The buds you smoke are the sexy parts of mature ADULT cannabis plants. They drink adult beverages, work in the sun and party at night—Completely inappropriate for young cannabis seedlings and clones! Innocence of youth happens in the vegetative garden.
Nurture early growth with a specific light cycle and temperate environmental conditions. Within a few weeks, plants harden and are ready for the world outside the vegetative garden. Early growth is the foundation of big harvests—don’t cut corners.
Optimum vegetative growth happens when environment accommodates evolving needs of enthusiastic young cannabis plants. Attentive care is essential because fledgling plant tissue can’t handle bright sun and fertilizer. In fact, seedlings don’t need any fertilizer at all during the first week! Once the plant develops new root and foliar growth the hardening process begins. Pay attention and gradually increase the light intensity, irrigation, fertilization and ventilation to avoid shocking or stunting plants in the vegetative garden.
As plants progress in the vegetative garden:
lower fluorescent lights from 16” to 6” above the canopy. Transition to Metal Halide or sunlight as plants mature in the vegetative garden.
increase air movement from stillness to a stiff breeze.
increase exhaust ventilation from stagnancy to maximum exchange or CO₂ enrichment.
increase fertilizer dosage from zero to full-strength label dosage.
begin irrigation with small gulps then transition to the technique specific to your grow medium.
Decrease temperature from 75°F to 72°F.
The Weakest Link
Liebig’s law of minimums states that the rate of growth of a plant is dictated by the scarcest resource—whether light, CO₂, grow medium, fertilizer or micronutrient. When any component is insufficient, growth slows down. That’s why it is critical to adjust to the plant’s needs most frequently when growth is just beginning to accelerate.
The growth rate at any given moment in the vegetative garden should always be greater than the moment before it. In calculus, this is called a positive derivative. As a graph against time, growth rate should be exponential. In other words, if growth rate were a racecar, it should always accelerate, avoid cruise control and never slow down! The of art gardening is anticipation of the moment that is about to come.
Cannabis evolved to bulk up during the long, crisp blue days of early summer. Indoor gardeners control the season, literally, at the flip of a switch. Correct light cycle (photoperiod), moderate light intensity and cool-spectrum bulbs are essential components of a vegetative garden.
Cannabis needs about 18 hours of light each day to maintain vegetative growth. When cannabis gets more than 10-12 hours of darkness each night, it stops vegetative growth and begins sexual reproduction to save the species. Long nights trigger flowering—save that for later.
When days are long and nights are short, cannabis grows abundant roots, stems and leaves. Length of day (photoperiod) is the only environmental condition that directly controls cannabis growth stage.
Young plants thrive under T5 fluorescent lights. These long bulbs have a larger surface area and more diffuse light than High Intensity Discharge fixtures. Use fluorescent lighting for clones, seedlings and juvenile plants.
The coolness, or warmth of light affects plant structure. Bulbs used in veg are usually “cool” bulbs, with a bluish light, rated 4000-6500 kelvin. This artificial lighting mimics the naturally blueish light of early summer sunshine. Cool lights promote lateral branching, dense foliage and short inter-node distance. Good vegetative structure increases the total number of bud sites on the plants.
Warm bulbs below 4000 kelvin are intended for flowering plants, not vegetative growth. Their glow mimics the hazy, low-angle qualities of late-summer sunlight. Harvest sunshine is tinted much the same as a harvest moon—orangish-yellow. Warm light improves bud structure but is not ideal for vegetative growth.
Mature plants with lots of roots are ready for brighter light. Metal Halide bulbs are perfect for the late vegetative phase because they are very bright, but still cool-spectrum. MH bulbs promote vigorous growth and prepare plants for the intense lights used in bloom. Position lights according to the focal distance and footprint recommended for your light fixture, usually 16-54” above the canopy.
A stable vegetative environment maximizes growth and minimizes disease. All life stages of cannabis enjoy temperate climate, around 72°F. If the grow room feels hot, cold or swampy to you, chances are your plants feel the same way. Temperature and humidity levels either prevent or promote disease. Avoid problems by keeping the temperature between 68°-78°F and the relative humidity between 30-50%.
Ideal Clone Environment
New cuttings lack roots and need high humidity to prevent wilting. Clear plastic propagation domes trap moisture and create a high humidity environment for the clones. As roots develop, open vents and eventually remove the dome. Check out our tutorial on How To Clone Cannabis for vegetative propagation tips.
Newly germinated seedlings have the opposite problem—they are all root and no foliage at first. Therefore, they are more susceptible to dampness than wilting. The same damp that helps tender cuttings will cause seedlings to get moldy and die from “damping off”. Don’t use propagation domes for seedlings. Check out How To Germinate Cannabis Seeds and How To Take Care of Cannabis Seedlings for more information.
Aside from cuttings, cannabis prefers humidity levels between 30-50%. Indoor and outdoor gardens trap moisture and need humidity mitigation. Control humidity with air conditioners, dehumidifiers, ventilation and forced air heating. Water plants in the morning so they have a chance to dry before lights turn off and clean up any puddles that don’t drain promptly.
Air circulation is essential to build stem strength and disperse humidity. Well-rooted cannabis benefits from “dancing” in a moderate breeze. Use oscillating fans set back a few feet from the canopy. When fans are too close to the plants they can cause leaves to fray and crisp at the edges.
Warm water holds less dissolved than cool water. Locate reservoirs in a cool, dark place outside of the grow room. Use an air pump to keep the water constantly bubbling. These conditions maximize dissolved oxygen availability and minimize algae growth in the reservoir. Water that is too cold shocks roots, so make sure that your water reservoir stays right at 60°F for best results.
Vegetative plants need frequent irrigation. Every grow medium has specific irrigation technique, and every plant has different irrigation needs. In general the goal is to maintain a 1:1 ration of air and water in the grow medium. Soil and soiless grow medium function best when they dry somewhat between irrigation cycles. The alternation of wet and dry cycles brings air to the roots and encourages them to grow towards remaining water. Occasional flooding flushes excess fertilizer from the soil.
Dry cycles are helpful, but wilting hurts. Drooping plants indicate extreme water stress. Wilting causes permanent root and foliar damage. Observe your plants and water on a regular schedule, or automate irrigation with a timer.
Do not fertilize seedlings or clones in the first week. Seedlings have enough stored carbohydrates to fuel the first 7-14 days of growth. Cuttings do not need fertilizer until roots appear.
Tender plants without abundant roots or foliage do not need much fertilizer. Increase the fertilizer application as growth progresses. Plant growth is exponential under ideal conditions. Therefore, a healthy clone should be hungry for a full-label dose of fertilizer 1-2 weeks after root emergence.
Juvenile and mature vegetative plants need an abundance of fertilizer, especially Nitrogen (N) to grow tall and lush. Phosphorous (P) and Potassium (K) and micronutrients are also essential for growth. Use a commercial fertilizer formulated for Vegetative growth-- sometimes called a “Grow” formula. Follow the manufacturer's instructions for your grow medium.
Transplanting at the right time accelerates plant growth. Roots need room to grow, otherwise overall plant growth will slow. Plants become stunted if left in a small container for too long. Transplanting too soon or too big hurts plants too because excessive grow medium is prone to over-saturation and stagnation.
Here are some signs that it is the right time to transplant:
Plants need water everyday.
Roots are visible through holes in the container.
Lateral roots are prominently visible where the stem meets the grow medium.
The root ball does not crumble and holds the shape of the container.
It’s a good idea to at least triple container volume when transplanting to a bigger nursery pot. Soil growers transplant roughly every 2-3 weeksRoot development slows to a stop when cannabis begins sexual reproduction. Transplant to the final container a few weeks before changing the light cycle to 12/12. .
Here is an approximate sequence: Quart-->3 gal--> 7 gal-->20 gal containers.
Without pruning cannabis will grow slender and tall, like a pine tree. Pruning the upper branches stimulates growth at the remaining nodes. Pruning the lead growth shoots:
Promotes lateral branching
Creates bushy plants
Optimizes canopy structure
Excessive pruning can stress and stunt plants. Never remove more than 20% of total foliage at a time. Allow at least a week of regeneration before flowering a heavily pruned plant. Check out our canopy management how-to for more tips on pruning cannabis.
Good timing ensures that growth is accelerating as the garden transitions into bloom. For example, a rootbound plant grows more slowly due to stress. It will underperform if transitioned to bloom without transplanting first. But transplanting just before the bloom phase is a problem too. Good timing ensures that the plant is neither rootbound nor in transplant shock at the start of bloom. Do not rush into flower when something is limiting plant growth.
The length of the veg cycle depends on your cultivation method. Large, bushy plants take months to veg and may be pruned and transplanted several times. Veg time is much shorter with small, single-cola plants used in the “sea of green.” The SOG method uses a large quantity of densely-spaced, small plants. With SOG veg time is less because more plants are used to fill the garden.
Pest management is most effective in the vegetative phase. Prevention is possible and treatment is easiest when plants are young with a small, treatable foliar surface. Young plants also have the time to grow, recover and outpace disease. Check out our guide to Integrated Pest Management for more information.
Glossary of Terms
Germination- Before the first leaves appear.
Seedling- A young plant from seed.
Cuttings- Clippings of apical meristem (shoots) for vegetative propagation.
Clones- Rooted cuttings.
Juvenile Plant- A seedling that is not yet sexually mature..
Mature Plant- Sexually developed and ready to flower.
Mother Plant- A plant only used to produce cuttings for vegetative propagation.