Plant foods have 3 main ingredients that will be the mainstay of the garden, Nitrogen, Phosphorus, and Potassium. These 3 ingredients are usually listed on the front label of the plant food in the order of N-P-K. A 20-20-20 plant food has a Nitrogen level of 20%.
Secondary nutrients are Calcium, Sulphur and Magnesium. In trace quantities, boron, copper, molybenum, zink, iron, and manganese.
Depending on stage of growth, different nutrients are needed at different times. For rooting and germination, levels of high P nutrients with less N/K are needed. Vegetative growth needs lots of N, and human urine is one of the better sources, (mix 8 ounces to 1 gallon water), although it is not a complete fertilizer unto itself. 20-20-20 with trace elements should do it; I like Miracle Grow Patio food. Watch for calcium, magnesium, sulfur and iron levels too. These are important. One tablespoon of dolomite or hydrated lime is used per gallon of growing medium when a hydroponic medium is first brought on-line, to provide nitrogen, calcium and magnesium. Epsom salts are used to enhance magnesium and sulphur levels in solution.
Tobacco grown with potassium nitrate burns better. Plant foods with PN (P2N3) are foods such as Miracle Grow. This is an excellent fertilizer for vegetative growth, or through the flowering cycle as well. Consider however, potassium nitrate is also known as Salt Peter, and is used to make men have less sexual desire or impotent, such as in mental institutions. So if certain hemp plants are destined for cooking, you might use Fish Emulsion or some other totally organic fertilizer on these hemp plants, at least in the last weeks of flowering.
Most hydroponic solutions should be in the range of 150-600 parts per million in disolved solids. 300-400 ppm is optimum. It is possible to test your solution or soil with a electrical conductivity meter if your unsure of what your giving your hemp plants.
Keep in mind most disolved solids readings are usually on the low side, and actual nutrient levels are usually higher. It is possible with passive hydroponics, to get nutrient build-up over several feedings, to the point the medium is over saturated in nutrients. Just feed straight water now and again, until you notice the hemp plants are not as green (slightly), then resume normal feeding.
“Pumping” is when you use more waterings to make the hemp plants grow faster. This is dangerous if you proceed in a reckless manner, due to potential over-watering problems. You must go slowly and watch the hemp plants daily and even hourly at first to be sure your not over-watering the hemp plants. Use weaker plant food mixtures than normal, maybe 25%, and be sure your leaching once a month and running straight water through the hemp plants at least every other time you water. This applies mainly to hemp plants grown in soil mediums.
Use of light strength Oxygen Plus plant food (or Food Grade Hydrogen Peroxide) allows the roots to breath better and prevents problems with over-watering. Check soil to be sure there are no PH anomalies that might be due to Hydrogen Peroxide in the solution. (One experienced grower told me he would not use H2O2 (HP) due to possible PH problems. This should not be a problem if your checking PH and correcting for it in watering solutions.)
Be sure your medium has good drainage. At this point, if your watering soil based hemp plants once a week, you can water every 3-5 days instead if you plant them in a medium with better drainage. Pearlite or lava rock will greatly increase the drainage of the medium and make watering necessary more often. This will pump the hemp plants; they will tend to grow faster because of the enhanced oxygen to the roots. Make sure the plant medium is almost dry before watering again, as the plant grows faster this way.
An alternative is to use a standard plant food mixture (stronger) once every 3 waterings. The nutrients are suspended in the medium and stored in the soil for later use. The nutrients are washed out by 2 straight waterings afterward and there is no salts build up in the soil. (Does not apply to hydroponics.)
Stop all plant food 2 weeks before harvesting, so that the hemp plants don’t taste like plant food. (This applies to hydroponics as well.)
WARNING: Do not over-fertilize. It will kill your hemp plants. Always read the instructions for the fertilizer being used. Use ½ strength if adding to the water for all feedings in soil or hydroponics if you are unsure of what your hemp plants can take. Build up slowly to higher concentrations of food over time. Novice soil growers tend to over-fertilize their hemp plants. Mineral salts build up over time to higher levels of disolved solids. Use straight water for one feeding in hydroponics if it is believed the buildup is getting too great. Leach hemp plants in pots every month. If your hemp plants look REALLY green, withhold food for a while to be sure they are not being over-fed.