Fertilizers are any organic or inorganic substances that provide the nutrients necessary for plant growth. They usually combine the macronutrients (the ones plants use the most) with micronutrients, or trace elements, that plants need for specific purposes. Besides carbon, hydrogen, and oxygen, which all plants need, the three most-needed macronutrients for growing marijuana are nitrogen, phosphorous, and potassium, indicated on fertilizer labels by their chemical designations: N, P, and K.
Plants differ in their nutrient needs, but basically marijuana needs nitrogen for vegetative growth (stems
and leaves), phosphorous for plant vigor and flowering, and potassium for good flowering, which is the
ultimate goal of the marijuana grower. Therefore, more nitrogen is needed during the early growth stages and more phosphorous and potassium are required during the flowering period. To deliver the nutrients in the best possible way, two types of fertilizers are recommended: timed-release fertilizers in granular form that are mixed into the soil, and water-soluble fertilizers that are mixed with the water used for watering the plants. Both are suitable for containers and outdoor gardens, but I recommend the water-soluble fertilizers because you can adjust the nutrient levels better for vegetative growth and then flowering.
Back when I was growing marijuana, I used weak solutions of Peters or Miracle-Gro 20-20-20 (N, P, K)
water-soluble fertilizer (the bright blue stuff), and they worked fine for me. A lot of other marijuana growers believe that organic fertilizers are superior to inorganic ones despite the lack of scientific evidence that this is true. Plant scientists at New Mexico State University, where I am a member of the adjunct faculty, have told me that, for example, as long as nitrogen is provided for the plant, it does not care whether the source is organic or synthetic.
Now you can choose from a myriad of fertilizers, some designed for vegetative growth and some for
flowering. The marijuana growers I know prefer FoxFarm organic fertilizers, including premixed Tiger Bloom. Compare that to synthetic Miracle-Gro LiquaFeed Bloom Booster Flower Food, which is about half the cost. The decision to use organic or synthetic fertilizers is a personal matter that sometimes comes down to individual belief systems. As with religion and politics, there are true believers in the garden world who fervently swear by organic-only techniques, but I agree with the plant scientists that the plant doesn’t really care as long as it receives the proper nutrients. This thinking is considered heresy by die-hard organic gardeners, who says, without any empirical evidence, “If it’s organic, it’s orgasmic—you can’t fake it.” Whichever you prefer, using a high-nitrogen fertilizer for vegetative growth and a high-phosphorous fertilizer when blooming begins will produce more flowers and could possibly increase the amount of THC in those flowers. People believe that marijuana’s THC level is determined only by a plant’s genetics, but that’s not true with the capsaicin in chile peppers, where environment plays up to a 50 percent role in the heat level of the pods. (For example, stressing chile pepper plants by withholding water until they wilt slightly can increase heat lein the pods.) Click on the link for more information; http://www.ilovegrowingmarijuana.com