My runoff number is high. Should I flush?

Usually not on the number alone. A high runoff reading is often a dry back spike: the pot dried out more than usual before this watering, the leftover nutrient got packed into less and less water, and the first stuff out the bottom is that concentrated leftover. If the plant is green, upright and clean, the urgency to fix the number just dropped close to zero.

A runoff cup is not a verdict. It's a clue.

This page is written for soil. Coco and hydro run on a different watering rhythm, so the soil reads below don't carry over as written.

Why runoff reads high in soil

What drips out of the pot has run through the soil, old nutrient residue and the salt sitting in the drier pockets, and it picks all of that up on the way down. So in soil, runoff commonly reads higher than what you fed. The first time you catch it, it's a shock. It's also normal.

That cup is what left the pot, one moment, one watering. It isn't a live feed from the roots, and it isn't her vital signs.

Is my runoff number bad?

There's no single bad number. Runoff by itself is half a measurement. Put it next to what went in and read the gap.

• A small gap on a healthy plant: normal. Leave it alone.

• A big jump right after the pot ran unusually dry: often a dry back spike. Water normally and read it again next time.

• A gap that climbs week after week, with tip burn showing up: that's a pattern worth acting on.

Why a flush is the biggest swing you can make

A big plain water flush can feel like the decisive move. Then two or three days later she droops, pales and slows down, and it looks like the salt was worse than you thought. Often it wasn't. A flush soaks the root zone well past normal, so the roots run short of oxygen, and it washes out nutrients she was using, both at once. That droop is often the roots reacting to the soak, not the salt winning.

Watch for the loop: the number scares you, you flush, she sulks, you read the sulk as more salt, and you flush harder.

Run three gates before you tip a jug into that pot

1. Read the plant first. Green, firm, no burnt tips, no clawing? The plant outranks the meter.

2. Trust the tool before the number. Calibrate the pH pen and the EC meter, because a meter that's off can invent a problem that doesn't exist. And know your ppm scale. Meters convert EC to ppm on different scales, so two growers can say the same ppm and mean different strengths.

3. Set the number next to what went in. Read the gap, not the number. If the gap is climbing and the plant agrees, make one small, reversible move: plain pH'd water or a very light feed for a watering or two, or a light flush, meaning one slow watering of plain, room temperature, pH'd water with a bit more runoff than usual, followed by a full dry back. Not gallons. Then wait a full watering before you judge it.

What not to do

Don't flush a healthy plant because of one reading. Often the reading was about how dry the pot got, not about her.

Don't flush harder because she drooped after the last flush. That droop is the root zone recovering from being soaked.

When it's something else

• Deciding whether she needs more food: see How can I tell when my plant wants more food?

• Droop and you're not sure why: see How often should I water, and why is she drooping?

• Yellow leaves along with a high number: see Yellow leaves: is it a deficiency, and is this too much?

On our shelf in Worcester: pH and EC pens, combo meters and calibration fluid for reading runoff are in pH, water & meters.

Keep going

Watch the episode: Runoff Reading High? Why Flushing a Healthy Plant Backfires on MyRemy Live.

The number tells you what came out. The system tells you why. The whole system is written down in the free Stability Playbook. Get the free Stability Playbook