Glossary

Hydroponic Terms Explained

By HiGroPonics Team · Updated June 2026

A plain-English reference for the terminology you'll encounter as a grower. Search for a term or browse by letter below.

A

Aeroponics: A growing method where plant roots are suspended in air and misted with nutrient solution at regular intervals. Very fast root development and high oxygen availability. A subset of hydroponics.
Aquaponics: A combined system that integrates fish farming (aquaculture) with hydroponic plant growing. Fish waste provides organic nutrients for plants; plants filter the water, which is returned to the fish tank. A closed-loop ecosystem. Requires careful balancing of fish stocking density, plant nutrient demand, and pH — fish prefer 6.8–7.2 while most hydroponic crops prefer 5.5–6.5. Tilapia and lettuce are the most common starter combination.
Air Stone: A porous stone connected to an air pump, used to oxygenate the nutrient solution in a reservoir. Essential in DWC systems to prevent root rot.
Antagonism: When one nutrient blocks the uptake of another due to an imbalance in the solution. For example, excess calcium can block magnesium absorption. Often confused with a true deficiency.

B

Buffer / Buffering: The ability of a solution to resist changes in pH. A well-buffered nutrient solution maintains stable pH for longer, reducing the frequency of adjustment.

C

CalMag: A calcium and magnesium supplement commonly used in hydroponics, particularly with soft or RO water which lacks these minerals. Deficiency causes yellowing between leaf veins (interveinal chlorosis) and tip burn on fast-growing leafy greens.
Chlorosis: Yellowing of leaf tissue caused by insufficient chlorophyll production. Interveinal chlorosis (yellowing between veins while veins stay green) typically indicates iron, manganese, or magnesium deficiency. Whole-leaf yellowing of older leaves suggests nitrogen deficiency. In hydroponics, chlorosis is most often caused by nutrient lockout from pH outside the absorption range rather than a true shortage of the nutrient.
Clone / Cutting: A cutting taken from a mother plant and rooted to produce a genetically identical copy. Clones preserve the traits of the original plant and skip the germination stage.
Coco Coir: A growing medium made from coconut husk fibres. Has excellent water retention and aeration. Technically an organic medium but behaves like a hydroponic substrate — it contains no nutrients of its own.

D

Deep Water Culture (DWC): A hydroponic system where plant roots are submerged directly in an oxygenated nutrient solution. Simple to build, fast-growing, and popular for beginners growing lettuce and leafy greens.
DLI (Daily Light Integral): The total quantity of photosynthetically active light delivered to a plant over a full 24-hour period, expressed in mol/m²/d. Calculated as: PPFD (μmol/m²/s) × photoperiod (hours) × 3.6 ÷ 1000. DLI is more useful than PPFD alone because it accounts for both light intensity and duration. Leafy greens grow well at 12–17 mol/m²/d; fruiting crops need 20–35 mol/m²/d.
Dissolved Oxygen (DO): The amount of oxygen dissolved in the nutrient solution, expressed in mg/L or % saturation. Higher DO supports healthy root development and suppresses Pythium root rot. Target 7–10 mg/L. Increases with cooler water temperatures and aeration. Below 6 mg/L, DWC roots begin to show stress.
Drip System: Nutrient solution is pumped and dripped slowly onto the base of each plant via emitters. The excess drains back to the reservoir (recirculating) or runs to waste. Common for fruiting crops and larger plants.
Dutch Bucket: A growing container used with drip irrigation, typically filled with perlite or clay pebbles. Each plant gets its own bucket connected to a shared drain line. Widely used for tomatoes, cucumbers, and peppers.

E

EC (Electrical Conductivity): A measure of how many dissolved salts (nutrients) are in the water, expressed in mS/cm or μS/cm. Higher EC means more nutrients. Too high causes nutrient burn; too low causes deficiency. The target range varies by crop and growth stage. Seedlings typically need 0.8–1.4; mature fruiting crops 2.5–3.5.
Ebb & Flood (Flood & Drain): A system where the growing tray is periodically flooded with nutrient solution, then drained back to the reservoir. Simple and reliable. Suitable for most crops and media types. Flood frequency is controlled by a timer and varies by crop size, media type, and ambient temperature.

G

Grow Panel / Pocket Panel: A flat, wall-mounted panel with individual growing pockets arranged in a grid. Each pocket holds a plant in growing medium and is fed via a drip line or irrigation pipe from the top. Commonly used for living herb walls in kitchens and restaurants. A vertical hydroponic format, not to be confused with lighting panels.
Growing Medium: The substrate that supports plant roots in a hydroponic system. Examples include clay pebbles (LECA), rockwool, coco coir, perlite, and rapid rooters. Unlike soil, the medium provides no nutrition — that comes from the nutrient solution.

H

High-Pressure Pump: A pump capable of generating 80–120 PSI (550–825 kPa) of water pressure, required to drive aeroponic misting nozzles. Standard submersible pumps (typically 0.3–3 PSI) cannot produce sufficient pressure for true aeroponics. High-pressure pumps are more expensive (€80–200) and require higher-quality plumbing fittings rated for the pressure. Do not substitute a submersible pump in an aeroponic system — it will not produce the fine mist that gives aeroponics its root development advantage.
Hydroton / Clay Pebbles (LECA): Expanded clay aggregate balls used as a growing medium. Excellent aeration and drainage, reusable, and pH neutral. Require more frequent watering as they retain little moisture. Also called LECA (Lightweight Expanded Clay Aggregate).

I

Irrigation Frequency: How many times per day the root zone is flooded, dripped, or misted with nutrient solution. Higher frequency keeps moisture and nutrients more consistent but risks anaerobic (low-oxygen) conditions if drainage is poor. Substrate growers (coco, rockwool) typically irrigate 4–8 times per day during peak growth; DWC and NFT provide continuous solution access.

K

Kratky Method: A passive, non-circulating DWC variant where the plant sits above a static reservoir of nutrient solution with an air gap that grows as roots drink the solution down. No pumps required. Ideal for lettuce and herbs in small spaces.

L

Leaching / Flushing: Running plain pH-adjusted water through the system to clear accumulated salts from the growing medium. Done at the end of a grow cycle or when nutrient lockout is suspected.
Light Spectrum: The wavelength composition of light emitted by a grow light. Plants primarily use red light (630–680 nm) for photosynthesis and fruiting, and blue light (400–500 nm) for vegetative growth and compact leaf structure. Far-red (720–740 nm) accelerates flowering. Full-spectrum LEDs cover all required wavelengths. Cheap lights heavy in the blue-white range may produce leafy plants that fruit poorly.

M

Misting Nozzle / Spray Head: A precision nozzle that atomises nutrient solution into a fine mist or fog, used in aeroponic systems. Requires high pressure (80–120 PSI) to function correctly — low-pressure nozzles produce droplets too large to provide adequate root oxygenation. Nozzles can block with mineral deposits; clean or replace every 2–4 weeks. Stainless steel or PTFE nozzles resist corrosion better than brass.
Macronutrients: The primary nutrients plants consume in large quantities: Nitrogen (N), Phosphorus (P), and Potassium (K) — the NPK on every nutrient label — plus secondary macros Calcium (Ca), Magnesium (Mg), and Sulphur (S).
Micronutrients: Nutrients needed in trace amounts: Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Boron (B), Molybdenum (Mo), and Chlorine (Cl). Deficiencies are less common but cause distinctive visual symptoms including chlorosis and distorted new growth.
Mother Plant: A plant kept in vegetative growth specifically to provide cuttings for cloning. Maintained under 18+ hours of light to prevent flowering. A good mother plant produces consistent, healthy clones.

N

Net Cup / Net Pot: A small perforated plastic cup (typically 25 mm–100 mm diameter) that holds the plant and its growing medium above or inside a nutrient solution. The mesh sides allow roots to grow through into the reservoir or channel below while the growing medium holds the plant upright. Net cups are reusable — clean and sterilise between grows.
NFT (Nutrient Film Technique): A system where a thin film of nutrient solution flows continuously along the bottom of slightly sloped channels, bathing the roots that hang inside. Low water usage, excellent oxygen exposure. Best for leafy greens and herbs.
NPK: The three primary macronutrients expressed as a ratio on nutrient labels: Nitrogen (N) for leafy growth, Phosphorus (P) for roots and flowers, Potassium (K) for overall plant health and fruiting. A grow (veg) formula is high-N; a bloom formula shifts to high-P and K.
Nutrient Lockout: A condition where nutrients are present in the solution but cannot be absorbed by the plant, typically due to incorrect pH or ionic antagonism. The plant shows deficiency symptoms even though the EC is correct. Corrected by adjusting pH to the target range and flushing the system.
Nutrient Solution: Water mixed with dissolved fertiliser salts to create the liquid feed delivered to hydroponic plants. Characterised by its EC (concentration) and pH (acidity). Must be prepared fresh and changed regularly — typically once per week.

P

Passive Hydroponics: Hydroponic systems that deliver nutrient solution without active pumps or power. Examples include the Kratky method (static reservoir with air gap) and wick systems (capillary action). Low cost and low maintenance, but less scalable and not suitable for large or thirsty plants that drain a reservoir quickly.
pH: A measure of how acidic or alkaline the nutrient solution is, on a scale of 0–14. Most hydroponic crops absorb nutrients best between pH 5.5 and 6.5. Outside this range, nutrients become chemically unavailable even if present in the solution — causing nutrient lockout. Check and adjust pH every 1–2 days.
pH Drift: The tendency of the nutrient solution pH to shift over time, due to plant uptake, microbial activity, or water chemistry. Requires regular monitoring and correction. Consistent drift upward is common as plants absorb nitrate; downward drift often indicates ammonium uptake or microbial activity.
PPFD (Photosynthetic Photon Flux Density): Measures the number of photons in the photosynthetically active range (400–700 nm) hitting a surface per second, expressed in μmol/m²/s. More meaningful than wattage alone for comparing grow lights. Seedlings and leafy greens need 150–350 μmol/m²/s; fruiting crops need 400–800+. Measure at canopy height with a quantum sensor for accurate readings.
Propagation: The process of starting new plants from seed or cuttings before moving them into the main growing system. Successful propagation requires stable temperature (20–25°C for most crops), high humidity, correct pH in the rooting medium, and patience.
Pythium: A genus of water moulds that causes root rot in hydroponic systems, particularly when water temperature exceeds 22°C or dissolved oxygen is low. Roots become brown, slimy, and develop an unpleasant odour. Prevented by maintaining cool water, high oxygen levels, and adding beneficial bacteria (e.g. Bacillus subtilis).

R

Raft DWC (Float-Bed): A variant of Deep Water Culture where plants in net cups are set into holes in a large floating foam or polystyrene board (raft) that sits directly on the surface of a shallow, aerated nutrient reservoir. The raft rises and falls as solution is consumed. Used commercially for high-density lettuce production — a 1.2 m × 2.4 m raft can hold 50–100 plants. Not to be confused with standard DWC buckets.
RDWC (Recirculating DWC): Recirculating Deep Water Culture — multiple DWC buckets connected by a pipe network to a central reservoir. A pump circulates oxygenated nutrient solution continuously between the buckets and the reservoir, maintaining consistent pH and EC across all plants. More complex than standard DWC but easier to manage at scale. Separate the control reservoir from plant buckets so you can adjust nutrients without disturbing roots.
Reservoir: The tank that holds the nutrient solution in a recirculating hydroponic system. Should be lightproof (to prevent algae growth), insulated, and large enough to buffer temperature and EC fluctuations. Typically drained and refilled once per week.
Rockwool: A mineral wool growing medium made from volcanic rock spun into fibres. Widely used for propagation and as a main growing medium in NFT and drip systems. Must be soaked and pH-adjusted before use — soak in water buffered to pH 5.5 for several hours.
Rooting Hormone: A gel or powder containing auxins (plant hormones) applied to the cut end of a clone to stimulate root development. Significantly improves success rate and reduces rooting time for cuttings.
Root Rot: A condition where roots become brown, slimy, and begin to decompose, caused primarily by Pythium water mould. Associated with warm water (>22°C), low dissolved oxygen, and light leaks into the reservoir. Treated with aeration, water cooling, and beneficial bacteria.
Runoff EC / Runoff pH: The EC and pH of drainage water collected after irrigating a substrate system (rockwool, coco coir). Reveals the true conditions in the root zone, which can differ significantly from the input feed. Runoff EC higher than feed EC indicates salt accumulation in the media. Runoff pH drifting outside target range indicates mineral precipitation. Essential monitoring data for substrate growers — check every 1–2 waterings.

S

Salt Buildup: Accumulation of mineral deposits in growing media or on system surfaces from repeated nutrient applications. Raises EC in the root zone above the feed EC, causing osmotic stress and nutrient burn. Detected by comparing runoff EC to feed EC. Prevented by periodic flushing and full reservoir changes.

T

Tower Garden: A vertical hydroponic system shaped as a freestanding column (tower) with growing pockets arranged around its circumference at multiple heights. Nutrient solution is pumped to the top and trickles down through each pocket (drip tower) or is misted inside the column (aeroponic tower). A single tower can hold 16–40 plants in under 0.5 m² of floor space. See also: Vertical Hydroponics.
TDS (Total Dissolved Solids): Another measure of nutrient concentration in water, expressed in ppm (parts per million). Related to EC but uses a conversion factor (typically 0.5 or 0.7 depending on the meter). EC meters are more commonly used in professional and European hydroponics.
Tip Burn: Brown, papery edges on young inner leaves, most common in fast-growing leafy greens like lettuce. Caused by localised calcium deficiency in the leaf tissue — not because the nutrient solution lacks calcium, but because poor airflow prevents calcium from reaching the leaf margins quickly enough. Fix: add a small oscillating fan to improve airflow across the plant canopy. Reducing EC slightly can also help.

V

Vertical Hydroponics: A category of hydroponic system in which plant sites are arranged vertically — stacked upward rather than spread across a flat surface — to maximise the number of plants per m² of floor space. Common formats include drip towers, aeroponic towers, Kratky towers, stacked NFT racks, and pocket wall panels. Lighting management is the defining challenge: upper sites receive more light than lower ones, requiring either rotating the system, adding side lighting, or per-level grow bars. Best suited to herbs, leafy greens, and strawberries.
VPD (Vapour Pressure Deficit): The difference between the amount of moisture in the air and the maximum moisture air can hold at a given temperature, expressed in kPa. Plants use VPD to regulate transpiration (water and nutrient movement). Too low (high humidity) slows transpiration and can cause tip burn and fungal disease. Too high (low humidity or high heat) causes wilting and stomatal closure. Optimal range: 0.8–1.2 kPa vegetative, 1.0–1.5 kPa fruiting/flowering.

W

Wick System: The simplest hydroponic method — an absorbent wick draws nutrient solution up from a reservoir into the growing medium by capillary action. No pumps, no electricity. Only suitable for small, low-demand plants such as herbs.