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Calcium For Plants: Deficiency, Toxicity, Sources, & More

Calcium is oftentimes an underestimated nutrient that is very important to plant growth. Calcium plays a huge part in optimal plant health and nutrition.

Calcium For Plants: Deficiency, Toxicity, Sources, & More


In this post, we're going to teach you everything you need to know about calcium for plants.

Calcium is often times an underestimated nutrient that is very important to plant growth.

We usually focus our efforts on supplementing and feeding our plants the primary three, nitrogen, phosphorus and potassium.

However, calcium plays a huge role in optimal plant health and growth. In fact, as we are able to research this plant more, we're learning that it may be even more important than some of the big three.

Its not often that new growers feed just the right amount of this nutrient, which is why we're going to talk about both toxicity and deficiency.

We'll start by explaining what exactly Calcium does for plants, and the best sources of this nutrient you can feed them.

What Does Calcium Do For Plants?

Calcium makes up to 4% of the Earth's crust, and it plays a similar role in maintaining our plant's structures.

To be specific, it is responsible for the structure of our plant’s cell walls. It is a component that is essential for the development of new plant tissue.

It also has a regulation effect in plant cells and helps to contribute to the stability of a plant.

How? It’s simple. Plants have two main transport systems, both the phloem and the xylem. For the most part, nutrients can be moved by either of these two systems, but not by calcium.

Simultaneously, calcium preserves membrane permeability, allowing the proper flow of nitrogen and sugars throughout the plant. It also stimulates enzymes that build strong root structures.

Calcium is an immobile nutrient, meaning that the plant cannot transport calcium from one area to another inside the plant.

What this means for you, the grower, is that you need to provide a constant supply of Calcium to prevent deficiency in your plant.

So, let's talk about some of the best sources of calcium for plants.

What is the Best Source of Calcium for Plants?

Like animals, plants need a wide range of nutrients. Calcium can be added to your soil or growing medium in several different ways.

Gypsum, also known as calcium sulfate, is a popular choice. It adheres well to clay particles and dissolves slowly, providing a ready source of calcium for your plants. 

Lime is another choice. Also known as calcium carbonate, it increases the alkalinity of your soil, which is often necessary if you have a calcium deficiency. It takes some time for lime to take full effect, though, so be patient with this.

You can add natural amendments like shell meal or eggshells, too. These also absorb slowly and can be found at most garden supply stores. 

You can also repurpose ones you have at home. You will want to pulverize either in a blender before adding to your plants.

Cal-Mag Supplements (Most Common)

A final, and best, option is a Cal-Mag supplement (Calcium & Magnesium). Both calcium and magnesium are vital secondary macronutrients for plants (along with sulfur).

More often than not, if a plant is deficient in calcium it will also be deficient in magnesium. Many growers use Cal-Mag supplements as preventive measures. 

If you are watering your plants with treated water, this is absolutely essential. Calcium and magnesium are only found in water with harder pH levels so you may be starting out with a deficiency and not even be aware of it.

If you are growing in high temperatures or high humidity, a deficiency in both nutrients might arise, too, so Cal-Mag is a smart choice.

Combined calcium and magnesium supplements can also be used as a foliar feed, giving plants a healthy dose of nutrients across their leaf surface.

Remember to spray the undersides of the leaves as well. Continue applying nutrients until the deficiency symptoms are no longer present.

Calcium Toxicity

More often than not, calcium is not a nutrient that is considered to be toxic to plants. In and of itself it is not a harmful nutrient. 

However, excess levels of calcium in the soil can affect a plant’s uptake of other nutrients. This can cause a deficiency in these vital elements.

For example, too much calcium in the oil can make it harder for plants to absorb magnesium, potassium, phosphorus, copper, zinc, iron, and boron.

Therefore, if you suspect a deficiency of any of these nutrients, you may want to check the calcium in your soil, too - you might be adding a bit too much. Our complete guide on nutrient ratios goes more in depth on this topic.

There’s only one other sign of calcium toxicity that you may notice at first glance, and that’s a cloudiness or residue in the water you are using to grow your plants in a hydroponic setting. 

If you are growing in a hydroponic system and notice that the reservoir appears to be clouded, it could be calcium to blame.

Again, this is not problematic in itself, but could lead to deficiencies of other nutrients.

Identifying Calcium Deficiency In Plants

Signs of a calcium deficiency can be detected on the upper, younger leaves, and on the overall plant growth.

Symptoms result in slight yellowing, and the tips of leaves will turn brown to black and die off.

Calcium deficiency causes the new leaves at the top of the plant to look misshapen. Crinkled, distorted leaves with curled tips are a definite sign of a deficiency.

Growth of the plant as a whole will be stunted, as a deficiency will fail to promote the growth of lateral shoots.

  • Youngest leaves will be stunted and deficient
  • Very little lateral shoots
  • Leaves will distort and curl at the tips
  • Young leaves will often turn a very dark green color

Examples Of Calcium Deficiency In Plants

The most telltale sign of calcium deficiency in plants is looking at the leaves. In the images below, you can see distorted leaves which are curling (or starting to curl) at the tips.

You can also see that the new growth is affected, and the leaves appear darker in the center than the outter edges.

calcium-1

How To Correct Calcium Deficiency

As with nearly all other required plant nutrient needs, one of the first things to take a look at is pH balance, in both soil and hydroponic growing systems.

A pH imbalance will block nutrient uptake through the plant’s roots. It is important to regularly check the pH, and to be sure to keep the pH within the appropriate range for soil or hydroponics.

The optimal pH range for most plants is roughly between 5.5 and 6.5. In this range, the nutrients present in the soil or water are soluble, and are easily taken up through the plant’s root system.

When the pH level is outside of this range, even when the proper nutrients like calcium are present, they are not able to be absorbed by the plant.

Flush your growing medium

If you discover that your calcium deficiency is a result of a pH imbalance, it is best to flush your entire growing medium with fresh water and then add the desired supplement, if still needed, in order to correct the deficiency.

This process should bring your pH level in balance with where it needs to be. In soil use 3 gallons of pure water for every gallon of grow media.

In hydroponic gardens, drain off part of your nutrient solution and replace with pure water in order to balance your pH.

After assurance that pH levels are where they need to be for proper nutrient uptake, you may discover that your plants do indeed need an extra boost.

Our complete guide on flushing plants will help you with this step, if needed.

If you want to learn more about deficiencies, check out our entire nutrient deficiency series.

Final Thoughts On Calcium For Plants

Although calcium deficiency is much more common than calcium toxicity, it’s important that you test your soil before adding any kind of nutrient. 

This will help you ensure that you aren’t overdoing it on any one mineral or element and are instead giving your garden exactly what it needs.

By following these tips when adding calcium for your plants, you’ll be able to grow a bountiful garden that thrives throughout the seasons.

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