Q:
If I start my plants indoors in March and want to plant them outdoor in April or May, will I need supplemental light to keep them from flowering early?
A:
The short answer is yes but to give you a more useful answer we’ll need to consider the strain, if you are growing from seed or clone, your latitude, and the last day of frost in your area.
Strain
Different strains have different flowering thresholds. Generally cannabis plants from equatorial regions take longer to begin flowering and subsequently continue to grow longer into the season. Sativa dominant strains usually fall under this category. Indica dominant strains are faster to enter flowering and finish sooner. I recommend greater care with Indica strains when adjusting photo-periods as they can easily begin flowering even from minor changes. A few years ago we published a helpful article on the mechanism behind what makes cannabis plants flower.
Seed or Clone?
Clones are normally in vegetative environments with 18 to 24 hours of light. Moving them outside at almost any time of year will tip the more temperamental strains into flowering. This phenomenon can be capitalized on, if you are using a growing method I call the “no-pull-dep”. With clones, it’s important to slowly begin reducing light exposure until it matches the natural daylight schedule on the day they are moved outside. Seeds on the other hand generally do very well when started early and in my experience are more resilient to changes in the photoperiod.
Latitude
It’s helpful to know exactly how many hours of light to expect on your target transplanting day. This will change depending on your gardens distance from the equator. Don’t guess, look it up! In almost all cases you will be reducing the hours of light. Use the information from the linked website and match your supplemental light to the expected natural light.
Frost
Cannabis plants don’t like to be cold. In most cases the cold will slow growth and in some cases it will kill your plants overnight. If you are moving plants outside when there is still the potential for a late frost, make sure you are using some kind of frost proofing system to keep them warm.
Pro Tip
My favorite cheap and easy method is to pound 4 stakes in the ground around the plant creating a square or rectangle about the size of a shipping pallet. Then wrap the stakes with clear pallet wrap. It’s basically a thick stretchy saran wrap and will make 4 clear walls like a mini greenhouse. If the ground is too soft you can nail the stakes to a planter box. If you space the stakes correctly, you can cover it at night with a clear waterproof pallet cover. If you add a 60 watt incandescent light to the inside of the plastic, not only can the light help stretch out the length of your plants day, but the heat from the light will help keep you plants warm at night. Repeat for each plant and you won’t be caught off guard by sneaky old Jack.
Photo-Period Control When Starting Cannabis Early,
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