How to Grow Cannabis Indoors: The Complete Beginner Guide

Growing cannabis indoors is simpler than most guides make it sound. You need a contained space, a light, some soil, water, and patience. The rest is optimization.

This guide covers everything from picking your equipment to harvesting your first plant. No assumptions about prior experience. If you've never grown anything before, start here.

What you need before you start

Here's the full equipment list for a basic indoor grow that will produce quality results on a first attempt.

The essentials (you cannot skip these):

A grow tent (60x60x160cm for 1-2 plants, 120x120x200cm for 4-6 plants). Tents contain light, manage airflow, and give you a controlled environment. You can grow without one, but a tent makes everything easier.

An LED grow light. For a 60x60 tent, a 150W LED is sufficient. For a 120x120 tent, go with 240-300W. Modern LEDs run cool, use less electricity than older HPS lights, and produce a full spectrum that works for both veg and flower stages.

An inline fan with carbon filter. This pulls air through the tent, controls temperature, and scrubs the smell. Cannabis in flower is pungent. Without a carbon filter, your neighbors will know.

Pots. Fabric pots (11-20 liters) are the standard choice. They prevent root circling, improve drainage, and are cheap. For autoflowers, 11L is fine. For photoperiods you plan to veg longer, go with 15-20L.

Growing medium. Start with quality potting soil that includes perlite for drainage. Brands vary by region, but look for soil marketed for tomatoes or cannabis specifically. Avoid heavy garden soil or anything with slow-release fertilizer pellets mixed in.

A pH meter. The single most important tool after your light. A basic pH pen costs 10-20 euros and prevents the most common cause of plant problems: nutrient lockout from incorrect pH. Cannabis in soil needs water between 6.0-6.5 pH.

Nice to have (helps but not required for first grow):

A small oscillating fan for air circulation inside the tent. A temperature and humidity monitor (hygrometer). Nutrients (your soil may have enough for the first few weeks). A timer for your light schedule (most LED drivers have built-in timers, but a basic outlet timer works too).

Budget breakdown

A complete setup for 1-2 plants costs roughly 150-300 euros depending on the quality of components you choose.

Grow tent: 50-80 euros. LED light (150W): 60-120 euros. Inline fan with carbon filter: 40-70 euros. Fabric pots (2-4): 10-15 euros. Soil and perlite: 15-20 euros. pH meter: 10-20 euros. Seeds: 10-30 euros for a 3-pack from a reputable seed bank.

Ongoing costs are minimal. Electricity adds roughly 15-30 euros per month for the light. Water and occasional nutrients are negligible.

Setting up your grow space

Step 1: Assemble the tent. Follow the manufacturer's instructions. Place it somewhere with access to a power outlet and ideally near a window or vent where you can exhaust warm air.

Step 2: Hang your light. Most tents have crossbars for hanging equipment. Hang the LED at the height recommended by the manufacturer (usually 40-60cm above the canopy for seedlings, closer during flower).

Step 3: Install ventilation. Mount the inline fan at the top of the tent (hot air rises). Connect the carbon filter to the fan inside the tent. Run ducting from the fan out through a tent port. This creates negative pressure: air gets pulled into the tent through the bottom vents and exhausted out the top through the filter.

Step 4: Set up your pots. Fill fabric pots with soil, leaving about 2cm from the rim. Water the soil thoroughly and let it drain before planting.

Step 5: Check your environment. Turn everything on and measure temperature and humidity after 30 minutes. You're aiming for 22-28C and 50-70% relative humidity. Adjust fan speed and tent vents as needed.

The grow timeline

Here's what to expect from seed to harvest with a typical indoor grow.

Weeks 1-2: Germination and seedling. Germinate your seed using the paper towel method (damp paper towels in a dark, warm place for 24-72 hours until a taproot appears). Plant the germinated seed 1cm deep in moist soil, taproot pointing down. Keep the light at low intensity or further away. Water sparingly. Seedlings need very little of everything.

Weeks 3-5: Vegetative growth. The plant is building its structure. Light schedule: 18 hours on, 6 hours off. This is when the plant grows rapidly. Start training (LST) once the plant has 4-5 sets of leaves. Begin nutrients at quarter strength if your soil is running low (yellowing lower leaves are the sign). Water when the top 2-3cm of soil is dry.

Weeks 6-8 (photoperiod) or weeks 5-6 (autoflower): Transition to flower. For photoperiod plants, switch your light to 12 hours on, 12 hours off. This triggers flowering. Autoflowers will begin flowering on their own regardless of light schedule. Switch to bloom nutrients (higher phosphorus and potassium, lower nitrogen). Reduce humidity to 40-50%.

Weeks 9-14 (photoperiod) or weeks 7-11 (autoflower): Flowering. Buds form and fatten. Smell increases significantly (your carbon filter earns its keep here). Monitor trichomes with a loupe or macro lens starting around week 3 of flower. When trichomes are mostly milky with a few turning amber, you're in the harvest window.

Week 15+ (photoperiod) or week 12 (autoflower): Harvest, dry, cure. Cut the plant, trim the buds, hang to dry for 7-14 days in a dark room at 18-22C and 55-65% humidity. Once dry, cure in glass jars for 2-4 weeks minimum.

Total time from seed to smokable flower: 3-4 months for autoflowers, 4-5 months for photoperiods.

The 5 most common beginner mistakes

Overwatering. The number one killer of first grows. Cannabis likes wet-dry cycles. Water thoroughly, then wait until the top few centimeters of soil are dry before watering again. If in doubt, wait another day.

Ignoring pH. If your water pH is outside 6.0-6.5 for soil, the plant cannot absorb nutrients regardless of how much you feed it. This creates deficiency symptoms that look like nutrient problems but are actually pH problems. Test and adjust every time you water.

Too many nutrients too early. Quality soil has enough food for the first 2-3 weeks. Starting nutrients at full strength immediately burns the plant. When you do start feeding, begin at 1/4 strength and increase slowly.

Harvesting too early. Impatience costs potency and weight. Wait for the trichomes to tell you. Clear trichomes mean the plant isn't ready. Milky trichomes mean peak THC. A few amber ones mean you're right on time.

Poor humidity control during flower. High humidity plus dense buds equals mold. Bud rot can destroy an entire harvest in days. Keep humidity below 50% during flowering and ensure good airflow around the buds.

What to grow first

For your first indoor grow, choose a strain labeled as beginner-friendly with known resilience and a forgiving growth pattern. Autoflowers are easier for beginners since there's no light schedule change to manage.

Strong first-grow options: Northern Lights Auto (fast, low odor, bulletproof), Gorilla Cookies Auto (good yields, forgiving, balanced effects), Blue Dream Auto (huge yields, easy to grow, great flavor).

All of these are available from major seed banks like ILGM, Seedsman, and Fast Buds.

Browse beginner-friendly seeds at ILGM Browse autoflower seeds at Seedsman

Next steps

Once your first grow is done and you've learned the basics by doing, you can optimize for the second round. Better training techniques, dialed-in nutrients, more ambitious strains. Every grow teaches you something the last one didn't.

If you want the full breakdown on nutrients, training, harvest timing, and curing, the Gorilla Grow Bible covers all seven stages in detail.