Yellow leaves: is it a deficiency, and is this too much?

A few yellow leaves at the very bottom of the plant are usually normal, not a deficiency. It becomes too much when the yellow climbs past the bottom two or three nodes, spreads across a lot of leaves in a few days, or shows up on the new growth at the top.

A yellow leaf is not a feeding order. It is an address. It tells you where to look, not what to pour.

Why the bottom leaves go yellow first

When the new growth needs more than the roots are bringing in, or an old leaf reaches the end of its life, a healthy plant pulls its mobile nutrients, nitrogen and magnesium included, out of the old lower leaves and ships them up to the top. That is not always starvation. Often it is a plant being a plant.

So the lowest, oldest leaves going pale while the top stays green can be completely normal: aging, a shaded leaf, or a planned fade late in flower. It can be hunger too. But yellow on its own is not proof of hunger.

How to tell when it is too much

Read two things before you touch a bottle.

Where it is.

• Oldest lower leaves: a normal fade, or one of the nutrients she can move (nitrogen, magnesium, potassium).

• New growth up top: more likely pH or a root problem, or one of the nutrients she cannot move easily, like calcium or iron.

• Only the tops nearest the light: heat or light stress, not food.

• The whole plant going pale: look at watering and roots first.

How fast it is moving.

• One or two of the lowest leaves fading slowly over a week is routine turnover.

• Yellow climbing fast across a lot of leaves, or the whole canopy going pale in a few days, is a problem worth diagnosing.

The pattern on the leaf narrows it further. A whole leaf gone evenly pale leans nitrogen or a normal fade. Yellow between veins that stay green leans magnesium. Yellow, crispy edges lean potassium, or salt at the roots.

The order to run before you feed

1. Look, do not touch. Where is the damage, and how fast is it moving? Location is half the diagnosis, and it costs nothing.

2. Check the stage. Lower leaves fading slowly late in flower can be a plant finishing on schedule.

3. Lift the pot. Heavy, soggy and droopy points at overwatering, not hunger. Soaked roots cannot drink or feed even when the food is right there. Let her dry back first.

4. Check the room. A light too close bleaches the tops. Heat, low humidity and a fan blasting one spot can all look like a deficiency.

5. Check the pH. In soil, roughly 6.2 to 6.8. In coco or hydro, roughly 5.8 to 6.2. Well outside that range, the food can be sitting in the pot while the roots cannot take it up, and the fix is the pH, not more food.

6. Feed last, and only if the clues agree. Feed modestly, change one thing at a time, and judge it by the new growth. The leaf that already turned will not green back up.

What not to do

Do not feed harder when the yellow spreads after a feed. Most of the time that plant never needed more nitrogen. The roots could not take up what was already there, usually because the pH drifted or salt built up. A stronger feed raises the salt and makes the root zone harsher, and the yellow keeps marching. When yellow spreads after a feed, stop feeding and check the pH.

Three yellow leaves we read for growers

Old leaves first. The damage started on the older leaves and worked in from the tips and edges, with purple in the leaf stems and pale but untwisted new growth. The grower had soft tap water and a bad pH pen that meant about a week of watering far too high. Our read was magnesium, with calcium close behind: the plant robbed its old leaves to feed the new ones, and the week of bad pH made it worse.

Past normal. A big plant in a half barrel, tipping into flower. The gold ran straight through the leaf, veins and all, and had climbed well up into the middle of the plant. Nothing was burnt or clawing. That one was hungry for nitrogen, and the answer was to feed her. A normal fade is the bottom two or three nodes while the canopy above stays dark green. Once it climbs, it is not age anymore.

Look at the veins. A couple of weeks into flower, one older leaf going pale from the edges in, veins still green. The leaf pointed at magnesium, but the pot told the story: demand was climbing and nothing had gone back into the soil since spring. The move was to feed the stage, not chase the leaf.

Same color, three different answers. That is why the location and the pattern come before the bottle.

When it is something else

• Tacoing, bleached or pale tops only: that is light or heat stress, not food.

• Drooping with yellow and a heavy pot: read How often should I water, and why is she drooping? first.

• Brown or grey mush inside a bud: that is not a leaf problem. See the Bud Rot Survival Guide.

Keep going

Watch the episode: Yellow Leaves, Nutrient Lockout and Reading the Direction on MyRemy Live.

Next: What humidity should I run, and what if I can't hit it?

Symptoms are signals, not instructions. The full diagnosis order is written down in the free Stability Playbook. Get the free Stability Playbook