How to Defoliate Cannabis Plants for Maximum Yield

Short answer

Defoliate in two windows. First, in late vegetative growth. Second, on day 21 of flowering. Remove leaves that block light to bud sites. Remove the lower third of the plant in veg. Leave the top two thirds alone. In flower, take fan leaves from the top canopy. Stop all leaf removal by week 5 of flower. Remove no more than 20 percent of the leaf mass in one pass.

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Defoliation does not guarantee a yield gain. Controlled cannabis trials report mixed results. It can help light reach lower bud sites. It also removes the leaves that feed the plant. The net effect depends on plant health, light intensity, and cultivar.

best time to defoliate cannabis plants

What defoliation does to the plant

Leaves are the source of sugars. Buds are the sink. Remove source leaves and the plant has less sugar to send to flowers. Light that reaches a bud site at less than 400 PPFD adds little flower mass. Light above 600 PPFD at the canopy drives photosynthesis. Open the canopy to move light down. Do not strip the plant.

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Vegetative stage

• Week 4 to week 6 of veg: remove the bottom 25 percent of leaves and small branches.
• Remove leaves with 5 or more blades that sit against the main stem.
• Keep 8 to 12 top fan leaves per main branch.
• Wait 3 to 5 days between passes. Let the plant recover.

Flower stage

• Day 1 of 12/12: remove dead leaves and lower growth.
• Day 21: main defoliation. Remove fan leaves that cover bud sites.
• Day 42: stop. After this point, take dead leaves and nothing else.

Do not remove sugar leaves. Sugar leaves sit inside the bud and carry trichomes.

Environment after a pass

Defoliation is a wound. The plant repairs tissue for 2 to 3 days. Hold air temp at 75 to 80 F. Hold relative humidity at 60 percent in veg and 45 to 55 percent in flower. Keep VPD between 0.8 and 1.0 kPa in veg, and 1.0 to 1.2 kPa in flower. Water as normal. Skip heavy nutrient changes on the same day.

What the evidence shows

Peer-reviewed cannabis defoliation studies are few. Trials in other crops show that heavy leaf removal can lower total yield. Light defoliation in the lower canopy improves airflow and lowers mold risk. Yield percentage claims come from grower reports, not from controlled trials with a fixed number.

Mistakes

• Removing more than 30 percent of leaf mass at one time.
• Defoliating in week 6 or later of flower.
• Defoliating a plant with nutrient burn, root problems, or pests.
• Heavy defoliation on autoflowers after week 3 of flower.