Glossary

Hydroponic Terms

A

Aeroponics: a form of hydroponics that applies nutrients directly to plant roots by mist in a closed system
Anion: a negatively charged ion
Antagonism: the effect of a deficiency or toxicity of an element that restricts or interferes with the uptake of another
Atomic weight: the relative weight of an atom

B

Beneficials: insects, fungi, bacteria or nematodes that feed or parasitize other pest organisms
Bibb lettuce: European type of lettuce varieties that form soft, semi heads which are the most popular lettuces grown hydroponically
Biological agents (Bioagents): biological organisms or natural extracts that control pests (see beneficials)
Blossom-end-rot (BER): a physiological and nutritional disorder on fruit creating a black, leathery, sunken appearance on the blossom end of the fruit – often associated with poor watering, root death, and calcium deficiency
Buffering action: the ability of a nutrient solution or raw water to resist changes in pH, that is, the pH is stable
Bumble bees: type of bees used in greenhouse culture of tomatoes and peppers to pollinate the plants

C

Calyx: that part of a fruit having leaf-like form, at the stem end of the fruit, opposite to the blossom end
Capillary mat: a polyester thin matting, about 1/8-inch thick, that moves a solution laterally along a surface through capillary action
Carbon dioxide: a component of the atmosphere that plants use in photosynthesis
Catfacing: large scars that form on the blossom end of tomato fruit under unfavorable temperatures and humidity
Cation: an ion that has a positive charge
Chlorophyll: the green pigment in plants where light is utilized in the process of photosynthesis
Chlorosis: a yellowing of plant tissue due to a physiological disorder such as a nutrient deficiency
Chiller: a refrigeration unit used to reduce the temperature of the nutrient solution
Cistern: A nutrient tank located below ground level so that the solution can return by gravity
Closed (recirculation) system: a hydroponic system in which the nutrient solution is collected, usually in a cistern, and then circulated through the system many times
Coco coir: a substrate of ground-up coco husks used in hydroponics
Controlled environmental agriculture (CEA): the growing of plants in structures as greenhouses that permit the regulation of optimum environmental conditions for the crop year-round regardless of ambient weather conditions
Cotyledons: these are the seed-like leaves of a plant, which are the first leaf-like structures that appear during germination, but are not true leaves
Cropping cycle: the time period during which the plant grows from seeding until final harvest and its subsequent removal

D

Deep flow/raft culture: a hydroponic system commonly used for lettuce production in hot climates where the plants are supported on top of a bed of nutrient solution by Styrofoam boards floating on the solution
Deficiency: the effect on a plant when one or more nutrients are not in sufficient supply
Determinate (bush) varieties: plants that do not continue growing upward but naturallyterminate their growth in a bush form having a short cropping period
Disease organism: a biological organism capable of upsetting the physiology of a plant,causing a reduction in productivity or eventual death
Drip irrigation: a type of irrigation system by which each plant is fed individually with a small drip tube and the flow is regulated by an emitter commonly used in most hydroponic systems

E

Ebb-and-flow: a hydroponic system in which the plants are sub-irrigated periodically and the nutrient solution drains back to a central cistern for subsequent cycles
Electrical conductivity (EC): a measure of the ability of a nutrient solution to conduct electricity, which is dependent upon the ion concentration and nature of the elements present
Emitter: a device that regulates the flow of water at a slow rate in drip irrigation systems
Essential elements: mineral elements that are essential for plant growth, the plant cannot complete its normal life cycle without any one of these elements
Evapotranspiration: the loss of water from a plant through evaporation and transpiration; critical to the uptake of minerals and cooling of the plant through movement of water within the entire plant

F

Flower cluster/truss: a group of flowers that form from the stem of tomato plants which when pollinated produce the fruit
Fruit set: small bead-like fruit that develop if pollination is successful; they continue growing into fruit

G

Generative growth: reproductive phase of a plant in which it produces flowers and fruit
Growing point: the apex of the plant containing cells multiplying and dividing to result in the growth of the plant
Guttation: plants having high root pressure under high relative humidity conditions will exude water at their leaf margins through specialized cells
Gutter NFT: a nutrient film technique water culture system in which plants are grown in small gutters or channels

H

Hydroponics: the word means “water working”, but includes all forms of soilless culture, that is, growing plants in a substrate without soil and providing their essential elements by a nutrient solution

I

Indeterminate (staking) varieties: plant that are normally trained to continue growing upward and capable of continuous production until they die or are terminated
Indicator paper: a litmus type paper that changes color with specific levels of acid or base and is used to check pH
Indicator solution: a solution that changes color with pH changes
Injector: a piece of equipment which proportions a concentrated nutrient stock solution with a precise amount of water in a ratio to give the resulting solution the exact nutrient formulation calculated by the operator for feeding his crop
Integrated pest management (IPM): the use of biological agents and natural pesticides for the control of pests on crops
Ion: an element in its free radical state when dissolved in water; available to plants through ionic exchange by the roots
Ion exchange: the process whereby plant elements from the nutrient solution are absorbed by plant roots

L

Leachate: the drainage from a substrate such as perlite, rockwool, peatlite, rice hulls, etc. contained in slabs, bags or pots; the spent part of a nutrient solution after passing through the plant roots

M

Macroelement (macronutrient): an essential element required in relatively large amounts
Microelement (micronutrient): an essential element required in relatively small amounts
Mineral disorder: a physiological upset in a plant produced by an excess or deficiency of an essential element; initially causes specific symptoms in the plant
Mineral excess (toxicity): a disorder produced in a plant by an element present in quantities higher than is tolerable by the plant
Mineral (nutrient) uptake: a mineral (essential element) being taken up (absorbed) by the plant roots
Molecular weight: the relative weight of a molecule

N

Necrosis: browning of leaf tissue due to a nutritional disorder
Nematodes: organisms in the soil or introduced in a soilless medium by water or other contamination and cause swelling of plant roots which in turn restricts water uptake leading to wilting of the plant
Node: area of plant stem where branches or leaves form
Nutrient film technique (NFT): a water culture system based upon constant flow of the nutrient solution past the plant roots; must be a thin film of water flowing through the roots to provide adequate oxygenation
Nutrient formulation: the specific makeup of the nutrient solution with each essential element expressed as parts per million (ppm) or milligrams/liter (mg/l)
Nutrient imbalance: when a nutrient solution does not have the correct ratios of elements and one or more elements may be in excess or deficiency that could lead to a nutritional disorder in the plant
Nutrient solution: the water solution containing all of the essential plant elements in their correct ratios; the basic nutrient supply to plant roots

O

Open (non-recirculating) system: a hydroponic system in which the nutrient solution passes only once through the plant roots; the leachate is not collected and returned to a cistern for repeated irrigations
Oxygenation: the supplying of oxygen; usually refers to the needs of plants’ roots
Oxygen deficit: when oxygen is inadequate to support normal plant physiological processes

P

Parts per million (ppm): a dilution factor of one part of one substance in a million parts of another; used to express nutrient formulations and calculations of amounts of various fertilizers to use in a given volume of water; also equivalent to 1 milligram (element) per liter (water)
Peat: a soilless medium that is partially decomposed aquatic, marsh, bog or swamp vegetation
Peatlite mix: a soilless medium consisting of a mixture of peat, sand, vermiculite and/or perlite
Perlite: a soilless medium that is fired volcanic pumice
Pesticide free: indicates that a product was grown without the use of synthetic pesticides, but by the use of beneficials and bioagents only
pH: a measure of the acid or base of a solution on a logarithmic scale where 7 is neutral; lower is acid and higher is base
Phloem: the conductive tissue of a plant that translocates manufactured foods within the plant
Pollination: the movement of pollen from the male part of a flower (stamens) to the female part (style and stigma); usually accomplished by wind or insects
Precipitation: when several chemical compounds react to form a new compound which is not soluble in water and settles to the bottom of a nutrient tank in the form of a white powder

R

Reverse osmosis (RO): equipment used to remove minerals from water; water is forced through a differentially permeable membrane by pressure; the mineral elements cannot pass through the membrane and are flushed from the outside to waste
Rockwool: a substrate used to grow plants hydroponically; an extruded wool-like product formed through a process of melting rock and extruding it into threads and pressing it into loosely woven sheets at high temperatures

S

Soilless culture: a form of hydroponics that uses a substrate other than soil such as sand, gravel, bark, sawdust, perlite, peatlite mixtures, coco coir, rockwool, etc.
Solubility: the ability of a fertilizer to dissolve in water to form a solution
Solution analysis: laboratory analysis of a nutrient solution or water to determine all elements present and their concentrations; results indicate adjustments needed to make in the solution to keep it in balance
Sucker (side shoot): a small shoot that grows between the stem and leaf of a tomato that must be removed to prevent the plant from having many stems resulting in few fruit; applicable to staking (indeterminate) tomato varieties
Symptomatology: the description in specific terms of nutritional disorders in plants

T

Tissue analysis: a laboratory analysis of plant tissue to determine levels of nutrients present in the plant
Total dissolved solutes (TDS): the concentration of all the elemental ions present in a nutrient solution; electrical conductivity (EC) is a measure of TDS generally expressed as mS (milliSiemens) or mMho (millimhos)

V

Vegetative growth: plant growth that is succulent without producing much fruit as the plant is not in a reproductive state
Viability of seed: the ability of seed to germinate expressed as percent germination
Vine clip: a plastic hook with a hinge on the back which attaches to a support string allowing it to secure the plant from falling; used on plants that are trained vertically such as tomatoes, cucumbers and peppers

W

Water culture: a true hydroponic system that does not use any substrate; such as NFT and raft culture
Water deficit: when available water to the plant is insufficient to provide the plant with at least the same amount as is lost to evapotranspiration; as this deficit of water continues it will cause the plant to wilt
Weed mat: a woven plastic matting which will prevent weeds from growing when placed on a soil or other medium; used as a barrier between the growing system and the underlying substrate of greenhouse floors
Wilting: as the plant losses more water than its uptake the plant losses turgor and becomes droopy and soft

X

Xylem: the conductive tissue within a plant that transports water and nutrients upward in plants to sites of photosynthesis