Causes of Calcium Deficiency in Plants, and How to Fix It


Calcium deficiency is one problem you may run into with your plants, and it can ruin the hard work you put in to make your garden great.  Luckily, there are ways to treat plants that are lacking calcium.

So, how do you treat calcium deficiency in plants?  Before planting your garden, put lime, gypsum, bone meal, or compost into the soil and mix thoroughly.  After plants are established, you can spray the leaves using a solution of calcium chloride or calcium nitrate.

Before you add calcium supplement or fertilizers to your soil or plants, it is important to be certain that a calcium deficiency is really the problem.  Otherwise, you might end up with too much calcium in your soil, which also causes problems.

Let’s start off with an explanation of why calcium is important for plants.  Then, we’ll get into the symptoms and causes of calcium deficiency, so that you can diagnose the problem when it appears.  We’ll end with some ways to add calcium to your soil.

Why is Calcium Important for Plants?

Calcium plays several important roles in a plant’s growth and development.  First of all, calcium is involved in the transport of other nutrients in the plant.

Calcium also contributes to strong cell walls in the plant.  A plant with strong cell walls will show stronger resistance to disease and pests.

In addition, calcium is vital for root and leaf development.  Strong roots and larger leaves allow a plant to absorb more water and nutrients from the soil, and more energy from sunlight.

tomato plant roots
The root system of a plant.

Symptoms of Calcium Deficiency in Plants

If your plants suffer from calcium deficiency, they will display some of the following tell-tale signs.  Keep your eyes peeled for them.

Necrosis

Necrosis simply means death of a part of the plant.  Most often, this will begin with browning of newer leaves, starting along the edges and working inward.  The necrotic leaves will eventually fall off.

Calcium is immobile nutrient, meaning that the plant cannot easily transport calcium between its tissues.  This is the reason that newer leaves are affected by calcium deficiency first.  The plant cannot easily move calcium from the older, established leaves to the younger ones, and so they turn brown.

Stunted Growth

When a plant has insufficient calcium, the roots will be poorly developed, inhibiting a plant’s ability to absorb nutrients and water from the soil.

New leaves may also be small or misshapen, meaning the plant will absorb less sunlight for energy.

When combined, these factors will lead to stunted growth of the plant.

Poor Production

A plant lacking calcium may also drop its flowers, resulting in less fruit at harvest.  The fruit that does appear may be small, misshapen, or diseased.

A common symptom of calcium deficiency that affects fruit is blossom end rot, pictured below.

Tomatoes with blossom end rot. It can get much worse than this!

Blossom end rot affects tomatoes and peppers, and it looks like brown or black spots on the bottom of the fruit.

Causes of Calcium Deficiency in Plants

There are several possible causes of calcium deficiency in plants.  In some cases, calcium deficiency may occur even when there is plenty of calcium in the soil!  Here are a few to look out for.

Incorrect Soil pH

For each nutrient, there is an ideal pH range where the plant can easily absorb the nutrient from the soil.  This range varies by nutrient, but a good general range to aim for is 5.5 to 6.5 (slightly acidic).  (Blueberries and some other plants like more acidic soil).

If your soil pH is too low or too high, the plant will have difficulty absorbing certain nutrients.  For instance, as soil pH goes below 6.0, the availability of calcium starts to decline rapidly.  The same thing happens when soil pH goes above 8.5.

For more information, check out this chart at Research Gate that shows nutrient availability based on pH levels.

The takeaway message here is that if your soil pH is too low or too high, then your plants can end up with a nutrient deficiency – even when there is plenty of the nutrient in your soil.

Before you add any calcium to your garden, check the pH of your soil.  You can send the soil away to your local agricultural extension, or you can buy a soil pH test kit online or at a local garden center. To learn more, check out my article on testing your soil.

If your soil pH is too low (acidic), you can add lime to raise the pH – for more information, check out my article on raising soil pH.

If your soil pH is too high (basic), you can add sulfur to lower the pH – for more information, check out my article on lowering soil pH.

If your soil pH turns out to be in an acceptable range (see the link above), then you will want to continue your investigation.  Let’s continue to the next possible cause of calcium deficiency.

Improper Watering

If your plants are not getting enough water, then they can end up with a calcium deficiency.  The reason is that the plant absorbs calcium via water.  So, if there is not enough water, then there is not enough calcium being absorbed.

dry soil
I would say that this soil is too dry, probably.

If your soil always seems dry, try watering in the morning, when the air is cooler and the sun is not as bright.  Water near the ground, and let the water sink in before adding more.

Otherwise, you can wash some of the soil away from the plant. For a more detailed treatment plan, see my article on dry garden soil.

Also, try not to get the leaves of the plant wet, especially if you are forced to water at night.  If the leaves stay wet for too long, you run the risk of rotten or moldy leaves.

On the other hand, it is also possible to over water your plants. For more information, check out my article on over watering.

Nutrient Imbalance

I don’t want to sound all philosophical, but gardening is all about balance.  You need to make sure there is enough of each nutrient in the soil, but you also need to pay attention to the ratio of nutrients.

For example, excessive magnesium in the soil can block a plant’s ability to uptake calcium.  This can happen you use too much Epsom salt (magnesium sulfate) as an additive in your soil, without adding any calcium by other means.

Excessive potassium in your soil can also prevent a plant from absorbing calcium.  When you buy fertilizer, you will see three numbers listed, representing N-P-K. For more information, check out my article on the NPK ratio listed on fertilizer packages.

The third number, K, represents potassium content by weight.  Make sure this third number is not too high, or you can end up with a calcium deficiency due to excessive potassium.

 The best way to tell if your nutrient levels are balanced is to test your soil.  You can send a soil sample to a local agricultural extension for testing, or you can buy a soil test kit online or at a garden center.

If your nutrient levels look balanced, there is still one more category to check before we diagnose a shortage of calcium in the soil.  Unfortunately, this next one is largely outside of your control.

Extreme Conditions

Extreme weather conditions can also affect a plant’s ability to absorb calcium and other nutrients from the soil.  If you plant too early or experience a prolonged period of unseasonably cold weather, then your plants may suffer from calcium deficiency.

High humidity can cause the same problem, for the same reason.  When temperatures are low or humidity is high, a plant’s rate of transpiration slows down.

Transpiration is the process where a plant moves water from its roots to its leaves, where they then evaporate.  When this process slows, calcium absorption slows also, since calcium must be absorbed via water.

Lack of Calcium in Soil

If you are able to rule out soil pH, improper watering, nutrient imbalances, and extreme conditions, then you may have inadequate calcium in your garden soil.

This can happen for a couple of different reasons.  First, it may be that there was never much calcium in your soil to begin with.

It could also be that your soil used to have plenty of calcium, but it has been depleted.  One common cause of nutrient depletion in a garden is planting the same crop in the same place for years on end.

To avoid nutrient depletion, use crop rotation.  This means that you plant a crop in a different location in your garden every year.

How to Add Calcium to Garden Soil

If you have decided that your soil is deficient in calcium, then you will want to supplement it with a natural or chemical additive.  The ideal situation is to add calcium to your soil in the early spring, before planting anything.  Here are some ways to do just that.

Gypsum

Gypsum, or calcium sulfate dehydrate, comes in powder or pellets, which can be added and mixed into your soil.  Adding gypsum has a negligible effect on soil pH, so if you are already in the proper pH range, then there is no need to worry when adding this supplement.

gypsum
Gypsum in crystal form.

Gypsum is widely available online and at garden centers.  In addition to adding calcium to soil, gypsum will add sulfur, another necessary nutrient for plants.

Lime

Lime, or calcium carbonate, usually comes in powder form, which you mix into your soil in the spring.  Adding lime will slightly raise soil pH, so keep this in mind if your pH runs a little high.  You can find lime online or in any garden center.

calcium carbonate
Lime, or calcium carbonate, in powder form.

Bone Meal

Bone meal is made from bones and waste products from slaughterhouses.  It comes in fine or coarse powders, and is mixed into the soil in the spring.  In addition to supplying calcium, bone meal provides phosphorus to your soil.  Many garden centers will carry bone meal.

Compost

You can make your own compost mix and incorporate it into your garden soil every spring.  Grass clippings, leaves, banana peels, coffee grounds, and other food scraps (not meat!) can all go into a compost pile.

With a little time, this compost will go great in the garden.

When bacteria break down the compost into soil, you end up with a rich, black mixture that should contain plenty of nutrients, including calcium, to supplement your garden.

Fertilizer

You can also buy fertilizers off the shelf at a garden center.  There are plenty of fertilizers that contain calcium to supplement your soil.  Just remember to avoid too much potassium or magnesium, which can block a plant’s uptake of calcium.

You can also use a liquid solution containing calcium chloride or calcium nitrate to spray onto your leaves.  This is known as foliar feeding, and it is a way to try to save your plants if you did not add calcium before planting in the spring.

A Few Words About Excessive Calcium

After a long discussion about calcium deficiency, it doesn’t seem possible to have too much calcium in your garden soil.

However, it can happen, especially if you add calcium without checking your pH and other possible causes of calcium deficiency in plants.  If you skipped the possible causes of calcium deficiency, go back and read that section now!

I mentioned earlier that too much magnesium or potassium can inhibit calcium uptake, since these nutrients compete for uptake.  On the other hand, if you end up with too much calcium in your soil, the tables can turn and you might end up with magnesium or potassium deficiency in your plants.

Conclusion

At this point, you should have a good idea of whether your plants have a calcium deficiency, and how you can treat the problem now and in future years.

I hope that this article was helpful.  If you have any questions, please leave them in the comments below.

jonathon.david.madore

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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