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Marijuana Growing Glossary

Plain-English definitions for the words growers use, from seed types and plant anatomy to lighting, nutrients and harvest.

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How to use this glossary

Seed listings and grow guides are full of shorthand: VPD, PPFD, LST, phenotype, 12/12. This glossary explains each term in plain language, with the numbers growers actually work with, so you can read a strain spec sheet or a how-to guide without guessing.

Every term is listed A to Z below. Each entry starts with a short definition, then explains why the term matters in a real grow and points you to related terms.

Where to start

  • Choosing seeds? Learn the seed types first: feminized, autoflower and photoperiod. Then read about phenotype, which explains why plants from one pack can differ.
  • Setting up a grow space? Focus on light and climate terms such as PPFD, DLI, VPD and relative humidity.
  • Getting close to harvest? Read up on trichomes, the harvest window, drying and curing.
  • Something looks wrong? The problems section covers pests, mold, nutrient burn and lockout.

If you’re brand new, the twelve terms below cover most of what you’ll meet in your first grow.

12 terms every grower should know

AutoflowerPlants that flower by age, not day length.PhotoperiodPlants that flower when nights reach about 12 hours.Feminized seedsSeeds bred to grow female, bud-producing plants.PhenotypeHow a plant's genes show up in your conditions.GerminationThe first step: a seed cracks and sends out a root.Vegetative stageThe leafy growth phase before flowering.Flowering stageWhen plants build buds, usually 7 to 12 weeks.TrichomeResin glands that hold cannabinoids and terpenes.TerpenesAroma compounds that give each strain its smell.VPDVapor pressure deficit, the link between heat and humidity.PPFDHow much usable light reaches your canopy.LSTLow-stress training: bending stems for an even canopy.

All 124 growing terms, A to Z

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Glossary FAQ

What does 12/12 mean in cannabis growing?

It means 12 hours of light followed by 12 hours of uninterrupted darkness every day. Switching photoperiod plants to 12/12 triggers flowering. Autoflowers don't need it and are usually kept on 18 or more hours of light for their whole life.

What is the difference between THC and THCA?
THCA is the form living cannabis plants actually produce, and it is not intoxicating in that form. Heat from smoking, vaping or cooking converts it to THC. That's why lab reports often show total THC, which combines both into one number. See THCA for details.
What is the difference between a phenotype and a genotype?

A genotype is a plant's genetic code. A phenotype is how that code shows up in a real plant, shaped by its environment. Seeds of the same strain can express different phenotypes, which is why plants from one pack may vary in height, aroma or flowering time.

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