How to grow marijuana seeds indoors: The complete indoor cannabis grower’s guide

Growing marijuana seeds indoors offers the ultimate control over your cannabis plant’s life cycle—from germination to harvest. By cultivating in a controlled environment, UK growers can achieve high-quality, potent yields all year round, regardless of weather, season, or daylight hours. Whether you're starting out with a single plant or setting up a dedicated grow tent, success starts with planning and genetics.

In this complete indoor cannabis cultivation guide, you’ll learn how to grow marijuana seeds indoors step by step. From equipment and lighting setups to nutrient schedules and training techniques, we’ll walk you through it all. And if you're starting with premium seeds from Mavericks Genetics, you're already one step ahead.

Why grow marijuana seeds indoors?

Indoor growing has become the preferred method for many UK growers because it offers:

• Total control over light, temperature, and humidity

• The ability to grow cannabis year-round

• Greater privacy and security

• Protection from UK weather, pests, and mould

• Consistent quality and higher potency

While it requires a bit more investment in gear, indoor cultivation lets you customise every detail of your grow to maximise results.

What you need to grow marijuana indoors

Before germinating your seeds, make sure you have the following essentials:

Seeds

Start with feminised or autoflowering seeds from Mavericks Genetics:

• Feminised seeds ensure you only grow bud-producing female plants.

• Autoflowers are great for small spaces, fast grows, and beginners.

Grow space

You can grow indoors in a:

• Grow tent

• Grow box

• Spare closet or cabinet

Make sure the space is lightproof, well-ventilated, and odour-controlled.

Basic equipment

• Grow lights (LEDs recommended for efficiency and lower heat)

• Carbon filter + inline fan for odour and ventilation

• Oscillating fan for air circulation

• Thermometer and hygrometer

• Timers for automating light cycles

• Pots (fabric pots preferred for better root health)

• Growing medium (soil or coco coir)

• Nutrient solution and pH testing kit

Step 1: Germinate your marijuana seeds

Kick off your grow with successful germination.

Recommended: Paper towel method

1. Dampen two clean paper towels with filtered or bottled water.

2. Place your marijuana seeds between them on a clean plate.

3. Enclose in a plastic bag or container to hold humidity.

4. Store in a warm, dark spot (21–26°C).

5. Check daily for a white taproot (1–5 days).

6. Once the root is 0.5–1.5 cm long, plant in your growing medium.

Step 2: Choose your growing medium

Soil (organic)

• Easy to use

• Contains beneficial microbes

• Great for beginners

• Ideal pH: 6.0–7.0

Use light, well-aerated potting mixes with compost, perlite, or worm castings.

Coco coir (soilless)

• Faster growth

• Precise nutrient control

• Needs more frequent feeding

• Ideal pH: 5.5–6.5

Step 3: Set up lighting

Lighting is the most important factor in indoor cannabis yields.

Light types

Lighting schedules

• Vegetative stage: 18 hours on / 6 off

• Flowering stage: 12 hours on / 12 off

Aim for 30–50 watts per square foot of canopy with LEDs.

Step 4: Manage temperature, humidity, and airflow

Maintaining the correct climate is critical for healthy plants.

Temperature guidelines

• Seedlings: 21–26°C

• Vegetative stage: 22–29°C

• Flowering: 18–26°C

Humidity levels by stage

Use humidifiers, dehumidifiers, or exhaust fans to manage levels.

Airflow

• Place an oscillating fan inside to circulate air.

• Install a carbon filter and inline fan for fresh air and odour control.

Step 5: Feed and water your plants

If growing in soil:

• Use organic nutrients or bottled fertilisers.

• Vegetative stage: high in nitrogen

• Flowering stage: high in phosphorus and potassium

• Water when the top 2–3 cm of soil is dry

• Target pH: 6.0–7.0

If growing in coco coir:

• Feed with every watering

• Use lower nutrient concentrations

• Monitor runoff pH (target: 5.5–6.5)

Step 6: Train your plants to maximise indoor yields

Training helps shape your plant and maximise bud exposure to light.

LST (Low Stress Training)

• Bend and tie stems outward

• Promotes more bud sites and airflow

Topping / FIMing

• Cut or pinch the main stem to encourage multiple colas

• Perform early in vegetative stage (4–6 nodes)

SCROG (Screen of Green)

• Use a mesh screen to spread branches horizontally

• Creates a flat canopy for even light distribution

Step 7: Flowering and switching the lights

For photoperiod strains, switch to 12/12 light when you’re ready to flower.

Signs of flowering:

• White pistils form at nodes

• Stretching slows down

• Buds begin to form

Autoflower strains will begin flowering automatically 3–5 weeks after sprouting.

Step 8: Monitor trichomes and harvest at the right time

Use a jeweller’s loupe or magnifier to examine trichomes on buds.

Harvest when most are cloudy, with 10–20% amber.

Step 9: Drying and curing your cannabis

Drying:

1. Trim fan leaves

2. Hang branches upside down in a dark room

3. Maintain 18–21°C and 50–60% RH

4. Dry for 7–10 days (stems should snap)

Curing:

• Place buds in glass jars

• Open daily for 10–15 mins (first week)

• Cure for 2–4 weeks for best flavour and potency

Best cannabis strains to grow indoors

These strains are ideal for indoor growers in the UK:

• Autoflower hybrids: quick harvest, compact size

• Short-flowering indicas: bushy and low-maintenance

• Mould-resistant hybrids: ideal for high-humidity homes

Explore top-tier indoor cannabis genetics at Mavericks Genetics for reliable performance and high germination rates.

Troubleshooting common indoor growing issues

Final thoughts: Indoor marijuana growing gives control and quality

Growing marijuana seeds indoors in the UK allows you to customise your environment, boost yield, and enjoy discreet, year-round harvests. With the right knowledge and top-shelf genetics from Mavericks Genetics, even small home setups can produce exceptional results.

Ready to start your indoor grow?

Explore our full selection of indoor cannabis seeds at Mavericks Genetics and choose the perfect strain for your space, experience level, and yield goals. All seeds are backed by elite breeding and strong germination rates—ideal for growers across the UK.