Vegetative Marijuana Growth

The first phase of marijuana growth is called the vegetative phase.

If you plan on using the mh or hps right away, start with the light about 20 inches or more above the top of the plant and lower the light an inch or so daily until you think the height is right. Too close and the plants will dry and turn brown. Too far and the plants grow too tall as they stretch to get closer to their light source.


You can also start the vegetative phase with a fluorescent light turned on for 18 to 24 hours a day for the first one or two weeks or longer. You can use a standard 48 inch fluorescent fixture (with two) 40 watt bulbs placed about 2 to 8 inches above the tops of the plants.

3 to 5 inches is ideal, but you might have to raise the light a bit higher so all the plants get some light, depending on your setup. Mix your hydroponic nutrient solution to 50% of the normal recommended strength for the first two weeks of growth regardless of lighting.

The reason for starting off with fluorescent lighting is to not give the plants too much light at the beginning of the growing process. Let them build up to it as they would in nature where the seeds would germinate in spring when the sun is not as strong as it will be in summer.

An alternative to growing under hps or mh during vegetation is to set up a vegetative area, and a flowering area.

The vegetative area would use a cloner or something similar that would allow seeds or clones to grow and two standard 48 inch fluorescent tubes, turned on 24 hours a day.

You can build a very good cloner yourself with the instructions found at overgrow and sometimes you can find a cloner at eBay. They range in price from $15.00 to $100.00 but are not always available.

The flowering area would use a standard hydroponic set up with hps and/or mh fixtures turned on for 12 hours a day.

While the flowering plants are going through their cycle with the hydroponic set up, the germinated seeds or clones will have a few months to develop in the cloner. After the flowering plants have been harvested, the plants in the vegetative area are ready to move to the flowering area. New seedlings or clones can then be started in the cloner.

There are two main benefits to this kind of set up. Electricity use will be about 25% to 35% less because the mh or hps light is only on 12 hours a day. The longer a plant has been growing in the vegetative phase, the quicker it will flower.

The only drawback I have found is the extra area needed to set up two different grow areas. Since the flowering plants need absolute darkness during the dark phase, the light from the vegetative area can't reach the flowering plants. So they need to be isolated, either by using curtains (or something similar) or by being located away from each other.

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Try to keep the mh or hps light about 12 or more inches above the tops of the plants. If the parts of the plants closest to the light dry out, raise the height of the light source, they are too close. If the plants are too far from the light they will stretch and be tall but not have much bud. That is a waste of space. Start high and lower the light an inch or two daily until you think the height is right.

During the first stage of growth, the vegetative stage, keep the light on 16 to 24 hours a day minimum. The longer it is on, the faster the plants will grow, but the higher you electricity bill will be.