What it is
It's short on calcium (ca). Calcium is part of every cell wall: without it, new tissue comes out weak and deformed.
How to tell
Rust-like brown spots on new or middle leaves, and twisted or crinkled edges. New growing tips can come out deformed. Unlike nitrogen, it starts on the new leaves: calcium doesn't move around inside the plant, so it can't "pull it out" of the old leaves.
Why it happens
It almost never runs out in the soil: it gets locked out. Typical causes are pH out of range, very soft water (or reverse osmosis water, which has no minerals), roots damaged after overwatering, coco coir (which holds onto it) and stress.
What to do
A calcium and magnesium supplement (cal-mag) and check the pH. LED lamps make the plant ask for more calcium: with LEDS it's common to use cal-mag all the time.
▲ Pros
- If you fix it early it hardly shows at harvest
▼ Cons
- Unfixed it lowers grams and quality
🎮 Practice it in UnderGrow
It shows up more after overwatering (3 times more chance of showing up for the next 3 days), with a stressed plant and with high pH. Cal-mag fixes it and protects for 10 days (10 real h).
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