Short answer
Bend it; don't cut it. In veg or the first two weeks of flower, supercrop or tie the tallest tops down and outward. Later, tie woody tops sideways. Raise or dim the light so the tops get no more than about 1,200 µmol/m²/s, lower the pot, and next run flip at half the final height. Grower practice.
Why
Most height arrives after the flip. Stems and internodes elongate fastest around days 5–10 of short days [1], and many cultivars finish 1.5–3 times their flip height (Grower practice).
Tops too close to the light burn. Yield rises with light [2], but at ambient CO₂ the practical ceiling for top colas is about 1,200 µmol/m²/s, and photosynthesis falls above about 30 °C (86 °F) [3]. Heat and light stress shows as bleached tops and foxtails.
Bending keeps the cola. A supercropped stem forms a knuckle in 3–7 days and keeps growing; a cut top is gone, and topping in flower costs recovery time the plant doesn't have. The house endorses supercropping: the founder snaps stems all the time.
The numbers
| Stage | Best fix | Notes |
|---|---|---|
| Veg | LST, topping, supercropping | Plenty of time to recover |
| Flower weeks 1–2 | Supercrop, tie down, tuck under a net | Stems still green |
| Flower week 3+ | Tie tops sideways; stakes | Woody stems crease |
| Any time | Raise or dim light; remove pot risers | Measure PPFD at tops |
| Top-cola PPFD limit, ambient CO₂ | About 1,200 µmol/m²/s | Measure, don't guess |
| Canopy temperature | Under 30 °C (86 °F) | 22–26 °C ideal in flower |
| Flip height | About half the usable height | Stretch 1.5–3× |
What to do
- Measure PPFD and temperature at the tallest top.
- Raise the light to the ceiling or dim it until the tops are under about 1,200 µmol/m²/s.
- Take the pot off any riser or saucer stack.
- Supercrop green tops 5–15 cm below the tip, or tie woody tops sideways to the pot rim.
- Next run, flip at half the final height and train during veg.
Common mistakes
- Cutting the main cola in flower.
- Leaving tops touching or almost touching the fixture.
- Bending woody stems sharply in late flower.
- Flipping a plant already two-thirds of the tent height.
Related
- Full article: LST: low-stress training
- Answers: when to stop training · how tall plants get indoors
- Training: supercropping · SCROG
- Terms: stretch · supercropping
