Acid - This is the term for a medium or solution with a pH less than 7.0 as measured using a digital pH meter or with litmus paper. A lower pH is more acid.

Aeration - Adding oxygen to a solution or adding a porous material to grow media to allow more oxygen to reach plant roots.

Aeroponics -  A method of growing plants in which the roots are supplied with necessary nutrients via misting with a nutrient solution that is pumped through sprayers.

Alkaline - This is the term for a medium or solution which has a pH greater than 7.0; a higher pH is more alkaline. Also referred to as basic.

Amendment - An addition to a growing medium which improves its structure, nutrient-content, water-holding capacity, cation exchange capacity or air porosity.

Auxin - A plant hormone which promotes root development and stem elongation. The plant-created form is known as indole acetic acid (IAA), while the synthetically-produced form is indole-butryic acid (IBA).

Bacteria - Single-celled microorganisms which can be beneficial or harmful to plant growth depending on species and function with respect to plants.

Beneficials - A term used in hydroponics which describes bacterial colonies which work synergistically with plants to defend against harmful diseases or fungi, increase the uptake of nutrients, and/or aid in the breakdown of organic materials.

Buffering capacity - The ability of a medium or solution to resist change in pH fluctuations.

CEA - Controlled Environment Agriculture, or greenhouse growing where an optimum environment for plants is maintained.

CEC - Cation Exchange Capacity. CEC is a measure of a grow medium or soil’s ability to hold positively charged ions.

Carbohydrate - A combination of carbon, hydrogen and oxygen. “Carbos,” or sugars and starches, are used to feed root zone beneficials.

Carbon dioxide - Known as CO2, this odorless gas is an integral part of plant growth. Given the proper amount and spectrum of light, if CO2 levels are increased up to 1500 PPMs plant photosynthesis is increased dramatically. (Ambient air is usually in the range of 300-400 PPMs of CO2.)

Chelate - A chemical compound composed of a metal ion and a chelating agent, usually organic such as an amino acid. Chelates bond with certain minerals to increase uptake in plants while preventing interactions with other minerals that could render minerals unavailable (lockout.)

Chlorosis - General yellowing of a plant due to a lack of chlorophyll production during photosynthesis. This is typically caused by a pH imbalance, or nitrogen or iron deficiency.

Cloning - Rooting a plant cutting to create another genetically identical plant.

Compost - Decayed organic matter from plant or animal sources that can provide plants with nutrients needed for growth.

Cotyledon - The first “leaves” of a dicot plant that emerge when a seed is planted that serve as the nutrient source until a plant develops roots for uptake of minerals.

Cutting - A portion of a plant that is cut off to generate a new, identical plant by rooting.

Damping off - A term used to describe the dieback of cuttings and seedlings caused by pythium fungi, or root rot.

Dioecious - A plant that has male and female organs on separate plants; one plant makes the flowers (female) and one plant makes the pollen (male.)

EC -
Stands for the Electrical Conductivity of a solution. An EC meter is helpful in determining the concentration of minerals, nutrients or salts affecting plant growth; the higher the concentration, the more conductive the solution is.

Elongation - When a plant begins to grow taller or longer in a fashion that creates a greater distance between the internodes of the plant.

Evapotranspiration - Critical to the uptake of minerals and cooling of the plant, through movement of water within the entire plant. Can also be described as loss of water through evaporation.

Feed - To supply nutrients to plants via solution or a dry fertilizer.

Fertigation - Supplying fertilizer to a plant via its irrigation water.

Foliage - The leaves of a plant.

Foliar feeding - Spraying or misting a plant with nutrient solution which plants absorb through their leaves.

Fulvic acid - The liquid part of humus that is light golden in color and has the ability to increase uptake of nutrients into plant tissues.

Flush - To remove buildup of salts from roots or media by using water or a specific solution designed for the purpose.

Genetics - Term used to describe the attributes of specific plants.

Gypsum - A naturally-occurring mineral complex that’s used to lower the pH of a grow medium.

Hormones - Chemicals that control the growth and development of plants: primarily auxins, cytokinens, gibberellins, ethylene, and abscisic acid (ABA.)

Humic acid - A liquid extracted from the principal component (humate) of the organic constituents of soil, humus, peat, etc. which is produced by biodegradation of dead organic matter.

Humidity - The amount of water in a given volume of air relative to the maximum amount of water it could hold.

Hybrid media - Soilless media that has been biologically enhanced using an array of organic inputs.

Hygrometer - A device that measures relative humidity.

IBA - Indole-3-Butyric Acid is an auxin or plant hormone used to initiate root development. Thought to be synthetic, it can also be derived from natural substances.

Inert - A solution or medium that is chemically non-reactive.

Leaching - The dissolving or washing out of soluble salts from a grow medium or soil.

Leaf curl - Malformation of a leaf due to under- or over-fertilization, over-watering or damage caused by insects or disease.

Lime - A naturally-occurring mined mineral complex which will raise pH.

Litmus paper - A chemically-sensitive paper that can be used to determine pH.

Lumen - A unit of measurement of light that is used to rate the amount of output based on electrical wattage and other factors.

Macronutrients - Classification for the major nutrients required for plant growth: Nitrogen (N), Phosphorus (P), and Potassium (K). Some systems include the secondary nutrients as macronutrients: Calcium (Ca), Magnesium (Mg) and Sulfur (S).

Micronutrients - Classification for the minor nutrients required for plant growth, also known as trace elements: Iron (Fe), Boron (B), Copper (Cu), Molybdenum (Mb), Zinc (Zn), Manganese (Mn), Nickel (Ni), Cobalt (Co). Chlorine (Cl) and Sodium (Na) are sometimes included in this classification.

Moisture meter - A device that measures the amount of moisture in a grow medium or soil.

Mycorrhizae -
Colonies of beneficial fungi which live on plant roots in a symbiotic association where fungireceive carbohydrates while plant roots receive enhanced mineral absorption capability.

Nanometer (nm) - 0.00000001 of a meter. Used as a scale to measure wavelength in the electromagnetic spectrum, which includes visible light.

Nutrient - A mineral that a plant can uptake and assimilate into its tissue; a plant food.

Nutrient burn - Leaf scorch that occurs from over-fertilization or application of excess salts, like nitrogen.

Organic - Carbon-based material, or a substance found in nature which is not processed.

pH - A measure of the molecular concentration of hydrogen ions in a solution in a scale ranging from 1-14 with neutral being 7. Keep in mind that the pH scale is algorithmic-a reading of 6 is 10 times more alkaline than a reading of 5-so make changes very slowly. From 5.5-6.2 is considered an ideal range for hydroponics, depending on the grow medium or hydro method being used.

pH meter - An electronic device that measures pH.

Peat moss - used in gardening as a soil additive, peat moss is harvested from arctic bogs which take centuries to form.

Photoperiod - The amount of light received by plants during a 24-hour period.

Photosynthesis - The conversion of light energy to chemical energy (carbohydrates) by plants which occurs in their green leaves.

Propagate - Growing plants by germinating their seeds or rooting cuttings from them.

Pruning - Altering a plant into a desired form by cutting its leaves, stems, shoots, flowers or fruits.

Recirculating system -
A hydro system which circulates or “feeds” nutrient solution from a reservoir over and over again, until the reservoir is either “topped off” with additional nutrients or drained out completely and replenished. Ebb & flow (flood & drain) is the most common recirculating system in hydro, although NFT (nutrient film technique) and drip systems can also recirculate nutrient solution.

Respiration - The exchange of gases by living organisms to support life; in the case of plants, consuming carbon dioxide and expelling oxygen as waste.

Rhizosphere -
The area directly surrounding the roots of a plant.
Rockwool - A grow medium made from molten rock or inert material “spun” at high temperatures into a fibrous mass.

Root bound - When a plant’s roots have grown to reach the limits of its container. Some plants prefer this, most should be transplanted.

Salt buildup - Characterized by an accumulation of white, off-white or brown sediment on the surface of a grow medium or soil, and sometimes at the base of drainage holes on potted plants. Salt buildup reduces the amount of water molecules available for plant uptake.

Salts - A colloquial term meaning plant nutrients. A salt is actually an ionic compound with a cation from a base and an anion from an acid. Too many salts in a grow medium can cause plants to burn.

Soluble - Able to be dissolved in water.

Starch - A complex carbohydrate that’s manufactured and stored by plants.

Stomata - Tiny openings in the leaves of plants though which they take up nutrients, release water and take in CO2 (carbon dioxide.)

Sugars - Simple carbohydrates manufactured by plants via photosynthesis. Sugars can also be added as supplements.

Systemic -
Refers to something that is transported throughout the plant.

Tap root - The main vertical root of a plant; lateral roots run out from the tap root.

Terpenes - A large class of organic compounds produced by plants which affects their smell.


Thin - To prune or remove parts of plants to allow remaining plant, flowers or fruits to develop more fully.

Top dress - To apply fertilizer or compost to the top of soil or grow media.

Transpiration - The evaporation of water through plant stomata.

Trellis - A frame or netting that supports plants.

Ultraviolet (UV) - Short wavelengths of light past the blue/violet colors on the electromagnetic spectrum whichare not visible.

Wetting Agent - A compound that reduces the surface tension of a liquid. Used in hydroponics to help a nutrient solution more easily infiltrate the grow media.