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Calcium & Magnesium – the Bond is Strong!

Calcium & Magnesium – the Bond is Strong!

Alex Grady

When it comes to nutrients, N, P & K love the limelight! It’s easy to overlook calcium and magnesium. Don’t do this – they’re both macro nutrients. Without them, plants won’t survive.

The good news is, it’s simple to add calcium and magnesium. A good ol’ CalMag will do the trick. In fact, adding CalMag is as a quick fix for most common deficiencies, since most CalMags also contains iron and nitrogen.

CalMag products


Calcium symbol

Calcium is key to plant growth and structure! Plants use it to bind cell walls - this thickens stems and strengthens your structure. This makes it tough for pests and pathogens to penetrate plant cell walls.

A big reason to add calcium is that it helps prevent other common deficiencies. Why? Calcium is involved in many metabolic processes that affect the uptake of other nutrients, like nitrogen (N), magnesium (Mg) and potassium (K).

It’s pretty well known that calcium helps plants cope with temperature and humidity stress. How? It helps stomata (tiny pores on leaves) function. These pores are used for gas exchange and transpiration. A lack of calcium can really mess up stomatal processes, making it tougher for plants to cope with environmental stresses.

Key benefits

  • Prevent other nutrient deficiencies
  • Thickens cell walls
  • Strengthens plant structure
  • Balances magnesium and potassium uptake
  • Prevents pests
  • Counters the calcium draw in coco

Causes of deficiency

Calcium is a tricky nutrient .

No energy is needed for uptake - plants absorb calcium passively, as they take up water. It’s then moved up the plant via transpiration. If the humidity in your grow room’s not very high, and plants aren’t taking up and losing water through leaves, calcium deficiencies often occur.

If humidity is very low, and the stomata close to save water, then calcium will again become an issue. You really have to keep an eye on your growing environment.

Calcium deficiencies are most common in coco.For all its virtues, coco notoriously holds onto calcium (Ca) and in some instances nitrogen (N).

To make matters worse, coco also releases potassium (K). Too much of this can cause a calcium deficiency, since the two are chemically similar.

Don’t panic – just make sure you use a coco nutrient and CalMag.

Calcium deficiencies can also occur in hydroponic systems. Especially if you use soft or RO water with a general base nutrient. To prevent problems, use a soft water formula, which contains more calcium.

As with all nutrients, you can get a calcium deficiency by underfeeding or having the wrong nutrient ratio. Adding too much potassium and magnesium, and the presence of too much sodium will cause calcium issues.

Brown leaf

Signs of deficiency

Calcium is immobile. Once deposited, it stays where it is. This means signs of deficiency mostly shows on newer leaves:

  • Necrosis on younger leaves
  • Brown and crispy growing tips
  • Deformed or bent leaf tips
  • Rusty brown spots on the older leaves



You’ll find magnesium in chlorophyll – the green stuff that absorbs light. Plants need it for photosynthesis. So, if you’ve got high intensity lights, you really don’t want a magnesium shortage.

Plants also need lots of it when they’re expending lots of energy and photosynthesizing more.

Make sure there‘s an ample supply of magnesium during periods of heavy fruiting and rapid growth.

Key benefits

  • Vital for photosynthesis
  • Crucial during periods of rapid growth

Causes of deficiency

Low pH can cause a magnesium shortage – it can precipitate out of your nutrient solution and be unavailable to your plants.

Over-watering can also cause a magnesium deficiency. As the media becomes saturated, oxygen content lowers, causing anaerobic conditions - this reduces the pH.

If you notice a magnesium deficiency, be mindful about what could’ve caused it. A good base nutrient should have enough already present - you normally only get a deficiency if you are underfeeding, or if you are over-feeding additives with high potassium, calcium or ammoniacal nitrogen.

Signs of deficiency

Unlike calcium, magnesium is a mobile nutrient – it can be transported to wherever it’s needed. Deficiencies show more on middle to older leaves:

  • Yellow leaf tissue, but veins stay green (early)
  • Brown rusty spots with burnt patches (later)
Yellow leaf

How to Add Ca & Mg

Adding CalMag

For best results, use a CalMag alongside your base feed to prevent deficiencies. You should always do this when growing in coco.

If you’ve already got a deficiency, a CalMag will correct it. To correct the deficiency quickly, it is best to apply as a foliar spray at 10-15ml per Litre. This may sound like a lot, but it is safe and will work quickly.

Use it as a regular addition to your nutrient solution if you have re-occurring problems. Just make sure you don’t overdo it when adding to the nutrient solution. Just 0.5ml per Litre is fine in most cases.

CalMag contains 3.2% calcium, 1.2% magnesium , 0.1% iron and 2.6% nitrogen.

1 comment


I’m using calmag with nitrogen,in Coco ,at 2ml per litre ,is that too much for seedlings

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