How Big Should Cannabis Plants Be Before Flowering?

How Big Should Cannabis Plants Be Before Flowering?

Flip indoor plants when they reach 12 to 18 inches tall, or when the canopy sits at about half the height you want at harvest. Cannabis stretches in the first two to three weeks of flower, so a 15 inch plant can finish near 30 to 40 inches. Outdoor growers do not pick the date. The shortening fall photoperiod starts flowering, so plant size at that point depends on when you sprouted and how much summer the plant had.

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Why Height at Flip Matters

Vertical space is the limit in most tents and closets. Lights need 18 to 24 inches of clearance above the canopy, and pots eat another 10 to 12 inches. If you flip a 30 inch plant in a 60 inch tent, the stretch pushes the top into the light and you spend flower bending stems instead of feeding buds. Measure the plant, estimate the stretch, then work backward from the ceiling.

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Size Targets by Grow Style

• Standard indoor soil or coco, 4 to 6 weeks of veg: 12 to 18 inches.
• SCROG: fill 70 to 80 percent of the screen, which lands near 10 to 14 inches tall.
• SOG with clones, one cola per plant: 8 to 12 inches.
• Sativa-dominant plants: 10 to 14 inches, since the stretch is longer.
• Compact indica-dominant plants: 15 to 20 inches, since the stretch is shorter.

Prerequisites

• Known ceiling height inside the grow space.
• A light you can raise 18 to 24 inches above the canopy.
• Plants in veg with no nutrient lockout, pests, or root problems.
• A timer that holds 12 hours light and 12 hours dark.

Steps to Set the Flip

1. Measure from the soil line to the tallest growing tip.
2. Multiply that number by 1.5 to 2 for hybrids and indicas, or 2 to 3 for sativas.
3. Add the result to your current height to get the projected finish height.
4. Subtract the projected height plus light clearance and pot height from the ceiling. If the number is negative, keep vegging and train the plant wider.
5. Check for alternating nodes on the main stem. This shows the plant is mature enough to flower.
6. Do your final defoliation and lollipop now, not after the stretch.
7. Set the timer to 12 hours light and 12 hours dark.
8. Keep the veg feed for the first week, then move to bloom nutrients.
9. Measure again at day 14 and day 21 of flower and raise the light as the stems climb.

Common Mistakes

• Flipping by calendar instead of by height. Two plants from the same pack can differ by 6 inches.
• Ignoring stretch on sativa-dominant cuts, which can triple in height.
• Vegging too long in a short tent to chase a bigger yield, then losing the top colas to light burn.
• Defoliating hard during the stretch, which slows the plant right when it needs leaves for rapid growth.