Cannabis Nutrient Deficiency Schedule: Signs by Week

Cannabis nutrient deficiencies follow a schedule tied to growth stage. Nitrogen and magnesium signs appear at week 3 to 4 of veg. Phosphorus and potassium signs appear at week 3 to 6 of flower. Calcium, iron, and boron signs appear on new growth at any week when pH drifts.

Mobile vs immobile nutrients

Mobile nutrients move from old leaves to new growth. Nitrogen, phosphorus, potassium, and magnesium are mobile. A shortage shows on lower leaves first. Immobile nutrients stay in place. Calcium, iron, boron, and zinc are immobile. A shortage shows on top leaves and new tips first.

Week 1 to 2: seedling

Seed leaves supply food. A shortage here comes from bad pH or a cold root zone, not from a missing bottle.
Yellow cotyledons at day 10 to 14 are normal.

Week 3 to 8: vegetative

Week 3 to 4: nitrogen shortage. Lower leaves turn pale green, then yellow. Stems stay thin.
Week 4 to 6: magnesium shortage. Leaf veins stay green. Space between veins turns yellow. Spots appear on middle leaves.
Week 5 to 8: calcium shortage. New leaf tips curl. Brown spots form on leaf edges.
Week 6 to 8: iron shortage. New leaves turn yellow with green veins. pH above 7.0 in soil or above 6.5 in coco causes this.

Week 1 to 10: flower

Week 3 to 4: phosphorus shortage. Leaves turn dark green. Stems and leaf stems turn purple. Bud sites stay small.
Week 4 to 6: potassium shortage. Leaf tips and edges turn brown and crisp. Buds stop swelling.
Week 6 to 8: sulfur shortage. New leaves turn light green. This is rare with most base nutrients.
Week 7 to 10: zinc and manganese shortages. New leaves show pale stripes and twisted tips.

Signs by nutrient

Nitrogen (N): pale lower leaves, week 3 to 4 veg.
Phosphorus (P): purple stems, dark leaves, week 3 to 6 flower.
Potassium (K): brown leaf edges, week 4 to 8 flower.
Calcium (Ca): crinkled new leaves, brown spots, week 4 veg to week 4 flower.
Magnesium (Mg): yellow between veins, week 4 veg to week 4 flower.
Iron (Fe): yellow new leaves with green veins, high pH.
Zinc (Zn): short leaf spacing, pale new growth.
Manganese (Mn): gray or brown spots on new leaves.
Boron (B): hollow stems, brown tips on new growth.
Sulfur (S): pale new leaves, week 6 to 8 flower.

Fix schedule

Check pH first. Soil range: 6.0 to 7.0. Coco and hydro range: 5.5 to 6.5. Water temperature: 18 to 22 C (65 to 72 F). EC for veg: 1.2 to 1.6 mS/cm. EC for flower: 1.6 to 2.2 mS/cm. Add a calcium and magnesium supplement at 1 to 2 ml per liter when using reverse osmosis water. Raise nitrogen by 50 to 100 ppm for a nitrogen shortage. Do not add more than one nutrient at a time. Wait 3 to 5 days for a response.

Overfeeding vs deficiency

Overfeeding causes dark green leaves, clawed tips, and brown leaf edges. A potassium shortage causes the same brown edges. Check the runoff EC. If runoff EC is 0.4 mS/cm above the input, flush with pH water at half strength. If runoff EC is below input, raise the feed.

cannabis nutrient feeding chart by week