Nitrogen (N) deficiency is the most commonly occurring nutrient deficiency in cannabis
Nitrogen toxicity in late flowering. Photo: BillyBob
Symptoms
Lower leaves first appear pale green. The leaves then yellow and die as the Nitrogen travels to support new growth. Eventually the deficiency travels up the plant until only the new growth is green, leaving the lowest leaves to yellow and wither. Lower leaves die from the leaf tips inward.
Other symptoms include smaller leaves, slow growth and a sparse profile. The stems and petioles turn a red/purple tinge.
Too much nitrogen causes a lush dark green growth that is more susceptible to insects and disease. The stalks become brittle and break from lack of flexibility.
Mobility
Nitrogen can travel anywhere on the plant. Usually deficiency starts on the lower of the plant because nitrogen travels to new growth.
The role Nitrogen plays in plant nutrition
Nitrogen deficiency. Photo: TheNewGuy
Nitrogen is directly responsible for the production of chlorophyll and amino acids, and it is essential to photosynthesis. It is an essential element of tissue; without it, growth quickly stops.
Any water-soluble nitrogen (especially nitrates, NO3) is quickly available to the roots. Insoluble nitrogen (such as urea) needs to be broken down by microbes in the soil before the roots can absorb it. After fertilization, Nitrogen-deficient plants absorb N as soon as it is available and start to change from pale to a healthy-looking Kelly green. Deficient plants usually recover in about a week, but the most-affected leaves do not recover.
Nitrogen is the first number of the three-number set found on all fertilizer packages, which list N-P-K, always in that order. Any water-soluble fertilizer much higher in N than P and K can be used to solve N deficiencies very quickly. Most hydro “Vegetative Formulas” fall into this category.
Calcium nitrate (CaNO3) is water-soluble and fast acting. It can be used as a foliar fertilizer and in the water/nutrient solution.
Urine, fish emulsion (5-1-1) high-Nitrogen bat or seabird guano also act quickly. In soils high-nitrogen fertilizers such as alfalfa and cottonseed meals, manure, feather meal and fish meal all sup-ply nitrogen fairly quickly but release it over the growing season.
How to support your plants back to healthy nitrogen levels
Nitrogen deficiency. Photo: TheNewGuy
Without high amounts of nitrogen, especially during the vegetative growth stage, the plant’s yield is greatly reduced. Water up-take slows from vascular breakdown in the plants. N issues happen throughout the entire growth cycle. Plants should never experience an N deficiency during vegetative growth. However, over-fertilizing with N causes problems too.
Tapering off the use of nitrogen towards flowering promotes flowering rather than vegetative growth. However, a small amount of N is always necessary in order for the plant to manufacture amino acids, which use N as an ingredient. This supports flower growth and utilization of P and K. Some “Bloom Boosters” have N-P-K ratios of “0-50-30.” While high numbers sound impressive, using this fertilizer too early causes the flowers to be smaller than they could have been. If there is not enough residual N available, the plants are not getting the most out of the fertilizer.
Nitrogen Deficiency in veg. Photo: M&M
In the middle to the end of the flowering stage, plants frequently show a N deficiency. They’re using the nutrients that were stored in the leaves and dropping the their oldest, bottom fan leaves. To prevent the deficiency from getting extreme, switch over to bloom nutrients gradually unless the bloom fertilizer contains some N.
The plants switch to flowering growth over a week. Then they need higher levels of P and K. But they still require N. For this reason, during the first week of flowering use 1 part each bloom and vegetative. The second week use 2 parts bloom, 1-part veg. During the third week use 3-parts bloom and 1-part veg. After that use just bloom formula. Although the plants still need N in flowering, it’s not near the amount they need when they are growing vegetatively. By gradually moving from grow nutrients the plants receive enough N to last through the flowering process.