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Indoor Garden 101

Water & Food Nutrient Solutions

All plants need nutrients. Outdoors, plants take certain elements from the earth and combine them with water and air. Using energy from sunlight they create simple sugars, carbohydrates, and proteins to feed both themselves and all living things on this planet. A hydroponic solution must supply all the necessary nutrients in the proper form and ratio for plant growth. All major, minor, and trace elements must be properly balanced and water soluble. The three major plant elements are nitrogen, phosphorus, and potassium— often abbreviated as N-P-K. The three numbers on every fertilizer label refer to the percentages of these three essential elements. The minor elements include calcium, magnesium, sulfur, and iron. The trace elements necessary for good plant development are manganese, boron, copper, zinc, chlorine, molybdenum, and cobalt. Plants need very small amounts of the trace elements, but they are important because they act as catalysts in the solution. Without the right amounts, a plant can't properly utilize the major elements, and may develop deficiencies, disease, reduced growth rates, and poor yield. It is important to use a nutrient that is designed specifically for hydroponic applications. While products like Peter's and Miracle Grow are good for soil plants, they will not perform well in hydroponic systems because they lack the proper ratios of trace elements. If you are using a dry or solid nutrient concentrate, make sure it's derived from soluble and chelated minerals.

Organic Nutrients

Think of organic nutrients as a raw food source for plants. While a synthetic, or chemically derived, nutrient will contain mineral elements (such as nitrogen, calcium, etc.) that are immediately available to the plant, an organic nutrient (such as bat guano or bone meal) must break down in order to release these mineral foods to the plant. Organic nutrients are excellent for use in soil because beneficial bacteria will speed up this process. In hydroponics, organic nutrients become trickier because these living "catalysts" are not usually present. However, many organic nutrients can be used successfully in hydroponic systems, and some gardeners find that the slower growth rates are worth it for better looking, better tasting produce. Depending on the type of hydro system you use, you will have to decide on the best type of organic nutrient. Consider if clogging will occur (drip emitters, lines, pumps, etc.), and also the different smells associated with organic fertilizers. An organic/synthetic combination will promote the aggressive growth associated with synthetics and the high quality and heavy yield standards of organically grown produce. Using organic nutrients or supplements will improve the overall health, taste, and texture of all types of plants.

Nutrient Cycles

A plant's nutritional requirements change depending upon its stage of growth. Generally, during the vegetative cycle a plant requires high amounts of nitrogen with lesser amounts of potassium and phosphorus. During this stage you should use a Grow formula nutrient. When the plant moves into the blooming or flowering stage, the plant needs more phosphorus and much less nitrogen. During this stage, use a Bloom formula nutrient instead of the Grow formula in your reservoir in order to slow vegetative growth and promote flowering and fruiting. You should also adjust nutrient strength depending on the age of your plants. Feed seedlings and cuttings with a mild strength nutrient solution for the first two weeks, then increase to a "normal" strength nutrient mixture. After the first month of growth is completed, you can determine the nutrient solution strength according to the needs of your plants. It is very easy to over fertilize, so remember—less is more!


The pH reading is a measure of a solution's acidity or alkalinity. It is measured on a scale from 1 to 14: an acidic solution has a pH less than 7.0, while an alkaline solution has a pH greater than 7.0. The pH of a solution is directly related to the plants' ability to absorb the necessary nutrients. Most plants perform best in a hydroponic solution maintained at an average pH of 6.3. Your pH will fluctuate constantly, so check and adjust it daily if possible. You can adjust pH by adding either pH up (base) or pH down (acid) to the water. Household chemicals, such as vinegar, are not recommended because they cannot maintain a stable pH after adjustment. To adjust pH of water already circulating in your system, add the acid (pH down) or base (pH up) to your system, then check pH again in about one hour--after the adjustor has fully mixed and stabilized.

Total Dissolved Solids (TDS)

A dissolved solids reading, measured in terms of parts per million (PPM), tells you how many parts of a dissolved solid are suspended in a solution. (A reading of 1500 ppm means there are 1500 solid parts dissolved in 1,000,000 parts of solution.) You should maintain your nutrient solution between 600 and 1200 ppm, although ideal levels change from plant to plant, and even from one growth stage to the next. If your dissolved solids reading is too high, add plain water to the solution to dilute the salts. If your TDS reading is too low, add nutrients to increase the concentration in your solution. A TDS reading is a helpful way to judge overall nutrient strength, but it cannot distinguish between different elements, or between dissolved solids that were present in the solution before you added the nutrient. Dissolved solids can only be measured using an electronic TDS meter.

Water Temperature

You should maintain a constant temperature between 70° and 80°F in your nutrient reservoir. This is important, especially during the cool months, to help increase plant performance. Do not increase the temperature above 85°F as this may cause root damage. You can use an aquarium heater to maintain the temperature in your reservoir. It takes at least 5 watts per gallon to heat and maintain a constant nutrient temperature (for example, a 10 gallon reservoir requires a 50 watt heater). You can also place the reservoir on a piece of Styrofoam or wood to provide some insulation if you are growing on a concrete or tiled floor.

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