Calcium isn’t as well-known as other macronutrients like nitrogen, phosphorus, and potassium, but it’s just as vital to plant health. It helps marijuana plants create and maintain strong cell walls, stalks, branches, and stems, assists in root system development and potassium uptake, and helps plants develop resilience to stressors like heat. Without sufficient calcium, marijuana plants won’t be able to grow and thrive.
Outdoor plants are less prone to calcium deficiency than plants grown indoors in hydroponic systems or containers. However, outdoor growers are not completely immune to this problem. If they are growing in or around pine forests, the soil may be more acidic, which makes plants more prone to calcium deficiency. Regardless of what kind of system they use, all growers should familiarize themselves with the symptoms of calcium deficiency, so they know when to take action to fix it.
Calcium is considered a semi-mobile nutrient. While the symptoms of calcium deficiency first become apparent in new growth, if left unchecked, they can move throughout the rest of the plant. These symptoms include a darkening of the leaves, spots of light brown necrosis, mottling, curling tips, distortion of new leaves, and leaf death.
Calcium can also cause young shoots to become discolored, turning purple or yellow, and cause mature stems to decay from the inside. These damaged stems and shoots will be weak and more easily broken, which can be problematic for both indoor and outdoor growers.
Plants afflicted with calcium deficiency will experience stunted growth. If the deficiency continues into the flowering stage, bud development may also be stunted and the buds may not fully develop. Beneath the ground or hydroponic medium, calcium deficiency leaves roots prone to bacterial disease and slimy root rot and can cause die-offs.
It’s common for calcium deficiencies to occur in tandem with other mineral and micronutrient deficiencies. Any time growers notice a calcium deficiency, they should also check for signs of magnesium and iron deficiencies.
Some strains of marijuana, and even some individual plants within the same strain, are more prone to calcium deficiency than others. Most growers aren’t willing to restrict themselves to a small number of uniquely hardy plants, though. Thankfully, they don’t have to. Buying high-quality seeds sets up plants of any strain for success, and growers can take other steps to increase calcium production in plants experiencing deficiencies.
The best way to deal with a calcium deficiency is to take preventative measures to stop it from occurring, to begin with. That means balancing the pH and working in soil amendments like dolomitic lime or garden lime prior to the growing season.
Growers who use distilled water may have more trouble with calcium deficiency than those who use tap water, which is typically richer in this trace mineral. Those who use LED lights may also find that their plants are more prone to calcium deficiency since LEDs produce a smaller spectrum of light that does not contain all the wavelengths plants need to generate calcium naturally.
Thankfully, those who are growing in sub-optimal conditions and haven’t had the chance to take preventative measures aren’t out of luck. It’s relatively easy to fix a calcium deficiency in soil-based grows.
The first step is to ensure that the soil pH is between 6.2 and 7.0. Both dolomitic and garden lime can help to stabilize soil pH, so they’re a great tool for growers dealing with both pH imbalance and calcium deficiency. If the soil pH is substantially off, growers should flush the soil before applying new nutrients.
Aside from lime, the most popular amendment for dealing with calcium deficiency is calcium nitrate (CaNO3). This compound is water soluble, so it’s easily absorbed by the roots. Growers should only use it during the vegetative stage, though, as it also contains nitrogen and can create problems with nutrient burns in flowering plants. Other useful products include liquid lime and liquid calcium, both of which can be applied directly to the soil during the seedling and vegetative stages.
Hydroponically grown marijuana plants are even more susceptible to calcium deficiency than those grown indoors in soil-based container systems. This is particularly true of systems that use distilled water or softened tap water. Since most tap water naturally contains some calcium, hydroponic nutrient solutions don’t usually have high concentrations of this mineral, which can exacerbate the problem.
Check the TDS of the nutrient solution. If it has more than 150 ppm of dissolved solids, there should be enough calcium in the mix to avoid problems with deficiency. If the reading is below 150 ppm, hydroponic growers may want to add both calcium and magnesium to the system.
Before applying calcium, magnesium, and other nutrients, hydroponic growers should flush their systems and check the pH of their nutrient solutions. The optimal pH range for hydroponic grows is 6.2 to 6.5, so make sure the water used for the flush falls within this range and test it again after adding other liquid nutrients. Some of them can alter the system’s pH values.
The best products for addressing calcium deficiency in hydroponic systems are liquid calcium and liquid lime. Use around one teaspoon of lime per gallon of water. The plant’s roots will absorb it quickly, and they should start to recover almost immediately.
As noted above, calcium deficiency is much less common in outdoor grows. However, there are several factors that can increase growers’ chances of finding calcium-deficient plants in their gardens.
Growers working with excessively acidic soil almost always have more problems with calcium deficiency. The best solution is to infuse calcium directly into the soil to help balance the pH. For outdoor grows, the optimal pH range is 6.0 to 6.5. Outdoor growers have a little more leeway than hydroponic growers when it comes to pH range, but those are good numbers to aim for.
The best soil amendments for adding calcium to acidic soils are dolomitic lime, garden lime, ground-up eggshells, seashells, and fish bones. These substances provide long-lasting relief from calcium deficiency and pH imbalance.
Some outdoor growers also apply either gypsum or calcium sulfate to their soils. Using these amendments requires a little more finesse, though. Adding gypsum to soil with a pH of 5.5 or less can actually increase the plant’s risk of developing aluminum toxicity, so growers should always test their soil pH in advance.
The flip side of using gypsum as an amendment is that it doesn’t substantially alter the soil pH. As long as the soil pH is already in an optimal range, it’s a great way to make some extra calcium available to the plants. Combine it with one or more of the slower-acting amendments listed above for maximum long-term effects.
Marijuana plants need sufficient calcium to grow and thrive, but growers shouldn’t go overboard when applying soil amendments. An excess of calcium can cause nutrient lockouts in soil-based grows. More specifically, excess calcium can cause plant’s roots to stop sufficient uptake of potassium, magnesium, manganese, and iron.
The easiest way to tell if there’s an excess of calcium in the soil is to look for signs that other nutrients are deficient. Symptoms of potassium deficiency include discoloration and death of the plant’s lower leaves, burnt leaf tips, and slowed growth.
The signs of magnesium deficiency are also most readily apparent near the bottom of the plants. The leaves will yellow and become weak, and their outer margins may become brittle and break off. Other signs of magnesium deficiency include blanched shoots and discolored stems and petioles.
Manganese deficiency typically affects new growth first, not mature leaves. It causes leaf yellowing and necrosis, as plants need magnesium to produce the chlorophyll that colors the leaves effectively.
Zinc deficiency causes the veins of mature leaves to turn yellow and creates twisted foliage. Zinc-deficient plants often lose their color and, in severe cases, begin to wilt, or even die.
Since excess calcium prevents the uptake of zinc, manganese, magnesium, and potassium, adding more of these macro- and micronutrients to the soil won’t do anything. Instead, growers should flush their soil thoroughly and reapply more balanced nutrient mixtures that contain more reasonable amounts of calcium along with other essential nutrients. Flushing the plants will also give growers the chance to balance the soil pH, which will improve nutrient absorption.
It takes more than just nitrogen, phosphorous, and potassium to grow healthy, hardy marijuana plants. Without sufficient calcium, the plant’s cell walls, stalks, branches, and roots can suffer, but it’s important to get calcium levels right, as an excess of this vital nutrient can cause an entirely new set of problems. All growers should buy high-quality seeds and pay careful attention to their plants throughout their life cycles to ensure that they are getting enough calcium, but also a full, balanced mix of nutrients appropriate to their current stage of life.