Should the marijuana clones I am going to plant outdoors grow under continuous fluorescent light, or should I root them under 18 hours of light? Will the shift from 24 hours of light to 14 1/2 when I transplant them outside shock the clones of an early variety into flowering? Can I take cuttings directly to the out- door garden?
Every marijuana variety, particularly early and mid-season types, can have problems when shifting from continuous indoor light to an outdoor regimen (which only gives them 13 to 16 hours of daylight). There are two reasons for most problems that arise in this regard.
The first problem is that every marijuana strain has a critical dark period (i.e. the number of hours of darkness needed to induce flowering). For the sake of convenience, we put every variety at under 12 hours of uninterrupted darkness to help them flower indoors. But, some marijuana plants flower with fewer hours of darkness. For example, many plants begin flowering in August when the dark period is 8 to 11 hours. If the amount of darkness exceeds the plant’s critical dark period, the plants will start to flower. To avoid that, you’re going to have to interrupt the dark period with temporary periods of light. You can use a bright incandescent light and shine it on your plants for only a few seconds every couple of hours during the dark period to prevent the plants from being induced into flowering.
Secondly, marijuana plants that generally need a short dark period to force flowering (e.g. indica hybrids), occasionally react to a sudden change of regimen from continual light to 9 or 11 hours of darkness by flowering. Late-ripening sativas might even start growing flowers while they are still in a vegetative state leading to eventual full flowering. Growing clones under an 18-hour light regimen with a 6-hour period of darkness is less likely to trigger flowering when they are placed outside. Plants with known critical dark periods can be grown under a slightly shorter dark period to ensure that vegetative growth remains in full force during rooting. When placed outside, it won’t be shocked by a dramatic shift in the light regimen. For example, a marijuana plant that is induced to flower with a dark period of 11 hours or more can be locked into a vegetative state with 9 hours of darkness and 15 hours of light. This plant will seamlessly make the transition to outdoor life.