Transition to Veg Phase: Hardening-Off and Transplanting
Creating the right environment for your young cannabis plants will pay dividends come harvest time. Andrew Taylor takes us step-by-step through the process.
The ability to move your plants seamlessly from stage to stage without stressing them out is key to achieving optimal yields. Extra care during the early days will pay massive dividends later on. Growers should be particularly aware of sudden changes in humidity, temperature, light intensity, and nutrient concentration.
Growing Freshly Rooted Cuttings
- Opening up propagator lid vents gradually will help wean your rooted cuttings from their high-humidity environment and prepare them for life in the main growroom. This process should be done over a few days. Eventually placing the propagation lid on an angle will provide a temperature and humidity that is closer to the eventual growroom environment.
- Placing your nursery pots or propagation blocks on a mesh and raising them slightly off the bottom of the tray will help your young plants develop better initial root structures — a technique known as air pruning (Fig 1). Air pruning dehydrates and kills any roots that try to grow beyond the propagation block (or pot). This is beneficial because it promotes root growth within the block itself. A block which is fully colonized is more likely to survive planting out into the larger system and provide rapid growth into the vegetative phase.
- Do not over-water a fresh transplant. Simply making sure the surrounding medium is moist will encourage the roots to explore. Make note of how heavy plants feel when watered. Then recheck their weight daily — if they still feel heavy then do not water them.
Moving to Vegetative Phase: When are plants ready for transplanting?
- Clones need to be fully hardened off. Test their capacity to withstand the humidity and temperature used in the vegetative phase. Test for an hour or two to begin with — gradual changes are key.
- There must be plenty of air-pruned roots on the outside of the propagation cube. Do not leave it too late, otherwise roots will begin to circle the pot and become root-bound. To inspect roots, gently lift the plant by tapping or squeezing the pot on all sides, particularly from beneath. If there are not many visible roots, or the medium is falling apart, then the plant is not ready for transplanting.
Keys for Transplanting
- Try to stage pot size appropriately. A young plant should not look lost in a large pot. Use an intermediate size pot and allow the roots time to fully colonize all the medium available to them before replanting into a larger pot. Transplanting to an oversized pot will discourage roots from searching for water. It will also cause the outer medium to become water-logged and prone to water-borne diseases such as pythium (Fig. 2).
- Fabric, breathable pots are recommended for use with coco coir or soil. Choose pots with a low, wide form. This will, in turn, encourage squat, wide plants.
- Ensure that the new medium is flushed and watered with fresh nutrient solution. Note, stonewool needs to be pre-soaked for up to 24 hours with nutrient solution pH corrected to below 6.0.
- Be careful changing from fluorescent to HID lighting. When transplants/clones are first exposed to HID, avoid stressing them with excessive light. Either use a dimmable ballast or lift the lights to a safe height (e.g. 600W is 3-4 ft., 1,000W is 4-5 ft.).
- A quality root stimulant and clone spray will help greatly to alleviate transplant stress and maximize root growth.
Creating the right environment is essential for promoting vegetative growth (leaves and roots). The right environment will also produce a short and stocky plant — the ideal shape for indoor growing.
- Metal halide (MH) lamps are ideal for fast-growing plants. They deliver high-intensity light (penetrates canopy) with a “blue-rich” spectrum. To avoid stretching, young plants should be positioned close to the light (but maintain minimum safe distance).
- Vegetative growth is powered by days of 18 hours (typically), and 24-hour days can be beneficial.
- Most species prefer relative humidity of 50-70 per cent and day (lights-on) temperatures of 68-82°F (20-27°C). Keep the night temperature cooler but within about 9°F (5°C) of the day temperature.