Many indoor cannabis growers use separate rooms for vegetative and flowering plant growth. This allows for rapid crop turnover and efficient use of valuable production space. Although shuffling plants from veg to flower may seem like a benign task—if not performed correctly, this process can result in increased cycle time, greater susceptibility to disease and hermaphroditic plants. If executed properly, a smooth transition can help growers achieve up to six full harvests per year in each flower room.
Be mindful of these factors as you move plants throughout the production process.
1. Relative Humidity
Commercial-scale vegetative growth rooms typically house thousands of young plants. Rooted clones and seedlings require little space, so they are grown “pot-to-pot” at a high density. As a result, relative humidity (RH) at the plant level can reach 75 percent or more. In flower, optimum RH levels hover around 45 percent to 50 percent, and new plants are arranged with considerable distance between each one to allow for ample airflow. These environmental extremes can rapidly strip moisture from plants during their first day in flower, resulting in leaf tip burn and wilted plants.
Avoid this risk by acclimating young plants to the dryness of the flower room. During the first week in flower, start RH levels equal to the veg room environment, but gradually decrease humidity each day until you reach 55 percent. During the following week, drop RH to 45 percent to 50 percent and hold that value throughout the remainder of the flowering cycle.
(Note: Each environment has its nuances, and will require fine-tuning to suit the exact needs of a given situation.)
2. Light Intensity
Young vegetative plants do not require the high light levels necessary for heavy flowering. For quality vegetative growth, a light intensity of 300 micromoles to 700 micromoles is sufficient, whereas optimum levels for flowering plants are 900 micromoles to 1,200 micromoles. If plants are not properly acclimated, this bright transition will cause light and heat burn, and produce symptoms such as whole-plant yellowing and leaves that turn away from the light source.
Avoid this undue stress with proper equipment selection and grow room design. Use grow lamps that can be dimmed, or have your electrician install lights that can be simultaneously turned on or off in a checkerboard pattern, allowing you to gradually spread the increase in light intensity over time. If you are using lights that can’t be dimmed, consider purchasing “yo-yos” that allow you to manually raise and lower lamps to adjust light intensity.
Judging how to irrigate recently transplanted cannabis can be tricky, especially if the new container is larger than the last. Cannabis roots will struggle to fill out massive new pots if the substrate remains constantly wet. Over-watered plants grow slower, are more susceptible to root disease and typically yield less.
Avoid this problem by only irrigating enough to comfortably settle the plant into the new container. Wait until you see new white roots emerge from the bottom of the container before you fully saturate the pot.