Glossary of Hydroponic Terms

  • Abscission:
    The shedding or dropping of fruits, flowers or leaves.

  • Acid:
    an acidic solution has a pH below 7.

  • Aeration:
    The process of providing oxygen to plant roots to encourage nutrient uptake, root development, and overall health.

  • Aeroponics:
    A growing technique in which plants are maintained without the aid of a growing medium. Done by exposing the bare roots to an atomized nutrient spray on a regular schedule. Aeroponic plants are typically suspended on a platform and supported by a collar, which makes it look like they’re growing on air.

  • Air Stone:
    An air pump accessory used to oxygenate liquid nutrients.

  • Alkaline:
    any pH over 7 is considered alkaline.

  • Ampere:
    The unit used to measure the strength of an electric current.

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

  • Arc:
    The luminous discharge of electricity between two electrodes in HID lighting.

  • Arc Discharge:
    A transfer of electricity across two electrodes (anode and cathode), characterized by high electrode current densities and a low voltage drop at the electrode.

  • Arc Tube:
    The enclosure which contains the luminous gases and also houses the arc.

  • Ballast:
    A mechanism in a light assembly that contains the controls and electronics.

  • Bloom Booster:
    A special fertilizer that contains high concentrations of phosphorus and other minerals that increase flowering.

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

  • BU:
    An industry code indicating that the bulb is to be operated only in a base-up position.

  • Burn:
    Leaf tips that turn dark from excess fertilizer and salt burn.

  • Calcium (Ca):
    A secondary macronutrient that aids in the development of strong plant stems and roots.

  • Candela:
    A unit used to measure light intensity.

  • Candle Power (CP):
    Light intensity based on the luminosity generated by an average candle and measured more accurately in candela units.

  • Capacitor:
    An electronic device that can store electrical charge. The capacitor is one of the main components of an HID lighting ballast. Because they can store a very strong electrical charge, capacitors can be very dangerous to someone who is unaware of this fact and opens a ballast in order to examine or repair it. If one does not know how to safely discharge the stored electricity, one should allow a trained technician to do any ballast repairs.

  • Carbon Dioxide (CO2):
    A colorless, odorless, tasteless gas in the air necessary for plant life. This occurs naturally in the atmosphere at .03%.

  • Chlorine (Cl):
    A micronutrient essential for photosynthesis, where it acts as an enzyme activator during the production of oxygen from water.

  • Chlorosis:
    A nutrient deficiency characterized by yellow or brown leaves that occurs when there is a drop in chlorophyll production. The most likely cause is a mineral deficiency or pH imbalance.

  • Clay Pebbles:
    A porous, clay-based medium used to grow plants without soil. Clay pebbles anchor plant roots, help retain moisture and enhance the aeration. Created using high heat, clay pebbles are highly textured, have a neutral pH and are typically reusable.

  • Clone:
    A plant produced through asexual reproduction including, but not limited to, cuttings, layering, and tissue culture.

  • Cloning:
    The asexual reproduction of a plant that results in a duplicate of the original.
  • Coco Coir:
    A popular, inert growing medium made from shredded coconut husks. Coco coir is considered flexible and easy to use.
  • Cold Start Time:
    The length of time required to bring an HID lamp to 90% light output from a cold condition.
  • Color or Kelvin Temperature:
    The unit of measurement to express the color (spectrum) of light emitted by a lamp; the absolute temperature of a blackbody radiator having a chromaticity equal to that of the light source (see correlated color temperature). 
  • Compact Fluorescent:
    A variety of fluorescent lightbulb in which the controls are attached to the bulb, not contained in the fixture.
  • Conversion Bulb:
    A bulb of a certain spectrum type (e.g. sodium) specially designed to operate while used in the fixture/ballast of a different type (e.g. metal halide). The most popular conversion bulbs by far are sodium conversion bulbs, which allow one to have the sodium spectrum while still using a metal halide system.

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

  • Correlated Color Temperature (CCT):
    A specification of the color appearance of a light source, relating its color to that of a blackbody radiator, as measured in Kelvins (K). CCT is a general measure of a lamp's "coolness" or "warmness".

  • Damping Off Fungus:
    A disease that attacks young seedlings and cuttings, causing stems to rot at the base; overwatering is the main cause of damping-off.

  • Deep Water Culture (DWC):
    A simple hydroponic system in which plant roots are totally submerged in a nutrient mixture and aerated using an air pump. DWC is the most suitable system for growing lettuces and other water-loving plants.

  • Discharge Lamp:
    A lamp that produces light by discharging an electric arc through a mixture of gases and gaseous metals.

  • Drip:
    A nutrient and water delivery system that works somewhat the way watering works in a soil-based garden. Although there are a number of ways to design a drip system, in many of the most popular, nutrients are delivered to the media (often slow-draining stone wool 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:
    A simple and reliable hydroponic system that uses timed irrigation to provide nutrients to plant roots. It does this by saturating the grow media and allowing the liquid nutrient to drain completely between applications. Flooding and draining also evacuate and replenishes stale air around plant roots for enhanced aeration.

  • Electrical Conductivity (EC):
    The measurement of water’s ability to conduct an electrical charge. Even a small amount of ions in a water solution make it capable of conducting electricity. The higher the solution’s salt concentration, the better it conducts electricity.

  • Fertilizer Burn:
    A symptom of over-fertilization in which leaf tips and margins turn yellow and distort.

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

  • Flood & Drain:
    See Ebb and Flow.

  • Fluorescent:
    An economical, artificial light source for plants. Fluorescent lights run cool and have a good spread, but provide a limited spectrum that may not be suitable for all applications. Fluorescent lighting is widely considered most effective for growing seedlings and leafy greens.

  • Fogponics:
    A form of aeroponics that uses a fine mist spray to produce nutrient vapor. This method of nutrient delivery may enhance absorption and reduce costs by using resources like nutrients, water, and energy more efficiently.

  • Foliar Feeding:
    A method of providing nutrition to plants through their leaves.

  • Foot Candle:
    A standard measurement of light intensity, representing the amount of illuminance on a surface one-foot square on which there is a uniformly distributed flux of one lumen. More simply, one footcandle of illuminance is equal to the light emitted by one candle at a distance of one foot.

  • 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.

  • Gravity Fed:
    See Drip.

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

  • Grow Tray:
    An open receptacle used to house plants.

  • High Intensity Discharge (HID):
    Highly efficient and long-lasting lighting technology that uses an integrated transformer, capacitor and lamp assembly. Available in metal halide (blue light) and high pressure sodium (red or orange light). Because they run hot, HID lamps are often used in open or large spaces or with enhanced ventilation.

  • High Pressure Sodium (HPS):
    A type of HID light that uses the red/orange end of the light spectrum. It is preferred for the flowering and fruiting phases of many plants.

  • Hood:
    The reflective cover used in conjunction with an HID lamp. The more reflectivity a hood can provide, the more effective it is.

  • HOR:
    An industry code indicating that the bulb is to be operated in a horizontal position.

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

  • Hot Spot:
    The area immediately under an HID lamp where the light intensity is strongest. Hot spots cause uneven growth but can be remedied by using light movers.

  • 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 the relative humidity in the atmosphere.

  • Ignitor:
    A component of the ballast necessary for the starting of the bulb in sodium systems.

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

  • Lamp Life:
    A measure of lamp performance, as measured in median hours of burning time under ANSI test conditions.

  • Lamp Starting:
    A generic term used to describe a discharge lamp's starting characteristics in terms of time to come to full output, flicker, etc.

  • Leaf Curl:
    Leaf malformation due to overwatering, over-fertilization, lack of magnesium, insect or fungus damage or negative tropism.

  • Light-emitting Diodes (LEDs):
    A versatile, low-energy, durable lighting option able to target different portions of the light spectrum. Believed to work best when paired with highly reflective materials like Mylar.

  • Luminaire:
    A complete lighting unit, consisting of a lamp or lamps together with the components required to distribute the light, position the lamps and connect the lamps to a power supply. Often referred to as a "fixture".

  • Lumen (lm):
    A measurement of the visible illumination emitted by a light source.

  • Macronutrients:
    A group of primary nutrients required by plants. Often referred to as the big three, they are nitrogen, phosphorus, and potassium (N-P-K).

  • 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. Also known as a substrate, these materials can enhance aeration, aid in nutrient distribution and help sustain beneficial bacteria.

  • Metal Halide (MH):
    A type of HID light that favors the blue end of the light spectrum. Preferred for the vegetative growth phase of many plants.

  • 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.

  • Mistponics:
    See Fogponics.

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

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

  • Necrosis:
    The dying of plant tissue, usually the result of serious nutrient deficiency or pest attack.

  • Nitrogen (N):
    One of the macronutrients, nitrogen is a colorless, odorless gas used in a number of forms to promote plant development.

  • 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.

  • Parabolic Reflector:
    A lighting distribution control device that is designed to redirect the light from an HID lamp in a specific direction. In most applications, the parabolic device directs light down and away from the direct glare zone.

  • Peat Moss:
    A relatively inert, organic grow medium. Retains a lot of moisture while allowing for plenty of oxygen to be present in the root zone. Falls apart easily and needs to be replaced periodically.

  • Perlite:
    An inert growing medium for hydroponic cultivation made from heat-expanded volcanic glass or sand. Perlite is often used in combination with other media to provide better aeration.

  • pH:
    pH is a scale representing acidity and alkalinity as a numbered range from 1-14. The low end of the scale represents acidic values (1-6), with 1 being the most acidic. The high end of the scale represents alkaline values (8-14), with 14 being the most alkaline. Seven is neutral (neither acidic nor alkaline).

  • Phosphorus (P):
    A macronutrient essential for plant growth. Promotes leaf and root development, blooming and seed production.

  • Photoperiod:
    Light duration in plant cultivation. This is also expressed as day length.

  • 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.

  • Plasma:
    One of the newest lighting technologies on the market. It offers a broad spectrum of light with lower heat output and possibly lower energy costs.

  • Potassium (K):
    A macronutrient essential to plant growth. Promotes fruit production and enhances resistance to disease.

  • PPM:
    Total Dissolved Solids.

  • Propagate / Propagation:
    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:
    A natural insecticide made from the blossoms of various chrysanthemums.

  • Reflector:
    The reflective hood of a light fixture designed to maximize light distribution and reduce hot spots.

  • Reservoir:
    A receptacle that holds nutrients within a hydroponic system.

  • Run to Waste:
    A basic hydroponic system that does not recycle unused nutrients.

  • 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, phosphorus, and potassium. Secondary macronutrients include calcium magnesium and sulfur.

  • Stonewool:
    Stonewool, also known as rock wool, is one of the most popular grow mediums. It is made by heating and spinning certain silica-based rock (basalt) into a material much like cotton candy. The end product is a firm, fibrous material that provides an ideal ratio of water to oxygen for optimal conditions for plant roots.

  • Substrate:
    Medium or Media.

  • Systemic:
    Used in reference to a disease within the plant tissue, not initiated from the external cells. It 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:
    Dissolved mineral nutrients present in water as measured in parts per million (ppm).

  • Vermiculite:
    Processed mica used as an inert, hydroponic grow medium.

  • Wick (or Wicking):
    A simple hydroponic technique in which nutrient solution is delivered to plant roots through a capillary action using a wick.

  • Zinc (Zn):
    A micronutrient that aids plants in the production of chlorophyll.


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