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Cannabis Glossary
49 grow terms explained in plain English, from autoflower to VPD. So you can follow every guide, even if you’re just starting out.
Overview
The Cannabis Glossary for Beginners
Our cannabis glossary covers the grow terms that keep popping up in our guides, each one explained in two to four sentences. Run into an unfamiliar word like stomata, EC or trichomes in an article? Just click the link and it takes you straight to the right explanation here.
If we have an in-depth guide or a matching calculator for a term, you’ll find the link right below the explanation. The glossary keeps growing: we add new terms as soon as they show up in our articles.
Pro Tip
You don’t need to memorize every term. Focus on pH, EC (electrical conductivity) and VPD (vapor pressure deficit). Those three already explain most problems in your grow.
A
- Autoflower
- Autoflowering strains start flowering on their own after a few weeks, no matter what light cycle you run. They get this trait from the subspecies Cannabis ruderalis. Seed to harvest usually takes just 8 to 12 weeks, and you don’t have to flip your lights to 12/12. Learn more →
B
- Botrytis (bud rot, gray mold)
- Botrytis cinerea is the fungus behind bud rot. It mostly attacks dense buds from the inside out when humidity runs high. Telltale signs are gray, fuzzy growth and brown, mushy spots inside the bud. Learn more →
C
- Cal-Mag
- Cal-Mag is a supplement that provides calcium and magnesium. You’ll mostly need it with coco coir, reverse osmosis (RO) water or very soft tap water, because those deliver little calcium and magnesium. Learn more →
- Cannabinoids
- Cannabinoids are the cannabis plant’s group of active compounds. The best known are THC and CBD. The plant produces them mainly in the trichomes on buds and sugar leaves.
- Carbon filter (odor filter for your exhaust)
- A carbon filter is a tube packed with activated carbon that sits on your grow tent’s exhaust system. Air gets pulled through the filter, and the carbon traps the odor molecules on the way. That way, the air leaving your tent barely smells like cannabis anymore. The carbon gets saturated over time, so you’ll need to replace the filter regularly. Learn more →
- Chlorophyll
- Chlorophyll is the green pigment in leaves that captures light for photosynthesis. Magnesium sits at the center of the molecule, and nitrogen is a key building block. If either one runs short, the leaves turn paler.
- Chlorosis
- Chlorosis means pale or yellow-green leaves because the plant isn’t making enough chlorophyll. Where it shows up points to the cause: on old or new leaves, across the whole leaf or only between the veins. Learn more →
- Coco coir (coco)
- Coco coir is made from shredded coconut husk fiber. It’s airy and holds water well, but it brings almost no nutrients with it. That’s why you feed from day one and usually add Cal-Mag. Learn more →
- Curing
- Curing means letting your dried buds mature in airtight jars for several weeks. By “burping” the jars briefly on a regular basis, leftover chlorophyll breaks down and the aroma and flavor get smoother. Learn more →
D
- Dark period
- The dark period is the lights-off part of the daily cycle. When photoperiod strains are flowering, it has to stay uninterrupted, because even light leaks can disrupt flowering or trigger hermaphrodites. Learn more →
- Defoliation
- With defoliation, you selectively remove big fan leaves so more light and air reach the inside of the plant. In moderation, this helps the lower buds. Overdo it, and you can stress the plant. Learn more →
- DLI (daily light integral)
- DLI is the total amount of light your plant gets in one day, measured in mol/m² per day. It comes from light intensity (PPFD) and how many hours the light is on. In the vegetative stage, about 28 to 40 mol/m² per day is a good range. Open the calculator →
- DWC (deep water culture)
- DWC stands for deep water culture and is a simple form of hydroponics. The roots hang permanently in a nutrient solution instead of soil. An air pump with an air stone keeps oxygenating the water so the roots don’t rot. That’s why you should keep an eye on the water temperature and oxygen level. Learn more →
E
- EC (electrical conductivity)
- EC shows how many nutrient salts are dissolved in your water, and that tells you how hard you’re feeding. Most US meters show it in ppm (500 scale), with EC in mS/cm, for example 800 ppm (1.6 mS/cm). Too high, and you risk nutrient burn and salt buildup. Too low, and deficiencies can show up. Learn more →
F
- Flowering stage
- During the flowering stage, your plant builds its buds. With photoperiod strains, it kicks off as soon as you switch to 12 hours of light and 12 hours of darkness. Depending on the strain, it lasts about 7 to 10 weeks, and some sativas take even longer. Learn more →
- Flushing
- When flushing, you run plenty of plain, pH-adjusted water through the growing medium to wash out built-up nutrient salts, for example after nutrient burn. Whether a flush right before harvest improves the taste is hotly debated among growers. Learn more →
H
- Hermaphrodite (hermie)
- A hermaphrodite is a female plant that also grows male pollen sacs, usually triggered by stress like light leaks or by its genetics. The pollen fertilizes the flowers, and you end up with seeds in your buds. Learn more →
- HST (high stress training)
- HST covers training methods where you deliberately injure the plant a little, like topping or supercropping. They can boost your yield, but the plant needs a few days to recover afterward. Learn more →
- Hydroponics (hydro)
- In hydroponics, roots grow without soil, either straight in a nutrient solution or in an inert medium like clay pebbles (LECA) or rockwool. Plants often grow faster, but you have to keep a very close eye on pH and EC. Learn more →
I
- Indica and Sativa
- Indica stands for compact plants with broad leaves and a shorter flowering time. Sativa stands for tall, lanky plants with narrow leaves and a longer flowering time. Most of today’s strains are hybrids of both. Learn more →
- Internodes
- Internodes are the sections of stem between two nodes, where the leaves branch off. If they get unusually long, the plant is usually stretching toward the light because the lamp is too weak or too far away. Learn more →
L
- Lollipopping
- With lollipopping, you strip the lower, shaded branches and leaves. The plant then puts its energy into the top buds that get plenty of light, and airflow down below improves. Learn more →
- LST (low stress training)
- With LST, you gently bend and tie the branches down without injuring them. This creates a flat, evenly lit canopy with several bud sites at the same height. Learn more →
M
- Macronutrients and micronutrients
- Your plant needs macronutrients in large amounts: nitrogen, phosphorus and potassium, plus calcium, magnesium and sulfur. Micronutrients like iron, manganese, zinc, copper, boron and molybdenum are only needed in trace amounts, but none of them can be missing. Learn more →
- Mobile and immobile nutrients
- The plant can move mobile nutrients like nitrogen, phosphorus, potassium and magnesium from old leaves to new ones, so a deficiency shows up at the bottom first. Immobile nutrients like calcium, iron, zinc and boron stay put, so their deficiency shows up on the young leaves at the top. Learn more →
- Mother plant
- A mother plant is a female plant that you keep in the vegetative stage permanently instead of letting it flower. You take cuttings from it regularly, also called clones. They are genetically identical to the mother and share her traits. That way you can grow a strain you like again and again. Learn more →
- Mycorrhizal fungi (mycorrhizae)
- Mycorrhizae are a partnership between roots and soil fungi. The fungal network extends the root surface, so the plant takes up water and nutrients, especially phosphorus, more easily. In return, the fungi get a share of the plant’s sugars. Learn more →
N
- NPK
- NPK stands for the three main nutrients nitrogen (N), phosphorus (P) and potassium (K). Nutrient labels list their ratio as three numbers, for example 3-1-2. In veg, your plant wants more nitrogen. In flower, it wants more phosphorus and potassium. Learn more →
- Nutrient lockout
- With nutrient lockout, there are enough nutrients in the growing medium, but the roots can’t take them up, usually because of the wrong pH or too much salt buildup. The plant shows deficiency symptoms, and adding more nutrients only makes things worse. Learn more →
O
- Overwatering (waterlogged roots)
- Waterlogging happens when water sits in the root zone and can’t drain away. The roots stop getting oxygen, the leaves droop, and root rot can set in. Learn more →
P
- Perlite (volcanic rock soil amendment)
- Perlite is small, white granules of expanded volcanic rock that you mix into your soil. It makes the growing medium looser and airier, so excess water drains away more easily. That gives the roots more oxygen and helps prevent waterlogged soil. Perlite doesn’t supply any nutrients itself. It just improves the soil structure. Learn more →
- pH
- pH tells you how acidic or alkaline your water and growing medium are. It decides which nutrients the roots can take up. As a rule of thumb, aim for 6.0 to 7.0 in soil, 5.8 to 6.3 in coco and 5.5 to 6.1 in hydro. Learn more →
- Photoperiod strains
- Photoperiod strains only start flowering when the days get shorter, meaning about 12 hours of light or less. Indoors, you control this with the light cycle: 18/6 in veg and 12/12 in flower are typical. Their counterpart is autoflowering strains. Learn more →
- Photosynthesis
- During photosynthesis, the plant turns light, CO2 and water into sugar, its fuel for growth. Oxygen is a byproduct. How fast it runs depends on light, temperature, CO2 levels and enough water.
- Pistils
- Pistils are the fine hairs on the female flower that are meant to catch pollen. As the buds mature, they turn from white to orange or brown. For pinpointing your harvest window, though, trichomes are more reliable. Learn more →
- Powdery mildew
- Powdery mildew is a fungus that forms a white, flour-like coating on the tops of the leaves that you can wipe off. It spreads mainly in stagnant air and with big temperature swings between day and night. Learn more →
- PPFD (photosynthetic photon flux density)
- PPFD tells you, in µmol/m² per second, how much light usable for photosynthesis actually reaches your plant. Unlike lumens, it measures exactly the light plants can use. Learn more →
- Pythium (pythium root rot)
- Pythium is a fungus-like pathogen (a water mold) that causes root rot. Infected roots turn brown and slimy. It spreads mainly with overwatering and in warm, oxygen-poor water. Learn more →
R
- RO water (reverse osmosis water)
- RO stands for reverse osmosis. Tap water is pushed through a very fine membrane that holds back almost all dissolved minerals. Because the water then also lacks calcium and magnesium, many growers add a Cal-Mag supplement. RO water lets you dial in pH more precisely, but it can also drift faster. Learn more →
- Runoff
- Runoff is the water that drains out of the bottom of the pot when you water. It shows you’ve watered thoroughly, and you can measure it: a runoff EC clearly higher than your input water points to salt buildup in the growing medium. Learn more →
S
- Stomata
- Stomata are tiny pores, mostly on the undersides of the leaves. Through them, the plant takes in CO2 and releases oxygen and water vapor. In heat or very dry air, the plant closes its stomata to save water, which also slows down photosynthesis.
- Stretch
- The stretch is the burst of vertical growth in the first two to three weeks after you flip to 12/12. Your plant can double its height, and sativa-dominant strains can grow even more. So plan for that headroom ahead of time. Learn more →
T
- Terpenes
- Terpenes are the plant’s scent and aroma compounds, for example myrcene or limonene. Like cannabinoids, they’re made in the trichomes, and they shape smell and taste. Since they’re sensitive to heat, a slow, gentle dry pays off. Learn more →
- Topping
- With topping, you cut off the tip of the main stem. The plant then grows two new main colas and gets bushier instead of just growing taller. Learn more →
- Transpiration
- Transpiration is water evaporating through the stomata. It works like a pump that pulls water and dissolved nutrients up from the roots. How strong it is depends mainly on temperature and humidity, which are combined in VPD (vapor pressure deficit).
- Trichoderma (beneficial soil fungi)
- Trichoderma is a genus of fungi that occurs naturally in soil and is beneficial for your plants. They colonize the root zone and compete with harmful fungi for space and food. That’s why trichoderma products are mainly used preventively, for example against root rot or bud rot. Once an infection is severe, trichoderma alone usually can’t get it under control.
- Trichomes
- Trichomes are tiny resin glands on buds and sugar leaves where cannabinoids and terpenes are made. Grab a loupe and check their color, from clear to cloudy to amber, to find the right harvest window. Learn more →
V
- Vegetative stage (veg)
- In the vegetative stage, your plant puts its energy into leaves, branches and roots, building the framework for flowering later on. For photoperiod strains, you usually run 18 hours of light per day. Learn more →
- VPD (vapor pressure deficit)
- VPD combines temperature and humidity into a single value (kPa) and shows how strongly the air pulls water out of the leaves. As a rule of thumb, aim for about 0.4 to 0.8 kPa for seedlings, 0.8 to 1.2 kPa in veg and 1.0 to 1.6 kPa in flower. Open the calculator →
