Does temperature have any effect on the flowering time of plants grown outdoors? Autumn can arrive relatively early in some places and it's not uncommon to have temperatures in the 30's by the end of September. Because flowering doesn't begin until the middle of August at the earliest, you generally don't harvest until the middle of October. Will the low temperatures speed up bud maturity and quicken resin gland production, or will they just limit growth and damage the buds and plants?
Botanists classify marijuana as a short-day plant, meaning that it flowers when receiving a long period of uninterrupted darkness each day. Flower initiation in marijuana plants, unlike some other plants, is not affected by things like moisture or temperature. Flower growth, however, does have an impact on both of these factors. Low temperatures limit growth while dry conditions end up hastening maturity and producing smaller buds.
Autumn's lower sunlight intensity and lower temperatures tend to slow bud growth because photosynthesis decelerates when light intensity diminishes. The low temperatures will also reduce respiration, and make the plant more vulnerable to fungal infections. Earlier maturity often results in a better crop, and there are three ways to speed that process up.
The first and most convenient way is to find a variety that naturally matures earlier. Short-season (Indica) varieties will always mature earlier than late-season (Sativa) ones. As far as long-term plans for early harvesting go, this is definitely the best.
The plants can be forced to flower by increasing the period of darkness to 12 hours per day by covering them with a lightproof tarp or other cover. If the plants are shaded early every evening beginning in late July and the cover is taken off every morning, the plant will start flowering a few weeks earlier and will ripen somewhere in the middle of September. In late August, at the time the plants would usually just be starting to flower, the plants can go without any covering because the dark period is naturally long enough in late summer.
There are other advantages to flowering early other than the fully-ripened buds. Because the plants will bloom in mid-summer (when the light is much more intense) the buds will be larger and tighter by leaps and bounds. The increased amount of UV-B rays will give the plants higher THC levels. Fewer people will be looking to steal your plants at this time of year and any molds will be entirely absent.
The third option presented to you is to pollinate the flowers yourself and harvest the plants only a week later as the plants start forming seed pods, but prior to any advanced seed formation. Growers generally want to harvest before a killing freeze. If this generally occurs September 30 and the plants are three week or a month from maturity on September 15, the flowers can be "painted" with pollen that you have already collected and stored.
As soon as the flowers are fertilized, the plants will quickly stop producing new flowers to focus their energy on seed production. The pistils start to dry and recede into the calyx as the ovary starts to transform into a seed. Before a hard shell develops around the seed, the buds are harvested. The glands will be developed fully and the buds will be firm and lush.