/providers of calcium. If it is depleted, stand deterioration or loss can occur.

• Calcium applied to lawns can decrease thatch build-up by promoting soil life, particularly earthworms. Although most lawns never receive calcium (e.g. periodic spreading of limestone), each cutting contains a small percentage of calcium. Thus, over time the soil under many yards can become calcium-deficient.

While available calcium is not directly related to pH levels (i.e., a soil with a high pH can be calcium deficient), its use on soils with a low pH will decrease its acidity. In acid soils, there may be an excess of soluble iron, aluminum and/or manganese, in conjunction with shortages of calcium and magnesium.

How to add calcium to soil

How to Add Calcium to Soil

Some garden crops, such as tomatoes, peas, and beans, have a high calcium requirement but do best in slightly acid soil. In this case, calcium can be provided in the form of a gypsum soil amendment (calcium sulfate). Agricultural gypsum is a good source of both calcium and sulfur, yet has little effect on soil pH.

(A commercial crop with a major need for calcium is tobacco. The tobacco belt was established primarily for two reasons: temperate climate and naturally available calcium in the soil. While mature grain crops and grasses contain from 0.25-0.5 percent calcium; and cotton, soybeans and alfalfa plants average 2.0 percent calcium, tobacco plants contain up to 4.0 percent calcium. When this land became “tobacco poor,” it was largely due to calcium being removed faster than it could be naturally made available to the plants.)

Available calcium levels can be determined by most soil tests. Here’s how to check soil pH. However, bear in mind in most cases the calcium application rate (in the form of tons of limestone per acre) will be for the upper 6-1/2 to seven inches of soil (plow depth). Thus, additional limestone may be required for the root zone below this depth.

Calcium is normally available locally in the form of limestone delivered and spread at a cost per ton. While the limestone use in this case if for its high concentration of calcium carbonate, the actual amount of calcium in it will be in the 35-45 percent range. Dolomitic limestone and should not be used if magnesium levels are already high.

While the cost of limestone should be prorated over about a five-year period to the cost of crop or livestock production, the actual returns from increased production will often repay the cost of application in the first or second year.

The calcium in limestone will take a period of time to dissolve and become available to plants. For quick results, calcium can also be applied directly to plants in a solution. In this manner, it goes directly to plant cells rather than having to cycle through the soil.

So now you know how to add calcium to soil, so remember, when it comes to fertilization, think C-N-P-K, rather than just N-P-K.

Originally published in Countryside 2003 and regularly vetted for accuracy.

How to add calcium to soil

If your plants are showing signs of calcium deficiency, a soil additive can supply the missing nutrient. However, sometimes low levels of calcium in the soil aren’t to blame for plants’ deficiency symptoms. Your soil could contain plenty of calcium, but it isn’t available to the plants. A soil test can indicate whether your soil would benefit from additional calcium and which additive is best. Dig the additive into the soil before planting your plants.

How to Add Calcium to Garden Soil

Limestone or gypsum supply your garden soil with calcium. If your soil is acidic, adding limestone helps boost most vegetable crops by increasing alkalinity. For example, if your soil pH is below 5.5, add 2 to 3 pounds of dolomitic lime per 100 square feet to raise the pH. Apply to your local cooperative extension office for a soil test to determine its pH. Add the lime two to three months before planting your vegetables or other plants to allow time for the it to dissolve into the soil. Dig the lime into the soil to a depth of about 6 inches, and water the soil afterward to the same depth.

For soils that have a pH of 6.5 to 6.7, gypsum is a better choice for adding calcium, because it doesn’t alter the soil’s pH. Before planting your plants, spread about 1 to 2 pounds of gypsum per 100 square feet, and dig it into the soil.

How Calcium Benefits Plants

Calcium is essential for the formation of roots, stems and new growth in plants. The nutrient forms calcium pectate, which plants use to construct cell walls and membranes. Consequently, calcium helps provide plants’ rigidity. Plants also use calcium to create carbohydrates like cellulose and starch. What’s more, calcium benefits your garden soil. It improves soil structure by helping soil particles stick together.

Calcium Deficiency in Plants

Symptoms of calcium deficiency in plants usually appear on new growth. The typical symptoms include stunted growth, distorted leaves and pale yellow patches between the leaf veins. The leaves may also be cupped. Weak stems, premature blossom and bud dropping, and dying stem and root tips are some more signs of calcium deficiency in plants. In certain vegetables like tomatoes (Lycopersicon esculentum_,_ hardy in U.S. Department of Agriculture plant hardiness zones 10 through 11), calcium deficiency causes a disorder called blossom end rot. A watery spot appears at the blossom end of the tomato, and the spot grows wider and darker as the fruit enlarges. Finally, the spot sinks or flattens, and the surface becomes firm.

Causes of Blossom End Rot

Blossom end rot can affect plants even when the soil they’re growing in contains plenty of calcium. The availability of calcium is affected by the presence of other minerals like magnesium, ammonium and potassium in the soil. If the soil contains an excess of other salts, calcium salts decrease in availability to plants. Similarly, excessively wet or dry soil can reduce the uptake of calcium by plant roots. The best method for assessing whether low levels of calcium are causing blossom end rot in your plants is to test the soil.

How to add calcium to soil

Is calcium required in garden soil? Isn’t that the stuff that builds strong teeth and bones? Yes, and it’s also essential for the “bones” of your plants — the cell walls. Like people and animals, can plants suffer from calcium deficiency? Plant experts say yes, calcium is required in garden soil.

Good soil and calcium are linked. Just as we need fluids to carry nutrients through our body, so is water needed to carry calcium. Too little water equals a calcium deficiency plant. If water is sufficient and problems still exist, it’s time to ask how to raise calcium in soil. First though, let’s ask the question, WHY is calcium required in garden soil?

How Calcium Affects Plants

There are many essential minerals in soil, and calcium is one of them. It’s not only needed to build strong cell walls to keep the plant upright, it provides transport for other minerals. It may also counteract alkali salts and organic acids. When you add calcium to the soil, it’s like giving your garden a vitamin pill.

A calcium deficiency plant is notable for its stunted growth in new leaves and tissues. Brown spots may appear along the edges and grow toward the center of the leaves. Blossom end rot in tomatoes and peppers, black heart in celery, and internal tip burn in cabbages are all signals to add calcium to the soil.

How to Raise Calcium in Soil

Adding lime to the soil in autumn is the easiest answer to how to raise calcium in the soil. Eggshells in your compost will also add calcium to soil. Some gardeners plant eggshells along with their tomato seedlings to add calcium to soil and prevent blossom end rot.

Once you recognize a calcium deficiency plant, foliar applications are the best answer to how to raise calcium. In soil, the roots take up calcium. In foliar feeding, calcium enters through the leaves. Spray your plants with a solution of 1/2 to 1 ounce (14-30 ml.) of calcium chloride or calcium nitrate to one gallon (4 L.) of water. Make sure the spray thoroughly covers the newest growth.

Calcium is essential to plant growth and it’s easy to ensure your plants get enough to grow healthy and strong.

How to add calcium to soil

In today’s post we will look into the importance of calcium in gardening and 6 easily available sources of calcium to plants, And What out of these really work and Why? Then, Finally Two Gardening Hacks or Tricks to get instant supply of calcium to your plants.

Well, before we start listing the 6 easy sources of calcium to plants, we will quickly know the importance or the function of calcium in plants. Calcium plays a very important role in overall growth of plants. It helps in absorption of major nutrients by the roots in the presence of water. It is essential for formation and integrity of plant cell wall and hence very essential for fruit formation.

So, What are the signs and symptoms of calcium deficiency in plants?

Calcium deficiency can cause necrosis or death of plant tissue at certain parts of the plant particularly at the tips of fruits and tips of growing leaves which appear like burnt tips. Blossom End rot Disease seen in tomatoes, peppers and squashes is the best example of such necrosis due to calcium deficiency. Plant chlorosis or leaf yellowing and stunted growth are also signs of calcium deficiency.

Having said that, now let’s list out the top 6 options or the sources of calcium to plants. If you do vegetable gardening or intend to grow veggies organically in your home or terrace garden, please follow this till the end!

6. Milk: This is the most expensive option and not recommended because most of the ingredients found in milk along with calcium are not required by plants. Like Fats, lactose and proteins are not essential to plants. But, If your milk is spoilt, you may dilute it and water it to your plants or make a foliar spray by mixing it with compost tea, like how we have done this in my previous posts.

5. Egg Shells: No doubt egg shell is composed of calcium carbonate. You know Even one of the hardest thing Marble is calcium carbonate and also the soft Chalk sticks is also calcium carbonate.
The point here is if you add crushed or even powdered egg shells into soil, it might take many months and even years for it to decompose and release that calcium for uptake into the soil. This option is least effective for treating a acute disease like Blossom end rot or a stunted plant. Perhaps this option of powdered eggshells may be utilized while preparing your potting mix before planting. Another option for instantly providing calcium for plants is to water the plants with the water used to boil eggs. Do not throw away this water. Cool it and water your plants with this. Egg shells release some calcium into water during the process of egg boiling.

4. Bone meal: Yes! It’s an excellent source of calcium, but the problem is the Plants can only get phosphorus from bone meal and cannot utilize calcium from bone meal. This is because of Garden Soil PH of around 6.5, that’s slightly acidic for most garden plants. And at this PH level, it’s not a good option to use bone meal as a source of calcium.

3. Expired Calcium or Iron Tablets: Are these of any use to the plants? Certainly not for instant supply of calcium unlike in humans. These are complex binding forms or compounds in these tablets that take time to decompose and release them for uptake by plants. The best way to use these expired tablets is to add them to your compost bin. The final compost formed will be rich in calcium and other minerals.

2. Lime: Agricultural Lime is chemically calcium Hydroxide. And another variety garden lime called Dolomite lime is more commonly used and It’s also a good source of magnesium for plants. No doubt, it’s a great source of calcium. The only draw back is it increases your soil PH level to alkaline levels which is not desirable for most plants. Unless, you have tested your soil PH and if its found too acidic like below 5.5 levels, you can safely use lime for your plants. This PH meter is quite handy and very inexpensive. You can buy that Online from amazon link in description. Well, The dosage of Lime should not be more than 1 teaspoon per litre of water or 1 tablespoon per gallon of water once in a while like once in 3 months. But still if you want to use this and keep your soil ph unchanged, you have many options – like adding lot of compost manure to raise the PH or you can mix about 10 gms of alum powder in 1 liter of water to compensate for the soil ph level because alum acidifies the soil or alternately add 1 or two teaspoons of white distilled vinegar into this.

1. Gypsum: Gypsum is one of the best sources of calcium to plants and the safest option simply because it will not alter the soil ph levels. Chemically its calcium sulfate dehydrate. Its also called Lime sulfate. Gypsum is also used in clayey soils to remove soil compaction and improve soil drainage. It drastically reduces the sodium levels or salinity in the soil, which is very important if you are watering your plants with salty or hard water.
Well, The Dosage for gyspum is 1 teaspoon per litre of water or 1 tablespoon per gallon of water once in about 3 months. Depending on the container size or the plant size you can safely increase the dosage if necessary.

And Finally, the most inexpensive sources of calcium for home gardening: The Calcium Hacks using Chalk Pieces, Egg shells and White Vinegar.

Firstly the Chalk Sticks Hack:

Chalk is chemically Calcium Carbonate. You can take white chalk sticks and bury them into the soil while planting your veggies. That’s in intital stages. This really works wonders for plants like Tomatoes, Peppers, squashes, egg plants and almost any vegetable plant. You can bury two chalk sticks per container for these vegetable plants safely if you soil ph is around 6.0. For other plants to provide slow release calcium source, you can bury one chalk stick per container.

The second hack is The Vinegar Hack. To treat blossom end rot disease or any acute deficiency of calcium in plants. You can mix lime and vinegar or egg shell powder + Vinegar to break down the compound and prepare a water soluble form of calcium that can be quickly absorbed by the roots. Make sure if you use egg shells, sun dry them for atleast two days or microwave them for few minutes.
Its simple! Just take a handful of egg shell powder or one or two spoons of lime and add same amount of white vinegar to this. You can see a chemical reaction between calcium carbonate and acetic acid which releases carbondioxide as gas and free calcium into the solution. You can leave this alone for few hours and then mix with water and water your plants. This is the cheapest source of calcium to treat acute deficiency. That’s it!

How to add calcium to soil

Calcium is one of the secondary macronutrients in the soil. Although it is not needed in the amounts of nitrogen, phosphorus and potassium, calcium is crucial for the growth of plants and makes them less susceptible to diseases and pests.

But when it comes to calcium, more is not always better. Excess calcium in garden soil can be associated with high pH, ​​which means that the soil is too alkaline, which affects the absorption of the macronutrients contained in other fertilizers.

The way to determine if you need to add calcium to your soil is a professional soil test. It is different from a simple pH test that you can do at home.

A professional soil test looks at the calcium level and pH of the soil. Professional soil tests, such as those offered by a cooperative extension across the state, will also tell you exactly what to add to the soil and in what quantities.

Remember that in a living plant, calcium moves from the root tips up through the entire plant with the water through perspiration.

That is why it is always important to water enough. Once the calcium reaches its destination, as young, new tissue or spikes, it remains in place.

How to add calcium to soil

When to add calcium to soil

The level of calcium in the soil says nothing about how much plants can actually absorb.

A key term for the absorption of calcium from the soil is the cation exchange capacity (CEC). Imagine the soil as a storage tank for plant nutrients for calcium and magnesium.

CCEC is the relative ability of the soil to absorb and retain a particular nutrient in the form of positively charged cations or ions. Knowing this, the questions about whether your plants are getting enough calcium, and what you can do if they aren’t, are directly related to the CEC level.

It is also related to the pH of your soil; Soils with a higher pH level generally contain more available calcium.

A professional soil test will determine the CEC of your soil. The higher the CEC, the more organic matter and clay there will be in your soil, which is good because it is a soil that retains water and nutrients like calcium better than a sandy soil.

A low CEC indicates a sandy soil that is more likely to lack nutrients because it seeps out of the soil more quickly.

According to the CEC, soil testing can tell you to add organic matter to the soil. It also indicates whether you need to make the soil less acidic by adding lime or more acid by adding sulfur.

The combination of increasing the CEC and adjusting the pH will increase the availability of calcium for your garden crops.

Signs of calcium deficiency

While soil testing is the surest way to determine if you need to correct the soil, there are also some tell-tale signs of calcium deficiency in plants.

Weak or stunted growth, curling of new leaves or shoots, burns or spots on young leaves, inhibited shoot growth, stunted or dead roots, burrows of mature leaves, chlorosis (yellowing of leaves), burnt leaf tips and damage to fruits, such as Flower tip rot in tomatoes and seeds in apples can be signs of calcium deficiency.

Enjoy This Video Tutorial About When To Add Calcium To Your Garden Soil

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How to add calcium to soil

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How to add calcium to soil

Wise gardeners know that the art of successful gardening begins with creating good soil. The time and effort spent in adding soil amendments such as compost, manure or clays such as calcium bentonite will be richly rewarded for years to come. Thin, porous, sandy soils benefit from calcium bentonite’s water-holding properties, and it can be added to a general soil improvement mix for raised beds or intensively cropped vegetable beds. Add dry calcium bentonite mixtures to new beds, but to avoid disrupting root systems in existing beds, use a suspension in water.

Sandy Soil

Put 2 pounds of calcium bentonite in a bucket and add 2 gallons of water. Leave for 24 hours.

Apply a wetting agent to about 2 square yards of ground, using a wetting agent applicator.

Stir the calcium bentonite and water vigorously with a stick. Leave the mixture to settle for 30 seconds before pouring into a watering can. Leave any lumps in the bucket.

Water the calcium bentonite suspension into the ground, allowing time for it to penetrate before applying more, to prevent runoff.

Mix remaining lumps with more water and pour the suspension onto the garden beds. Scatter any lumps that don’t break down across the soil.

General Soil Improvement

Mix 2 pounds of calcium bentonite with equal parts horticultural sand and organic matter, such as garden compost or leaf mold. Add an equal volume of aged manure if you’re growing vegetables that require high levels of nutrients.

Spread the mixture across 2 square yards of soil before putting any plants in the ground.

Dig the mixture in to a depth of about 9 inches, mixing it thoroughly into the existing soil. The ground is now ready for planting.

  • The Plantsman: It’s Clay Time
  • North Carolina State Univerisity Cooperative Extension: Improving Your Soil
  • Cornell University Department of Horticulture: Soil Basics
  • U.S. Environmental Protection Agency: Backyard Composting — It’s Only Natural
  • Calcium bentonite also helps increase the pH in acidic soil.
  • Wait five or six weeks before reapplying calcium bentonite suspended in water, to allow time for it to be incorporated into the soil.
  • Don’t apply calcium bentonite and sand alone to soil. This creates a concrete-like mixture.

A graduate of Leeds University, Jenny Green completed Master of Arts in English literature in 1998 and has been writing about travel, gardening, science and pets since 2007. Green's work appears in Diva, Whole Life Times, Listverse, Earthtimes, Lamplight, Stupefying Stories and other websites and magazines.

How to add calcium to soil

Made up of calcium sulfate dihydrate, gypsum is a non-toxic mineral that's naturally occurring and contains high levels of calcium and sulfur.

It’s sold commercially in a granular, powdered, or pellet form for use in home gardens. Touted as being a great option for breaking up heavily compacted clay soils, it’s also argued that the calcium and sulfur content in gypsum can help to promote healthy plant growth.

Some horticulturists believe, however, that there are more efficient and scientifically-proven solutions that are more beneficial.

What Is Gypsum Used For Globally?

Gypsum is the most commonly utilized sulfate mineral mined across the world. Amongst other things, it's used in the building trade to make up drywall, plaster, and building blocks. It's even used to produce writing chalk, as a food additive, and, in its fine-grained alabaster variety, it's made into ornamental sculptures.

Another common usage for gypsum is for soil conditioning and fertilizing on an industrial or large-scale agricultural level.

Why Is Gypsum Used in Gardening?

The granular or powdered form of gypsum specifically marketed towards garden use has a variety of different applications.

Primarily, gypsum is used for helping to break up heavily compacted clay soils making them more porous and able to absorb moisture. This is particularly helpful in areas prone to drought. The addition of gypsum can promote better drainage and air circulation, which can aid root development and nutrient absorption.

Gypsum changes the soil composition through a process called flocculation. The gypsum enables the small and dense clay particles to join together to form bigger particles, more closely resembling loose sand.

Another occasion when gypsum is often introduced in a garden setting is if the soil in your garden lacks calcium. The addition of gypsum can help to restore the balance. Soils lacking in calcium can lead to slow and poor root development.

Most soils in North America are unlikely to be suffering from calcium deficiencies. When they are, adding lime is often recommended. Unlike limestone, gypsum is more soluble and effective at migrating deep into the soil. This can be an advantage when trying to balance out acidic soils and access deep plant roots. Plus, the gypsum won’t change the pH level of the soil like lime will.

It can also be helpful if you have a coastal garden that's subjected to strong salty winds. The gypsum can reduce the sodium levels in the soil.

How Much Gypsum Should Be Used?

Applying too much gypsum to your garden soil can be problematic. To minimize any problems, you should first establish if your soil will benefit from any addition, and you should carefully follow any pack instructions.

Doing a soil analysis will establish how much calcium and sulfur are already present.

Why Gypsum Might Not Be the Best Solution

Over-application of gypsum can strip essential nutrients from your soil, and this can harm plant growth. It can also strip out too much sodium from soils that are already low in salt.

You also need to apply gypsum regularly to ensure it has a continued benefit. It isn't enough to do one treatment and think this will be a permanent solution. After a few months, the effects will begin to wear off and the soil composition will revert to its original state. Applying a treatment at least annually will be required.

Despite claims by some manufacturers, there isn't any strong evidence to suggest that gypsum is a worthwhile addition in terms of fertility.

What Are the Other Alternatives?

There have been studies that have suggested that providing your soil has at least 10% organic matter, there will be no major benefit from adding gypsum.

Taking the time to enrich your soil with organic matter is not only cheaper, but it will benefit your soil in terms of nutrients for promoting healthy growth. It can also improve movement and water drainage in heavy clay soils.

If you are impacted by strong coastal winds, you could always look into plants that are known for being salt-tolerant.

Unless you have a severely compacted soil, and you want to lessen the physical work you'll have in loosening it, then there isn't any strong reason to do a gypsum application.