Why is my plant growing so slowly, and what do I check first?

A plant that's barely growing is usually telling you about the room or the roots, not asking for more food. In winter, check the cold first. Then the pot, the feed, the light, the pot size and the timer, in that order. Find the cause before you feed.

Slow is a symptom, not a feeding order.

First: is she slow, or resting?

Some slow weeks are normal.

• After topping: 3 to 7 days of slower growth is normal, longer on a slow or older plant.

• After a transplant: the droop eases in 1 to 3 days, and she needs 5 to 10 days before the next big stress.

• Plants differ. Two plants from one pack can grow at different speeds. A plant with a slow reputation is often slow to finish in flower, not slow in veg.

If none of that fits and the new growth has stalled, work down the list.

Check in this order

1. The cold. Winter's first suspect. Lights-on should sit at 75 to 82°F in veg, and lights-off not below the mid-60s. Below about 55°F at the canopy, growth slows hard. Cold roots take up water and food slowly, so a cold plant can look pale and hungry when she's only cold. Keep the pot at 68 to 75°F and off a cold floor. See How cold is too cold for my grow room at night?

2. The pot. Lift it. A pot that's still heavy days after watering means the roots are sitting wet and short of air; roots like that grow poorly and can start to rot. In a cold room the pot dries even slower. Water when it's noticeably lighter. See How often should I water, and why is she drooping?

3. The feed. A feed that's too strong stalls a plant as surely as one that's too weak. In coco and hydro, a bottled mineral feed in veg usually goes in around 0.8 to 1.4 EC. A soil that comes pre-fed may need little or no feed for weeks, so in soil start lower, from the maker's chart. If your feed reads far above that, a hot mix is the likely cause. If the feed is hot, give plain pH'd water or a very light feed for a watering or two, then let the pot dry back. Check the pH going in too: 6.2 to 6.8 in soil, 5.8 to 6.2 in coco and hydro.

4. The light. Too little light makes slow, pale, stretchy growth. In veg, aim for 300 to 600 PPFD at the canopy, with 18 hours on and 6 off. See How many hours of light, and how high should the light hang?

5. The pot size. Roots circling the inside of a small pot slow the whole plant down. See What size pot, and when do I pot up (or what if she's out of room)?

6. The timer. Last on the list, but first if she stalls right after the switch to flower. A timer that lost its place after a power cut, or a light leak in the dark period, can stall a plant in flower for weeks.

Give her time to answer

Change one thing at a time, then wait. A temperature change needs at least an hour to settle, and a full day and night before you judge it. After a feed or pH change, the first signs show within a watering cycle; judge the fix on the new growth about 7 to 10 days later. Judge by the newest leaves, not the old ones; old damage doesn't heal.

What not to do

Don't feed harder to speed her up. If the cause is cold, wet roots or too little light, more feed only builds salt in the pot.

Don't stack a fix on a fix. Two changes at once means you won't know which one worked.

Don't top or transplant a stalled plant. Wait for fresh upward growth first. A second stress on a slow plant sets her back further.

When it's something else

• Pale, but still growing: see How can I tell when my plant wants more food?

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

• Purple stems or leaves: see My plant is turning purple. Is it the cold, hunger, or just her genes?

On our shelf in Worcester: EC and pH pens and calibration fluids are in pH, water & meters, and fan speed controllers are in Climate, air & controls. Call (508) 459-9609 or get directions.

Keep going

Running the exhaust slower in a cold room: see our tent airflow shelf guide.

Fix the cause, then let her grow. The whole system for a steady grow is written down in the free Stability Playbook. Get the free Stability Playbook

More answers: all grow guides. Every shelf guide and maker feed chart: Grower Resources.