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Many cannabis afflictions seem to get blamed on a cal-mag deficiency. While cannabis depends on many nutrients for optimal health, calcium and magnesium certainly play a fundamental role. You've probably noticed that they almost always appear as a pair in plant supplements. Find out why they work so well together, and how they help plants thrive.
You’ve come across cal-mag supplements while browsing the shelves at gardening shops and weed-centric websites. But why do these elements always show up as a pair? Manufacturers typically include the two in a specific ratio that prevents either of them from becoming locked out of plant roots.
Below, you’ll learn more about why cal-mag is an excellent duo, what they do for cannabis plants, and what the signs of cal-mag deficiencies look like.
Contents:
Cannabis plants require certain nutrients in order to fulfil key physiological functions and thrive. These substances are typically divided into two broad categories: macronutrients and micronutrients. As their names suggest, macronutrients are required in larger amounts while micronutrients are needed in only trace amounts.
The primary macronutrients required by cannabis are:
The micronutrients needed by cannabis are:
So, where do calcium and magnesium fit into the picture? These two elements are known as secondary macronutrients. They aren’t required in the same quantities as nitrogen, phosphorus, and potassium, but plants are more hungry for them than all of the micronutrients. Find out exactly how they help to direct plant development below.
As an essential secondary macronutrient, calcium plays several key roles in plant health and growth. These functions include:
Alongside calcium, magnesium also facilitates vital processes that enable plants to grow properly and create energy. These functions include:
Germination: Mg is a component of pectic substances essential for the stability of the cell structure, as well as phytin. Phytin, a low-energy phosphorus accumulator (phytin phosphorus), is of great significance for seed germination.
Cannabis plants first uptake calcium and magnesium through the process of cation exchange[1]. Because both elements are cations, they feature a positive electric charge. In the soil, they cling to clay and organic matter particles that possess a net negative electric charge. In order to dislodge calcium and magnesium, plants pump hydrogen cations into the soil. Because they have a stronger positive charge, they compete with both elements at negatively charged particles and liberate them. From here, plant roots absorb the elements through diffusion.
Once inside, they are transported through the xylem—the vascular network responsible for moving water and dissolved nutrients through plants. They are then deposited where they are needed in order to assist in cellular processes. However, the story doesn’t end here. Magnesium and calcium differ in their mobility. As a mobile nutrient, plants are able to move magnesium around[2] the plant from older tissues to newer tissues. This comes in handy particularly for new tissues when magnesium levels are low. In contrast, plants are unable to move immobile nutrients such as calcium; as such, deficiencies manifest in new growth.
When shopping for plant nutrients, you’ve probably noticed that calcium and magnesium are often paired together in cal-mag supplements. There are several reasons for this. First, both elements support plants in similar ways; applying them together gives rise to a synergistic relationship. Second, manufacturers include both together because growers can quickly run into trouble when applying them separately.
Adding too much magnesium or calcium can obstruct the optimal uptake of either nutrient. Therefore, getting too heavy-handed with either in isolation can quickly result in deficiencies. Cal-mag supplements provide these nutrients in an ideal ratio of between 3:1–4:1 calcium to magnesium, thereby removing the risk of over-administering either element.
Before applying cal-mag supplements to the soil, you need to know whether your growing medium requires it. If you’re growing outdoors, a simple soil test will help you determine its nutrient composition. Furthermore, soils with higher levels of clay and organic matter provide higher levels of these elements thanks to superior cation exchange capacity.
If you decide to apply cal-mag to weed plants growing in a container or directly in the ground, it’ll help to take a pH reading first. Your plants might seem starved of these nutrients, but adequate amounts may already exist in the soil. Oftentimes, a pH level that is too high or too low is the culprit, preventing the roots from absorbing available calcium and magnesium. Your weed specimens will have an easier time taking up calcium at a pH of 6.0–7.0, and magnesium at 6.5–7.5. Even if you find you need to add cal-mag, make sure to dial in your pH to optimise absorption.
Hydroponic growing necessitates that growers apply all nutrients themselves; therefore, it's necessary to add cal-mag from the get-go. In this scenario, calcium and magnesium form part of a complete nutrient regimen alongside all of the other macronutrients and micronutrients. Add calcium and magnesium at a ratio of 3:1–4:1 and maintain a pH of around 6.0.
Why Is Cal-Mag Deficiency So Common in Weed Plants?
If you frequent cannabis growing forums, you’re likely under the impression that calcium and magnesium deficiency is an epidemic. Almost every picture of a discoloured leaf and withering plant gets a reply of “just hit it with cal-mag, bro”. While this deficiency certainly causes issues in many growing operations, in some circumstances, adding it fails to address the root cause of the issue.
Calcium and magnesium deficiencies certainly exist in cannabis, but this hasn’t stopped some growers from taking the hard-line position that it doesn’t. Rather than blaming a lack of cal-mag in soil, they blame environmental variables instead, including poor pH management and an excessive application of other nutrients. If you’re sure that you’ve dialled in your pH and haven’t swamped your plants with potassium, they’ll benefit from a dose of cal-mag.
So, what exactly does a lack of calcium and magnesium look like? Whether your growing medium genuinely lacks these elements or your pH levels are to blame, you can expect similar symptoms. Check out what calcium deficiency and magnesium deficiency look like during each stage of the growing cycle.
Plants are extremely vulnerable during the seedling stage. Any sort of deficiency or disease at this time can send plants off on a negative trajectory from the start. The signs of a cal-mag deficiency during the seedling stage include:
Cannabis plants put all of their energy into photosynthesising and packing on size during the vegetative phase. A lack of cal-mag during this time can inhibit this process, leading to underwhelming results down the line. Look out for these signs:
Because calcium and magnesium assist in protein synthesis and energy capture, they are vital during flowering formation. A deficiency during bloom with give rise to the following symptoms:
You just upgraded your cannabis cultivation knowledge! You’re now aware of why calcium and magnesium almost always occur as a pair in plant supplements. You also know why these elements are so important for plant health, and what the signs of deficiencies look like.
So, before you start pouring cal-mag onto your weed plants, remember to make sure that your pH is within the proper range, and that you’re not adding too much potassium to your growing medium. If everything checks out, then add cal-mag, and watch your plants bounce back in style.