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.
ALLELE: different forms of the same gene; allele "A" may produce a tall plant, while allele "a" gives a short plant.
ALKALINE: Refers to medium or nutrient solution with a high pH; any pH over 7 is considered alkaline.
ANTHER: Part at the top of the male flower that produces the pollen.
AQUAPONICS: The integration of aquaculture (the raising of marine animals, such as fish) with hydroponics; the waste products from the fish are treated and then used to fertilize hydroponically growing plants.
BLOOM BOOSTER, BLOSSOM BOOSTER: Fertilizer high in phosphorus (P) that increases flower yield.
BOLTING: For a plant to prematurely begin the development of a flowering stalk and, subsequently, seed.
BORON (B): The function of this micronutrient is not well understood, but it is suspected that it might aid carbohydrate transport.
BOTRYTIS: any of seval fungal diseases that afflict plants; commonly called bacterial soft rot or gray mold.
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.
CAPILLARY ACTION: When the surface of a liquid is in conact with a solid, the liquid is elevated or depressed depending upon the relative attraction of the molecules of the liquid for each other or for those of the solid. This is similar to how plants seemingly defy gravity when they transport liquid from the roots upward through the plant.
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.
CHLOROPHYLL: The green material in plants that is created in the presence of light and is instrumental in photosynthesis.
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.
CLADOSPORIUM: Any of several fungal diseases that afflict plants; commonly called leaf mold.
CLONE: A plant produced through asexual reproduction including, but not limited to, cuttings, layering and tissue culture.
CLOSED SYSTEM: A hydroponic system, like nutrient film technique (NFT) systems, that recirculates the nutrient solution.
CONDITIONING: To soak new Rockwool in an acidic solution to lower the pH from 8.0 to 5.5.
CONDUCTIVITY: The scale, described as electrical conductivity (EC) or conductivity factor (CF), that is used to measure the strength of nutrient solution.
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.
CROSS-POLLINATION: transferring pollen from the flowers of one plant of a species to the stigma of another plant of the same species.
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.
DIOECIOUS: Varieties or species with male and female flowers on separate plants.
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.
F1, F2, F3, etc.: the F1 generation is the result of crossing two different varieties; a cross of two F1 plants produces F2 seed; and so on.
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.
FUSARIUM: any of several fungal diseases that afflict plants; commonly called dry rot or wilt.
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.
GROWING MEDIUM: Materials that are sometimes used in hydroponic growing to support the plant's roots and, sometimes, to hold nutrient.
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.
INSECTS: A variety of insects attack plants. These include aphids, caterpillars, cutworms, fungus gnats, leaf miners, nematodes, spider mites, thrips, and whiteflies.
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.
MICRONUTRIENTS: The minor minerals that are used by plants in small amounts, consisting of boron (B), copper (Cu), cobalt (Co), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (Zn).
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.
MINERAL DEFICIENCY: when a plant is not receiving a required nutrient--at all or in an insufficient amount--a disorder will result.
MOLYBDENUM (Mo): This micronutrient is essential for nitrogen fixation and nitrate reduction.
MONOECIOUS: Varieties or species with separate male and female flowers on each plant.
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.
OSMOSIS: The flow or diffusion that takes place through a semipermeable membrane typically separating a solvent and a solution that strives to bring about a condition of equilibrium.
PARTS PER MILLION (ppm): A ratio figure that represents the amount of one substance that is in one million parts of another substance; commonly used to describe the relative concentrations of nutrient solutions.
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.
PHOTOSYNTHESIS: The formation of carbohydrates from carbon dioxide (CO2) and a source of hydrogen (H)--such as water--in chlorophyll-containing cells exposed to light involving a photochemical release of oxygen through the decomposition of water.
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.
PISTILL: The entire female section of the flower, including the eggs, ovary, style, and stigma.
POLLEN: The mass of microspores in a seed plant that usually appears as a fine dust and is the agent of pollination.
POLLINATION: The transfer of pollen from the male part of a flower (stamen) to the female part of a flower (the style and stigma).
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.
REVERSE OSMOSIS: The process of removing minerals from water, which is forced by pressure through a differentially permeable membrane, filtering out the minerals; can happen when growers accidentally apply too strong of a nutrient to a plant's roots, leeching life out of the plant.
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.
STALK: On a male flower, the portion of the stamen that supports the anther.
STAMEN: The basic part of the male flower that includes the stalk (or filament), anther, and pollen.
STERILIZATION: The act of rendering something free from living cells. In hydroponics it is essential that all materials (especially any growing medium) used are sterile to avoid contaminating the hydroponic system. Steam and chemical agents are often used in this process.
STIGMA: The surface at the end of the pistil on a female flower where pollen lands and germinates.
STYLE: The part of a female flower that supports the stigma.
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.
VERTICILLIUM: Any of several fungal diseases that afflict plants; commonly called wilt. See also Fusarium.
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.
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