Marijuana Cultivation/Vegetative Growth
The vegetative growth cycle is about growing the plant mass in preparation for flowering. Outdoor you will have several months of vegetative growth. Indoors you can have as little as a week (if using clones), 4-6wks (typical), or as much as you want.
The adult life cycle of the marijuana plant consists of two stages of growth. Vegetative and Flowering. The plant determines which of these stages of growth it should be in through the presence of a flowering hormone (phytochrome) which is sensitive to light. As long as light levels above 12-14 hours are maintained the flowering hormone will never be present in high enough levels to induce flowering in the plant. At any point during the plants life if the light is on for more than 12 hours a day it will cause the levels of flowering hormone to be reduced and the plant to revert to the vegetative growth stage. If a plant is reverted during flowering by irregular light patterns it can cause stress in the plant and stress can cause hermaphroditism. A plant can be maintained in vegetative growth without being allowed to flower indefinitely with no adverse effects.
Typically indoor growers who can control their light cycles will use either 18 hours of light per day or 24 hours of light per day. There are mythical claims that a darkness period is needed but there is no evidence to support this. Extremely healthy and potent marijuana is grown under 24-hour vegetative light. What is in dispute is whether the extra light hours bring a great deal of benefit compared with 18-hour light. Most 24-hour growers claim some increase in plant vegetation but few claim a large increase.
During vegetative growth you will want to use a fertilizer that is high in nitrogen at full strength. Nitrogen is used by the plant to grow stems, leaves, and other green parts and so is absolutely essential to the vegetative phase of growth. As always you should begin with the manufacturers suggestions for the period of growth you are in when adding fertilizer and then adjust up or down based on how your plants respond.
There is another section on plant problems but a good hint to know at this stage is that it is common to mistake too many nutrients or PH misadjustment for nutrient deficiency. Always carefully check PH before adjusting nutrients to fix a problem and if adding nutrients doesn't seem to be fixing your 'deficiency' try flushing the system instead. Unlike the drooping leaves that result from under or over watering yellowing and necrosis from nutrient problems generally don't recover but they stop getting worse and new growth will be green and healthy.
Training and Trimming
Different techniques have developed for training plants. The goal of training a marijuana plant is to optimize yield with the available light and space. Outside a plant in the middle of a clearing with a full year of vegetation can probably be left to do what it wants and give great yields. Indoors the light is more precious and and many growers are using small cabinets. They just train their plants to utilize the space they have.
A couple things that any grower should be aware of are that leaves are solar panels. You might be twisting and directing the branches but the plant knows better than you when and where it needs leaves, leave them alone. If a gentle pull on the leaf doesn't cause it to give way immediately then it is healthy tissue. Usually you will only want to remove browned leaves. With a thick canopy under indoor light the lower growth will yellow and die, this is because the plant isn't getting much light there and steals the nutrients from these now unneeded leaves. This is nature at work and not always a sign of too much or few nutrients.
Another thing that is important to know is that the tops of the plant produce the most potent and largest flowers. Most training techniques focus on maximizing the number of those top flowers and on removing smaller lower flowers the plant will direct all its energy to the larger tops. How much difference different training techniques make is debated but trimming lower growth that is far from the light is universally agreed to improve yield. Any time you bend a branch horizontally it will cause the plant to produce a hormone that encourages lateral growth.
When training plants you will occasionally snap a stem. It happens. Plants can usually recover from this. Just position the stem back together and tape it in place. Give the stem time to recover before applying more pressure to that spot. A small knot will develop at the break and in the end the plant stem will grow back healthier and stronger than before.
Jogging also known as the jungle of green or JOG technique is a useful way to maximize the yield from your crop. It is very effective in a low grow space as well.
With the jog technique you will use wires shaped into "U"'s to hold down the stem into the desired positions as you gradually shape it around the perimeter of the pot. The goal is to make the plant entirely fill the pots space with top buds. No matter how much training you do a plant will have a genetic maximum bud capacity that can not be exceeded. Training will help you reach that potential but nothing can allow you to exceed it.
Sea of Green
Sea of a green is a technique whereby you grow a far greater number of smaller plants rather than a small number of large plants. Usually clones are used for uniform growth characteristics and each plant is trimmed so that only the main stalk grows.
Screen of Green
With the screen of green, or SCROG technique, a screen of wire such as chicken wire is held up as a horizontal plane above the plants. The plants are nudged through the screen to create a uniform canopy so that all light is utilized by growth. Generally anything below the canopy is trimmed off.
LST is a technique where a plant is trained through the use of ties or ropes. The idea is that you use a support rope at the base of the plant pulled one direction and another tied to the top pulling it down in a different direction. Every couple days the top will be pointing upward again while axins (branching hormones) reach the other nodes. Each time the top pulls up above the other branches the top rope should be moved up and the top pulled down. Continue doing this until the top does not pull above the other branches.
Topping is one of the oldest tricks. No matter what you have heard topping is not clipping off bud tops. Topping is removing about 3/4 of the top growth tip. This will cause the plant top to split into two tops. This technique can be used to produce as many tops on a plant as you want. Begin topping off after the first pair of serrated leaves. Topping below the first set of serrated leaves will kill the plant. Making the first topping here forces 4 new tops to grow. When you see a new set of sprouts with each a set of leaves and when their tops are big enough pinch it off to make another set of sprouts on that limb. When you have 8 tops you're ready to begin flowering.