Hydroponics and Growing Terms Explained: A Growers' Glossary

Growing has a language of its own, and half of it is initials. Here are plain definitions of the terms we are asked about most in the shop, grouped by subject, with links to the full guides. Figures come from those guides, or the product page or maker named.

Water and feeding

EC - electrical conductivity: how well the water carries a current, which rises with the salts dissolved in it, so it shows how strong a feed is. Plain tap water has an EC of its own. Measured in mS/cm with an EC meter.
CF - conductivity factor: EC multiplied by ten, so EC 1.5 is CF 15.
TDS and ppm - total dissolved solids, in parts per million: feed strength again, worked out from the EC. Check which scale a chart or meter uses: on Athena's chart EC 2.0 is 1,000 ppm on the 500 scale and 1,400 on the 700. The BlueLab Truncheon reads EC, CF and TDS.
pH - how acidic or alkaline the water or feed is. It decides which nutrients the roots can take up. The right range depends on what you grow in: Athena's chart gives 5.8-6.2 for coco and rockwool and 6.0-6.4 for peat-based mixes, and our pH and EC guide has the other ranges.
pH up and pH down - an alkali and an acid, added a few drops at a time to raise or lower the pH of a mixed feed. Both can be corrosive neat: follow the label and never mix one with the other. We sell Essentials Lab pH Down & Up.
Buffer - three uses. A buffer solution has a known pH, for calibrating a pH meter (pH Pen Calibration Fluid). Buffering is whatever holds a feed's pH steady, such as the minerals in tap water. Buffered coco is under Growing media.
Cal-mag - a calcium and magnesium supplement, used mostly with soft or RO water and in coco.
NPK - nitrogen (N), phosphorus (P) and potassium (K), the three main nutrients in a fertiliser. The numbers on a label show how much of each it holds, in that order.
Base nutrient - the main feed. Many base nutrients come in two parts, A and B, added to the water one after the other and never mixed neat.
Feed chart - a nutrient maker's week-by-week schedule of what to feed and how much, often with an EC to aim for. We have set out the makers' own figures for Canna Coco, Athena, Plant Magic and Biobizz.
Additive - anything used alongside the base feed for one job: root stimulants, bloom boosters, enzymes, cal-mag, silicon. All are under nutrients.
Root stimulant - an additive fed to a plant that already has roots, to build them up. Not the same as a rooting gel (under Propagation): see root stimulants and rooting gels.
PK booster - an additive of phosphorus and potassium for the flowering and fruiting stages. Canna PK 13/14 is one of our PK boosters; its page says plants need both in relatively large doses then.
Enzyme - an additive that breaks down dead roots in the medium. The Cannazym page calls enzymes vital if you plan to reuse coco, and says not to use them with liquid oxygen (hydrogen peroxide): see root rot.
Flush - watering with plain water or a flushing product to wash built-up feed out of the medium, typically before harvest or after overfeeding.
Run-off - the feed that drains from the bottom of the pot. Coco growers commonly water until some runs off, so salts do not build up.
RO water - reverse osmosis water: tap water forced through a very fine membrane that holds back most of what is dissolved in it, leaving a low EC.
Hard and soft water - hard water carries a lot of dissolved calcium and magnesium, soft water little. Canna count tap water with an EC under 0.4 as soft; Canna Hydro comes in a version for each.
Lock-out - when a nutrient is in the feed but the roots cannot take it up, often because the pH is out or the plants have been overfed. It looks like a deficiency, so check pH first.

Light

PAR - photosynthetically active radiation: the light plants can use to grow, roughly the visible spectrum. A Maxibright PAR Meter measures it.
PPF - photosynthetic photon flux: the total usable light a fixture gives out each second, in µmol/s.
PPFD - photosynthetic photon flux density: the usable light landing on each square metre of canopy (the tops of the plants) each second, in µmol/m²/s. It changes with hanging height, and a PAR meter reads it directly. Our LED wattage guide gives 300-600 for veg and 600-900 for flowering.
Micromole (µmol) - the unit light is counted in: a fixed, very large number of photons. Efficiency in µmol/J is a light's PPF divided by the watts it draws.
Lumen - a unit of light as the human eye sees it, not as a plant uses it, still used to rate lamps: the Sunmaster 600W Super HPS page gives 95,000.
HPS - high-pressure sodium: an HID (high-intensity discharge) lamp with a warm, orange-red light, long the standard for flowering and fruiting.
MH - metal halide: an HID lamp with a cool, bluer light, traditionally used for vegetative growth.
CMH - ceramic metal halide, also sold as CDM: a broad-spectrum lamp with a ceramic arc tube. Philips 315W CMH Lamps run on a CMH ballast, not an HPS one.
LED - light-emitting diode. Good LED grow lights give more usable light for the electricity than HID lamps, run cooler for the same light and need no lamp changes. See our LED or HPS guide.
Ballast - the box that starts an HID lamp and controls the power to it. The Varidrive Ballast runs 250, 400 or 600 W HPS or metal halide lamps.
Reflector - the shade over an HID lamp that throws its light down onto the plants, such as the open-ended Euro Reflector.
Photoperiod - the hours of light a plant gets in every 24. Many plants take their cue to flower from it.
18/6 and 12/12 - light schedules, as hours on and hours off: commonly 18/6 for vegetative growth and 12/12 for flowering and fruiting.
Dimming - running a light at part of its power. Our LED wattage guide suggests a dimmable LED at 25-50 per cent in veg and full in flower.

Air and environment

Relative humidity (RH) - the water vapour in the air, as a percentage of the most it could hold at that temperature; warm air can hold more. See grow tent humidity.
VPD - vapour pressure deficit: temperature and humidity joined into one number, in kilopascals (kPa), that says how hard the air is pulling water out of the leaves.
Hygrometer - a humidity meter. The Digital Hygrometer shows temperature too and has a max/min memory.
Extraction - pulling warm, stale air out of a tent or room with an inline fan, usually through a carbon filter.
Intake - how fresh air gets in. Passive intake is drawn through the tent's vents by the extraction fan; active intake is pushed in by a second fan.
Carbon filter - a cylinder of activated carbon on the extraction fan, which holds on to smells as air is pulled through. Carbon filters should be rated at or above the fan's airflow.
Ducting - the flexible pipe joining fan, filter and outlet. Keep runs short and straight: every bend costs airflow. Acoustic Ducting is insulated to deaden fan noise.
Cubic metres per hour (m³/h) - the airflow figure printed on fans and filters. The widely used rule is to change all a tent's air every one to three minutes: see sizing a fan and carbon filter.
EC fan - a fan with an electronically commutated motor, which turns down quietly and uses less power at low speed, such as the Rhino Ultra Silenced EC Fans. Not the EC of a feed.
Negative pressure - air pressure a little lower inside than outside, because the extraction pulls harder than the intake lets air in. With the fan running, the walls of a grow tent pull in a little and air is drawn in at the zips, so smell does not leak out: see how to set up a grow tent.

Growing media

Coco coir - the fibre and pith from coconut husks. Coco holds water and air together and carries almost no food.
Buffered coco - coco treated so that it does not hold on to the calcium and magnesium in your feed. Canna Coco Professional Plus is rinsed and buffered.
Perlite - volcanic glass heated until it puffs into light, white granules, mixed into soil or coco for drainage and air. See perlite and vermiculite.
Vermiculite - a mineral from mica rock, heated into soft flakes that hold water and nutrients. Often mixed with perlite.
Clay pebbles - expanded clay balls, also called LECA, which drain almost at once, do not rot and can be washed and reused.
Rockwool - also called stone wool: basalt rock melted and spun into fibres, sold as slabs and as Rockwool Propagation Cubes. It holds a lot of water with air still in it.
Inert medium - a growing medium with little or no food of its own, such as clay pebbles, rockwool, perlite or coco. The plant's food comes from the feed.

Hydroponic systems

Hydroponics - growing without soil: the roots sit in an inert medium or straight in the water, and all their food comes from the nutrient solution (water with the feed mixed in).
Recirculating - feed that drains from the roots goes back to the tank. Tank pH and EC drift, so check them every day or two.
Run-to-waste - the opposite of recirculating: the feed passes the roots once and the run-off is thrown away.
DWC - deep water culture: roots hang from a net pot into a bucket of nutrient solution, aerated by an air pump and air stone.
NFT - nutrient film technique: a pump runs a constant, shallow flow of nutrient solution across a tray, over bare roots and back to the tank. The GT205i is a starter kit.
Flood and drain - also called ebb and flow: a pump floods the roots with nutrient solution from below, it drains back to the tank, and a timer repeats it.
Drip system - a pump feeds each pot through its own dripper, usually on a timer. Dripper systems can be run-to-waste or recirculating.
Autopot - a gravity-fed watering system: pots feed from a shared tank with no pump, timer or electricity. See the Autopot guide.
AquaValve - the valve in each Autopot tray: it fills the tray to 20 mm, then stays shut until the tray is completely empty. Spares are under Autopot Accessories & AquaValves.
Pythium - a water mould that causes root rot: roots turn brown and slimy. Warm water holds less oxygen and suits it.

Propagation and plant stages

Cutting - a shoot cut from a plant and rooted to make a new one, genetically identical to its parent; also called a clone. See propagators and cuttings.
Mother plant - a plant kept in vegetative growth so cuttings can be taken from it.
Propagator - a tray with a clear lid that holds warmth and humidity around seeds and cuttings. Propagators come heated or unheated.
Rooting gel - a gel containing rooting hormone, such as Clonex: the cut end of a cutting is dipped in it. See also root stimulant.
Vegetative stage - veg for short: when a plant puts on leaves, stems and roots, before it flowers.
Flowering stage - when the plant makes flowers, then fruit. Short-day plants, which flower as the nights lengthen, are switched to 12/12 indoors.
Hardening off - getting young plants used to tougher conditions gradually: opening a propagator's vents bit by bit, or standing greenhouse plants outside for longer each day.

Pots and electrics

Air-pruning - a root tip that reaches the air at the pot wall stops growing, and the plant makes more fine feeder roots instead of long ones circling the pot. See our pots guide.
Fabric pot - a pot of porous fabric, which drains well and air-prunes the roots. Fabric Plant Pots dry out faster than plastic and need a saucer.
Air-Pot - a brand of recycled-plastic pot with holes all over its wall to air-prune the roots. Air-Pots also dry out faster than standard pots.
Net pot - a mesh pot for hydroponic systems such as DWC, which lets roots grow out into the nutrient solution or the medium around it.
Timer - switches a light, pump or fan on and off to a schedule; the Time-R Digital Timer also does repeat cycles and countdowns. Plug-in timers are limited in the load they can switch, so check before you put an HID light on one.
Contactor - a heavy-duty switch, worked by a timer, that carries a load the timer cannot safely switch itself, such as several lights together. The Loadstar 8-Way Contactor page says it controls up to 8 lights. Our grow tent set-up guide covers timers and contactors.
kWh - kilowatt-hour, the unit electricity is billed in: one kilowatt used for one hour. See grow room running costs.

More Growers' Guides

Not sure what you need? Call the shop on 0117 971 3000 or pop in to the Bristol store and we'll help you pick.