The vegetative stage, or veg, is the growth phase between the seedling stage and flowering. During veg a cannabis plant builds roots, stems, branches and leaves, but does not form buds. Photoperiod plants stay vegetative as long as their days are long; the phase ends when shorter days, or in autoflowers simply age, trigger flowering. Feeding and pruning in veg are aimed at building a strong frame. Indoors the usual schedule is 18 hours of light and 6 hours of darkness. Most growers keep plants in veg for a few weeks, then switch to 12 hours of light and 12 hours of darkness to start flowering.
Where veg fits in the life cycle
Researchers divide the cannabis life cycle into four stages: germination or cloning, vegetative growth, flowering and seed formation, and senescence.
The seedling phase comes first. One grow book puts it at about two to three weeks after germination, under 16 to 18 hours of light per day. You can watch the plant change as it grows: the first true leaves usually have a single blade, the next pair three blades, then five, seven, nine, and in some strains up to eleven. After about five leaf tiers the root system and leaf system are well established, and growth speeds up. That is when real veg begins.
Veg lasts from the moment a seedling or rooted clone is established until you trigger flowering. With enough light, nutrients, CO2 and water, a plant in veg can grow 1.5 to 5 cm per day. Stems thicken, side branches develop, and roots expand.
How many hours of light
| Phase | Typical light schedule |
|---|---|
| Seedling | 16 to 18 hours per day |
| Vegetative | 18 hours light, 6 hours dark |
| Keeping plants in veg long term | 16 hours or more |
| Flowering | 12 hours light, 12 hours dark |
The 18/6 schedule is standard, and research reviews describe veg as at least 18 hours of long-day lighting. Grow books add that a plant can stay in veg indefinitely as long as it gets 16 hours of light or more. This is how mother plants are kept for years of cuttings.
Why not 14 hours? Because some modern cultivars flower at longer days than growers expect. In a study of ten drug-type cultivars, flowering began in all of them under every day length up to 14 hours. A comfortable margin above that, such as 18 hours, keeps veg reliable.
What the plant needs in veg
Veg is about building structure. One grow handbook gives these conditions for the main veg phase:
- Light rich in blue for 18 hours a day
- Temperature around 20 to 27 °C
- Relative humidity around 50 to 70%
- More nitrogen in the feed
Another grow book summarises veg nutrition as high nitrogen with calcium, magnesium and moderate micronutrients. Seedlings need much less. Too much nutrient at the start damages young plants.
Other veg tasks:
- Repot on time. When roots fill a small pot, move the plant to a larger one.
- Train early. Topping and bending are done in veg, while the plant can recover.
- Keep leaves clean. Leaves breathe through stomata on their undersides. Dust and dirt reduce photosynthesis.
How long to veg
There is no single right answer. A 2021 meta-analysis of published cannabis studies found that researchers kept plants in veg for anywhere from 13 to 180 days. The mean was 37.1 days, the median 30 days and the most common value 21 days. Academic growers often recommend 14 to 21 days, while grow guides suggest 3 to 16 weeks.
The authors found that longer veg did not simply mean more flower. Their model linked shorter veg with higher floral biomass per plant, while cannabinoid content peaked at intermediate veg lengths. They also stress that cultivars differ. Treat any number as a starting point.
In practice, veg length depends on three things: space, lights and genetics. When several strains share one room, one handbook suggests about 4 weeks of veg for pure indica, 2 to 3 weeks for hybrids and about 1 week for pure sativa, so they reach similar heights before flowering.
How to tell your plant is ready to flip
- Half the final height. A common rule is to switch when the plant is about half the size you want. The flowering stretch can double or even triple the height of sativa types.
- Strong structure. A mature plant with five to eight strong side branches and a sturdy stem is ready.
- Pre-flowers visible. Single flowers at the nodes appear with age, not day length. They are the first visible sign of sex. Seeing them tells you the plant is mature enough to flower.
- Space left above. Leave room for stretch between the tops and the light.
Veg outdoors in the tropics
This is where many growers in Southeast Asia get caught out. Near the equator, days never get as long as a temperate summer. Hemp researchers note that the short day lengths of tropical and subtropical regions reduce vegetative growth and cause early flowering. A photoperiod plant planted outdoors in Thailand may therefore get only a short veg and begin flowering while small.
Options:
- Choose adapted genetics. Cultivars from lower latitudes tend to flower later, which gives them more vegetative growth before short days trigger flowering.
- Add light. Greenhouse growers keep short-day crops vegetative with end-of-day lighting or a short burst of light in the middle of the night. Grow books describe low-wattage bulbs around the plants for the same purpose.
- Veg indoors, then plant out. Remember that a plant moved from 18 hours to shorter natural days will start flowering soon after.
Autoflowers
Autoflowering plants are photoperiod-insensitive. They flower on their own as they mature, even under long days. There is no switch to plan, and their veg phase is short.
Common mistakes
- Overfeeding seedlings. Young plants need only a little nitrogen.
- Vegging too long for the space. Plants that are already at full height when flipped will hit the lights during stretch.
- Reading pre-flowers as flowering. A few white hairs during veg are normal.
- Short days outdoors. Without extra light, tropical day length can end veg much earlier than you planned.