A complete reference guide to the terminology used in indoor growing, hydroponics, and controlled environment agriculture. Each definition is written for practical use — not academic abstraction. If you encounter a term not listed here, get in touch and we’ll add it.
A
Aeroponics
A hydroponic growing method where plant roots are suspended in air and nutrient solution is delivered as a fine mist at regular intervals. Aeroponics delivers oxygen directly to roots, producing very fast growth rates, but requires precise timing and reliable pump systems.
Autoflowering
A plant variety that flowers based on age rather than light cycle changes. Autoflowering plants typically complete their full grow cycle in 8–12 weeks regardless of how many hours of light they receive per day, making them popular for year-round and multi-harvest growing.
C
CalMag
A calcium and magnesium supplement used to prevent and correct deficiencies, particularly in coco coir and soft water regions. Calcium and magnesium are secondary macronutrients required for cell wall structure, chlorophyll production, and enzyme function.
Coco Coir
A growing medium made from the fibrous outer husk of coconut shells. Coco coir is an inert, pH-neutral substrate that holds moisture while maintaining excellent aeration for roots. It is used as a standalone hydroponic medium or blended with perlite for improved drainage.
D
DLI (Daily Light Integral)
The total amount of photosynthetically active light a plant receives over a full 24-hour period, measured in moles per square metre per day (mol/m²/d). DLI combines both light intensity (PPFD) and the number of hours lights are on. Most flowering crops require 20–40 mol/m²/d for optimum yields.
DWC (Deep Water Culture)
A hydroponic system where plant roots are suspended in oxygenated nutrient solution contained in a reservoir. An air pump and air stones keep the solution oxygenated. DWC is known for fast growth rates and simplicity, making it popular with beginner hydroponic growers.
E
Ebb and Flow (Flood and Drain)
A hydroponic system where the growing tray is periodically flooded with nutrient solution from a reservoir below, then drained back by gravity. The intermittent flooding and draining delivers nutrients while maintaining high oxygen levels in the root zone between cycles.
EC (Electrical Conductivity)
A measure of the concentration of dissolved nutrients (salts) in a nutrient solution, expressed in milliSiemens per centimetre (mS/cm) or EC units. EC is used to monitor and adjust nutrient strength — too low indicates underfeeding; too high indicates overfeeding or salt build-up.
F
Flushing
The practice of watering plants with plain pH-adjusted water (no nutrients) in the final one to two weeks before harvest. Flushing is intended to clear residual nutrient salts from the growing medium and, in theory, improve the taste and burn quality of the final product.
H
HID (High Intensity Discharge)
A category of grow light that includes HPS (High Pressure Sodium) and MH (Metal Halide) technologies. HID lights require a separate ballast and produce significant heat output, but deliver high light intensity at relatively low upfront cost.
HPS (High Pressure Sodium)
A high-intensity discharge lighting technology widely used for indoor growing, producing light with a spectrum heavy in orange and red wavelengths. HPS has a long track record in commercial and hobbyist growing, and remains competitive with LED on yield per watt in optimised conditions.
I
IBA (Indole-3-Butyric Acid)
A synthetic plant hormone (auxin) used in rooting gels and powders to stimulate root formation at the cut surface of cuttings. IBA is the active ingredient in most commercial rooting products and is effective at low concentrations.
L
Living Soil
A growing approach that builds and maintains a soil ecosystem rich in bacteria, fungi, protozoa, and other microorganisms. In living soil, organic matter is continuously broken down by microbes into plant-available nutrients, reducing or eliminating the need for synthetic nutrient inputs.
Lux
A measure of light intensity as perceived by the human eye, expressed in lumens per square metre. Lux is not an accurate measure of light useful to plants because it weights green wavelengths (visible to humans) more heavily than red and blue wavelengths (most important to plants). PPFD is the correct metric for plant lighting.
M
Mycelium
The vegetative body of a fungus, consisting of a network of thread-like filaments (hyphae). In growing media, beneficial mycorrhizal fungi form mycelium networks that extend the effective root zone of plants, improving water and nutrient uptake. Products like Dynomyco contain mycorrhizal spores that colonise plant roots.
N
NFT (Nutrient Film Technique)
A hydroponic system where a thin film of nutrient solution flows continuously over the roots of plants growing in channels or gutters. The thin film keeps roots moist while exposing most of the root mass to oxygen. NFT is efficient and widely used for leafy crops and light-fruiting plants.
NPK
The three primary macronutrients required by plants: nitrogen (N), phosphorus (P), and potassium (K). Fertiliser products display NPK ratios on their label indicating the percentage of each nutrient. High-nitrogen formulas (e.g. 5-1-4) support vegetative growth; high-phosphorus and potassium formulas support flowering and fruiting.
Nutrient Lockout
A condition where nutrients are present in the growing medium but unavailable to plants due to incorrect pH. Each nutrient has a specific pH range within which it is soluble and plant-available. Outside this range, nutrients bind to substrate particles and cannot be absorbed, producing deficiency symptoms despite adequate feeding.
P
PAR (Photosynthetically Active Radiation)
The range of light wavelengths between 400 and 700 nanometres that plants use for photosynthesis. PAR is a wavelength range, not a unit of measurement. The intensity of PAR light is measured as PPFD (micromoles per square metre per second).
Photoperiod
The relationship between the duration of light and dark periods that controls flowering in many plant species. Photoperiod-sensitive plants require a specific number of uninterrupted dark hours to trigger and maintain the flowering stage, typically 12 hours darkness for most flowering crops.
PPFD (Photosynthetic Photon Flux Density)
The number of photosynthetically active photons hitting one square metre of surface per second, measured in micromoles per square metre per second (µmol/m²/s). PPFD is the most accurate metric for measuring grow light intensity at canopy level. Vegetative crops need 400–600 µmol/m²/s; flowering crops need 600–1,000 µmol/m²/s.
PPM (Parts Per Million)
An alternative unit for measuring dissolved solids concentration in nutrient solution, used in some countries alongside or instead of EC. PPM and EC measure the same thing — nutrient solution strength — but use different scales. 1 EC (mS/cm) is approximately 500–700 PPM depending on the conversion factor used.
Propagation
The process of producing new plants from seeds, cuttings, or other plant material. Indoor propagation typically involves rooting cuttings taken from a mother plant in a sealed propagator at high humidity (80–90%) and controlled root zone temperature (22–24°C), using rooting gel to stimulate root formation.
R
Root Zone
The area of growing medium directly surrounding and occupied by a plant’s roots. Maintaining optimal root zone conditions — correct temperature (18–22°C), adequate oxygen, consistent moisture, and correct pH — is critical for nutrient uptake, plant health, and growth rate.
Runoff
The excess nutrient solution that drains from the bottom of a container after watering. Measuring the pH and EC of runoff provides important information about conditions in the root zone — particularly salt build-up and pH drift within the growing medium, which may differ from the input solution.
V
VPD (Vapour Pressure Deficit)
A measure of the drying power of air — specifically the difference between the moisture the air could hold at a given temperature and how much it actually holds. VPD determines how fast a plant transpires. Target VPD for most crops is 0.8–1.2 kPa in veg and 1.0–1.5 kPa in flower. VPD combines temperature and relative humidity into a single actionable metric.
W
Wicking
A simple, passive hydroponic method where plants draw up nutrient solution from a reservoir through an absorbent wick material (such as rope or felt). Wicking systems require no pumps or electricity but are limited to smaller plants with modest water demands due to the slow rate of solution delivery.