Short answer
Raise light intensity and root volume, hold CO2 and climate inside known ranges, then shape the canopy so every bud site sits in the same light band. Genetics sets the ceiling. Light, CO2, water, and root space decide how close the plant gets to that ceiling.
cannabis yield per plant photoperiod
Light: PPFD and DLI
Indoor flower rooms run 700 to 1000 µmol/m²/s at the canopy, about 30 to 40 mol/m²/day of DLI. Vegetative plants need 400 to 600 µmol/m²/s, or 20 to 30 mol/m²/day.
how to increase cannabis yield per plant
Measure at 12 to 20 points across the canopy. A fixture rated at 1000 µmol/m²/s at 12 in gives less at 24 in. Flower weight tracks total light delivered, not fixture wattage.
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- Keep the canopy flat within 6 in.
- Replace 8 week old HPS lamps. Output drops before they fail.
- Run 12 hours of light and 12 hours of dark in flower.
CO2
Ambient air holds about 420 ppm CO2. A sealed flower room at 800 to 1200 ppm raises net photosynthesis when light, water, and nutrients are not limiting. Leaf temperature must reach 82 to 86°F for the response. Below 75°F the gain is small.
Above 1500 ppm there is no added yield and CO2 displaces oxygen for workers. Exhaust fans and CO2 enrichment cancel each other out.
Canopy shape: topping, LST, SCROG
Topping at node 4 to 6 turns one apex into two. Repeat once for 4 to 8 colas, twice for 8 to 16. Each new top adds flower sites and adds shade.
Low stress training bends the main stem. Tie the top below the tallest side branches and the plant stops favoring one cola.
A SCROG screen at 1 plant per 2 to 4 sq ft fills the footprint. Weave shoots under the net for the first 2 weeks of flower, then stop. Stems that stay under the screen during stretch produce small buds.
Defoliation
Commercial rooms strip large fan leaves near flower day 21 and day 42. Peer reviewed data on the practice is thin. Remove leaves that cover bud sites. Leave upper fan leaves that feed the colas. Heavy stripping in week 1 to 3 of flower removes the sugar source the plant needs to build weight.
Root zone: pot size, media, water
Root volume caps yield. A 3 to 5 gal pot of soil supports a 4 to 6 week veg. Coco and drain to waste setups run 2 to 3 gal with the same veg time. A root bound plant stalls in week 4 of flower.
- Media temperature: 65 to 72°F.
- pH: 5.8 to 6.2 in coco and hydro, 6.0 to 6.8 in soil.
- Runoff: 10 to 20% of the input volume in drain to waste.
- Wet and dry cycles pull oxygen into the root zone.
Nutrients and EC by stage
Flower EC sits at 1.6 to 2.4 mS/cm. Nitrogen drops after week 3. Phosphorus and potassium rise, but excess phosphorus blocks zinc and iron. Calcium at 100 to 150 ppm and magnesium at 40 to 60 ppm cover most cultivars.
EC above 2.6 mS/cm in soil and coco salts the media and burns tips. It does not add flower weight.
Climate: VPD and temperature
Vegetative VPD: 0.8 to 1.1 kPa. Flower VPD: 1.2 to 1.5 kPa. Day air 75 to 80°F, night 68 to 72°F. Relative humidity 45 to 55% in mid flower.
Humidity above 60% with dense colas raises botrytis risk. Rot removes whole tops at harvest.
Genetics and plant count
Genetics sets the upper limit. Two plants from seed of the same strain can differ by a factor of two in dry weight. A mother plant and clones keep a known yield.
Fewer, larger plants beat more, smaller plants in most rooms. Extra plants shade each other and each one yields less. Common ranges: 1 to 2 oz per plant in soil under 400 W, 4 to 8 oz per plant in a 1000 µmol/m²/s room with CO2. Reports above that come from long veg cycles and large root volumes.
Harvest timing and dry weight
Sample buds from mid canopy. Clear trichomes mean the harvest window has not opened, cloudy means peak THC, amber means THC is breaking down. Harvest too late and rot and terpene loss cut the final weight.
Dry at 60°F and 55 to 60% RH for 10 to 14 days. Dry weight lands at 20 to 25% of wet weight. Cure 2 to 4 weeks in sealed jars at 58 to 62% RH.
What does not raise yield
- CO2 without high light and 82°F leaf temperature.
- Nutrient doses above EC 2.6.
- Extra plants that shade the canopy.
- Defoliation that strips upper fan leaves.