What are Cal-Mag products used for and how to use them?

Plants cannot develop healthily without an adequate intake of calcium and magnesium. To replenish these vital minerals or to act as an agent for stabilizing pH, most growers use supplementary fertilizers commonly known by the abbreviation Cal-Mag. It is hard to find a grower who does not use Cal-Mag. In this article we will therefore tell you everything you need to know and recommend proven products.

Why is Cal-Mag so widely used?

• The synergistic combination of calcium and magnesium benefits plant structure and facilitates photosynthesis.
• Calcium also improves the plant’s defenses against pathogens and helps with the uptake of other minerals such as iron and magnesium. Once calcium levels drop, the plant will also suffer from iron and magnesium deficiency.
• Plants need different amounts of calcium and magnesium at different developmental stages. Hitting the optimal levels of both elements for the current phase is therefore a challenge for every grower.
• You can read about what a potential deficiency of these two elements causes in a separate article below. Of course, an excess of these elements is also harmful to plants.

How to dose Cal-Mag?

• Depending on the specific Cal-Mag product you choose, also follow the dosing charts from the respective manufacturer. We recommend selected products at the end of this article.
• Dosage will always vary depending on the situation you are addressing:
  • When using Cal-Mag to correct existing deficiencies, use 5 ml per 4l of water.
  • For preventive use to avoid deficiency, use 1.5 ml per gallon.
• If the plant is in good condition, stop adding Cal-Mag to the irrigation when the flowering phase peaks. Supplementing calcium and magnesium in later flowering stages would unnecessarily risk harvest quality due to nutrient residues in the buds.
• The frequency and dosage of any Cal-Mag supplement also depend on other factors, such as the growing medium or the water you use for watering (What water do you water your plants with?).
• Diagnose your plants and the growing environment. Use measuring tools, but also your own observation. Look for any signs of calcium and magnesium deficiency. Symptoms of nutrient deficiencies such as calcium and magnesium are described in a separate article HERE.
• The degree or severity of calcium and magnesium deficiency in the plant will influence how often you use Cal-Mag.

Cal-Mag and pH values pH

• Cal-Mag is not used only to supplement calcium and magnesium, as it might seem at first glance.
• Sometimes the issue is a pH imbalance that causes nutrient lockout, resulting in the plant “starving.”
• Remember that:
  • Adding Cal-Mag will not solve problems if you do not stabilize pH.
  • Before concluding that yellowing leaves or other common symptoms are due to a calcium deficiency, always first check pH with a pH meter!
• Does Cal-Mag raise or lower pH? Adding Cal-Mag fertilizer affects pH in different ways depending on the concentration of its components. Fertilizers with higher nitrate nitrogen content, such as Cal-Mag 15:5:15, raise pH, while fertilizers with higher ammoniacal nitrogen like 20:20:20 tend to lower the growing medium’s pH.
• Although adding Cal-Mag can affect substrate pH, you should not use supplements to lower pH. Adding too much calcium can lock out other nutrients, further stressing your plants. We recommend using pH calibration solution. It will help you keep the growing medium in the correct pH range. When you perform control pH measurements of the growing medium, don’t focus only on values at the soil surface—primarily check the pH of the runoff water to determine the pH conditions in the root zone.

Cal-Mag and reverse osmosis (RO)

• RO water is typically more challenging for growers to maintain stable pH values. Cal-Mag in this regard serves as a reliable agent for pH stabilization.
• When using hydro systems in combination with reverse osmosis water, you will use Cal-Mag supplements more often and at higher doses than when using tap water.
• Unlike tap water, which contains varying levels of minerals, reverse osmosis leaves no calcium or magnesium in the water.
• If you are not yet familiar with reverse osmosis, read the separate article we link to below.

Use Cal-Mag at every watering?

• Growers worldwide have found it effective to use Cal-Mag at every watering from rooting through the late growth phase.
• If you use coconut fiber, then you should use Cal-Mag throughout the plant’s growth.
• Even with soil mixes it is advisable to add Cal-Mag, because these products considerably speed up photosynthesis.

Use Cal-Mag during flowering?

• There is a lot of misleading information circulating about adding Cal-Mag during flowering. The truth is that the plant needs the most nutrients precisely during flowering.
• If you fail to sufficiently supplement calcium and magnesium during flowering, you will usually see yellowing leaves and brown spots.
• A quality Cal-Mag ensures that your plants do not stop developing and producing buds.

Cal-Mag and coconut substrates

• When growing plants in coco, you will need more Cal-Mag supplements than when cultivating plants in soil.
• Coconut fiber is known to bind calcium, so it is essential to appropriately supplement Cal-Mag.

If you have any questions about CAL-MAG, we will gladly answer them at the known address info@higarden.cz.

When it comes to Cal-Mag type supplements, we recommend these products:

• Canna Calmag Agent (from 369 Kč)
• BioBizz Calmag (from 159 Kč)
• Atami ATA CalMag (from 89 Kč)
• VitaLink CalMag (from 199 Kč)
• Advanced Nutrients Sensi Cal-Mag Xtra (from 199 Kč)
• Mills Cal-Mag (from 519 Kč)

What to read next?

• Symptoms of important nutrient deficiencies
• Reverse osmosis (RO)
• Avoid the most common mistakes when growing plants