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Flowering Stretch
Definition: The flowering stretch is the burst of vertical growth cannabis plants make during the first 2 to 3 weeks after switching to a 12/12 light schedule. Plants commonly grow 50 to 100 percent taller, and some sativa-leaning strains triple their height. Planning for the stretch keeps tops from crowding or burning under grow lights.
How Flowering Stretch works
Once nights lengthen, the plant races to build enough stem and branch structure to hold its flowers. Internodes lengthen, new bud sites form at the tips, and growth can reach 1 to 3 inches a day. By about week 3 of flower, the stretch slows and energy shifts into building buds. Most of a plant’s final height is decided in this short window, so mistakes made here are hard to undo later.
How much to expect
- Indica-dominant: roughly 25 to 75 percent added height.
- Balanced hybrids: about 50 to 100 percent.
- Sativa-dominant: 100 to 200 percent, sometimes more.
A simple rule: flip when plants are about half the height you can afford, after subtracting room for the pot, the fixture, and 12 to 18 inches between canopy and LED.
Controlling stretch
- Keep training during weeks 1 to 2 with LST or a trellis net.
- Use supercropping on any branch racing ahead of the rest.
- Keep the day-night temperature gap small. Warm days with much cooler nights encourage stretch, while a brief temperature dip in the first 2 hours of lights-on can shorten internodes.
- Give strong light from day one of flower, since dim light encourages extra stretch.