First-time cannabis growers should start with a soil-based system rather than other more complicated methods such as hydroponics. 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 gardening or potting soil naturally. Good quality soil is inexpensively available at any gardening store 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, a natural volcanic glass, 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. Do not use soil from your yard as it may have pH imbalances, lack nutrients, or contain insects or mold spores that could harm your plants.
If growing indoors, use a high-intensity discharge (HID) light, either a high-pressure sodium (HPS) or a Metal Halide (MH) bulb. Both work well, but HPS systems are the best for flowering.
While fluorescent grow bulbs work for the vegetative growth of the plant, they lack the proper light spectrum and intensity to produce dense buds. Never use regular incandescent bulbs —they will not provide the correct spectrum of light for the plants and are expensive to run. Specialty incandescent “grow bulbs” don't have the intensity needed to grow dense buds, but they will definitely keep the plants alive. New LED bulb technology draws far less power and generates much less heat than HIDs, with better light spectrum output than fluorescents, though yield may not be quite as good as with an HID.
Cannabis flowers form naturally outdoors in the fall, as the nights grow longer. Indoors, we can force cannabis to flower when we want by creating a growing space where the light cycle can be controlled. At least 12 hours of uninterrupted darkness is necessary to force cannabis to flower. This period, known as the flowering period, lasts approximately 6-10 weeks, depending on the strain of cannabis.
The vegetative period, which precedes the flowering period, is usually done under 24 hours of continuous light. If starting with clones, that is rooted cuttings from a mature plant, this period usually lasts from five days to a month depending on strain, vigor, and the desired plant size. If starting from seed (not recommended), the vegetative period will be longer to allow the plant to mature.
Seeds will produce both male and female plants. Males should be culled before they can pollinate the female plants. You can determine the sex of the plant as it begins the flowering cycle.
Cannabis plants will usually increase in size 50% during the flowering period, so plan for that in relation to the height and width of your garden.
There are three main nutrients that plants need to flourish: Nitrogen (N), Phosphorus (P) and Potassium (K). Plant food labels show their N-P-K content as relative percentages. That means a high-nitrogen food good for vegetative growth would be listed as 20-10-10 or 20% nitrogen, 10% phosphorus, and 10% potassium.
When forcing the plants from vegetative to flowering growth (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 and K to make flowers or “buds.” During the flowering stage, feed your plants a plant food high in P and K. Something like 1-10-12 would be appropriate, but some nitrogen is necessary. Don't get hung up on the actual numbers. It is the ratio that is actually important. Follow the instructions on the label and be careful not to overfeed!
Water your plants once the top two inches of soil are dry. Overwatering is a common cause of death for cannabis. Overwatered plants droop and may look like they need water. What the plants are actually lacking is air, because the roots are drowning. 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 don't. 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. The right pH is critical to the plant's ability to absorb nutrients. In general cannabis likes the root zone to be acidic; around 5.8-6.5 is the ideal range for soil, and no lower than 5.5. The only way to know and adjust the pH of your plants' environment is with pH test strips or a pH test kit that you can use to check the plants' runoff. The pH of your tap water may change from season to season, so it's best to check it frequently.
If you are maintaining proper pH and providing appropriate nutrients and your plants are still not thriving, or are turning yellow or appear to be burning at the edges of the leaf, you should consult a more exhaustive source of information about how to go about solving these problems.
Air and temperature
Cannabis needs circulating air rich in carbon dioxide or CO2. Fresh air from the outside can be used if you are ventilating an indoor garden with fans. Cannabis plants can consume far more CO2 than is in the atmosphere naturally, so for maximum yield some method of CO2 enrichment is frequently used. The easiest is using a regulator attached to a CO2 tank, which can be found at beverage supply stores. Without enrichment or fresh air, plants will consume all the CO2 in the environment and replace it with oxygen, leaving them without the carbon dioxide needed to grow well.
Whether enriched or not, air circulation also helps manage temperature and create stronger plants. HID lights in particular generate a lot of heat, and temperatures above 95 degrees will inhibit growth. Keep the cultivation area temperature between 80 and 85 degrees, using an air conditioner or fans with outside air to cool the space. Too cold is bad as well, especially in the root zone. Below 60 degrees, the plant will be unable to photosynthesize and stops growing.
If you're using fans to bring in outside air and exhausting air from the garden, you may want to use carbon filters or other odor-scrubbing devices on the exhaust. Cannabis emits powerful, distinctive aromas, particularly during flowering, that can attract unwanted attention.
If you keep the basic needs of the plant in mind, cannabis will reward you enormously. For information on managing pests or creating sophisticated hydroponic systems, consult one of the books by experts such as Ed Rosenthal or Jorge Cervantes. Suggested reading for detailed information on cannabis cultivation:
- 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