All plants need calcium. Calcium is used by plants in the formation of cell walls and cell membranes. Calcium for plants is an immobile nutrient, meaning it cannot be moved by the plant from one area of the plant to another (plants can do this with mobile nutrients such as nitrogen). It is therefore important that plants have a consistent supply of calcium throughout the life of the plant.
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The role of calcium in plants
Calcium is a secondary nutrient that is critical to crop development. It is needed in large amounts by all plants for the formation of cell walls and cell membranes, and it plays a vital role in soil structure.
Ensuring your plants have an adequate supply of calcium is also important to ensure your fruits and vegetables have a long shelf life. The application of calcium in growing tomatoes has been studied and found to make plants more disease resistant while slowing the reduction in fruit firmness during ripening. When your tomato plants have an adequate supply of calcium, you will notice yourtomatoes can last weeks on your countertop without refrigeration.
The importance of calcium in soil
Calcium is a very important part of maintaining a healthy soil structure. Soils need the right amount of calcium so that the soil has:
- Good pore space. Calcium is a large molecule that helps porosity.
- Good microbial life
- Good air movement and
- Good water infiltration
Calcium is also important for nutrient uptake and maintaining soil pH. If your soil isn’t in the right pH range it makes it difficult for the pant to absorb certain nutrients.
Sources of calcium for plants
If you’ve already added calcium to your compost before adding it to your soil you should be good to go. There are many options to add calcium to your soil. We discussed a few of these here.
Eggshells
Eggshells are a great free slow-release form of calcium. A significant amount of eggshells are calcium carbonate. If you add them to your soil as is it can take years to break down. Your best options would be to turn it into eggshell powder or compost it before adding it to your soil.
Water the plant with the water used to boil the eggs is also another way to add a small boost of calcium to your soil. The eggshells release some calcium during the egg boiling process. If you are using this method you shouldn’t add anything to the water (such as salt or oil).
Chalk
Chalk is also made primarily of calcium. For a slow release of calcium in your potted plants add a couple of sticks of chalk to the soil in your container after transplanting.
Calcium Tablets
If you have some calcium tablets lying around that may have expired, instead of throwing them away, why not feed them to your plants? Before adding the calcium tablets to your soil should crush them with a hammer or rolling pin before mixing into the soil or compost pile.
The form of calcium available in calcium tablets is usually more complex than what is found in gardening products. Calcium from calcium tablets can take a long time to break down. Consider this option a long term investment rather than a quick fix.
Gypsum
Gypsum can be used as a source of calcium and sulfur. However, gypsum is more soluble than lime and can add calcium more rapidly to the soil. This may result in decreasing potassium or magnesium levels in the soil.
Lime
Limestone
Limestone is a source of calcium carbonate and is used as a fertilizer for agricultural soils since it increases the pH of acidic soils. This increase in PH increases soil fertility and makes plants better assimilate nitrogen, phosphorus and potassium.
Dolomite Lime
The preferred form of limestone as a soil supplement is dolomite lime, because not only does it contain calcium, but it also contains magnesium. Both of these elements are essential to healthy growth in vegetables. Most vegetables also require slightly acid soil to grow well.
What is Lime?
The by-product and natural limes contain calcium carbonate (CaCO3), calcium hydroxide (Ca(OH)2), or calcium oxide (CaO). Dolomitic limes contain magnesium carbonate (MgCO3) in addition to CaCO3. Pure lime is 100% calcium carbonate (CaCO3)
Is calcium carbonate the same as agricultural lime?
No. The term agricultural lime, or “aglime,” usually refers to crushed limestone. Limestone (calcium carbonate) is not the same as hydrated lime (calcium hydroxide).
Lime and soil pH
Utilizing lime in your soil will increase the soil pH. Too much calcium cal take a long time to fix. It’s much better to add too much than too little. To a certain extent you can add vinegar to reduce the effects of altering the soil pH.
How to make Calcium immediately available in soil
Most commercial Calcium products for the garden work fairly quickly. When choosing an option keep in mind – the finer the particle size the quicker it is going to have an impact on your soil and ultimately your plants.
Eggshells as a calcium source can take some time to break down and become available to plants. If you are interested in getting calcium available to your plants using eggshells, I discuss that in detail in this article.
How to fix calcium deficiency in plants
If your plant is showing signs of a calcium deficiency the fastest way to fix it is by foliar application (i.e. feeding the plant through the leaves). Most, but not all vegetable plants, can take up nutrients through their leaves.
Another option is to add calcium directly to the soil using any of the options mentioned previously. This can be:
- Mixing the source of calcium with water in line with the instructions and using it as a soil drench
- Adding powdered calcium to the soil
- Utilizing a compost mix that contains added calcium
- Adding calcium to the planting hole when transplanting into the ground.
- Adding a couple of sticks of chalk into your container at transplanting
Does your soil actually have a calcium deficiency?
This is a really important point to consider. Just because there is a calcium deficiency in your plant doesn’t automatically mean that there is a calcium deficiency in your soil. In most cases, the calcium in your soil is present but, for a variety of reasons that calcium wasn’t able to be taken up by the plant.
There are main 3 reasons why your plant may not be getting the calcium it needs that is already present from your soil:
- Poor uptake of calcium by the plant
- Soil type
- Soil PH
1. Poor uptake of calcium
This can happen when there are heavy rains followed by an extended dry spell. The fluctuation in watering can make it difficult for the plant to take up calcium through its roots. This can also happen if plants like tomatoes are growing in a high humidity environment for an extended period of time.
2. Soil type
Sandy soils have a harder time maintaining calcium than clay soils. If your soil is course or sandy it’s possible your soil either doesn’t have enough calcium or isn’t able to exchange the calcium present with the plant roots. Adding compost to your soil is the best way to resolve this issue.
3. Soil pH
You are more likely to have a calcium problem with a low (acidic) pH soils than with neutral or high (alkaline) pH soils. Most plants can absorb calcium efficiently at a pH between 6.5 to 7.
The calcium in eggshells is in the form of calcium carbonate. Calcium carbonate dissolves in acid solutions, but not in alkaline solutions. If the pH of your soil is VERY acidic (below 5) and the eggshells are pulverized into a very fine powder you can use the eggshells to raise the pH of your soil and make the calcium available to your plants.
Another option would be to adjust your soil pH using garden lime (which is also primarily made of calcium carbonate). The garden lime, however, will have a more immediate effect than the eggshells.
What if I have too much calcium in my soil?
If you have too much calcium in your soil the most probable reason is that you added too much lime to your soil. If this is the case, one of the easiest ways to fix it is to reduce the concentration of calcium in the soil by adding compost to amend the soil. Unfortunately, this can take some time for the microbes in the soil to restore balance but it should normalize over time.
If you have a large area you could do a soil test and raise the concentration of the other nutrients/ element to correct the problem.
Final Thoughts
Calcium is an important nutrient in maintaining soil health, healthy plants and healthy fruits and vegetables that have a long shelf life. Calcium plays an important role in the overall growth of plants
And helps in the absorption of major nutrients. It is also essential for the formation and integrity of plant cell walls and hence important for fruit formation.
There are many options when for us to choose from when deciding on how to add calcium to our soils. The best option is always the one that is easiest for you.
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