The majority of marijuana cultivators are cultivating for unpollinated female flowers and breeding purposes. Naturally most readers are highly interested in this particular phase of adult marijuana growth. The truth is that flowering is actually pretty simple.
When do I Flower?
When to flower is a decision every grower must make for themselves. During the flowering stage a plant may grow 2 - 2.5 times the size it achieved in vegetation. An indoor grower in particular will need to plan space accordingly. Up until then the grower will have been trimming and training plants but during flowering these things should be avoided if possible. Growers with limited space should take note.
Whenever you want to flower your plant should be at a level of maturity where it is producing alternating nodes. If grown from seed this will usually occur a few weeks into vegetative growth. Clones taken from a mature plant will be sexually mature upon rooting and can be flowered immediately.
Towards the end of flowering, plants will begin robbing nutrients from their leaves. This is perfectly normal and nothing to be alarmed about as yellowing leaves are normal. You do not need to make an effort to remove the leaves unless they are brown and dead.
Lighting and Nutrient Changes
In order to make a plant flower you will need to reduce its light cycle down to 12hrs a day. During flowering it is absolutely essential to make the dark period as dark as possible and to never interrupt that cycle with light. Light up to the level of moonlight can be present without preventing the plant from flowering but any light reduces flowering hormone and will reduce the output of your plants. Light interruptions during the flowering period causes stress on the plants and can result in stress induced hermaphrodites. To avoid this, just place a green light bulb in the room. Use ONLY the green light when working in the room during the dark cycle. The plants cannot absorb the green light and thus it is safe to use, with no risk of ruining your crop. Attempts to remove all the pollen sacks on hermaphrodites are never successful and will result in a seedy crop. The best course of action if you find a hermaphrodite is to (1) spray the affected plants with water to hold the pollen in place, (2) put a trash bag around the whole plant (use a twist tie or something at the stem to hold it in place), (3) remove it quickly.
Some growers believe that it is important to begin using flowering nutrients 1-2 weeks before switching over the light for flowering. Others begin flowering nutrients when they switch the light. There may be benefits to switching nutrients early but it is certainly not a requirement.
Growth and Rough Timeline
It should be noted that this is just a general average guideline. There are wide variations from this, some strains will move faster and other much more slowly. In some cases that wait is worthwhile and in others it is not.
1-2wks - During this time your plants will be changing over to their flowering period. It is generally during this time that the first evidence of flowers will appear.
2-4wks - During this time the plants will begin to stretch for the light. Flowers will appear at all the nodes but they will be light and airy no matter what you have done.
5+ - During this period you will likely see lots of yellowing on leaves and if you have done everything else right you will see the buds fill in and thicken substantially.
Last two weeks - During the last 1-2wks of your plants life you will want to water it with clean water and feed it no nutrients. Before the last 72hrs you will want to flush the grow medium thoroughly. During the last 24-48hrs you should shut off the lights (thc is light sensitive and the plants will be utilizing sugars already produced by photosynthesis during this period). Overall this will increase taste and potency by flushing the plant of fertilizers and sugars which simply don't taste good when burned.
There are a plethora of supplements on the market and no attempt will be made here to list them all at this time but there are a few general types that most flowering supplements fall into that can be addressed here.
Sugar supplements such as sweet, molasses, etc - This type of supplement does NOT feed the plant directly. Plants can not utilize already processed sugars like this. What this does do is nourish organisms living in the grow medium. If you are using an organic grow process or growing in soil this can be very beneficial but should be stopped during the flush period.
Hormone Supplements - Naturally the effects depend on the hormone but all in all these are beneficial but expensive. Plant growth hormone extracted from algea is helpful but provides far more benefit during the vegetative grow cycle than the flowering cycle. Plant flowering hormones are beneficial during flowering, largely for creating more flowering sites than without. Most hormone supplements tend to be very expensive which limits their practical utility. FT Protein (Florigen) extracts have been extracted by Florigen Labs efficiently enough to make them affordable to most growers.
Taste enhancers - There are products with citrus and other flavors that claim if you feed them to plants the plants will take on some aspect of their flavor. This is generally reported to be false.
Nutrient supplements - Some boosters are simply more flowering nutrient. How well they work depends on how ideal the mix you are using is already.
Calcium/Magnesium Supplements - These are very useful for balancing out your nutrient mix, this underrated nutrients are important for plant growth. The use of a supplement like this is highly recommended for all phases of growth.