The cannabis veg stage light schedule and requirements come down to a few numbers: 18 hours of light and 6 hours of dark each day, a PPFD of 300 to 600 µmol/m²/s, and a daily light integral (DLI) of 20 to 40 mol/m²/day. Hang LED fixtures 18 to 24 inches above the canopy and hold air temps near 75°F. Hit those targets and a veg plant builds thick stems, tight node spacing, and enough leaf mass to carry a heavy flower set.

Cannabis Vegetative Stage: Light, Nutrients, and Timing Guide

Veg is the stretch of growth between seedling and flowering, when the plant builds roots, stems, and leaves instead of buds. Light is the main lever you control in that window, and it sets the pace for everything else. Get the schedule and intensity right, and the rest of the grow gets easier.

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What light schedule should cannabis have in veg?

18/6 is the standard veg photoperiod: 18 hours on, 6 hours off. It gives plants a long day for growth plus a dark window for respiration and root development. Other schedules work, with tradeoffs in speed, power cost, and plant stress.

signs of problems in cannabis vegetative stage

Why does the dark period matter in veg?

Plants use dark hours for respiration, burning sugars made during the light cycle and shipping energy into roots and new tissue. A 6-hour dark window also lets the grow space cool and lets you run lights during cheaper off-peak power hours. Cutting darkness to zero is not a problem by itself, but it removes those benefits.

cannabis vegetative vs flowering stage differences

Can you veg cannabis under 24 hours of light?

Yes, cannabis can stay in veg under 24/0, and some commercial growers use it to root clones fast. The tradeoff is power and plant stress: 24 hours uses about a third more electricity than 18/6, and plants that never rest can droop, pale, or slow root growth. If you try it, give the run a week and drop to 20/4 at the first sign of fatigue.

How much light intensity do veg plants need?

Vegetating cannabis wants a PPFD of 300 to 600 µmol/m²/s at the canopy, which lands in a DLI of 20 to 40 mol/m²/day. Seedlings and fresh clones need less: 100 to 300 PPFD. Push past 700 PPFD in veg without added CO2 and you risk leaf bleaching, curled edges, and stalled growth.

No PAR meter on hand? Use a lux app or a watt-per-square-foot estimate. Most modern LEDs need 25 to 40 watts per square foot of canopy for veg, which puts a 4x4 tent (16 sq ft) in the 400 to 640 watt range.

DLI matters more than raw intensity. 600 PPFD for 12 hours gives the same DLI as 400 PPFD for 18 hours. Since veg runs 18 hours, you can hit a solid DLI with moderate intensity and less heat.

How far should veg lights hang from the canopy?

Distance depends on the fixture. LEDs run cooler and sit closer, while HID lamps run hot and need a wider air gap.

Judge by the plant, not the tape measure. Leaves that taco, point up, or turn lime green at the top mean too much light, while long gaps between nodes and thin stems mean too little. Raise or dim in small steps and give the plant two days to react.

What light spectrum works for veg?

Blue-heavy full spectrum in the 4000K to 5000K range keeps internode spacing tight and favors leaf and stem growth. A blend with some 660 nm red helps too, since red light drives photosynthesis and root mass.

What other requirements matter during veg?

Light sets the pace, but temperature, humidity, and airflow decide whether the plant uses that light well. Aim for 70 to 85°F with lights on, 65 to 75°F at night, and 55 to 70 percent relative humidity. Keep VPD between 0.8 and 1.2 kPa in veg.

Light and heat travel together. A 600W HPS in a small tent can push canopy temps past 90°F even with the lamp 30 inches up. Vent the room before you add more light.

When do you switch from veg to flower?

Flip to 12/12 when the canopy fills 50 to 70 percent of the tent and plants show pre-flowers at the nodes. Most indoor growers veg for 3 to 6 weeks from a rooted clone, or 4 to 8 weeks from seed. Plants stretch 50 to 100 percent in the first three weeks of flower, so leave headroom above the canopy.

Do autoflowers follow the same veg light schedule?

No. Autoflowering cannabis runs on its own clock, so growers keep them on 18/6 or 20/4 from sprout to harvest. There is no 12/12 flip. More light hours mean more total energy over the plant's short life, which is why 20/4 is common for autos.

Does the veg light schedule change yield?

Total light delivered during veg, called DLI, shapes plant size, and plant size sets the ceiling on flower weight. A veg run at DLI 35 with healthy roots will produce more flower than the same cut vegged at DLI 15. Past DLI 45 without CO2, extra light stops paying for itself.

Quick veg light checklist