Level 1 
Green Thumb
Foundations — your first healthy harvest, mistake-first.
22 lessons Level overview →
0/7 topics
Free · online · Dublin, Ireland
The free online cannabis cultivation course
60 research-backed lessons, beginner to advanced — a complete cannabis growing course, seedling to cure. Start free at Level 1; filter by level or topic below.
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Level 2
Skilled Grower
The science layer — light, nutrition, environment, water.
18 lessons Level overview →
0/6 topics
Level 3
Advanced Cultivator
Plant biology — cannabinoids, terpenes and the deep how.
12 lessons Level overview →
0/6 topics
Level 4
Master Grower
Mastery — breeding, scale and the finished craft.
8 lessons Level overview →
0/5 topics
Level 1 · Green Thumb 22 lessons
Foundations 6 min read
FoundationsAutoflowers: The Plant on a Clock
Autoflowers flower on a timer, not a light switch. That makes them beginner-friendly — as long as you stop treating them like a photoperiod plant.
Level 1 · Green Thumb
Nutrition 6 min read
NutritionFeeding: Not Yet, and Then Barely
The governing principle of feeding is the simplest rule in the whole book: less is more. You can always add more food. You can't un-feed a plant.
Level 1 · Green Thumb
Plant health 6 min read
Plant healthFirst-Grow Triage
The single most important skill in growing isn't feeding, watering, or training.
Level 1 · Green Thumb
Foundations 6 min read
The First Three Weeks: What Normal Looks Like
You can't spot a problem if you don't know what healthy looks like. That's the whole point of this lesson.
Level 1 · Green Thumb
Foundations 6 min read
Germination Without Drama
Germination is waking the seed up. Three things make it happen: moisture, warmth, and darkness.
Level 1 · Green Thumb
Light 7 min read
Light Water & media 5 min read
Water & mediaThere's No Best Growing Medium (But There's a Best One for You)
I switched mediums every few grows. Soil because someone said it was forgiving. Coco because the forums said it was faster.
Level 1 · Green Thumb
Plant health 4 min read
That Yellow Leaf Isn't What You Think
A leaf goes yellow. You panic. You Google it, find a colourful deficiency chart with sixteen options, decide it's nitrogen, and dump more nitrogen into the pot.
Level 1 · Green Thumb
Foundations 6 min read
Harvest & cure 4 min read
Harvest & cureDrying Out Your Plant Won't Make It Stronger
Someone on a forum told me to stop watering in the last two weeks of flower. "The plant puts out more trichomes when it's stressed," they said.
Level 1 · Green Thumb
Genetics 5 min read
The Entourage Effect Isn't That Simple
I became an entourage effect evangelist.
Level 1 · Green Thumb
Foundations 6 min read
The Shopping List (and the Overspender)
A grow room isn't a room with a plant in it. It's a controlled environment: light-tight, air-managed, containable.
Level 1 · Green Thumb
Foundations 6 min read
The Veg Weeks: What to Actually Do
Veg is where the plant builds the frame that holds your harvest. The main job is patience — and resisting the urge to fiddle.
Level 1 · Green Thumb
Light 4 min read
12/12 Isn't the Only Way to Flower
Twelve hours on, twelve hours off. That's what you learn on day one. Cannabis needs twelve hours of darkness to flower. Don't mess with it. It's the rule.
Level 1 · Green Thumb
Light 3 min read
UV Lights Won't Make Your Bud Stronger
A lad I know spent €180 on a UV-B bar for his tent. The listing said it would boost trichome production and increase potency.
Level 1 · Green Thumb
Water & media 6 min read
Watering and the Root Zone
Roots need air more than they need water. Not instead of — more than. In order of priority, roots want air, then water, then nutrients.
Level 1 · Green Thumb
Foundations 7 min read
Water & media 5 min read
You Will Overwater (Everyone Does)
You're going to overwater your plant. Everyone does.
Level 1 · Green Thumb
Harvest & cure 4 min read
Your Lower Buds Aren't Worth Keeping
I used to trim everything. Top colas, middle branches, bottom buds — all went into the same jar, dried and cured together.
Level 1 · Green Thumb
Genetics 4 min read
Your Plant's Potency Ceiling Is Genetic
I spent two years trying to push a cultivar past its limits. Better lights. Stronger nutrients. UV bars. PK boosters.
Level 1 · Green Thumb
Genetics 5 min read
Your Strain's Smell Is in Its DNA
I spent a year trying to change how my plants smelled. I read that cold night temperatures bring out certain aromas. That flushing with molasses boosts sweetness.
Level 1 · Green Thumb
Nutrition 4 min read
You're Probably Overfeeding
I followed the feed chart on the bottle. EC north of 2. 0 in flower. Whenever I saw burnt tips I backed off just barely enough to keep things moving.
Level 1 · Green Thumb
Level 2 · Skilled Grower 18 lessons
Plant health 7 min read
Deficiency or Lockout? Reading the Leaves
This is the lesson the whole level has been building toward. You've learned the air (2. 2–2. 4), the medium (2. 5), the door (2. 6) and the food (2. 7).
Level 2 · Skilled Grower
Environment 8 min read
EnvironmentEnvironment: The Air Is Doing Half the Work
You can photograph a leaf. You can photograph a root if you tip the pot out.
Level 2 · Skilled Grower
Environment 8 min read
Extraction and the Irish Problem
Two lessons ago you learned the air does half the work.
Level 2 · Skilled Grower
Nutrition 7 min read
Feeding for Real: EC and the Trend
Last lesson, pH decided whether food gets through the door.
Level 2 · Skilled Grower
Water & media 10 min read
Which growing medium forgives your watering?
The medium is not just a container for roots.
Level 2 · Skilled Grower
Light 9 min read
What your plant actually does with light
Here's the foundation: plants don't absorb light the way your eyes perceive it.
Level 2 · Skilled Grower
Nutrition 10 min read
How much to feed in flower (and where it's wasted)
The conventional wisdom says PK boosters drive flower size. Buy the bottle with the big numbers, push it in weeks 3–6, and watch the buds pack on. Sounds good.
Level 2 · Skilled Grower
Nutrition 11 min read
What a hungry plant is trying to tell you
Visual deficiency charts have been part of grow guides for thirty years. They're everywhere. The problem: most of them were never validated on cannabis.
Level 2 · Skilled Grower
Nutrition 10 min read
Organic or mineral — does the plant care?
Most growers feed to the ceiling. The bottle says 300 ppm nitrogen in flower, so they run 300. Or higher. The assumption: maximum input produces maximum yield.
Level 2 · Skilled Grower
Nutrition 7 min read
pH: The Bouncer at the Nutrient Door
You can do everything right at the feeding bench — perfect ratios, premium nutrients, measured to the millilitre — and still watch the plant starve in front of you.
Level 2 · Skilled Grower
Light 8 min read
Is 12/12 the only way to flower?
The 12/12 photoperiod is ubiquitous in flower rooms because it works — and because no one bothered to test the alternatives properly.
Level 2 · Skilled Grower
Training 9 min read
More plants, or bigger plants?
Plant density and architecture directly control the chemical gradient within your canopy.
Level 2 · Skilled Grower
Water & media 8 min read
Soil, Coco, and What Roots Want
Here's the line that took me three dead plants to believe: roots need air more than they need water.
Level 2 · Skilled Grower
Training 8 min read
Training I: Bend, Don't Break
A plant left to its own devices grows like a Christmas tree: one tall main cola hogging the light at the top, a ring of runts underneath sitting in its shadow.
Level 2 · Skilled Grower
Light 8 min read
Does UV-B really boost potency?
The narrative around UV-B supplementation is compelling: cannabis evolved in high-altitude environments with intense UV-B; trichomes function as sunscreen; therefore, more…
Level 2 · Skilled Grower
Environment 7 min read
VPD Without the Physics Degree
VPD. Three letters that have launched a thousand panicked forum threads.
Level 2 · Skilled Grower
Water & media 9 min read
Can you stress a plant into more potency?
There's persistent forum wisdom that restricting water in the final weeks triggers a stress response that increases resin and potency.
Level 2 · Skilled Grower
Light 9 min read
How much light is enough?
The research on light intensity and cannabis yield is unambiguous.
Level 2 · Skilled Grower
Level 3 · Advanced Cultivator 12 lessons
Plant biology 9 min read
How a plant actually builds potency
Here's what catches most growers off guard: your plant doesn't produce THC.
Level 3 · Advanced Cultivator
Harvest & cure 8 min read
Curing: Where Good Bud Becomes Good Bud
Most beginners have never heard of curing before their first grow.
Level 3 · Advanced Cultivator
Harvest & cure 8 min read
Drying: The Slow Part You'll Want to Rush
After I chopped that first harvest ten days early, I made it worse.
Level 3 · Advanced Cultivator
Flower & finish 8 min read
Flower Feeding and the Taper
Here's the thing most beginners get backwards: flowering is not the time to feed harder. It's the time to feed differently, and then feed less.
Level 3 · Advanced Cultivator
Flower & finish 7 min read
Humidity in Flower: The Bud-Rot Window
The Sleepwalker did everything else right. Light dialled. Nutrients dialled. Temperature dialled. Never checked humidity once.
Level 3 · Advanced Cultivator
Water & media 8 min read
Environment 8 min read
Outdoor and the Irish Climate
I read that outdoor cannabis grows bigger, costs nothing, and the sun does all the work.
Level 3 · Advanced Cultivator
Plant health 8 min read
Pests and Diseases: The Unwanted Guests
There was a single white dot on the underside of a fan leaf. I noticed it on a Tuesday, decided it was probably dust, flicked it off, and carried on.
Level 3 · Advanced Cultivator
Plant biology 8 min read
Is the entourage effect real?
The "entourage effect" — the idea that cannabis compounds work synergistically to produce effects different from isolated cannabinoids — is a plausible hypothesis with…
Level 3 · Advanced Cultivator
Plant biology 9 min read
Can you change how a strain smells?
Your strain's smell is determined by which terpene synthase genes it expresses and at what level.
Level 3 · Advanced Cultivator
Flower & finish 9 min read
The Flip: 12/12 and What Changes
You've kept a plant alive and vegged one without helping it to death. Now comes the part where the money is made or lost: the flip.
Level 3 · Advanced Cultivator
Harvest & cure 7 min read
When to Harvest: Trichomes Don't Lie
I'd been staring at it for two weeks. Is it ready? Is it ready now?
Level 3 · Advanced Cultivator
Level 4 · Master Grower 8 lessons
Genetics 7 min read
Breeding I: How Strains Happen
A grower crosses the two plants he loves with a paintbrush, gets four seeds, grows them out, and ends up with four plants that have nothing in common with each other and…
Level 4 · Master Grower
Plant biology 6 min read
Cannabinoid Biosynthesis: The Short Version
You've been told a hundred times that a strain "is" 22% THC. That number is the end of a long assembly line.
Level 4 · Master Grower
Harvest & cure 6 min read
Concentrates and What They Demand of the Flower
A grower spends an afternoon making bubble hash from a bucket of trim and pulls out a smear of green sludge that tastes like burnt lawn.
Level 4 · Master Grower
Training 7 min read
Density, Training, and Canopy Economics
Ask ten growers how many plants to run in a square metre and you'll get ten answers and at least one argument.
Level 4 · Master Grower
Plant biology 7 min read
Mythbusting as a Discipline
The most expensive thing in growing isn't a light or a tent. It's a confident claim with no control behind it. "Crank the PK." "UV boosts THC."
Level 4 · Master Grower
Light 7 min read
Spectrum Engineering
Somewhere out there is a grower who spent four hundred euro on a UV bar because a forum told him it would push his THC up. He ran it for a full flower cycle.
Level 4 · Master Grower
Plant biology 7 min read
Stress as a Tool (and as a Cult)
There's a corner of growing that has gone slightly religious. Stress the plant, the gospel says, and she'll reward you.
Level 4 · Master Grower
Plant biology 7 min read
Terpenes: The Other Half of Quality
Two growers, same THC number on the lab report. One jar smells like cut grass and the other like lemon peel and diesel.
Level 4 · Master Grower
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Common questions
Is this online cannabis cultivation course really free?
Yes. All 60 lessons are free to read — no signup, no paywall, no card. The course is funded independently, not by sponsors.
Is the whole cannabis course online and self-paced?
Yes — every lesson is online and self-paced. Start at Level 1, work through at your own speed, and come back to any lesson whenever you need it.
Are there cannabis courses in Ireland?
Grow Good Bud is an independent online cannabis cultivation course made in Dublin, Ireland. It is open to anyone, anywhere, and written in plain English.
Do I need any growing experience to start?
No. Level 1 assumes zero experience and starts from your very first seed. Levels 2–4 then go deeper into nutrition, environment, plant biology and breeding.
What does the course teach?
The full grow, seedling to cure: light, nutrition, water, grow-room environment, diagnosing problems, plus the plant biology and genetics behind it — each lesson grounded in cited research.