Nutrients can be used in indoor and outdoor growing. They are especially important if the soil is deficient in nutrients itself. If growing marijuana hydroponically, nutrients are vital. When growing hydroponically, and as a general rule, it is advised to put less nutrients in than stated on the bottle or container. You can always steadily increase. If you put too much in from the start, the plant can be burnt and sometimes harmed irreversibly.
Growers will also sometimes add extras like fish oils, when experimenting. Just remember be careful. To help nutrients to be absorbed, a wetting agent can be used. Wetting agents help the nutrients to be delivered. You can buy them, but basically they are almost like dishwashing liquid, so a very small amount of that could be used instead.
There are lots of ready made nutrients on the market some aimed at marijuana some not. In the end there's not much difference between any of them. As long as the nutrients are complete and given in the correct dosage results should be good.
Nutrients have an N.P.K. ratio on the packet. This shows the amount of Nitrogen (N), Phosphorus (P) and Potassium (K) the nutrient contains as a percentage. A complete fertiliser will also contain all the other nutrients and minerals a plant needs for good growth.
Marijuana is a nitrogen lover and whilst in its growing stage it will need a feed with extra nitrogen. When flowering starts it will require extra phosphorus and potassium instead. This is why a lot of cannabis nutrients come in two or even three part formulas.
To easily control the rate and amount of food a plant receives use bland nutrient free mediums, with or without standard potting compost mixed in. Then add a soluble complete feed to the plants water in the recommended amounts.
Mixing organic nutrients takes time and knowledge. Getting a good safe balanced mix for plants grown in the ground can take months. Start planning now if you want to grow organic and remember that you may still need to feed with a nutrient solution as well.
If a plant looks under fed check the p.h. of the medium and water before adding more nutrients. If your growing in soil make sure your not over watering and suffocating the plants roots. Soil should be allowed to dry a little between watering.
Some nutrient ratios:
Whatever nutrient you use you should always stop feeding at least 10 days before harvest. Only give the plant p.h. balanced water from then on. Doing this will help "flush" the nutrients out the plant and produce better tasting and better burning buds.