Glossary
Clear definitions for cannabis cultivation, plant science, and production.
59 terms
Quick reference
All terms
- Allele
- An alternative DNA sequence found at a particular position in the genome. In a diploid cannabis plant, the two copies at that position may carry the same or different alleles.
- Plant Biology
- Anemometer
- An instrument that measures air speed. Vane and hot-wire anemometers differ in sensitivity, response time, and the airflow ranges they can measure reliably.
- Environment
- Anthocyanin
- Water-soluble flavonoid pigments stored in plant cell vacuoles. They produce purple, red and blue tones in cannabis and in many fruits and vegetables.
- Chemistry
- Bag appeal
- The visual and aromatic impression of cannabis flower before it is used or tested, including color, trichome coverage, structure, trim, and aroma.
- Post-Harvest
- Botrytis cinerea
- The fungus behind bud rot, also called gray mold. Its spores germinate in prolonged leaf wetness at high humidity, at roughly 55 to 75 °F (13 to 24 °C).
- Environment
- Boundary layer
- A thin layer of relatively still air next to a leaf or flower surface. Its thickness affects heat, carbon dioxide, and water-vapor exchange with the surrounding air.
- Environment
- C3 photosynthesis
- The photosynthetic pathway used by cannabis and most plant species, named for the three-carbon compound formed when carbon dioxide first enters the Calvin cycle.
- Plant Biology
- Cannabinoid
- A member of a chemically related group of compounds found in cannabis, including THC, CBD and CBG, that can interact with biological targets in different ways.
- Chemistry
- Carboxylation
- The reaction in which Rubisco adds carbon dioxide to ribulose-1,5-bisphosphate, beginning carbon fixation in the Calvin cycle.
- Plant Biology
- Chlorophyll
- The green pigment that captures light for photosynthesis. It dominates the color of healthy plant tissue and breaks down as a plant senesces.
- Plant Biology
- Coco coir
- A coconut-husk growing substrate. It holds little nutrient charge of its own, so it is fed every irrigation and reacts fast to changes in temperature or EC.
- Cultivation
- Cola
- A dense cluster of cannabis flowers arranged along a stem. The main cola forms near the shoot tip, while smaller colas develop on lateral branches.
- Plant Biology
- CO₂ compensation point
- The carbon dioxide concentration at which a leaf's photosynthetic uptake equals its carbon loss through respiration and photorespiration, producing zero net exchange.
- Plant Biology
- Crop steering
- The deliberate use of irrigation, root-zone conditions and climate to influence the balance between vegetative and reproductive growth.
- Cultivation
- Cultivar
- A specific cultivated variety maintained by propagation. It is the precise term for what is loosely called a "strain".
- Plant Biology
- Daily light integral (DLI)
- The total photosynthetically active photons reaching one square meter over a day, expressed in mol·m⁻²·d⁻¹. DLI combines light intensity with duration.
- Environment
- Dew point
- The temperature at which air with its current water-vapor content reaches saturation. Cooling a surface to or below the dew point can produce condensation.
- Environment
- DIF
- Day temperature minus night temperature. DIF can influence stem elongation, but the direction and size of the response vary with species, cultivar, timing, and conditions.
- Environment
- Diploid
- Having two complete sets of chromosomes, one inherited from each parent. Cannabis is normally diploid, with 20 chromosomes arranged in 10 pairs.
- Plant Biology
- Dose-response curve
- A graph showing how a measured response changes across a range of doses or input levels, used to reveal thresholds, useful ranges, and saturation.
- Plant Biology
- Drain-to-waste
- An irrigation strategy where runoff is discarded rather than recirculated. Runoff readings become the main window into what the root zone is doing.
- Cultivation
- Dryback
- The decrease in a growing substrate's water content between irrigation events, commonly tracked as a change in volumetric water content.
- Cultivation
- Electrical conductivity (EC)
- A measure of a solution's ability to carry electric current, used as a fast indicator of total dissolved ion concentration but not of any specific nutrient.
- Nutrition
- Flavonoid
- A large class of plant compounds covering pigments, UV protectants and antioxidants, found throughout the plant kingdom. Anthocyanins are one flavonoid subclass.
- Chemistry
- Genotype
- The genetic makeup an organism carries, as distinct from the phenotype (the observable traits that result from a genotype interacting with its environment).
- Plant Biology
- Guttation
- The release of liquid droplets from leaf edges or tips through hydathodes, usually when root pressure continues while transpiration is low.
- Plant Biology
- Inflorescence
- The botanical term for a flower cluster, what the trade calls a bud. Research reports cannabis yield as inflorescence dry weight.
- Plant Biology
- Leaf wetness
- Liquid water sitting on plant tissue, from condensation, guttation or irrigation. It is a different measurement from humidity, and several pathogens require it.
- Environment
- Lockout
- A cultivation term for impaired nutrient uptake even though nutrients are present, often associated with unsuitable pH, excess salts or root stress.
- Nutrition
- Magnus equation
- An empirical equation that estimates saturation vapor pressure from temperature. Magnus-form coefficients are fitted to measured vapor-pressure data.
- Environment
- Mass flow
- The movement of dissolved nutrients with bulk water toward a root surface. Transpiration and water uptake help maintain this flow through the root zone.
- Plant Biology
- MBW complex
- A regulatory protein complex formed by MYB, bHLH, and WD40 proteins. In flowering plants, MBW complexes control the expression of genes in several flavonoid pathways.
- Plant Biology
- MYB transcription factor
- A member of a large family of DNA-binding regulatory proteins. Different plant MYB proteins control processes including development, stress responses, and flavonoid production.
- Plant Biology
- Net photosynthesis
- The rate at which a leaf gains carbon through photosynthesis after subtracting carbon released by respiration and photorespiration.
- Plant Biology
- Parts per million (ppm)
- A concentration ratio meaning one part of a substance per million parts of the mixture, abbreviated ppm. The exact interpretation depends on what is being measured.
- Environment
- Phenohunting
- Growing out a seed population and selecting the individual plants worth keeping. It is how a breeder finds the one phenotype that becomes a named cultivar.
- Cultivation
- Phenylpropanoid pathway
- A branching network of plant metabolism that begins with phenylalanine and produces compounds including lignin and flavonoids. Anthocyanins arise from one flavonoid branch.
- Chemistry
- Phloem
- Living vascular tissue that transports sugars and other compounds from source tissues to growing, storing, or metabolically active sink tissues.
- Plant Biology
- Photoperiod
- The duration and timing of light and darkness in a repeating daily cycle. Photoperiod-sensitive cannabis uses night length as a flowering signal.
- Environment
- Photorespiration
- A carbon-recycling pathway initiated when Rubisco reacts with oxygen instead of carbon dioxide, consuming energy and releasing some previously fixed carbon.
- Plant Biology
- Photosynthetic acclimation
- A change in photosynthetic capacity after sustained growing conditions, such as a partial reduction in the initial response to elevated carbon dioxide.
- Plant Biology
- Powdery mildew
- A group of host-specific fungal diseases that produce white, powdery growth on plant surfaces. Infection is often favored by humidity and generally does not require free water.
- Environment
- PPFD
- Photosynthetic photon flux density: the number of photons from 400 to 700 nanometers reaching one square meter each second, expressed in µmol·m⁻²·s⁻¹.
- Environment
- Relative humidity
- The share of moisture air is holding against the most it could hold at that temperature. Because it moves with temperature, cooling air raises RH with no water added.
- Environment
- Rockwool
- A mineral-fiber growing substrate formed by spinning molten rock into fibers and shaping them into propagation plugs, blocks, or slabs.
- Cultivation
- RuBisCO
- The enzyme that begins carbon fixation by adding carbon dioxide to RuBP. It can also react with oxygen, initiating photorespiration.
- Plant Biology
- Saturation vapor pressure (SVP)
- The equilibrium pressure of water vapor over a flat water surface at a given temperature. It rises nonlinearly as temperature increases.
- Environment
- Senescence
- The natural winding-down at the end of a plant's life cycle, when nitrogen moves out of the leaves and chlorophyll breaks down.
- Plant Biology
- Stomata
- Microscopic pores in the plant epidermis, each controlled by guard cells, that regulate carbon dioxide entry and water-vapor loss.
- Plant Biology
- Stomatal conductance
- A measure of how readily carbon dioxide and water vapor pass through a leaf's stomata, reflecting pore opening and the gas-exchange capacity of the leaf surface.
- Plant Biology
- Terpene
- A member of a large class of compounds built from isoprene units. Volatile terpenes contribute strongly to the aroma and flavor of cannabis.
- Chemistry
- Transcription factor
- A protein that binds specific DNA sequences and influences whether nearby genes are transcribed into RNA. A transcription factor can activate or repress its targets.
- Plant Biology
- Translocation
- The movement of sugars and nutrients through a plant's phloem, from where they are made or stored to where they are needed.
- Plant Biology
- Transpiration
- Water moving up through the plant and evaporating out through the stomata. It drives nutrient uptake, and carries calcium, which moves almost entirely by that flow.
- Plant Biology
- Trichome
- A hairlike structure on a plant surface. In cannabis, glandular trichomes on female flowers synthesize and store cannabinoids, terpenes and other metabolites.
- Plant Biology
- Vacuole
- The large fluid-filled compartment inside a plant cell, used for storage and to maintain turgor pressure. Water-soluble pigments such as anthocyanins are held here.
- Plant Biology
- Vapor pressure deficit
- The difference between saturation vapor pressure and actual water-vapor pressure. Leaf-to-air VPD is one driver of transpiration, moderated by stomata and water supply.
- Environment
- Water use efficiency (WUE)
- The amount of carbon gained or biomass produced relative to water used. Its numerical meaning depends on whether it is measured at a leaf, plant, or crop scale.
- Plant Biology
- Xylem
- The vascular tissue that carries water and dissolved minerals from root to leaf. Flow is one way and pulled by transpiration, so anything that slows transpiration slows delivery.
- Plant Biology
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