First time growers should start with a soil-based grow rather than other more complicated methods. Your first harvest will help you get the feel for the growth and life cycle of cannabis. This will help you build confidence that things are going well for your next harvest.
Soil is the easiest medium to grow from for a number of reasons. First, micronutrients, which are critical to proper growth and vigor of the plan, exist in soil naturally. Soil is inexpensive and not suspicious to neighbors who may wonder what all the equipment is for otherwise. Make sure that the soil is not too dense. Use Perlite to lighten and loosen the soil. This provides necessary space in the medium for air. Air is an important factor in cultivating any type of plant.
Get a high intensity discharge (HID) light. High-pressure sodium systems are the best for vegetative and flowering. Without a HID light, you will not produce dense buds. You may substitute fluorescent fixtures with warm bulbs (not cool white), but the yield from such a system would be lower. Do not use regular incandescent bulbs - they will not provide the correct spectrum of light for the plants and are expensive to run. Fancy specialty "grow bulbs" donít have the intensity needed to grow dense buds, but they will definitely keep the plants alive.
Cannabis flowers form naturally outdoors in the fall, as the nights grow longer. Indoors, we can force cannabis to flower by creating a growing space where the light cycle can be controlled. 12 hours of uninterrupted darkness is necessary to force cannabis to flower. This period, known as the flowering period, continues for approximately 6-10 weeks depending on the strain of cannabis.
The vegetative period, which precedes the flowering period, is usually done (with clones) under 24 hours of continuous light. This period usually lasts from five days to a month depending on strain, vigor, and the desired plant size. Plants will usually increase 50% during the flowering period. You may want to make a note of that in order to accommodate the height and width of your garden.
There are three main nutrients that plants use: Nitrogen (N), Phosphorus (P) and Potassium (K). These are noted on the plant food label with relative % numbers as N-P-K. A good balance for the vegetative cycle would be something with a high N ratio, such as 20-10-10. When changing the plants from vegetative to flowering (i.e. changing the light cycle from 24 hours of continuous light to 12 hours of light and 12 hours of uninterrupted darkness), the nutrient ratio must change as well. Plants use P & K to make flowers or ďbudsĒ. During the flowering stage, feed your plants a plant food high in P and K. Something like 1-10-12 would be appropriate. Donít get hung up on the actual numbers. It is the ratio that is actually important. Feed cannabis like a vegetable. Follow the instructions on the label and be careful not to overfeed!
Water your plants whenever the top 2 inches are dry. Overwatering is a common cause of death to cannabis. Overwatered plants droop and look like they need water. The first reaction is to water a plant that looks droopy. What the plants are actually lacking is air. The roots are drowning and the last thing that they need is more water. One simple way to check for the proper time to water is with a wand type water meter, another is to lift the pot after watering. Feel its weight or put it on a scale and make a note. Next time you think the plant needs water lift the pot and see how heavy it is. If it is light, then water it. If it feels heavy then donít. Young plants will use less water. As the plant grows and the root ball fills the container, it will use more water.
pH is a measure of the acidity or alkalinity of the planting mix and water. In general cannabis likes the root zone to be acidic, around 5.6 - 6.3 is the range. You may want to get a pH test kit and check your tap water to see if it skewed in one direction or the other. If your plants are not thriving, are turning yellow or appear to be burning at the edges of the leaf, then you may need to consult a more exhaustive source of information about how to go about solving these problems.
Air and temperature
Cannabis needs fresh air. You will have to find a way to circulate the air in the growing chamber a re-circulating system with carbon dioxide enrichment is best . Fresh air from the outside can also be used if you are ventilating the garden. Fans will move air sufficiently in and out of the closet from the house. You just need to be aware. Without enrichment or fresh air, plants wonít have the carbon dioxide needed to grow. No fresh air, no CO2, enrichment, no big buds. Temperature is another reason to circulate the air. HID lights create a lot of heat and high temperatures will inhibit growth. Keep the temperature between 80 and 85 degrees and you will not have growth problems related to heat enclosed system, using an A/C to cool the space. Too cold is bad as well, especially in the root zone. Under 60 degrees, the plant will be unable to photosynthesize and it stops growing.
By keeping the basic needs of the plant in mind cannabis will reward you enormously. Light, food, water, carbon dioxide and correct temperature (80-85 degrees) are all critical to the proper growth of the cannabis plant. Good luck!
Suggested reading for growing cannabis
Marijuana Growers Handbook : Official Course Book of Oaksterdam University by Ed Rosenthal
Marijuana Garden Saver by Ed Rosenthal and JC Stitch
Indoor Horticulture by Jorge Cervantes