7 most common cannabis deficiencies and how to fix them

Cannabis plants are nutrient-hungry—but not just for any nutrients, and not at every stage of growth. When something goes wrong in feeding, the plant usually shows it through leaf discolouration, curling, spotting, or stunted growth. Recognising deficiencies early is key to saving your harvest and unlocking the plant’s full genetic potential.

This guide covers the most common cannabis deficiencies, how to spot the warning signs, what causes them, and how to correct each issue quickly. Whether you’re growing autoflowers in a tent or elite feminised seeds from Mavericks Genetics, mastering deficiency diagnosis is a core skill for every grower.

Why nutrient deficiencies happen in cannabis

Not all deficiencies come from underfeeding. In fact, many are caused by:

• pH imbalances that block nutrient uptake

• Overwatering or underwatering

• Poor-quality soil or depleted coco/hydro systems

• Root damage or pest issues

• Salt buildup leading to nutrient lockout

That’s why the first step in correcting any deficiency is always testing your pH and reviewing your feeding routine.

Nitrogen deficiency

Symptoms:

• Yellowing of lower, older leaves

• Leaves fall off if left untreated

• Pale plant colour and weak overall growth

When it happens:
Early to mid-vegetative stage

Fix:

• Add nitrogen-rich nutrients (especially during veg)

• Check runoff pH: ideal range is 6.0–6.5 in soil, 5.5–6.1 in hydro

• Avoid overcorrecting—too much nitrogen can cause toxicity

Phosphorus deficiency

Symptoms:

• Dark green or purplish leaves

• Stunted growth and weak stems

• Red or purple stem colouring

• Bud development slows or stops during flowering

When it happens:
Late veg into early flowering

Fix:

• Apply a bloom booster high in phosphorus

• Flush and reset nutrients if pH is too low

• Ideal pH: 6.2–6.5 in soil, 5.8–6.2 in hydro

Potassium deficiency

Symptoms:

• Burnt or curled leaf tips

• Yellow or brown spots on older leaves

• Small, underdeveloped buds

When it happens:
Early to mid-flowering stage

Fix:

• Use potassium-rich bloom supplements

• Ensure pH is above 6.0 to allow uptake

• Consider kelp or seaweed-based additives

Calcium deficiency

Symptoms:

• Brown spotting on leaves

• Crispy edges or malformed growth

• Slowed root expansion

When it happens:
Throughout the entire grow, especially when using soft or RO water

Fix:

• Add a Cal-Mag supplement

• Maintain soil pH between 6.2 and 6.5

• Avoid waterlogging—damp soil reduces calcium absorption

Magnesium deficiency

Symptoms:

• Yellowing between leaf veins (interveinal chlorosis)

• Usually starts on older, lower leaves

• Leaf edges curl upwards

When it happens:
From vegetative into early flowering

Fix:

• Use Epsom salts (1 teaspoon per gallon) or Cal-Mag products

• Slightly raise pH if it’s too acidic

• Be patient—magnesium takes time to show visible results

Iron deficiency

Symptoms:

• New leaves turn pale yellow or white

• Veins remain green

• Stems may look thin or weak

When it happens:
Most often in early veg or shortly after transplanting

Fix:

• Add iron chelates (e.g. Fe-EDDHA)

• Adjust pH to 6.0–6.2 for optimal absorption

• Avoid cold roots and overwatering

Zinc deficiency

Symptoms:

• Deformed or discoloured leaf tips

• New growth appears small and thin

• Yellowing between veins at the leaf tips

When it happens:
Primarily during early veg and early flower

Fix:

• Apply a micronutrient supplement containing zinc

• Maintain correct pH levels

• Improve aeration around the roots to prevent compaction

Deficiency chart for quick reference

How to prevent cannabis deficiencies

• Use high-quality nutrients formulated for cannabis

• Regularly check pH levels, especially in runoff

• Avoid overfeeding and overwatering

• Keep a detailed grow journal with feed schedules

• Flush periodically with clean water to remove excess salts

Pro tip: The better the genetics, the better the nutrient efficiency. At Mavericks Genetics, our feminised strains are bred for resilience, strength, and nutrient uptake—helping your plants thrive with fewer issues.

Final thoughts: Know your leaves, save your harvest

Most cannabis deficiencies begin with subtle signs in the leaves. If you learn to spot those signs and understand which nutrients are lacking, you can fix the problem before it affects your buds.

Whether you’re growing in soil, coco, or hydro, healthy plants come from balanced nutrition and close observation.

Looking for seeds that can handle tough grow conditions?
Explore the full range at Mavericks Genetics and discover elite feminised strains bred to flourish—even when the environment pushes back.