Glossary of 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
