AERATION Supplying soil and roots with air or oxygen. Geolite is an example of a medium with excellent aeration. In some hydroponic systems, a nutrient solution is aerated by the output of an aquarium pump. AEROPONICS A system in which the roots of a plant are consistently or intermittently misted with fine droplets of nutrient solution. ACID Refers to medium or nutrient solution with a low pH; an acidic solution has a pH below 7. ALKALINE Refers to medium or nutrient solution with a high pH; any pH over 7 is considered alkaline. BLOOM BOOSTER, BLOSSOM BOOSTER Fertilizer high in phosphorus (P) that increases flower yield. BORON (B) The function of this micronutrient is not well understood, but it is suspected that it might aid carbohydrate transport. BURN Leaf tips that turn dark from excess fertilizer and salt burn. CALCIUM (Ca) Calcium is vital in all parts of plants to promote the translocation of carbohydrates, healthy cell wall structure, strong stems, membrane maintenance and root structure development. Calcium is a macronutrient. CARBON DIOXIDE (CO2) A colorless, odorless, tasteless gas in the air necessary for plant life. Occurs naturally in the atmosphere at .03%. CHLORINE (Cl) This micronutrient is essential for photosynthesis, where it acts as an enzyme activator during the production of oxygen from water. CHLOROSIS The condition of a sick plant with yellowing leaves due to inadequate formation of chlorophyll. Chlorosis is caused by a nutrient deficiency, usually iron or nitrogen; nutrient deficiencies are themselves often caused by a pH that is out of the acceptable range. CLONE A plant produced through asexual reproduction including, but not limited to, cuttings, layering and tissue culture. CONDITIONING To soak new Rockwool in an acidic solution to lower the pH from 8.0 to 5.5. COPPER (Cu) This micronutrient is an internal catalyst and acts as an electron carrier; it is also believed to play a role in nitrogen fixation. DAMPING-OFF FUNGUS Disease that attacks young seedlings and cuttings, causing stems to rot at the base; overwatering is the main cause of damping-off. DISSOLVED SOLIDS or TOTAL DISSOLVED SOLIDS The amount of dissolved solids, usually fertilizer salts, that are measured in water in parts per million. DRIP AERATION A hydroponic method wherein air pressure from a small air pump is used to percolate nutrient solution out through a ring of feeder tubing which encircles the plant. DRIP SYSTEM (DRIP EMITTER SYSTEM) A very efficient watering system that employs a main hose with small water emitters. Water is metered out of the emitters, one drop at a time. EBB-AND-FLOW (or FLOOD and DRAIN) A hydroponic system in which the medium, usually aggregate pebbles, is periodically flooded with nutrient solution and then drained again, feeding and aerating the medium and root system. FOLIAR FEEDING Misting plants with fertilizer solution, which is absorbed by the foliage. FUNGICIDE A product that destroys or inhibits fungus. FUNGUS Any of a major group (Fungi) of saprophytic and parasitic spore-producing organisms usually classified as plants that lack chlorophyll and include molds, rusts, mildews, smuts, mushrooms, and yeasts. Common fungal diseases that attack plants are "damping-off," Botrytis, and powdery mildew. GERMINATION The process of causing the initiation and development of a plant from seed. GEOLITE One of several brand names/varieties of clay aggregate medium (also known as LECA for light expanded clay aggregate). It is a lightweight, porous substrate with excellent aeration. Because it does not really wick water effectively, Geolite and other LECA mediums are favorites in ebb-and-flow and drip hydroponic systems. HARDEN-OFF To gradually acclimatize a plant to a more harsh environment. A seedling must be hardened-off before planting outdoors. HORMONE Chemical substance that controls the growth and development of a plant. Root-inducing hormones help cuttings root. HYBRID The offspring from two plants of different breeds, variety or genetic make-up. HYDRATED LIME Instantly soluble lime, used to raise or lower pH. HYGROMETER An instrument for measuring relative humidity in the atmosphere. IRON (Fe) This micronutrient acts as a catalyst in the photosynthesis/respiration process, and is essential for the formation of sugars and starches. Iron also activates certain other enzymes. LEAF CURL Leaf malformation due to overwatering, over fertilization, lack of magnesium, insect or fungus damage or negative tropism. MACRONUTRIENTS The primary nutrients N-P-K or the secondary nutrients magnesium and calcium. MANGANESE (Mn) This micronutrient activates one or more enzymes in fatty acid synthesis; it also activates the enzymes responsible for DNA and RNA production. Closely associated with copper and zinc, manganese also participates directly in the photosynthetic creation of oxygen from water. MEDIUM The substrate or soilless material which supports the plant and absorbs and releases the nutrient solution in hydroponic horticulture. MICRONUTRIENTS Also referred to a TRACE ELEMENTS, including S, Fe, Mn, B, Mb, An and Cu. MOLYBDENUM (Mo) This micronutrient is essential for nitrogen fixation and nitrate reduction. NECROSIS The dying of plant tissue, usually the result of serious nutrient deficiency or pest attack. NITROGEN (N) Nitrogen is used in various forms to promote rapid vegetative growth, leaf, flower, fruit and seed development, and chlorophyll development; and to increase the protein content in all plants. NFT (NUTRIENT FILM TECHNIQUE) A hydroponic method in which nutrient is fed into grow tubes or trays in a thin film where the roots draw it up. This "nutrient film" allows the roots to have constant contact with the nutrient and the air layer above at the same time. NUTRIENTS The elements needed by plants for normal growth and health. The major nutrients (MACRONUTRIENTS) are nitrogen (N), phosphorus (P), and potassium (K), but there are numerous MICRONUTRIENTS (also called TRACE ELEMENTS) which also have integral roles in maintaining plant health. A good quality hydroponic nutrient formula will contain all of the major nutrients and micronutrients needed by the vast majority of plants. NUTRIENT SOLUTION The mixture of water and water-soluble nutrients which is provided to the plants for nourishment in a hydroponic system. NUTRIENTS, SECONDARY The elements other than N, P and K which are considered nearly as important as N, P and K but are not considered micronutrients. Calcium (Ca), magnesium (Mg), and sulphur (S) are the elements usually referred to by this term. pH A scale from 1 to 14 that measures the acid to alkaline balance of a growing medium (or any other substance). In general, plants grow best in a pH range of 6 to 6.8; 6.3 is considered ideal. If the pH is not within the acceptable range, nutrients may not be absorbed to maximum capacity. PHOSPHORUS (P) Phosphorus promotes and stimulates early growth and blooming and root growth. It hastens maturity and seed growth, and contributes to the general hardiness of plants. Phosphorus is a macronutrient. POTASSIUM (K) Potassium promotes disease resistance and good development of carbohydrates, starches and sugars, and it increases fruit production. Potassium is a macronutrient. PERLITE 1. Sand or volcanic glass which has been expanded by heat; perlite holds water and nutrients on its many irregular surfaces. 2. Mineral soil amendment. PHOTOPERIOD Day length; the relationship between the length of light and dark in a 24 hour period. PHOTOSYNTHESIS The process by which plants use light energy to collect carbon dioxide from the atmosphere and convert it to chemical energy in the form of sugar. PROPAGATE Sexual propagation: to produce seed by breeding different male and female flowers. Asexual propagation: to produce plantlets (also known as CLONES) by taking cuttings. PYRETHRUM Natural insecticide made from the blossoms of various chrysanthemums. RESERVOIR The container in a hydroponic system which holds nutrient solution in reserve for use. ROCKWOOL Inert, soilless growing medium consisting of woven, thin strand-like fibers made from molten volcanic rock and limestone, which is heated to over 2900 degrees F, extruded, and formed into slabs, cubes and blocks. SECONDARY NUTRIENTS Calcium (Ca) and magnesium (Mg) are considered to be the secondary nutrients. SYSTEMIC Used in reference to a disease within the plant tissue, not initiated from the external cells. Also refers to materials and compounds which are taken up or absorbed by the plant and designed to fight disease (e.g. systemic fungicide). VERMICULITE Mica which has been processed and expanded by heat. Vermiculite has excellent water-retention qualities and is a good soil amendment and medium for rooting cuttings. WICK Part of a passive hydroponic system using a wick suspended in the nutrient solution. The nutrients pass up the wick and are absorbed by the medium and roots. ZINC (Zn) Like copper and manganese, zinc is linked to chlorophyll synthesis.