Your carefully propagated young cannabis plants are rooted in the propagation area and ready to move to the vegetation room. Make the move stress-free for these young plants by gradually transitioning the light intensity from propagation to vegetative levels while minimizing environmental changes.

STEP 1: Transition to LED Spectrum

If you’re switching from a LED propagation environment to a LED veg environment, you won’t need to worry as much about this step.

If you grow young plants under T5 fluorescent or metal halide lights in propagation, the first step in the transition to the vegetative phase is to acclimate your plants to the enriched spectrum of LEDs. This is a relatively quick process, taking only one to two days. During this step, match the light intensity of your LEDs in your vegetative rooms with that of the propagation room. This step is only to transition to the new spectrum. All other environmental variables remain the same.

Average light intensity for cannabis propagation is between 100-200 μmol·m−2·s−1.

If you don’t know your propagation area’s light intensity, you’ll need to take light measurements for this step.

How Do You Measure Light Intensity?

To measure light intensity, use a quantum-sensor light meter.

Quantum-sensor light meters measure photosynthetic photon flux density (PPFD). This allows you to match the light intensity as the plants see it, rather than the visible light seen by humans.

Full-spectrum quantum-sensor light meters measure light differently than meters that measure lumens or footcandles.  Light intensity measurements of lumens or footcandles will significantly understate PPFD intensity. This is because they measure the light intensity based on how humans perceive visible light.

With a quantum sensor, take a few intensity readings at canopy level and average the readings to establish the average PPFD in your propagation area.

STEP 2: Begin to Increase Light Intensity

After your plants have acclimated to the LED spectrum, you can begin gradually increasing light intensity by 50% every 1-2 days. This allows for a gradual but timely transition. If you are growing more sensitive cultivars, you can increase the light intensity as slowly as every 7 days. If you are growing hardier cultivars, you can increase light intensity more quickly to complete the transition faster.

Each time you increase the light intensity, review the environmental settings and plants’ responses regularly. Gradually transition the other growing area conditions and settings to vegetative levels. If you spot anything of concern, slow down the transition period to minimize stress on your plants. Each transition period can be as long as 7 days.

STEP 3: Repeat Until Ideal Light Intensity Reached

Continue to increase your light intensity until you’ve reached the vegetative intensity level. The ideal light intensity for vegetative growth is 400-600 μmol·m−2·s−1. Once your light intensity has reached the level you want for veg and your plants are happy, let them veg away!

See the next article in this series, “How to Transition Cannabis from Veg to Flower”, to prepare for the transition from the vegetative to flowering stages.

How Do You Use Spectrum to Control Plant Morphology?

Different varieties of cannabis respond differently to lighting applications. To see the effects of varying spectral ratios on a variety’s growth development, adjust the spectral ratios once plants have successfully transitioned to the vegetative stage and then monitor their growth to identify from these spectral ratios.

To keep stretchy or elongated varieties compact, try a high blue ratio (70% Red: 30% Blue) throughout the vegetative stage.

To help compact varieties stretch to allow space for buds to develop between nodes, try a high red ratio with less than 10% Blue.