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Glossary Hydroponica Class

| Insect Glossary | | Plant Glossary |

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absorption - intake of water and materials by plants.

acidity - sourness or amount of hydrogen ions in solution. Having a pH less than 7.0.

adobe - a construction material made of clay, sand and soil. It is used to build buildings, cooking stoves and garden walls.

adsorption - removal of materials from solution by soils or media.

annual - a plant that only lasts for one season, and reproduces itself the next year from seed.

antibiotic - tending to prevent, inhibit, or destroy life. Used to treat and remove infections.

antiviral - a substance that should prevent, inhibit or destroy viral infections.

anti-inflammatory - a substance to treat inflammation.

aphids - a small fat looking insect that can reproduce by laying live female larvae. They are spread by ants that milk the dew from the aphid.

arsenic- a toxic element, which is metallic, gray, crystalline and brittle. Commonly used as an insecticide or weed killer.


bacteria - single celled microbes that both decomposed dead plant material and atack live plants. Those that attack live plants are called pathogens . Rots decay leaves and stems. Blockages cause a blockage to occur in plant vascular system causing distress. Galls are excessive growth in infected areas. Many bacteria are carried by insects.

bed grower - a hydroponic grower made of a container used for media or floating bed.

biennial- a plant that requires two growing seasons to produce seed.

blanching - a loss of pigments from the leaves of plants.

boron - a metallic element found in nature only in combination.

budding - grafting and bud onto a shoot.


calcium - a silver white metallic element occurring only in compounds in the natural environment. It is used in cell wall structure and in bones in animals.

capillary attraction - the surface of a liquid and solids are attracted, an attraction of molecules.

carbohydrate - a chemical compound of carbon, hydrogen and oxygen that is used for energy in plants and animals. Includes sugars, starches and cellulose.

carbon - a non-metallic element found in a pure form in diamond and graphite. Also a chief component in living tissue and in coals and petroleum products.

Centigrade - temperature scale giving freezing water 0 degrees and boiling water 100 degrees. A degree of centigrade equals 1.8 degrees in Fahrenheit.

Ceramic grow rock - a clay material also called Geolite, which is often used for aquaculture because the porous material is a good media for growing bacteria to clean water. It does not break down.

chlorine - a halogen element which is a heavy greenish yellow gas used as a bleaching agent and a disinfectant of water.

chlorophyll - a green pigment in plant leaves that is necessary for photosynthesis.

chlorosis - yellowing or loss of green color in a portion or entire leaf. Chlorophyll is lacking or missing.

chromium - a blue white metallic element found naturally only ion combined forms.

cob - a form of construction that uses adobe mud and applies layers by hand.

cobalt - a lustrous white metal which occurs with iron and nickel ores. An essential element for root nodules that fix nitrogen for plants, and a part of vitamin B12.

compound - a chemical substance made up of one or more elements.

concentration - the amount of one substance within another, such as the amount of salt in water.

conducting roots - those roots which conduct water and materials through their tissues.

copper - a reddish metal which is ductile and easily conducts heat and electricity.


deciduous- a perennial plant that loses its leaves in the winter season

density - how many plants or seeds can be planted per unit area

dermatitis - inflammation of the skin.

determinant - in plants, a type which will produce all its fruits at once and tends to form in a bush shape.

dormancy- a period of rest with low metabolic rates and little or no growth

downy mildew - a mildew common to plants that looks like a soft downy feather on the plant surface.

drowning - death caused by no respiration due to water with low on no oxygen

dry weight - the weight of the plant or material with water removed by frying or heat.


ecology - a science of the interrelationships or organisms and their environment

electric dissociation - some molecules break down into separate ions of positive and negative charge

element - one of the distinct materials of which all other materials are composed. The periodic table of the elements lists 120 known elements.

embryo flower - the young flower within a bulb, seed or plant.


Fahrenheit - the temperature scale where freezing of water is at 32 degrees and boiling of water is at 212 degrees. One degree Fahrenheit is 5/9 degree Centigrade.

fermentation - the chemical and biological processes by which organic materials are broken down by bacteria and other agents.

feeding roots - the new roots which have the capacity to absorb nutrients.

fibrous roots - larger roots that grow from the root crown or large roots.

filtration - water or solution that has passed through a substance that alters its matter in suspension. Solution passing through a porous article or mass such as soil or media.

fine veins - network of veins near edges of leaves.

fluorine - a nonmetallic halogen that is a toxic gas when isolated

fungus - fungus are multicellular organisms that include powdery mildew and mushrooms. Most fungus is soil born and not very common in hydroponics. Powdery mildew is air born and spread by white fly. It can be controlled by adequate air movement and ventilation.

forcing a crop - plants are grown by heating the solution, media or air.


gangrene - pervasive decay or corruption, common in potatoes.

germination - seed sprouting and the first signs of growth.

graft - propagation of a plant by placing a bud or scion in a rooted live plant.


hard water - water that contains bicarbonate of calcium or magnesium. It tends to leave a hard white deposit on surfaces where water is frequently used.

herbs - any of a number of green plants used for flavoring foods, teas, or medicinal purposes. Some of the parts of herbs used include flowers, stems and roots as well as leaves.

hybrid - the offspring of two species, often used in plants to develop new breeds of plants.

hydrogen - a gas which makes up about 6% of the earth's atmosphere. Also a primary component, along with oxygen of water. A necessary component of carbohydrates and proteins.

hydroponics - the science of growing plants without soil. Nutrients are given to the plant through the water.


ignition loss - the loss in weight by combustion heating.

indeterminant - in plants, the fruit will appear in stages, or not all at once. Usually a vine crop with successions of blossoms.

indicator - chemical used to determine the pH of a solution of water.

inter-cropping - growing more than one crop together.

inorganic - chemicals not containing carbon molecules as a nucleus.

insoluble - not soluble in water.

internode - space along shoot between two adjacent leaves

iodine - a non metallic halogen which forms heavy blackish gray crystals. Used as a disinfectant as it kills most bacteria.

ion - a part of a molecule which dissociates and carries a negative or a positive charge.

iron - a heavy magnetic metallic element that readily rusts in moist air. Is in most igneous rocks and commonly used for nails in carpentry.




lateral veins - veins connected to mid-rib vein that run to outer edges of leaf

liter -a measure of volume containing 1000 cubic centimeters or 1.0567 liquid quarts.

litter - any vegetable matter used as a growing media.


manganese - a grayish white brittle element which resembles iron but in not magnetic.

magnesium - a silver white metallic element used in light weight alloys. It forms the central molecule in chlorophyll and is essential to plant growth and survival.

media - the substance used to support plant roots in hydroponic culture. Can be rocks, pebbles, sand, perlite, vermiculite, sawdust, or various types of plant litter.

mid-rib - Main vein of leaf extending from tip to stem

mosaic - a pattern of mottled appearance of plant leaves. Usually caused by a disease spread by insects.

molecular concentration - quantity of dissolved solution expressed in molecules per unit of volume.

molybdenum - a metallic element that resembles chromium and is used to strengthen and harden steel. It is a trace element in plants and animals

multiple cropping - growing more than one crop in a unit area to make greater use of space.


necrosis - tissue which has died

nematodes - very small soil born worms that live on the roots of plants. They can be introduced to hydroponic culture on the soil of transplanted plants.

nickel - a silver white hard malleable metal resistant to corrosion. Used in compounds as a catalyst.

nitrogen - a tasteless odorless gas that makes up 78% of the earth's atmosphere by volume. It is an essential part of amino acids or proteins.

no media - There are many hydroponic systems that use no media whatsoever. The plant is usually started in a small piece of rockwool, or specially designed plastic collar. The plant is then placed in a growing tube or container that applies nutrient water to the roots.

nutrient - food, either organic or inorganic used for plant growth.

nutrient solution - a solution containing the necessary elements required for plant growth.


organic decomposition - decay or disintegration of plant or animal materials.

osmosis - diffusion of liquids, usually passing through a membrane changing concentrations on either side.

osmotic pressure - measure of force or pressure caused by osmosis.

oxygen - an element that makes up 21% of the earth's atmosphere. It is, along with hydrogen, a component of water.


pea gravel - this media is just simple gravel but has been graded for size and shape. It is not a porous media so it does not wick water from below and must be used in a system that provides aeration for the water. It can be used to grow bacteria as well as plants.

peat - There are three types of peat: peat moss, reed sedge and peat humus. Peat is very acid and can lower the pH of the nutrient water. It breaks down after one or two growing seasons.

perennial - a plant that continues to grow after two years.

Perlite - a volcanic rock of gray obsidian, that has been heated to 1500 0F in a kiln and expanded. It is a light weight porous material that can "wick" water from a bottom container of water.

permeable membrane - a membrane that allows some materials to pass through.

petiole - part of leaf between blade and shoot where leaf is attached to shoot

pH - a measurement of the acid or alkalinity of a solution or media. Lower pH (under 7) is more acid and higher pH (above 7) is more basic or alkaline.

physiology - the study of the functions and activities of living matter; organic processes and function of living organisms.

phosphorus - a nonmetallic element that occurs in phosphates.

photosynthesis - process where plants convert light energy to organic sugar molecules. Building carbohydrates from carbon dioxide and water.

pigmentation - color other than green of chlorophyll

plant food - the elements in nutrient solution required for plant growth.

pollination - introducing pollen into seed cells, fertilization of the plant reproductive organisms.

potassium - a silver white metallic element that occurs commonly in nature as an ash form left after the burning of vegetable matter.

powdery mildew - a mildew that appears as small white spots on plants. Then the spots grow larger and spread. Often caused by poor air movement or circulation.

ppm - parts per million. A measure of the concentration of one substance in another.

protein - chemical compounds in plants that are made up of amino acids. These molecules include nitrogen and some also include sulfur.

precipitate - insoluble compounds formed in solution by chemical reactions.

pumice - A silicon material of volcanic origin can break down after repeated use.



rammed earth - a form of coinstruction that uses adobe mud and some concrete. The adobe is rammed into forms and then allowed to harden.

respiration - taking in air and giving off carbon dioxide. The process of using sugar for energy and continuing life process.

rockwool - a material made from rock spun into a fiber like material. A phenol based resin is added as a binder. Rockwool also tends to increase the pH of the water.

root crown - the junction between stem and the root section.

root stock - the stock which is used for grafting buds or scions.

root-top ratio - the ratio of weight of root section of the plant as compared to the top portion of plant growth.

root zone - the area in which the roots are growing


salad greens - any greens used in a salad including spinach, watercress, lettuces and other leafy green vegetables

salinity - the amount of inorganic materials in solution of water.

sand - many sands, such as beach sand, have salts already in the media, that can cause problems in hydroponics. However, sand is a useful media that retains water. It has to be sterilized between crops.

sawdust - where there is an extensive timber production, sawdust may be available. The species of tree is important, with softwoods decaying more slowly than hardwoods. Douglas fir and western hemlock work great but red cedar is toxic to plants. Some sawdust is from logs soaked in salt water and is therefore toxic to plants.

selective absorption - differences in the rate of intake of elements by plants.

sets - young rooted plants transplanted into a larger space for full grow out.

scion - a bud or shoot used for grafting onto another plant.

seedling - a small plant, just after germination.

selenium - a non metallic element that is perhaps important to prevent cancers in animals. It occurs in varying amounts in soils, and can be deficient or toxic.

self-pollinating - a plant like tomato that can use the pollen from its own reproductive organs to fertilize its flowers.

shoot - the most recent terminal extension of a twig or branch, current seasonal growth.

silicon - a non-metallic element that is a very common element in the earth's crust. It may be required nutrient for some plants, especially cereals.

sodium - a soft white waxy element that occurs commonly in nature as sodium chloride, the salt most common in the earth's oceans.

soft water - water free from calcium or magnesium bicarbonate.

soil - earth material which supports plants, usually made up of organic and inorganic materials.

soil solution - film of liquid around soil particles.

solute - the substance which has been dissolved in water.

spider mites - a very small spider that attacks leaves and looks like a mosiac virus.

staple gun - a hand tool that allows for staples to be used in construction hydroponic growers. It uses a special type of building staple.

suckers - new shoots arising from buds at the base of plants.

sulfur - (also spelled sulphur) - a non-metallic element that occurs as a yellow powder, which forms in nature as sulfites and sulfates. Sulfur is used to vulcanize rubber, and treating skin diseases. It can be used in its pure form to treat plants for fungus diseases.

synthesis - building up new compounds from simpler ones.


tap root - main vertical root of the plant

terminal - outermost extremity of a branch or shoot along axis

tillers - shoots from buds at the base of a plant. Commonly applied to grasses and cereals.

toxic - poisonous

total solids - weight of materials after all water has been removed.

trace elements - elements available or necessary in small quantities

transpiration - loss of water from stems and leaves of plant.

transplanting - the action of taking a plant from one location, removing it and replanting it in another.

trowel - a small hand tool used to dig up and help transplant seedlings. Soil growers often use these to help pull weeds.

tub grower - any hydroponic grower that uses a small container with a drain hole at the bottom.



vanadium - a grayish white malleable metal used as an alloy for steel.

vegetable litter - litter from plants.

vermiculite - This is a volcanic mica which has been popped in a kiln. It is a magnesium aluminum iron silicon material that can be compressed and lose its porosity.

vine crops - crops that ordinarily put out vines to grow. This includes plants such as cucumber, pumpkin and beans.

virus - very small diseases which cannot be fought with plant antibodies. Diseased plants must be removed and destroyed. A disease DNA which can be transmitted from plant to plant.


water culture - growing plants in water.

weather - climate or environmental conditions pertaining to temperature, rainfall, dryness, and wind condition.

weeds - in soil culture, any plants that are not desired in the crop. Weeds and weeding and the need for herbicides is eliminated in hydroponics.

white fly - a very small (less than 1/8 inch) white fly that lays larvae on the underside of leaves.

worms - in hydroponics, earthworms are used in a worm farm to create worm castings used as a hydroponic nutrient.

worm farm - a home for worms that allows worms to convert vegetable materials to a worm waste used as a hydroponic nutrient.




zinc - a bluish white crystalline element that is often used as a protective coating of iron and steel.

Revised: 1 May 2021
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