What nitrogen does
Chlorophyll
Nitrogen is required to make the green pigment that runs photosynthesis
Amino acids
It is a building block of tissue. Growth stops quickly without it
Mobile
The plant pulls nitrogen from old leaves to feed new growth
Label position
Nitrogen is the first number in every N-P-K ratio
Deficiency pattern
Starts low
Lower leaves fade from pale green to yellow, then die from the tips inward
Climbs
The yellowing walks up the plant until only new growth stays green
Other clues
Smaller leaves, slow growth, a sparse look, and red or purple stems and petioles
Recovery
Soluble nitrate greens the plant in about a week. The worst leaves do not come back
Too much nitrogen
Lush dark green
Excess N makes soft, attractive growth that pests and disease like
Brittle stalks
Stems lose flexibility and snap more easily
Hot weather
Extra transpiration concentrates a rich feed, so cut N 10 to 20 percent in heat
Low light
Excess N is more of a problem when lamps or sun are weak
Stage management
Never starve veg
A nitrogen shortage before flip cuts yield hard
Taper, do not cliff
Ease nitrogen down as flowering starts so the plant shifts into bloom
Keep a residual
Bloom boosters listed 0-50-30 can shrink flowers if no leftover nitrogen remains
Late flower fade
Mid to late bloom often shows a mild N fade as the plant empties old fans. Switch to bloom feed gradually if that formula still has some N
Fast corrections
Veg formulas
Water-soluble mixes much higher in N than P and K act quickly
Calcium nitrate
Fast through roots or as a foliar, but skip it in flower
Organics
Fish emulsion, high-nitrogen guano, alfalfa, cottonseed, feather meal and manure all supply N
Insoluble forms
Urea and similar sources wait on soil microbes before roots can use them