Calcium also plays a vital role as a secondary messenger helping to regulate cellular functions and assisting in general plant functions like nutrient uptake. Within a plant’s rhizosphere, calcium stimulates the protein channels that uptake nutrients. If there is not enough calcium present, this process will not function properly and nutrient uptake is slowed down.
Calcium works very similarly to the hormones that regulate various cell functions. Calcium is thought to help the development of heat shock proteins that make it possible for a plant to tolerate stresses caused by excess heat. The stomatal function of a plant’s leaves are improved with sufficient calcium levels. This also directly impacts a plant’s ability to mitigate stress.
Like most micronutrient deficiencies, calcium deficiencies will show up in the new growth (the top) of the plant. This is because calcium moves rather slowly within the plant so its concentration is higher in the roots and in older growth (leaves toward the bottom). One dead giveaway of insufficient calcium levels is hollow stems. Most of the time this is identified after harvesting, but throughout the plant’s life you can lightly pinch a stalk or stem to feel if it is hollow or if it has a nice woody core.
Many fertilizer formulations do not provide enough calcium for growing medical marijuana. This is either because they expect the grower’s water source to contain the calcium or because it is assumed the grower will be supplementing calcium specifically. I like to use Sensi Cal by Advanced Nutrients for my calcium supplementation. Sensi Cal is the only calcium and magnesium formula that has two formulations, one for the vegetative stage and one for the blooming stage. Most companies expect growers to use the same formula for both stages of growth. Experienced medical marijuana growers know that their plants require much different nutrient compositions for different stages of growth. Advanced Nutrients is the only company that has rectified this problem by designing a calcium supplement made specifically for each stage.
The fastest way to correct a calcium deficiency is a foliar treatment of calcium. As previously stated, calcium moves very slowly within the plant, so supplying calcium directly to the leaves treats the problem quickly. I always recommend using some sort of calcium supplement in conjunction with a balanced fertilizer program.
It is always much easier to supply calcium to the plant before a deficiency is created. Proper calcium levels will result in stronger stems and branches, which will be needed to hold up the massive buds produced by healthy medical marijuana plants.