Most plant foods have 3 main nutrients that are essential to healthy plant growth. These nutrients are nitrogen, phosphorus, and potassium. Usually you can find a number listing, such as 20-20-20, on the front of the bag of plant food. This is in the order of n-p-k, or nitrogen-phosphorus-potassium. A 20-20-20 has 20% nitrogen content. There are several secondary nutrients that are necessary too. These are: sulfur, magnesium and calcium. There are also trace quantities of boron, zinc, iron, copper, molybdenum, and manganese.
Each stage of growth requires different nutrients. For instance, high P foods are necessary for germination and rooting, and not too much N or K is needed. When plants develop further and are in vegetative growth, lots of N, or Nitrogen, is required. Strangely enough, human urine is actually a great source of nitrogen. Mix about 8 oz to 1 gallon of water, and use it to water your plants. However, you must use this is combination with plant food to get the best results. Personally I use Miracle Grow Patio Food, but any 20-20-20 will do. It’s hard to get enough calcium, sulfur and magnesium, as most plant foods don’t include any. To fix this deficiency, I use 1 tablespoon of dolomite or hydrated lime in each gallon of water. Epsom salts can also be used to increase sulfur and magnesium levels.
Plant foods with PN (P2N3) such as Miracle Grow are great for vegetative growth, as well as flowering. However, make sure that if you plan on using some plants for cooking, you don’t use too much potassium nitrate. Potassium nitrate has been proven to reduce sexual desire in men, or even cause impotency. I’m sure you don’t want that, so substitute fish emulsion or another organic fertilizer for the plants you plan on cooking with. 150-600 parts per million in dissolved liquids is the typical range for hydroponic growing mediums, but 300-400 ppm is ideal. If you’re not sure what your plants are getting, you can do a test with an electrical conductivity meter.
Hydroponic growing requires close monitoring of nutrient levels. However, you should know that most tests, even the expensive ones, generally come out on the low side, meaning the actual results are usually a bit higher than what your test will tell you. It’s possible to get too much nutrient build up, which actually damages plants. If you have a feeling this is happening, just water with pure h2o with no additives. You will notice that the plants will get a little less green, then you can go back to using nutrients.
Some growers want (or need) to make their plants grow faster. Many people use as system called pumping to accomplish this. Pumping is basically just watering more often in order to make plants grow faster. This works, if you do it right. If you do it wrong, you can severely damage your plants or even kill them by overwatering. If you are pumping your plants, reduce the amount of nutrients in the water, and closely watch your plants so you’ll notice signs of overwatering as soon as possible. Especially if you’re growing in soil, you should flush your plants regularly by watering with straight water.
The main problem with over-watering is that roots don’t get enough oxygen. If this happens, you should use light strength Oxygen Plus plant food. When you do use this food, be sure to monitor pH levels, as some growers have experienced rapid pH changes when using solutions with hydrogen peroxide in it. As your plants grow, you only have to water them about every 3-5 days, unless of course you have a great drainage system in place. In this case, plants will actually grow faster with less water, as the roots will get more oxygen. A good rule of thumb is to make sure the growing medium is completely dry before you water again. This makes sure you don’t overwater, and ensures that roots will get enough oxygen.
If you’d rather not use the above method, you can use stronger plant food less often. Generally speaking, you should water with the food every 3 times you water, and all the other ones should be straight water. Soil and Pearlite mediums do a good job of storing nutrients for later use, so using this method will work well for soil mediums.
WARNING: Do not over fertilize your plants. It can kill them or severely weaken them. If you’re new to growing and not sure how much your plants can handle, use half the recommended amount and slowly work your way up. If you do end up using too much nutrients, it’s not the end of the world. Just flush the soil by watering with pure water. Note: you should stop using plant food and nutrients about 2 weeks before crop out. If you continue to use nutrients, your weed will taste like plant food.