Adequate nutrient supply is essential for the healthy development of cannabis. In cases of deficiency or excess, the plant quickly shows signs – the key is recognizing symptoms and applying the correct intervention.

Everyone knows that cannabis plants, like humans, need proper nutrition for optimal growth and development. If we do not care for our plants appropriately, nutrient deficiencies or excesses can develop. These can cause serious problems that affect plant health and yield. That’s why it is important to review the most common nutrient issues, how to recognize them and how to address them.

But first, it’s worth understanding the difference between two main categories. Cannabis plant nutrients are divided into two groups based on their mobility within the plant.

 

Mobile nutrients

These nutrients can move freely within the plant, mostly from older leaves to newer parts.
If a plant lacks a mobile nutrient, symptoms will first appear on the lower, older leaves, as the plant reallocates nutrients to the new, young growth.

Key mobile nutrients include:

Nitrogen (N)

Phosphorus (P)

Potassium (K)

Magnesium (Mg)

Calcium (Ca)

In these cases, deficiency symptoms first appear on the lower, older leaves.

 

Immobile nutrients

These nutrients cannot move within the plant. If the plant cannot absorb enough of them, deficiency symptoms first show on young, new leaves.
The plant cannot reallocate these nutrients from older leaves.

Key immobile nutrients include:

Zinc (Zn)

Manganese (Mn)

Iron (Fe)

Sulfur (S)

Deficiency symptoms here are first noticeable on young leaves and new growth.

Understanding these differences helps identify whether the issue is a deficiency or an excess. Below, we present common symptoms, their causes and solutions in detail.

 

Nutrient deficiencies

A deficiency occurs when the plant does not receive enough of an essential element. Here are some common deficiencies and their symptoms:

 

Nitrogen (N) deficiency

Symptoms: Yellowing (chlorosis) of lower leaves that gradually spreads upward. Growth slows and leaves become smaller and paler.

Causes: Insufficient nitrogen in the soil or nutrient solution, poor soil quality, or improper pH level.

Solution: Apply a nitrogen-rich fertilizer and check the soil pH to ensure proper nutrient uptake.

Phosphorus (P) deficiency

Symptoms: Plant growth slows down and the leaves become dark green or develop a purplish tint. Lower leaves may discolor and leaf edges can turn brown.

Causes: Low phosphorus levels in the soil, cold soil temperatures or improper pH level.

Solution: Use a phosphorus-rich fertilizer and ensure that the soil temperature and pH level are optimal for phosphorus uptake.

Optimal soil temperature: 18–22°C

Optimal pH range in soil: 6.2 – 7.0 and in hydroponics/coco coir: 5.5 – 6.2

 

Potassium (K) deficiency

Symptoms: The edges and tips of the leaves turn yellow or brown, while the leaf veins remain green. Plants appear weak and show reduced resistance to diseases.

Causes: Insufficient potassium levels in the soil or nutrient solution, overwatering or improper pH levels.

Solution: Apply a magnesium-rich fertilizer and check both your watering practices and soil pH levels.

 

Magnesium (Mg) deficiency

Symptoms: Yellowing between the veins (interveinal chlorosis) of older leaves, while the veins remain green. Leaf edges may turn brown and die off. The overall vitality of the plant decreases.

Causes: Magnesium deficiency often arises due to an excess of potassium, calcium or ammonium in the soil or nutrient solution, which inhibits the uptake of magnesium.

Improper pH levels or heavily leached soil can also be contributing factors.

 

Solution: Use a magnesium-containing nutrient solution, such as Epsom salt (magnesium sulfate). Check the pH level (ideally between 6.0–6.5) to ensure proper nutrient uptake.

 

Calcium (Ca) deficiency

Symptoms: Deformation and necrosis of new shoots and young leaves. Apical growth slows down and the root system is weak and underdeveloped. Leaf edges may show browning and drying.

Causes: Low calcium content in the growing medium, excessive application of potassium or magnesium or overly acidic conditions (low pH), which hinder calcium uptake.

Poor watering habits (such as irregular irrigation) can also contribute.

Solution: Use a nutrient solution containing calcium, such as calcium nitrate. Ensure balanced watering and maintain the pH level between 6.2 and 6.5 to improve nutrient uptake.

 

Manganese (Mn) deficiency

Symptoms: Interveinal chlorosis first appears on young leaves, with the veins remaining green. A fine, mosaic-like pattern develops and discoloration may spread in patches. Leaves can become brittle and growth may be stunted.

 

Causes: Manganese deficiency is often caused by excessively high pH levels (alkaline medium) or by excess iron, calcium or copper, which inhibit manganese uptake. It is common in hydroponic systems or highly calcareous soils.

Solution: Lower the pH value to between 5.5 and 6.2 to improve manganese availability. Use a foliar fertilizer containing manganese or a chelated micronutrient mix. For faster results, foliar spraying can also be effective.

Proper watering practice means watering when the top 2–3 cm layer of soil has dried out, but the deeper layers are not yet completely dry. Ideally, the soil should be evenly moist but not overly wet.

Avoid soil that is constantly wet or completely dried out.

 

Nutrient excesses

Excessive nutrient intake can also be harmful to cannabis plants. Below are some common nutrient excesses and their effects.

Nitrogen (N) excess

Symptoms: Excessively dark green leaves, lush foliage and delayed flowering. Leaf tips may burn and curl downward, appearing claw-like. In this state, the plant becomes more susceptible to pests and diseases.

Causes: Excessive nitrogen input from fertilizers or the soil.

Solution: Reduce the use of nitrogen-rich fertilizers and flush the soil with clean water to remove excess nutrients. By clean water, we mean nutrient-free water with a properly adjusted pH level.

 

Phosphorus (P) excess

Symptoms: Excess phosphorus can inhibit the uptake of other nutrients, such as iron and zinc, leading to secondary deficiency symptoms.

Causes: Overuse of phosphorus-rich fertilizers.

Solution: Reduce the use of phosphorus-rich fertilizers and, if necessary, flush the soil using the method described above.

 

Potassium (K) excess

Symptoms: Weak stems and brittle leaves appear, growth slows down and leaf burn is visible along the edges. Potassium excess hinders the uptake of other nutrients such as magnesium and calcium, leading to deficiencies in those elements.

Causes: Overuse of fertilizers, poor nutrient ratios in the soil or nutrient solution, salt buildup in the soil or hydroponic system and improper pH levels.

Solution: The first and most important step is to flush the soil with clean, pH-adjusted water.

 

Nutrient lockout

Despite the presence of nutrients in the soil or nutrient solution, the cannabis plant may still be unable to absorb them properly. This can be a serious issue, as the plant may show signs of nutrient deficiency even when adequate nutrients are available.

 

What can cause nutrient lockout?

1. Incorrect pH value

Cannabis plants can only absorb nutrients effectively within a specific pH range. Therefore, it is very important to always maintain the optimal range:

• In soil: 6.0 - 7.0
• In hydroponics/coco coir: 5.5 - 6.5

It is also essential to consider the pH recommendations provided by the specific nutrient brand. If the pH is too high or too low, certain nutrients (e.g., iron, calcium, magnesium) become unavailable to the plant, causing deficiency symptoms.

 

2. Excessive nutrient intake (salt buildup)

Overuse of fertilizers or nutrient solutions can lead to the accumulation of mineral salts in the soil or root zone, which blocks the uptake of nutrients. This is especially common in hydroponic systems and coco-based media where dissolved salts can concentrate more rapidly.

 

3. Excess calcium, phosphorus or potassium

These elements can interfere with the uptake of others:

Too much calcium can inhibit magnesium and iron absorption.

Too much phosphorus can block zinc and copper uptake.

Too much potassium can restrict calcium and magnesium uptake.

 

4. Improper watering practices

Overwatering can reduce oxygen levels in the soil, leading to root damage and nutrient uptake issues.

Underwatering, on the other hand, can prevent nutrients from dissolving properly, making it difficult or impossible for the roots to absorb them.

 

5. Root damage or diseases

Fungal infections (such as root rot) or mechanical injuries can impair the roots' ability to absorb nutrients.

Poor quality soil or overly compacted growing media can also restrict proper root development, laying the groundwork for nutrient lockout.

 

Preventing and managing nutrient problems

 

Soil and pH monitoring: Regularly test the soil's pH and nutrient levels to ensure optimal growing conditions. The simplest method is to use a pH meter. If the pH is outside the optimal range, adjust it using pH up or pH down solutions.

Use three times the volume of pH-adjusted water relative to the growing medium. For example, a 10-liter pot requires about 30 liters of water to be properly flushed.

Proper fertilization: Use balanced nutrient formulas and follow the manufacturer's dosage recommendations. Do not over-fertilize your plants.

If you detect a problem, flush the soil or growing medium with clean, pH-adjusted water to remove any accumulated salts.

Watering practices: Avoid overwatering or underwatering, as both can affect nutrient uptake. Water when the top 2–3 cm of the soil has dried out, but the deeper layers are still slightly moist.

Plant observation: Regularly observe your plants to detect early symptoms and intervene in time to resolve any issues.

Loosen the soil with perlite or coco coir to promote easier root development.

If growing in hydroponics or coco coir, use a calcium-magnesium supplement to prevent deficiencies.

Maintaining proper nutrient balance is essential to preserving cannabis plant health. The guideline chart provided by your selected nutrient brand can assist in this process, although values may vary between brands.

Avoid excessively warm or cold root zones, as they can also hinder nutrient uptake. It is important to monitor the temperature of both the root zone and the irrigation water.

Nutrient deficiencies, excesses or lockout are serious issues in cannabis cultivation, but with proper pH management, balanced nutrition and a consistent watering routine, they can be prevented and corrected. If your plants show signs of deficiency despite proper feeding, check the pH and possible salt buildup using an EC meter.