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Nutrients

Reading a nutrient deficiency: the leaf cheat sheet

Old growth vs new growth tells you almost everything.

1 min read2026-05-2610 views

Most deficiencies show up first in either old growth or new growth — and that tells you which mineral is missing.

Where the symptom shows up
Old growth (bottom leaves)
  • Mobile nutrients: N, P, K, Mg
  • The plant strips these from old leaves to feed new ones
  • Yellowing lower leaves → nitrogen low
  • Purple stems + dark leaves → phosphorus low
New growth (top leaves)
  • Immobile nutrients: Ca, Fe, S, B, Zn
  • Plant can't move these from old to new
  • Pale new growth, dark veins → iron low
  • Brown spots + leaf curl → calcium low
Should I flush at the first sign of yellowing?+
Almost never. Diagnose first — flushing dilutes the issue.
Are 'cal-mag' supplements always needed?+
In hydro and coco — usually yes. In peat-based soil — sometimes no.
Related
pH, EC, and runoff: the only three numbers that matter
Master these and 80% of nutrient issues disappear.
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