Nutrient (or fertilizer) is food for plants. Marijuana plants need a certain amount of food in order to grow properly. The primary nutrients in plant foods are Nitrogen (N), Phosphorus (P), and Potassium (K).
In addition to nitrogen-phosphorus-potassium, marijuana plants require a lesser amount of secondary nutrients and trace quantities of other elements.
Secondary nutrients are calcium, sulphur, and magnesium. Trace elements are small quantities of boron, copper, molybdenum, zinc, iron, and manganese.
Plant foods are measured in an N-P-K format
N is Nitrogen
P is Phosphorus
K is Potassium
A 15-15-15 plant food contains:
15% Nitrogen
15% Phosphorus
15% Potassium
A 20-10-10 plant food contains:
20% Nitrogen
10% Phosphorus
10% Potassium
The percentage of the solution not used by nitrogen-phosphorus-potassium is secondary nutrients, trace elements, and inert material.
An all purpose fertilizer with secondary elements like calcium, sulphur and magnesium and trace elements boron, copper, molybdenum, zinc, iron, and manganese will get you through all stages of growth. But during different stages of life, you can adjust the different nutrient levels needed at different times to optimize growth.
After germination, when growing marijuana in soil, you should water feed (no nutrients) the plants for the first week or two. Almost all soil will contain some amount of fertilizer for the plant to feed on.
A minimal amount (or no) fertilizer should be added to the water for the first week or two. Then use a 50% solution for two weeks, then go to a 100% solution.
Plants are delicate at this stage and can go for a week or two with a minimal amount of food. At the maximum, use a solution that is no more than 50% of the strength of the recommended level.
That is, if the nutrient manufacturer recommends mixing one tablespoon of nutrient to every gallon of water, you should add less than half a tablespoon of nutrient to every gallon of water for the first two weeks after germinating.
Do not give your plants extra fertilizer thinking it will make them grow faster. Too much will kill your plants. If you under fertilize, plants will take longer to grow but will not die. Follow the mixing instructions on the package, if you aren't sure, use less rather than more.
During vegetative growth the plants need lots of N (nitrogen). They also need a fair amount of P (phosphorus) and K (potassium). A plant food that is 20-10-10, or 30-15-15, or something similar, with trace elements should do a very good job.
During flowering the plants need more P (phosphorus) and more K (potassium) than they did during vegetative growth. They need some N (nitrogen) but not as much as they did during vegetative growth. They also need calcium.
If you used:
--- something like 20-10-10 for vegetative growth, then try using 10-20-20 (or similar) for flowering.
--- something like 30-15-15 for vegetative growth, then try using 15-30-30 (or similar) for flowering.
If you can't find nutrients containing the proper combination for your needs (or you are not sure what kind of nutrient to get), look for a plant food recommended for growth when the plant is in the first stages of life.
Look for a plant food recommended for blooming (or flowering) when the plant is in the flowering stage. Make sure any plant food you use contains nutrients and trace elements. And remember that during flowering, calcium is important.
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