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Nutrient deficiencies in cannabis

Yellowing of:
Younger leaves: Fe Mn
Middle leaves: Mo
Older leaves: N K Mg Zn
Between veins: Mg Mn
Old leaves drop: N
Leaf curl over: Mg
Leaf curl under: Overfertilization, K, Cu
Leaf tips burn:
Younger leaves: B
Older leaves: N Zn
Young leaves wrinkle and curl: K Zn B Mo
Necrosis: K Mg Fe Zn Mn
Leaf growth stunted: N P
Dark green/ purplish leaves and stems: P
Pale green leaf colour: N Mo
Mottling: Zn
Spindly: N
Soft stems: N K
Hard, brittle stems: P K
Growing tips die: K B
Stunted root growth: P
Wilting: Cu


Nitrogen (N)

Marijuana uses more nitrogen than any other nutrient. It is used in the manufacture of chlorophyll. N migrates from old growth to new, so that a shortage is likely to cause first pale green leaves and then the yellowing and withering of the lowest leaves as the nitrogen travels to new buds. Other deficiency symptoms include smaller leaves, slow growth and a sparse rather than bushy profile.
N-deficient plants respond quickly to fertilisation. Good water-soluble sources are most indoor and hydroponic fertilisers, fish emulsion, urine, and teas made from manures, dried blood and bloodmeal. The N in urine is immediately available to the plants.


Phosphorous (P)

P is used in the transfer of light energy to chemical compounds and in large quantities for root growth and flowering. Mostly used during early growth and flowering.
Fertilizers and nutrient mixes usually supply adequate amounts of P during growth stages so plants usually do not experience a deficiency. Rock Phosphate and bone meal are the organic fertilizers usually recommended for P deficiency. They are slow release and more suited to outdoor gardening.
P deficient plants have small dark green leaves, with red stems and red veins. The tips of lower leaves sometimes die. Eventually all lower leaves yellow and die. Fertilization affects only new growth.
Marijuana uses large quantities of P during flowering. Many fertilizing mixes cater for blooming plants.


Potassium (K)

K is used to regulate carbohydrate metabolism, chlorophyll synthesis, and protein synthesis as well as resistance to disease. Adequate amounts of K result in strong sturdy stems while slightly deficient plants often grow taller, thinner stems. Seed production uses large amounts of K. Give breeding plants K supplements to assure well-developed seeds.
Symptoms of greater deficiencies are more apparent on the sun leaves – large lower leaves. Necrotic patches appear on the leaf tips and thin in patches throughout the leaf. The leaves also look pale green.
Stems and flowers on some plants turn deep red or purple as a result of K deficiencies. However, red stems are a genetic trait in some strains. Outdoors, a cold spell can precipitate K and make it unavailable, so that overnight the flowers and stems turn purple.
Treat deficiency with a high K fertiliser. Old growth does not absorb the nutrient and will not be affected. New growth will show no sign of deficiency within 2 weeks. For faster results the fertilizer can be used as a foliar spray. K deficiencies do not seem to be a crucial problem. Except for the few symptoms, plants do not seem to be affected by it.


Calcium (Ca)

Used for cell splitting and in cell membranes. MJ stores excess Ca for some unknown reason. I have never seen a case of Ca deficient cannabis; soils and fertilizers usually contain adequate amounts. It should be added to planting mediums upon mixing at 1 tablespoon per gallon or ½ cup per cubic foot of medium.


Sulphur (S)

Used to regulate metabolism and as a constituent of some vitamins, amino acids and proteins. It is plentiful in soil and hydro mixes.
S deficiencies are rare. First new growth yellows and then the entire plant pales.
S deficiencies are easily solved using 1 tablespoon of epsom salts per gallon of water.


Magnesium (Mg)

Mg is the central atom in chlorophyll and is used in production of carbohydrates. (Chlorophyll looks just like hemoglobin in blood but has a Mg atom). In potted plants Mg deficiency is fairly common since many otherwise well-balanced fertilizers do not contain it.
Deficiency symptoms start on the lower leaves that turn yellow, leaving only the veins green. The leaves curl up and die along the tips and edges. Growing shoots are pale green and turn almost white as the condition continues. [also see Fe below as the symptoms are similar]
Treat with epsom salts at 1 tablespoon per gallon of water. Use a foliar spray for faster results. Once Mg deficiency occurs, epsom salts should be added to hydro solutions every time it is changed. Dolomitic limestone contains large amounts of Mg.


Iron (Fe)

Deficiency is not uncommon. Growing shoots are pale or white, leaving only dark green veins. Appears similar to Mg deficiencies except for the lower leaves not being affected in this case. Deficiency is often cause by unbalanced PH level (acid to alkaline on a scale of 0 to 14, 7 being neutral).
Fe deficiencies sometimes occur together with Zn and Mn deficiencies so that several symptoms appear simultaneously.
To correct, adjust the PH level, adding rusty water, or using a commercial supplement. To prevent deficiencies some growers add rusty nails to each container.
Dilute foliar spray can be used.


Manganese (Mn)

Seen in yellowing and dying of tissue between veins, first appearing on new growth and then throughout the plant.
Use a Fe-Zn-Mn supplement.


Zinc (Zn)

Seen first in yellowing and necrosis of older leaf margins and tips, and then a twisted, curled new growth. Treat with a supplement as above, which quickly relieves symptoms. A foliar spray speeds nutrients to the leaf tissue.


Boron (B)

Deficiency is uncommon and does not usually occur indoors. Symptoms start at the growing tips that turn grey or brown and then die. This then spreads to the lateral shoots.
B deficiency is treated using a ½ teaspoon boric acid – available in pharmacies – added to a gallon of water. One treatment is usually enough.


Molybdenum (Mo)

Used in conversion of N to forms that the plant can use and also a constituent of some enzymes. Deficiency is unusual indoors.
Symptoms start with paleness, then yellowing of middle leaves which progresses to the new shoots and growing tips which grow twisted. Early symptoms are very similar to N deficiency. Treatment for N may temporarily alleviate the symptoms but they will return in a few weeks.
Mo is included in hydro fertilizers and some trace element mixes. Can be used as a foliar spray.


Copper (Cu)

Used in the transfer of electrical charges that are manipulated by the plant to absorb nutrients and water. Also used in the regulation of water content and is a constituent of some enzymes.
Cu deficiencies are rare and mimic symptoms of overfertilization. The leaves are limp and turn under at the edges. Tips and edges of the leaves may die and the whole plant may look wilted.
A fungicide, Copper sulfate, can be used as a foliar spray to relieve the deficiency.