When to Stop Using Cal-Mag? – Get the Answer Here!

All living things require a sufficient amount of nutrients to survive. Plants too require various types of nutrients to thrive healthily. Some of the important nutrients for plants are Potassium, Nitrogen, Phosphorus, Calcium, and Magnesium, which are also called Cal-Mag together.

These nutrient supplements are not only essential for plants that grow in soil, but also for coco and hydroponically grown plants. Using cal-mag supplements will help your plants from several problems, but too much of them will also harm the plants.

So, in this article, you will get to learn more about the importance of cal-mag and when to stop using cal-mag for plants.

ScenarioWhen to Consider Stopping Cal-Mag
Plant HealthWhen plants show no signs of calcium or magnesium deficiencies, such as leaf yellowing, curling, or spots.
Nutrient LevelsWhen calcium and magnesium levels in the soil or nutrient solution are within the optimal range for plant growth.
Growth StageWhen plants transition to the flowering or fruiting stage, as calcium and magnesium requirements may change.
Nutrient PlanWhen following a specific nutrient plan that does not require continuous Cal-Mag supplementation.
Expert AdviceWhen recommended by experienced growers or a horticulturist to discontinue Cal-Mag based on plant health and growth observations.
ConsultationAfter consulting with a healthcare professional for personal health concerns or conditions that required Cal-Mag supplementation.

One of our articles –When to Use Cal-Mag in Your Garden?

What Does Calcium and Magnesium Do for Plants?

Calcium, magnesium, and sulfur are the secondary macro nutrients that are quite essential for the plants. They are regarded as secondary as they are needed in fewer quantities by the plants than the primary nutrients like Nitrogen, phosphorus, and potassium.

Calcium and magnesium help in developing flowers and fruits and aid the plants to yield more. They play an essential role in the proper functioning of the structure and system of the plants differently, let us take a look:


Plants need calcium to maintain it’s structure. The cell wall present in every plant helps them to have a rigid shape and structure and keep them functioning. Calcium, in the form of calcium pectate, helps to strengthen the structure of the cell wall by making it stable and binding it together with other cells.

If the cell wall of a plant is strong, then the absorption and transfer of nutrients from one part to another part of the plants become easy. A weak cell wall will lead to an unhealthy growth of the plant.

Calcium also protects the plants from heat stress by acting like a protective layer and helps them to function during hot weather. Moreover, it protects the plant from different bacteria and fungus and helps in the process of several enzymes and hormones in the plants.

A healthy and rigid fruit structure is achieved in fruit plants and trees when there is a sufficient amount of calcium present in the plant.


Like calcium, magnesium also has a significant role in the growth of the plants. It helps in the activation of enzymes and uptake of nutrients and water. Magnesium also helps in the photosynthesis process of plants that takes place in the green pigment- Chlorophyll.

Each molecule of chlorophyll contains magnesium as the central component that helps in absorbing sunlight during photosynthesis and makes the leaves greener in color. It also helps in the respiration of plants, the transfer of nutrients, and in full maturity of fruits.

Cal-Mag Deficiency and Toxicity in Plants

Cal-mag deficiency can affect the plants and so does cal-mag overdose. Before we describe them, let us tell you about the mobility and immobility of some nutrients.

It means when the roots absorb the nutrients, some nutrients stay in one part of the plant and do not move to the other parts, which is called immobile nutrient. Whereas, a mobile nutrient can move to different parts of the plant where it is needed.

The symptoms of deficiency show in new leaves for an immobile nutrient, as the nutrients are locked in one part. Mobile nutrients can move to other or new growth from the older ones, when they need them, which leads to the deficiency of the older parts of the plants.

Deficiency and Toxicity of Calcium

Calcium is a nutrient, which is immobile. The symptoms of calcium deficiency are shown on the growth of the plants, such as stunted or mishappen growth of new leaves, rust spots on the veins and edges of leaves, and slow growth of the plant. Plus, underdeveloped roots, more heat stress and weak protection against bacteria and fungi are some other calcium deficiency symptoms.

Calcium toxicity in plants can block the plant from uptaking other nutrients like magnesium, copper, iron, and more, and cause deficiency of these nutrients.

Deficiency and Toxicity of Magnesium

As magnesium is a mobile nutrient, the symptoms of deficiency will first occur in the older parts of the plants. Yellow or brown spots appear on the leaves while the veins are still green, curling of the leaves, and slow growth. In most cases, the leaves become too dry and die in extreme cases.

Magnesium toxicity in plants is quite rare, but when it happens, the plants become deficient of calcium and shows stunted growth with burned leaves.

when to use cal mag
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When to Use Cal-Mag in Plants?

Both the nutrients are available as dissolved minerals in natural water. Plants that grow in the external environment can get a sufficient amount of cal-mag from the soil and water.

Untreated tap water has a high Ph level and contains these nutrients, so you don’t need to add the nutrient supplements in most cases when you water the plants with untreated or hard water.

But, if you are using RO or distilled water, then you definitely need cal-mag supplements, as distilled water contains minimum minerals and has a low Ph level.

Cal-mag supplements should also be used when you see any signs of cal-mag deficiency on your plants. For coco and hydroponically grown plants, cal-mag supplements are necessary too.

Hydroponic plants grow without any soil, so the demand for cal-mag and other nutrients is quite high for them. The supplements are available in stores in the form of a mixed soluble powder or liquid.

when to stop using cal mag in flower
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When to Stop Using Cal-Mag in Plants?

When using pre-mixed or liquid cal-mag supplements, the amount of cal-mag supplements should be added is specified. Add only the specified amount with other nutrients, so that they don’t become excess.

Start using cal-mag from the early growth of the plant, little by little, as prescribed. In the flowering phase, cal-mag should be used until the late flowering stage, that is, you should stop using cal-mag in the 4th or 6th week of the flowering stage (depending on the plant) before flushing it.

Some people don’t stop using cal-mag supplements even after the end of the flowering stage, they just drop down the number of supplements from the regular amount. But, it is better to stop using them at the right time to prevent an excess of these nutrients.

Related Questions

Should you use Cal-Mag during flowering?

– Yes, it can be beneficial.

Should I use Cal-Mag every watering?

– It depends on your plant’s needs and the quality of your water.

Can you overdo Cal-Mag?

– Yes, too much can cause nutrient lockout and harm your plants.

Will Cal-Mag burn plants?

– Not typically, but it can cause issues if used improperly.

Can too much Cal-Mag hurt plants?

– Yes, it can lead to nutrient imbalances and harm your plants.

What are the signs of Cal-Mag deficiency?

– Yellowing leaves, stunted growth, and leaf curling.

How often should you feed Cal-Mag?

– It depends on your plant’s needs, but typically every other feeding.

Should I use Cal-Mag during veg?

– It can be helpful, but it depends on your plant’s needs and the quality of your water.

Is Cal-Mag necessary?

– It depends on your plant’s needs and the quality of your water.

Do you add Cal-Mag before or after nutrients?

– It is typically added alongside nutrients.

Do LED lights need more Cal-Mag?

– It depends on the quality of your water and your plant’s needs.

Final Words

Calcium and magnesium might be secondary micro nutrients and they may be available in soil and water abundantly. But still, they are quite essential, especially when using distilled water, for boosting the growth of the plants and flowers, to keep them healthy, and for heavy yield.

Always check the PH level of the soil and according to that, feed the plant with a sufficient amount of cal-mag supplements. I hope this article has helped you in learning ‘when to stop using cal-mag’ for plants.

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