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Nutrient Deficiencies

Healthy cannabis plants yield a lot. Healthy cuttings (or seeds), good air circulation, ventilation, clean water, and proper fertiliser management should all be studied and developed properly to generate healthy plants. Absent one of the prerequisites, plants do not thrive.

Plants need around 18 mineral nutrients. In an ideal environment, most crop plants’ yields rise linearly with nutrient absorption. Toxic zones for plants are defined by the link between yield and nutrient content of plant tissue. 

Yield increases dramatically at first and then plateaus after attaining nutritional saturation in plant tissue. Before the hazardous zone, there is a broad sufficient zone where additional nutrients do not boost yield. In spite of the fact that this zone is difficult to see without worrying signs, farmers continue to waste nutrients by applying extra plant fertilisers when it’s doing more harm than good.

In an ideal setting, we would provide just enough nutrients so plants show no signs of nutrient insufficiency. However, in the actual world, it is challenging due to various variables such as plant species, maturity stage, and environmental influences. Managing optimal nutrition content is a constant process of trial and error.

The mobility of minerals is used to diagnose nutrient insufficiency symptoms. If the element is mobile, it can move freely around the plant as needed. Because the plant will carry the elements to nourish its younger tissue, we detect symptoms on older or lower leaves initially.

If the element is immobile, the deficiency symptoms appear first in the newer leaves or tissues.

Mobile elements include nitrogen, phosphorus, potassium, magnesium, molybdenum, and nickel (Ni).

Sulfur, calcium, iron, manganese, zinc, boron, and copper are immobile.

Immobile vs Mobile Elements

Macronutrients (N, P, K, Ca, Mg, and S) are the most commonly insufficient nutrients. Other micronutrients (Fe, Mn, Cu, Zn, and B) can cause aberrant growth.

Deficiency in nitrogen (N) causes yellowing of older leaves towards the plant’s base. If left untreated, the leaves become yellow and fall off the plants.

Unlike a nitrogen deficit, phosphorus deficiency does not cause yellowing of the leaves. Rather, the margins of the leaves turn dark green or purple. The petioles turn red-purple.

Potassium deficiency: leaf edges and tips yellow and red, older leaves curl and crumple. Plants become narrow and fragile as stem branches grow.

Deficiency of calcium causes yellow-brown uneven patches on immature leaf edges. Young leaves may also appear curled.

Magnesium (Mg) shortage causes yellowing between the veins while the veins remain green. Older leaves have irregular yellow-brown patches, and eventually curl and fall.

Sulfur (S) insufficiency causes yellowing of young leaves and tiny plants. Unlike nitrogen deficit, it affects the young leaves.

Deficiency of Boron (B) causes yellow-brown necrosis between leaf veins and terminal buds. Stem and shoot growth is aberrant and burnt. Leaves may thicken and crack.

Iron (Fe) deficiency: young leaves yellow between veins. Iron shortage (an immobile element) starts with young leaves, whereas magnesium insufficiency starts with older leaves.

Copper (Cu) deficiency: twisted and malformed young leaves Leaf margins and tips turn dark green with necrotic patches.

Symptoms of manganese insufficiency include yellowing between the veins and tiny necrotic patches. It is rare for cannabis plants.

Deficiency in zinc causes tiny, grouped new shoots and leaves. Young leaf tips and margins begin to yellow between veins. Internode spacing (the distance between two nodes on a stem) becomes narrow.

Check the pH of the growth media (soil, coco…) and the water solution before diagnosing nutritional deficit. It is important to know the pH of nutritional solutions. Even with all the nutrients present in the water, the plant roots cannot absorb nutrition when the pH is out of range. We can determine nutritional deficits by first measuring the pH range. See “Water EC and pH” for more on pH and nutrient management.

Also, keep in mind that some plant pests or environmental stress might create identical symptoms, so always assess the whole picture. Is the temperature right? Do flying insects feed on plants? Even when there is plenty of nourishment, plants cannot thrive.