Chapter 14

NUTRIENTS and FERTILIZING

Plants require nutrients in order to grow. The roots absorb the nutrients from the water as dissolved salts. These are the simple compounds found in chemical fertilizers. Organic fertilizers travel a more circuitous route, first breaking down from complex molecules through microbial action, and then dissolving into the water.       Nitrogen (N), Phosphorous (P) and Potassium (K) are called the macro-nutrients because plants use large quantities of them. The percentages of N, P and K are always listed in the same order (N-P-K) on fertilizer packages.       Calcium (Ca), sulfur (S), and magnesium (Mg) are also required in fairly large quantities. They are often called secondary nutrients.       Smaller amounts of iron (Fe), zinc (Zn), manganese (Mn), boron (B), cobalt (Co), copper (Cu), molybdenum (Mo), and chlorine (Cl) are also required. These are called the micro-nutrients.       When marijuana germinates, it requires a modest amount of N and larger amounts of P. This supports vigorous root growth and limits etoliation (stretching) of the stem. When it goes into its vigorous growth stage, usually within two weeks, marijuana's need for N increases. The nutrient is used in building amino acids, the stuff protein is made from. During the reproductive stage when the plant flowers, the female’s flower growth is promoted by P and K.       Plants which are being grown in soil mixes or mixes with nutrients added such compost, worm castings or manure do better when watered with a dilute soluble fertilizer, too. When a non-nutritive medium is used, the nutrients are supplied as a solution in the water from the beginning.       Typical formulas used for the seedling and early growth stages include: 7-9-5, 5-10-5, 4-5-3. Formulas for the fast growth stage usually have a little more nitrogen. Most growers use different formulas for the different growth stages. Other growers supplement low nitrogen formulas with fish emulsion or other high nitrogen formulas. Some gardeners use the same fertilizers throughout the plant’s life cycle. A typical formula for this is 20-20-20.       Plants growing under warm conditions (over 80 degrees) are given less N to prevent stem etoliation. Plants grown in cool environments are given more N.       During flowering a high P formula promotes flower growth. Formulas such as 3-10-4, 5-20-5 and 4-30-12 are used. Plants are sometimes grown using a nutrient solution containing no N for the last 10 days. Many of the larger leaves yellow and wither as N migrates from old to new growth.       The fertilizer should be complete, that is, it should contain all of the secondary and trace elements. Some fertilizers do not contain Mg. This is supplemented using Epsom salts, available at drug stores. Sometimes growers prefer to use more than one fertilizer. They find that changing the formulas and ingredients helps to prevent stresses and deficiencies. However, the chemicals in each fertilizer are blended to remain soluble. Different fertilizer formulas may react with each other. As a result some of the chemicals may precipitate and become unavailable to the plants. To prevent this growers use only one fertilizer at each watering.       Overfertilization is very dangerous. When plants are under-fertilized more nutrient can be added, no harm done. Overfertilization can kill a plant quickly.       Growers take no chances when they change hydroponic nutrient water solutions every 2 weeks. Even though the solution may have nutrients left, it is probably unbalanced since the plants have used some of the nutrients, and not others.

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