Calcium
Calcium uptake by the plant is passive and does not require energy input. Calcium mobility in the plant takes places mainly in the xylem, together with water. Therefore calcium uptake is directly related to the plant transpiration rate.
Conditions of high humidity, cold and a low transpiration rates may result in calcium deficiency. Salinity buildup might also cause calcium deficiency because it decreases the water uptake by the plant.
Often your calcium deficiency may be caused by too high humidity or too low temps, worth adjusting these to optimun growing conditions before adding extra calcium.
Calcium forms insoluble compounds with other elements in soil, such as phosphorous. Calcium that is in the form of an insoluble compound is not available to plants. Ever wondered why your plant looks calcium deficient and dropped a lot of fan leaves at the end of flowering when using fertilizers with high phosphorous?
Calcium is a positivley charged ion and hence when the plant spits out positivly charged ions from the roots in exchange for uptaking positively charged ions from the soil it needs to be balanced against the levels of magnesium available to the plant. Whatever ratios of calcium to magnesium available in the soil will result in the same ratio of uptake from the plant.
Calcium competes with other positively charged ions, such as sodium (Na+), potassium (K+), and magnesium (Mg+2). Applying too much of these positively charged ions might decrease calcium uptake by plants.
Put basically you need a calcium magnesium ratio of about 3 parts calcium to every one part magnesium in the soil which is what a marijuan plant generally prefers. This can sometimes rise as high as 5:1 calcium to magnesium.
Calcium deficiency is usually caused due to low calcium availability or due to water stress which results in low transpiration rates. The symptoms of calcium deficiency include curling of young leaves or shoots. Leaf curling or early calcium deficiency in seedlings or young plants can easily show when the leaf starts to curl at the edges inwards from the base of the leaf near the stem up to the leaf tip. I believe calcium promotes proper cell elongation which is a factor of the leaf rolling. Leaf cupping may deform, wrinkle or curl leaves as they grow.
Schorching and spotting of yellowing leaves as in the above chart always accompanied by purple leaf stems and leaf veins are again a dead give away of calcium deficiency.
Calcium is an alkaline ion and hence found in soils with higher ph, it will work against the acidic ions hence buffering the soil and helping to prevent soil acidity.
