Plant health

How to identify and treat a calcium deficiency in plants

By Michelle Joe on August, 11 2021
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Michelle Joe

Michelle is a creative copywriter and storyteller who loves to connect brands with their audiences. She enjoys being a part of Bluelab’s innovative growing journey.


If your plants are not looking their best, your plants may be suffering from a nutrient deficiency. While it’s not always easy to pinpoint a particular deficiency, if your plants have a low growth rate, have curling leaves or browning apical meristems (growing points), low calcium may be the culprit. 

Calcium plays such a pivotal part in plant growth that left untreated, young leaves will struggle to grow and flowering and fruiting are inhibited. Catch a calcium nutrient deficiency in time, though, and you just might save your crop! 

 

Why do plants display these symptoms?


If calcium doesn’t reach new cells, this will affect the growing points of a plant and it will lead to calcium deficiency symptoms, such as leaf tip burns or blossom end rot.

Water needs to be moving through the plant in order for calcium to be present. Often, a calcium deficiency occurs in greenhouse plants because of the conditions of the environment. For example, temperature and light can affect the amount of water taken up by the roots. The amount of salt dissolved in water may also cause a calcium deficiency as it will decrease the uptake of water by the plant.

 

A primer on essential nutrients

Plants obtain carbon, hydrogen and oxygen from water, air and sunlight, to make food for growth for photosynthesis. They also require macronutrients (like calcium) and micronutrients:

Macronutrients

Nitrogen, phosphorus, potassium, sulphur, calcium and magnesium. These are required by plants in relatively large amounts. 

Micronutrients (also known as trace or minor elements)

Copper, manganese, zinc, iron, boron and molybdenum. These are required by plants in smaller quantities.

 

Calcium in plant health 

Calcium is essential for a healthy plant structure as it helps to form new cell walls and membranes. It also gives stability to existing cell structures, forming compounds and binding agents to give stability to cell walls. This is why a calcium deficiency can show up quite early compared to other macronutrients deficiencies—it just takes a couple of weeks for the cell walls to weaken causing deformed new shoots and leaf tips.

 

 

As the plant becomes weaker, it becomes more susceptible to heat stress. The opening and closing of the stomata rely on strong cell walls. Weakened cell walls also encourage fungi and bacteria to prey on the plant. 

It’s not all about the shoots, though. As above, so below—that is—if your plant shows signs of unhealthiness, then the roots can also be stunted and discoloured. 

It is difficult to diagnose which nutrient deficiencies are affecting your plants, as it could be a mix of the above toxicities and deficiencies. 

 

Calcium deficiency signs: what to look for

During your regular daily health checks, there are some tell-tale signs that your plant may be struggling with a lack of calcium. Deficiency will usually affect the new growing points (apical meristems) of the crop and the newer leaves, so if you suspect something, start there.

 

Tip burn and curling leaves

The strawberry plants on the right are showing signs of tip burn. Once the tips are burned like this, you can't bring them back, so wait for new growth. 

 

 

 

 Pale leaves and stunted or twisted growth

 The strawberry leaves here are also showing signs   of calcium deficiency, as they look withered and   twisted.

 

 

Blossom end rot 

A serious disease caused by a lack of calcium uptake. Dark spots will start as watery, yellow spots, then go on to destroy much of the fruit. Peppers, eggplant and tomatoes are susceptible to blossom end rot

 

 

Common causes of a calcium deficiency

1. Root zone pH is too high or too low 

Plant nutrients become accessible or inaccessible depending on pH levels, which measure the acidity or alkalinity of soil. The pH measurement scale runs from pH 0 to pH 14, with pH 6.5 to pH 7.5 being generally the optimum measurement range for the growth of plants. 

 

2. Nutrient imbalance in your growing medium
When plants lack a particular nutrient, they cannot create new cells, DNA or other vital components. When there is too much of a particular nutrient, it may prevent the uptake of another nutrient, or the nutrient excess can make plants ill. Think of how humans consume fat. It’s key to providing energy and allows us to store certain nutrients – but too much of it will increase the risk of diseases.

 

3. Over or underwatering 
This is a common reason for unhealthy, wilting and dying plants. Water is essential for the survival of crops and some of the most crucial reasons why plants need enough water include:

  • Maintains the ability for plants to stay upright
  • Transports nutrients from the soil up to the stem
  • Creates food and energy during photosynthesis

 

It is helpful to remember that when calcium is absorbed, it becomes immovable and will stay within the developed and older plant tissues, which is why a calcium deficiency affects younger leaves. Having a stable supply of calcium is important so it can be absorbed by other younger developing parts of the plant.

 

How to fix a calcium deficiency in plants

Firstly, it’s important to make sure you are using a water-soluble calcium source, such as calcium nitrate so this nutrient can move through the plants. When growing in soil, you can opt to apply calcium sources such as lime, bone meal or gypsum. However, keep in mind this can alter your pH or add additional nutrients along with calcium.

When you are growing in hydroponics, you don’t want to oversupply your plants with other nutrients, so it is best to use a calcium-only additive. If you’re using hard water for your plants, it’s essential to note this particular type of water normally contains a high level of dissolved calcium and other nutrients.

If you are seeing signs of calcium deficiency in your plants, it may be tempting to simply add more calcium. However, this could cause other issues and it is possible your soil or solution does not require more calcium. The problem could be that this nutrient isn’t making its way into your plants.

Calcium uptake is greatly affected by climate. 

Assess the following to see what you could be doing differently to treat a calcium deficiency.

Irrigation 
Water is necessary for obtaining calcium. Without it, plants will not be able to access this particular nutrient. Consistent watering is key to avoiding a calcium deficiency. 
 
pH level 
The optimum pH depends on the species. Low calcium levels occur at a low pH due to a lack of lime. You can measure pH by using a Bluelab pH pen or the Bluelab Combo Meter.

Temperature
Whether you’re growing outdoors inside a grow house, transpiration rates will be low which leads to a lack of calcium in the plant. The Bluelab Soil pH Pen and Conductivity Pen are ideal for measuring temperature on the go.

Humidity
High humidity levels in your greenhouse can lead to low transpiration rates. Resolve this by adding fans to boost airflow and help the plant to transpire. Monitor and manage your greenhouse environment. 

 

Prevention is key

When it comes to optimal health for your crops, the prevention route is much easier than the cure. A few important pointers to keep in mind are:

 

  • Check the fertiliser stock solution is maintained in multiple tanks
  • Your fertigation system is running properly
  • There are consistent solution levels in reservoirs
  • All of the nutrients are being delivered proportionately to your crops  


Your plants need to access a range of macronutrients and micronutrients, which makes it difficult to diagnose a single nutrient deficiency. It is likely and common to find that your plants are suffering from a mix of nutrient deficiencies at one time.

Remember to regularly monitor the fundamental parameters of plant health in your plant growing journey to ensure your plants are thriving rather than just surviving.

 

More resources on calcium and nutrient deficiencies in plants 

 

How to recognise potassium nutrient deficiency in plants

How to identify phosphorus nutrient deficiency in plants

Signs that your plants may be struggling with incorrect EC

Common nutrient deficiencies in plants – and how to fix them

 

 

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