Hydroponic Glossary of Terms

PowerHouse Hydroponics’ Glossary of Terms will help you navigate your way through building or buying your hydroponics system and supplies, and assisting you in choosing alternative methods for indoor growing.


Aeration is the process of introducing and integrating oxygen into a liquid or other substance.


Aerobic generally refers to a situation that requires, or involves free oxygen.


Unlike other forms of hydroponics, plants in aeroponic systems are not grown in any sort of soilless substrate. A sprayed or atomized nutrient solution is applied to the roots. Read more


Agriculture is a broad term used to describe cultivation of plants, livestock, fungi, and other life forms to serve human interests in the form of resources.


Aquaculture is a division of agriculture that focuses specifically on the farming of aquatic organisms such as fish, crustaceans, and mollusks like oysters and clams, and aquatic plants.


A closed-loop, symbiotic system that combines hydroponics with aquaculture. Fish are used to provide nutrients to the plants, while the plants provide clean water that is cycled back to the fish. Read more

Automated Gardening System

An automated gardening system is generally defined by its usage of self-watering technology, such as drip irrigation. There are other aspects of the system that can be automated, such as humidity control, temperature control, etc.

Chlorophyll A

Chlorophyll A is a pigment that participates directly in light acquisition, and the light reactions of photosynthesis. It’s thus considered the primary photosynthetic pigment. It absorbs both red and blue light, and reflects green, hence its color.

Chlorophyll B

Chlorophyll B serves essentially the same function as Chlorophyll A, absorbing light for the process of photosynthesis. Its contribution is slightly more indirect however, as it transfers the absorbed light to A for it to do its work in the light reactions of photosynthesis. B absorbs more blue light than A, so it aids A by expanding on its range of light.


Cultivation is the act of preparing, and subsequently maintaining land or, in the case of hydroponics, a soilless system to produce crops.


Energy is power derived from either physical or chemical resources, which is mostly used to create light or heat, or to power machinery. Energy can be produced from sustainable sources such as solar or wind power, or from non-renewable resources such as coal or natural gas.

Feed Conversion Ratio

A ratio that measures an animal’s efficiency regarding the conversion of food to an increase in output, usually body mass.


Fertilizer is material that is added to either soil or, in the case of hydroponics, the nutrient solution that provides one or multiple necessary nutrients. It can be derived from synthetic or naturally-occurring sources, and can be either organic or inorganic.


Also known as “mistponics”, fogponics is a variety of aeroponics that uses an ultrasonic fogger to create vaporized water. The reason for using a fogger is that plants typically better absorb the smaller particles produced by the fogger, resulting in reduced nutrient, water and energy usage. Read more

Grow Tray

A tray used to hold hydroponically-grown plants. Different grow trays are needed for different hydroponic setups. For example, a grow tray for an ebb and flow system must be relatively deep to allow for flooding.


Horticulture is a component of agriculture that is defined by smaller-scale cultivation in a domestic environment. In Latin, agri means “field”, while culture means “cultivation”. Horti means “garden”, so the difference essentially is cultivating a field vs. cultivating a garden.


The most common, longest-tenured soilless growing method. Based on fact that plants do not need soil to grow. Rather, they simply require nutrients (which are inorganic and therefore do not need soil) and water. In hydroponics the plants’ roots are suspended in a nutrient-rich water solution. Roots are supported by soilless substrates such as coco coir or perlite. Read more

Indoor Gardening

Indoor gardening is often done to foster a controlled environment for whatever plants are being grown. It’s a great method for growing all year around (even in Winter), and hydroponics is often employed.


Nutrients are components in food that are utilized by organisms to survive and grow. They are typically divided into macronutrients, which provide the majority of energy needed, and micronutrients, which aid in metabolism.


Organic refers to any material that is, or is derived from, living matter. The term is also used in food production, referring to food that is produced without synthetic fertilizers or pesticides, among other rules as set forth by the USDA.


pH stands for “potential of hydrogen”, and represents the acidity or alkalinity of a solution. Soil pH typically falls between 4 and 8, with optimal nutrient availability for most plants existing between 6.5 and 7.0.

Photosynthentically Active Radiation

PAR is the wavelength range of solar radiation that plants are able to utilize for photosynthesis. The range is 400-700 nanometers.


Photosynthesis is the process employed by plants to convert light energy from the sun and other sources, such as grow lights, to chemical energy. The required inputs are light, CO2 and water, with the outputs being sugar and oxygen.

Plant Hormones

Plant hormones essentially regulate the growth of a plant. They regulate cell processes, and also control the formation of fruits, stems, flowers, and when leaves are shed among other functions.


In general terms, a reservoir is an area, usually man-made, where a liquid is stored. In hydroponics, it refers to the area of the setup where nutrient solution is stored.

Rotary Frame

A rotary frame is a circular hydroponics setup that rotates constantly during the plants’ life cycles. Usually, a high intensity light is situated in the middle of the setup.

Soilless Growing

Soilless growing broadly refers to, and is based on the concept that plants do not require soil to grow. A variety of methods are employed, all of them allowing for significant environmental benefits.


Timers can be used in automated hydroponic systems to control growing conditions, allowing users to set nutrient application intervals, etc.


Vermicompost is a method of composting that utilizes earthworms (often red wrigglers) to break down organic matter at an accelerated rate compared to most methods of composting. The result is a rich, aerated compost that contains worm castings that feature higher levels of microbial activity than most soil.

Substrates | Glossary of Terms

Clay Pebbles

Commonly known as Hydrocorn or Hydroleca, clay pebbles are an organic growing media for hydroponics. They are made from clay that has been heated in a rotating kiln to 1100 – 1200 degrees Celsius. The result is a rough finished, highly porous medium that is brilliant at retaining moisture, trapping air, and oxygenating any nutrient solution which flows over it, which in turn provides plenty of aeration to the root zone. Clay pebbles support plants and the root system and as a non-degradable, PH neutral medium, they can be re-used providing they are properly sterilized before being used again. Overall, clay pebbles are an easy growing medium to work with.

Coir / Coco

Made from the husk of coconuts. Coco is a very popular choice with many growers as it brings the forgiving buffering properties of soil together with the high performance and aeration properties that are typical of good hydroponic systems. Coco is an inert medium, meaning growers have full control over maintining optimum nutrient levels. It is also better than most other mediums at promoting beneficial bacteria growth and protecting the root zone from heat stress. Plant performance in coco has been well documented. A lengthy study by the International Symposium on Growing Media and Hydroponics found coco to outperform rockwool, increasing yields by almost 20%. Overall, coco is a highly versatile substrate that can be used in most hydroponic systems and can be mixed with other mediums like clay pebbles.


Perlite is composed mainly of minerals and is an expanded volcanic glass. The expansion process gives perlite a very porous structure and fantastic aeration properties. It is also pH neutral and a highly absorbent substance that’s great at retaining water and nutrients, without shrinking or getting soggy. As an inert substrate, hydroponic growers can benefit from optimum nutrient control when using perlite. However, growers rarely use perlite as a sole growing medium.


Rockwool, which is also commonly known as mineral wool or stone wool, is widely used in commercial hydroponic applications and for plant propagation. Most of the tomatoes you see in your local store are grown hydroponically using rockwool. However, rockwool can be used in various hydroponic set-ups to grow a whole host of delicious crops. Rockwool itself is an inert medium which is made by melting basaltic rock. This melted mixture is then spun into thin fibers which are cooled by air.


May also be referred to as “growing mediums”. Substrates are necessary in hydroponic systems in the absence of soil, as plants still require support. Non-organic materials such as coconut coir, perlite, rockwool, or clay pebbles are used. The materials ensure proper aeration and access to nutrients.

Lighting | Glossary of Terms

Blue Light

Blue grow lights are used to foster vegetative growth of plants, and have a wavelength between 400-500 nm.

Compact Fluorescent Light

Compact fluorescent lights (CFLs) can serve as relatively efficient grow lights. They’re a good, inexpensive option for small-scale growers.

Red Light

Red grow lights are used to foster flowering in plants, and have a wavelength between 600-700 nm.

Grow Lamps

Grow lamps are required for any growing operation that cannot provide adequate sunlight for photosynthesis. Grow lamps provide the red and blue wavelength spectrums necessary for plants to grow.

High Intensity Discharge Grow Lamps

Two types of high intensity discharge (HID) grow lights are used in indoor and soilless growing. The first is a metal halide lamp, which provides blue spectrum light needed for vegetative growth. Second, high pressure sodium (HPS) lights provide the red spectrum light required for flowering. HID grow lights are generally more suitable for larger-scale growers, as they’re more expensive, and require more attention than CFLs, as they can get quite hot. HIDs are significantly more efficient than CFLs overall, however. Read more

Induction Grow Lamps

Induction grow lighting has only recently become more widely used among growers. Invented by Nikola Tesla, they operate on the principle of electromagnetic induction, and thus are very efficient. As of now, they’re a rather expensive investment, but have the potential to pay for themselves over time due to their efficiency.

Light Emitting Diode

Light emitting diodes, or LEDs, are a relatively inexpensive and efficient lighting option for any grower. The spectrum they provide can be easily customized, as a wide variety of color options are now offered.

Metal Halide Lamps

Metal halide lamps (MH) provide blue spectrum light needed for vegetative growth. Therefore, they are used during this period of a plant’s life cycle, before the grower switches to high pressure sodium (HPS) lights for the flowering stage.


In order to absorb light for photosynthesis, plants need the help of cells known as ‘photopigments’. The two most significant photopigments in the process are Chlorophyll A & B. Carotenoids also serve as accessory pigments, expanding the spectrum of absorbable light.


Spectrum in the context of plant growth refers to the range of wavelengths that are used for photosynthesis. Red spectrum (wavelengths between 600-700 nm) and blue spectrum (wavelengths between 400-500 nm) are primarily utilized.

Sulphur Plasma Lights

Sulphur plasma lights are a newer technology and are thus quite expensive. They’re a form of induction grow lights that use sulphur halides.