Here’s a problem many of us have encountered at least once in our cannabis gardens during bloom phase: Lower leaves developing reddish-brown spots, leaf tips curling down, declining plant health and stalled bud growth. Side stalks with heavy buds tend to crack and fall because stalks are unusually brittle and weak. Talk to enough professional growers and you’ll begin to hear suggestions that these problems come from a deficiency of calcium, magnesium, or of both.
If you see cannabis leaves that look like the above photo, and there are no sucking insects on the underside of the leaf corresponding to the leaf damage you see on the top side, then you may well have a calcium and magnesium deficiency in your crops.
Calcium and magnesium deficiencies can be a common occurrence in hydroponic grow setups, but can also show up in soil grows. These deficiencies often arise because the root-zone media or nutrient solution are improperly configured by the grower. If you’re using well water or municipal water instead of reverse osmosis water, your H2O may contain elements that interfere with the absorption of other nutrient elements or negatively affect root-zone pH, resulting in such deficiencies.
In many cannabis gardens, the root zone becomes oversaturated with nutrients or drifts to the wrong pH, blocking absorption of calcium or magnesium. Some soils also have physical or chemical structural issues that block calcium and magnesium absorption, while coco coir needs its own specialized hydroponic nutrients feed program. Root-zone temperatures that are too warm or too cold also interfere with the uptake of nutrient elements.
Calcium or magnesium deficiencies will most likely be encountered in bloom phase, especially when using intense grow lights such as professional LEDs and double-ended HIDs. Intense lighting stimulates accelerated photosynthesis that increases your plants’ need for calcium and magnesium.
Symptoms, Signs Of Calcium And Magnesium Deficiencies In Cannabis
Deficiencies of either of these key nutrients can create unhealthy, vulnerable plants with slow or stunted growth, weak stems and stalks, and smaller, less-potent yields. For example, cannabis research indicates that drought, extreme heat or cold, wind, pests, diseases and other stressors induce cannabis to defend itself by transferring calcium to affected areas of the plant. Calcium deficiency cripples this defensive response, making plants more susceptible to damage from garden attackers, like spider mites.
And just like calcium is an integral component of healthy human skeletons, it’s also integral to plant cell walls and membranes. Calcium deficiency weakens plants structurally, reducing their ability to build healthy new tissue, including roots, stalks, stems and buds.
Magnesium deficiencies often occur in tandem with calcium deficiencies. Magnesium is essential for the primary engine of all plant life: photosynthesis. It’s a central element in chlorophyll, the substance that allows plants the ability to absorb light and turn it into energy to power their metabolism. Magnesium is key to metabolic processes that assist your plants in nutrient absorption and processing, utilization of carbon dioxide, activating enzymes, and creating proteins and carbohydrates essential to floral and seed production.
Although it’s difficult to definitively diagnose deficiencies based on leaf appearance alone, the following indicators taken together may indicate a calcium deficit:
- Your cannabis plants grow slowly and fail to reach normal height.
- Leaves initially turn dark green.
- Leaf edges may turn brown or dry out. The same can happen to leaf tips, which may also exhibit slight downward curling.
- Root growth is slow. Root mass is small. Calcium-deficient roots suffer increased risk of diseases such as root rot, and are less efficient at intaking nutrients, oxygen and water.
- In late-stage calcium deficiency, rust-colored spots or larger-sized blotches appear on leaves. On the undersides, blotches appear to be red, pale, transparent or white. These problems start on younger leaves and later appear on older leaves.
- Stems and stalks are weak and brittle, leading to branches that break if heavy buds form on them.
Signs of magnesium deficiency somewhat overlap with but aren’t always identical to those of calcium deficiency. These signs include:
- Growing shoots that are spindly, narrower, weaker than normal. Yellowing of new growth may also be present.
- Root growth is slower and root mass is smaller than normal.
- Necrotic (dark, dead, reddish-brown) spots appear on leaf margins. Parts of the leaf begin to die off.
- Yellowing between leaf veins, with the central area of the leaf still green.
- Magnesium deficiency shows first in older, larger leaves, usually the ones that are lower on the plant. If the deficiency isn’t corrected, leaves may die and fall off the plant.
How To Fix Calcium And Magnesium Deficiencies in Cannabis Plants
Fixing calcium and magnesium deficiencies isn’t as easy as cannabis growers have been led to believe. The common tactic is to add calcium and magnesium into the root zone or as a foliar spray. This could work, depending on what’s causing the deficiencies, but can also create more nutrient absorption problems than it solves. Here’s a better program for dealing with a suspected calcium or magnesium deficiency:
- First, foliar spray a cal-mag supplement mixed with a surfactant and B-52 vitamin booster at 240 parts per million and 5.7 pH.
- Flush the root zone using reverse osmosis water and a full dose of Flawless Finish flushing formula, with a pH of 5.9 for the flushing water.
- After the root zone has dried out from the flush, feed the plants a moderate dose of quality base nutrients, such as Connoisseur or Sensi. I recommend these base nutrients over all others because they automatically balance pH, they’re made specifically for cannabis, and they contain the correct ratios and amounts of all essential elements.
- Wait at least five days to see the effects of the flushing by examining leaf color and health, along with overall plant growth. The leaves that were already damaged won’t heal, but newer leaves will look better and growth rate and overall vigor should improve.
- If you still suspect calcium/magnesium deficiencies, root feed a cal-mag formula made for cannabis, following the manufacturer’s instructions. In most cases, you wouldn’t do the cal-mag root feed supplementation for more than once a week, and only for two to three weeks maximum.
Use The Only Cal-Mag Supplement Made For Cannabis
There are many cal-mag supplements on the market, most of which are generic and ineffective. Some are sold at discount stores, intended for fighting blossom-end rot in tomatoes, while others are available at hydroponic grow stores.
Sensi Cal-Mag Xtra is made specifically to feed cannabis plants and contains stable, absorbable forms of calcium and magnesium in the correct ratios. It also contains chelated iron — often undersupplied or marginally bioavailable in hydroponic root zones — which assists in calcium and magnesium absorption and utilization.
It’s not just extra calcium, magnesium and iron that Sensi Cal-Mag Xtra boasts. There is also the bioactive L-form of all 20 essential amino acids that plants use for metabolism, protein formation and bud building. These aminos work in synergy with calcium and magnesium to assist plants’ recovery from deficiency, leading to a yield-boosting restoration of maximum function.
Be aware that solving cannabis nutrient deficiencies can be endlessly frustrating. Many growers panic when they see leaf problems or glitches with plant growth, and subsequently start dumping cal-mag supplements and other materials onto their crops, ultimately making the problems much worse. Be very cautious and attentive as you try to fix what you believe are nutrient problems.
By following our program, you’ll have the best chance of fixing calcium and magnesium deficiencies in your crops so they return to optimal performance that gives you heavy harvests of the most potent buds.