How to Grow Cannabis Indoors: The Complete Guide

Start with the space, not the shopping list

Every other decision downstream — wattage, fan size, pot size, plant count, nutrient volume — is set by the square footage of your canopy. A 2x2 corner holds one well-trained plant under about 150 watts. A 4x4 tent holds four plants under roughly 450 watts and needs a 6-inch inline fan to keep temperature and humidity in range.

Pick the footprint first and let the kit follow. If you want that done for you, the kit builder asks seven questions and sizes the whole system, including how many seeds you actually need.

• 2x2 — 1 plant, ~150W, 4" fan, 3 gallon pots
• 2x4 — 2 plants, ~260W, 4" fan, 5 gallon pots
• 4x4 — 4 plants, ~450W, 6" fan, 5 gallon pots
• 5x5 — 5-6 plants, ~650W, 6" fan, 7 gallon pots

The five things that decide your result

Light intensity, air exchange, water rhythm, feed strength and harvest timing account for nearly every difference between a disappointing first run and a great one. Genetics matter, but a strong strain in a hot, stagnant, overwatered tent still underperforms an ordinary strain in a dialed one.

• Light: enough PPFD across the whole canopy, not just under the centre of the fixture
• Air: full tent air exchange about once a minute, with leaves always gently moving
• Water: water to 10-20% runoff, then let the pot get light before watering again
• Feed: build strength up slowly and read the plant instead of the bottle label
• Timing: harvest by trichome colour, not by the breeder's day count

A realistic timeline

Germination takes two to five days. Seedlings need one to two weeks. Vegetative growth runs four to six weeks for photoperiods. Flower runs eight to ten weeks. Drying takes ten to fourteen days and curing at least two more weeks. Call it four to five months from seed to a jar that is actually good.

Autoflowers compress that to roughly ten to twelve weeks total because they flower on age rather than light schedule, at the cost of a smaller plant and no chance to fix a slow start.

The mistakes that cost people their first harvest

Almost all first-run failures come from the same short list: overwatering seedlings, running the light too close or too far, ignoring humidity in late flower, feeding full strength too early, and harvesting a week or two early out of impatience.

None of those cost money to fix. They cost attention. A cheap temp and humidity reader plus a timer removes two of them entirely.