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Hydroponics Glossary


Abscisic Acid - A growth-inhibiting hormone.

Abscission - The dropping of leaves, flowers, or fruit by a plant. This can result from natural growth processes (i.e. fruit ripening) or from external factors such as temperature or chemicals.

Abscission Layer - Specialized cells, usually at the base of a leaf stalk or fruit stem, that trigger the separation of the leaf or fruit and the development of scar tissue to protect the plant.

Absorption - The uptake of substances into plants. This can be liquids (i.e. nutrients) or gases such as oxygen.

Acid - Having a pH below 7.

Adsorption - When substances attach to the plant surface. Such as foliar sprays.

Adult - A plant capable of forming flowering tissues.

Aeration - Supplying soil and roots with air or oxygen. 

Aeroponic - A growing technique where plants are maintained without a grow medium. The bare roots are exposed to a nutrient spray on a regular schedule. Aeroponic plants are typically suspended, making it look like they’re growing on air.

After-Ripening - The seed maturation process that must be completed before germination can occur.

Aggregate Fruit - A group of small fruits derived from several ovaries within a single flower.

Air Stone - An air pump used to oxygenate liquid nutrients.

Alkaline - Having a pH over 7.

Ammonium (NH4+) - A plant-available form of nitrogen contained in many fertilizers and generated in the soil by the breakdown of organic matter.

Anaerobic - Active in the absence of free oxygen.

Anthocyanin - A blue, violet, or red flavonoid pigment found in plants.

Antiseptics - Micro-organism deterring substance that reduces the risk of infection when applied to plants.

Aquaponics - A mutually beneficial growing arrangement where fish and plants are cultivated together.

Auxin - One of the most important plant hormones. It is most abundantly produced in a plant's actively growing tips. Auxin generally stimulates growth by cell division in the tip region and by cell elongation lower down the shoot. Growth of lateral buds is strongly inhibited by the normal concentration of auxin in the growing tip. 



Bio Solids - Sewage removed during wastewater treatment that is sometimes sold as, or included in, fertilizer.

Blight-Rapid, extensive discoloration, wilting, and death of plant tissue.

Bloom Booster - Nutrients that are high in phosphorus (P) which increases flower yield.

Bloom Phase - The period when a plant produces flowers.

Blossom-End-Rot (BER) - BER is caused by calcium deficiency either in the soil or due to poor watering. If the plants are not watered adequately the roots will not be able to take calcium into the plant. More often than not the soil contains plenty of calcium.  Blossom end rot presents as a black, leathery, sunken appearance on the blossom end of the fruit.

Blotch - A blot or spot (usually superficial and irregular in shape) on leaves, shoots, or fruit.

Bolting - Producing seeds or flowering prematurely typically due to heat. For example, cool-weather crops such as lettuce bolt during the summer. Leaf crops are discouraged from bolting by removal of flower heads. See deadhead.

Boron (B) - A micronutrient that helps regulate other nutrients.

Botrytis - A fungal disease promoted by cool, moist weather. Also known as gray mold or fruit rot.

Branch Training - Tying or guiding the stems and limbs of plants to grow in directions that allow light to reach more of the plant.

Bud Cycle - The period of a plants’ life when it is flowering. 

Buffering - Reducing dramatic pH level variation in a solution.

Burn - Leaf tips brown due to excess nutrients and salt causing the plants to burn. 



Calcium (Ca) - A micro-nutrient plants require to hold the cell walls together. It also activates specific plant enzymes that which send signals to the plant cells that coordinate certain growth activities. 

Calcium Carbonate (CaCO3) - A compound found in limestone, ashes, bones, and shells; the primary component of lime. 

Canopy - The top branches and foliage of a plant.

Capillary Action - The method in which fibers soak up water.

Carbon Dioxide (CO2) - A colorless, odorless, tasteless gas in the air, essential for plant life. Occurs naturally in the atmosphere.

Carbon Filters - Are used to scrub the air in a grow room of Volatile Organic Compounds (V.O.C.’s) before it leaves the grow room. 

The absorbency of the carbon draws V.O.C.’s in and traps them in its porous body. 

Cell - Smallest living organism able to live independently.

Chelate - A complex organic substance that holds micronutrients, usually iron, in a form available for absorption by plants. 

Chlorine (Cl) - A micronutrient essential for photosynthesis. It acts as an enzyme activator during the production of oxygen from water.

Chlorophyll - A plants green pigment. It is essential to photosynthesis because captures the photon of light.

Chlorosis - A plant disease that results in yellowing leaves caused by an inadequate formation of chlorophyll. It is caused by a nutrient deficiency, usually iron or nitrogen. It can also be caused by pH that is out of balance. 

Clay Pellets - Growing medium of small hard-baked clay pellets. 

Clone - The asexual reproduction of a plant that results in a duplicate of the original. It is usually done through cuttings, layering, or tissue culture.

Closed System - A hydroponic system in which the nutrient solution is continually recycled. Nutrient film technique setups are the most common example.

Coco Coir - Growing media created from the natural fiber of coconut husks. 

Colas - The nodes, or meeting points of bigger limbs, where flower buds form.

Color or Kelvin Temperature - The unit of measurement used to express the color spectrum of light emitted by a lamp.

Combination Day Plants - A plant requiring exposure to short day conditions and long day conditions in a particular order to encourage flowering.

Conditioning - Soaking new Rockwool in an acidic solution to specifically lower the pH from 8.0 to 5.5. 

Copper (Cu) - A micronutrient that helps promote growth and flowering.

Cutting - A piece of leaf and stem that’s been snipped from a mature plant to be replanted and grown into a clone.



Damping Off - A fungal disease that primarily affects young seedlings and cuttings causing the stems rot at the base. Overwatering is the main cause of this issue. 

Day-Neutral Plant - A species capable of flowering without regard to day length. See short-day plant and long-day plant.

Deadhead - To remove individual, spent flowers from a plant to preventing the plant from going dormant and prolonging blooming. 

Deep Water Culture (DWC) - A simple hydroponic system where plant roots are totally submerged in a nutrient mixture and aerated using an air pump or air stone. DWC is most suitable system for growing water-loving plants.

Dilution - When nutrient solutions are made less concentrated by adding water.

Dissolved Solids aka Total Dissolved Solids - Fertilizer salts measured in parts per million. 

DNA - A structure containing the characteristics of a living organism.

Drainage - Waste water that is removed from a system or re-circulated.

Drip Aeration - A hydroponic method where air pressure is utilized from a small air pump to percolate the nutrient solution throughout the feed tubing that surrounds the plant.

Drip - A nutrient and water delivery system that works somewhat the way watering works in a soil-based garden. Although there are several ways to design a drip system, in many of the most popular, nutrients are delivered to the media (often slow-draining stonewool or coco coir) through a series of large distribution tubes and small, perforated feeder tubes. The excess drains into a reservoir and is recycled using an electric water pump, manual pulley system or other means. This is sometimes referred to as a gravity-fed system, particularly when no electric pump is used.



Ebb and Flow (Flood and Drain) - An easy, reliable hydroponic system that uses timed irrigation to provide nutrients to plant roots. It saturates the grow media and allows the liquid nutrient to drain completely between applications. Flooding and draining also evacuates and replenishes stale air around plant roots for enhanced aeration.

Electric Conductivity (EC) - Used to measure ion concentration (salt concentration) in water.



F1, F2, F3, etc. - Filial Generation - the F1 generation is the result of crossing two different varieties; a cross of two F1 plants produces F2 seed; and so on.

Feeder Roots - Fine roots and root branches with a large absorbing area (root hairs). Feeder roots are responsible for taking up most of a plant's water and nutrients from the soil.

Fertigation - Nutrient application through an irrigation system.

Fertilizer - A natural or synthetic product added to the soil/grow medium or sprayed on plants to supply nutrients. 

Fertilizer Analysis - The amount of nitrogen (N), phosphorous (as P2O5), and potassium (as K2O) in a fertilizer expressed as a percentage of total fertilizer weight. The percentage of N-P-K, by weight, on a fertilizer label always lists nitrogen (N) first, phosphorous (P) second, and potassium (K) third.

Fertilizer Burn - Leaf tips and margins turn yellow and distort due to over-fertilization.

Fibrous Root - A root system that branches in all directions, often directly from the plant's crown, rather than branching in a hierarchical fashion from a central root. 

Fixture - The electrical fitting used to contain the electric components of a lighting system.

Flood & Drain - See Ebb and Flow

Floral Phase - The period when plants put on floral structures.

Flower Cluster/Truss - A group of flowers that form from the stem of tomato plants which when pollinated produce the fruit.

Flushing - Only giving hydroponic plants water (rather than a nutrient solution) can wash out excess or imbalanced nutrients. Flushing is a great strategy whenever plants are ailing.

Fogponics - A form of aeroponics that uses a fine mist spray to produce nutrient vapor. This method of nutrient delivery can enhance absorption and reduce costs because you are using resources like nutrients, water and energy more efficiently.

Foliar Feeding - Fertilization of a plant by applying diluted soluble fertilizer, such as fish emulsion or kelp, directly to the leaves.

Fructification - When a plant forms fruits.

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.



Geolite - A general term for various brands of clay aggregate medium. This is a lightweight and porous substrate that provides for excellent aeration. Also known as LECA–light expanded clay aggregate. Geolite is better for ebb-and-flow types of drip hydroponic systems. 

Germination - The development of a plant from a seed.

Grafting - Inserting a shoot or bud of one plant into the trunk, branch, or root of another and it grows and becomes a permanent part of the plant.

Granulates - The size of a dry solution that is slightly larger than powder size.

Grow Light or Lamp - Lighting designed to enhance plant growth by mimicking sunlight or the specific light wavelengths preferred by plants during different times in their development (primarily blue or red light).

Grow Room - An area inside a home used for an indoor garden. It’s usually sealed off from outside light but ideally is well ventilated.

Grow Tent - A soft-sided enclosure for plants supported by a sturdy internal frame.

Grow Tray - An open receptacle used to house plants.

Growing Medium - The various materials that hydroponic growers use to support plants’ stems, including clay pebbles, coir, vermiculite, or rock wool.

Growing Phase - The period when plants grow. This usually before the flower stage.



Harden Off - The process of gradually exposing seedlings started indoors to outdoor conditions before transplanting.

Herbicide - A chemical used to kill undesirable plants.

HID Lamps - High Intensity Discharge (HID) lamps encompass a range of Hydroponic lighting such as HPS (high pressure sodium) and MH (metal halide) All produce light spectrums that create a natural environment for plants being grown indoors.

Hormone - A chemical substance that controls the growth and development of a plant. Root-inducing hormones help cuttings root.

Horticultural Oil - An oil made from petroleum products, vegetable oil, or fish oil, used to control insect pests and diseases. Oils work by smothering insects and their eggs, and by protectively coating buds against pathogen entry. 

Humus - The end-product of decomposed animal or vegetable matter. 

Hybrid - A cross between two varieties or species of plants creating new offspring.

Hybrid Vigor - The increased vigor, size, and fertility of a hybrid compared to its parents.

Hydrated Lime - Instantly soluble lime, used to raise or lower pH.

Hydroponics - Growing plants in nutrient solutions or inert material rather than soil. 

Hygrometer - A measuring tool to monitor humidity in the atmosphere.



Indeterminate - A plant growth habit in which stems continue growing in length indefinitely. For example, indeterminate tomatoes are tall, late-fruiting, and require staking for improved yield. See determinate.

Inert Medium - A media form that will not add or take nutrients from feeding solutions.

Insecticidal Soap - Specially formulated soap that cause many pests to dehydrate when they are sprayed with it.

Insecticide - Any material that kills insects. 

Integrated Pest Management (IPM) - The practice of eliminating insect problems with the least harmful solution, which is often organic, but not strictly.

Intensive Gardening - The practice of maximizing use of garden space, for example by using trellises, intercropping, succession planting, and raised beds.

Intercropping - Mixing plant varieties to break up stands of a single crop.

Interplanting - See intercropping.

Iron (Fe) - A micronutrient important for photosynthesis and many other plant functions.

Irrigation - Application of water go a growing medium.



Juvenile - The initial period when a plant is unable to form flowers.



Leachate - The fluids that drain out after a nutrient solution passes through a plants’ roots.

Leaf Curl - Leaf malformation caused by overwatering, over fertilization, lack of magnesium, insect or fungus damage, or negative tropism.

Lime - A rock powder, consisting primarily of calcium carbonate, used to raise soil pH (decrease acidity).

Loam - A soil with roughly equal parts of sand, silt, and clay particles.

Lollipopping - Cutting off the lower third of a plants’ leaves and branches so that all the energy goes into the remaining leaves. The plant is then shaped like a lollipop.

Long Day Plants - A plant requiring more than 12 hours of continuous daylight to stimulate a change in growth, e.g., a shift from the vegetative to reproductive phase. See short-day plant, day-neutral plant.



Macronutrients - major elements that plants must have in large amounts, specifically nitrogen, phosphorus, potassium, calcium, and magnesium.

Manganese (Mn) - A micronutrient important for photosynthesis and the activation of enzymes that trigger different phases in a plant’s life cycle.

Medium or Media - An inert anchoring material that supports plants in a hydroponic system. It is also known as a substrate. These materials can enhance aeration, aid in nutrient distribution and help sustain beneficial bacteria.

Metabolism - Biochemical processes that takes place in cells to sustain life.

Micronutrients - A group of trace elements that work with macronutrients to sustain plants. Although dozens of minerals may be of use to plants in nature, hydroponic nutrient blends use the most beneficial. Manufacturers add micronutrients to their products using proprietary recipes. Trace elements include boron, chlorine, copper, iron, manganese, molybdenum and zinc.

Mineral - An inorganic element, such as sodium, zinc, potassium, calcium, or iron, that is essential to the nutrition of plants.

Mineral Deficiency - When a plant is not receiving a required nutrient--at all or in an insufficient amount--a disorder will result.

Mistponic - See Fogponics

Molybdenum (Mo) - A micronutrient used in plant cultivation that aids in nitrogen fixing.

Mycorrhiza - A fungus that grows in association with the roots of a plant creating a symbiotic relationship that aid root cells in increasing uptake of water and nutrients.



Nanometer (nm) - A metric unit used to measure light wavelengths. A nanometer is equal to one billionth (.000000001) of a meter.

Necrosis - Leaves turning brown and dying. It can be caused by a pest attack or from a serious nutrient deficiency.

Neem Oil - An oil pressed from the seeds of the neem tree (Azadirachta Indica), an evergreen tree native to India, that is a highly effective insecticide and fungicide but is no danger to people or pets.

Nitrate (NO3-) - A plant-available form of nitrogen contained in many fertilizers and generated in the soil by the breakdown of organic matter. 

Nitrifier - A microbe that converts ammonium to nitrate. 

Nitrogen (N) - A macronutrient essential for vegative plant growth. It also increases the protein content in all plants.

Nitrogen Cycle - The sequence of biochemical changes undergone by nitrogen as it moves from living organisms, to decomposing organic matter, to inorganic forms, and back to living organisms.

N-P-K - Represents the three primary macronutrients contained in manure, compost, and fertilizers. The N stands for nitrogen, P for phosphorus, and K for potassium. On a fertilizer label, the N-P-K numbers refer to the percentage of the primary nutrients (by weight) in the fertilizer so you can choose the right nutrients for each stage of the plants' life cycle. For example, a 5-10-5 fertilizer contains 5% nitrogen, 10% phosphorous, and 5% potassium.

Nute Burn - A condition that occurs when plants are overfed with fertilizer. Often it is first noticeable by yellow leaf tips.

Nutes - Slang for liquid fertilizer or nutrients.

Nutrient - Any substance, especially in the soil, that is essential for and promotes plant growth. See macronutrient, micronutrient.

Nutrient Film Technique (NFT) - A method of hydroponic cultivation that uses sloping trays or tubes, a recirculating pump and sometimes a wicking system to deliver a thin-but-continuous stream of nutrients to plant roots. Good air flow is also built into the system. This type of scalable hydroponic set-up is popular for both small and large applications.

Nutrient Solution - A mixture of macronutrients, micronutrients and water used to nourish plants in a soilless growing system.

Nutrients - The elements plants naturally need for health and growth. They include macronutrients (N-P-K) and micronutrients (also known as Trace Elements). A good quality hydroponic nutrient formula will contain all the nutrients needed by the majority of plants. 

Nymph - The immature stage of an insect that undergoes simple metamorphosis.



Open (Non-Recirculating) System - A hydroponic system where the nutrient solution passes only once through the plant roots. The leachate is not collected and returned to a cistern for a repeated cycle.

Open-Pollinated Seed - Seed produced from natural, random pollination so the resulting plants are varied.

Organic - Referring to substances that contain both carbon and nitrogen.

Organic Fertilizer - A natural fertilizer material that has undergone little or no processing. It can include plant, animal, or mineral materials. 

Organic Matter - Any material originating from a living organism (peat moss, plant residue, compost, ground bark, manure, etc.).

Organic Nutrients - Nutrients bound to organic structure.

Oxygenation - Typically refers to supplying of oxygen to the plants’ roots to support normal plant physiological processes. 



Parts Per Million (PPM) - The relative concentration of individual nutrients in a nutrient solution. PPM readings are important in letting you know it you are fertilizing plants properly.

Pathogens - Any organisms, such as bacteria, viruses, or fungi that cause plant diseases.

Peat Moss - A relatively inert, organic grow medium that retains a lot of moisture while allowing for plenty of oxygen to be present in the root zone. Peat moss falls apart easily and needs to be replaced periodically.

Perlite - An inert growing medium made of sand or heat-expanded volcanic glass. Perlite is often used in combination with other media to provide better aeration.

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.

Phosphate - The form of phosphorous listed in most fertilizer analysis (P2O5).

Phosphorus (P) - Phosphorus promotes and stimulates early growth and blooming as well as root growth. It hastens maturity and seed growth and contributes to the general hardiness of plants. Phosphorus is a macronutrient. 

Photoperiod - The amount of time a plant is or isn’t exposed to light

Photosynthesis - A plant process that uses carbon dioxide and water to turn sunlight into usable energy in the form of carbohydrates (sugar).

Phototropism - The gravitation of a plant part toward a light source.

Potash - The form of potassium listed in most fertilizer analysis (K2O).

Potassium (K) - A primary macronutrient essential to plant growth. Promotes fruit production and enhances resistance to disease. In fertilizers it is usually expressed as potash. See potash.

Potting Mix - Media developed for Potting and consists of organic and inorganic materials.

Processed Fertilizer - A fertilizer that is manufactured or refined from natural ingredients to be more concentrated and more available to plants.

Propagate/Propagation - Sexual propagation: to produce seed by breeding different male and female flowers. Asexual propagation: to produce new plants by seeding, budding, grafting, dividing, etc.

Propagation Medium - Media specially developed for seedlings or cuttings.

Protoplasm - The living substance of cells, including cytoplasm and nucleus. Visit our selection of plant propagation tools and rooting solutions.

Prune - To remove plant parts to improve a plant's health, appearance, or productivity

Pyrethrum - A compound found in chrysanthemums that is a natural, nontoxic insecticide.



Richtlijn Hollandse Potgronden (R.H.P) - A Dutch quality standard for Media. 

Recirculating System - A system that re-uses drainage water. 

Reservoir - Where the fluid is stored in a hydroponic system that pumps a nutrient solution to plants, such as an ebb-and-flow system.

Resistant - A plant having qualities that make it retard the activities of a pathogen or insect pest. See immune, tolerant.

Reverse Osmosis - A process in which a very fine filter stops minerals of specific sizes from passing through. This process removes salts and minerals from the water.

Rockwool - This is a soilless growing medium that is made from woven strand-like fibers sourced from molten volcanic rock and limestone. It has been heated to over 2900 degrees F, enabling it to be formed into slabs, blocks, and cubes from where the growing medium is scraped. 

Root - Generally, the underground portion of a plant. It anchors the plant and absorbs water and nutrients.

Root Cap - A protective cover over a root tip.

Root Cutting - A section of root prepared for the purpose of vegetative propagation.

Root Hair - A delicate, elongated epidermal cell that occurs just behind a root's growing tip. Root hairs increase the root's surface area and absorptive capacity.

Root- Bound - A plant's roots have completely filled its container. Typically, the roots begin to encircle the pot's outer edge. Further growth is prevented until the plant is removed from the container. 

Rootstock - A plant which has an established healthy root system used for grafting, a cutting, or budding from another plant. Rootstocks are most commonly used with fruiting and flowering plants that are susceptible to root diseases. By grafting to a healthy vigorous rootstock, typical root diseases are prevented.

Run to Waste - A hydroponics system where nutrients are not recycled. Run-to-waste systems typically use an inert medium that has similar fluid retention rates to that of soil.



Secondary Macronutrients - The dissolved nutrients used to maintain plants hydroponically are broken into three categories: macronutrients, secondary macronutrients and micronutrients. Secondary macronutrients are considered vital but less essential that the big three: nitrogen, phosphorous and potassium. Secondary macronutrients include calcium magnesium and sulfur.

Short-Day Plant - A plant requiring more than 12 hours of continuous darkness to stimulate a change in growth. (i.e. a shift from the vegetative to reproductive phase. See long-day plant, day-neutral plant.)

Side-Dress - To apply fertilizer to the soil around a growing plant.

Slow-Release Fertilizer - A fertilizer that must be converted into a plant-available form by soil micro-organisms.

Stonewool - See Rockwool.

Strain - Plants of the same species with unique characteristics (vigor, aroma, flavor, etc.) that are reproduced from one generation to the next.

Substrate - Growing media that enables roots to grow and the plant to stand up.

Sustainable Gardening - Gardening practices that allow plants to thrive with minimal inputs of labor, water, fertilizer, and pesticides.

Symbiotic - Mutually beneficial.

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).



Total Dissolved Solids (TDS) - A measure of the concentration of elements in a nutrient solution. Measuring TDS helps you be sure that you’re giving your plants sufficient but not excessive nutrients.

Trace Element - Elements that must be in the nutrients of an organism for growth. Only a small quantity of trace elements are required.

Trichoderma - Group of related fungus. Good Trichoderma protect the plant against harmful fungi. There are also 'bad' Trichoderma that eat beneficial fungi.



Vermiculite - A type of mica that has been expanded by heat energy. It’s used because of its excellent water-retention properties. It’s a good medium for rooting cuttings and works well for soil health. 

Volatile Organic Compound (V.O.C.)   - Organic chemicals that have a high vapor pressure (scent) at ordinary room temperature.



Wick (Wicking) - A simple hydroponic technique using a wick suspended in the nutrient solution. Nutrients feed up through the wick and are absorbed by the media and plant roots. 

Wilt - (1) The drooping of leaves from a lack of water. (2) A vascular disease that interrupts a plant's normal uptake and distribution of water.

Wilting Point (WP) - The point at which water content within plant cells is low enough that cellular turgor is lost and the plant wilts.



Zinc (Zn) - A micronutrient that aids plants in the production of chlorophyll. Similar to the purpose of copper or manganese.

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