How to Grow Marijuana Indoors: The Ultimate Guide for Growing Cannabis

Growing cannabis indoors offers better environmental control, consistent conditions, and easier pest management, making it a great option for beginners.

However, it can be more expensive than growing outside (truth be told). But if you know what you’re doing, the benefits are worth the cost.

Successfully growing cannabis indoors involves several steps, such as choosing a suitable space, setting up a good lighting system, managing temperature and humidity and so on. It might seem overwhelming if it’s your first time.

We’ve put together this ultimate guide with all the information you need for successful indoor cannabis cultivation. Interested in learning more? Keep reading to find out how to grow cannabis indoors.

How to Grow Cannabis Indoors: Planning Your Indoor Grow

First things first: To start growing marijuana indoors, you need to find the best location. It should be a clean, safe, and unobstructed space. Next, decide on your growing method. Let’s focus on these two important steps first.

Choosing Your Grow Space

You need a well-lit, clean, and organized space. You can use any of the following:

A closet
Greenhouse
Spare room
Garage
Grow box
Grow tent — most recommended*
Extra bathroom

Make sure the area is secure, keeping pets and children out. Also, if you’re concerned about theft or privacy issues, use heavy curtains or blackout sheets to block light and protect your plants.

A grow tent is a great option if you want to grow weed indoors without using an entire room. It helps you manage your plants’ environment and keep odors in check.

Grow tents come in various sizes, from small ones in a cupboard to large ones for bigger plants.

They’re more than just plastic sheets—they have inlets and outlets for power, water, and ventilation. Quality grow tents are made from durable materials that help regulate temperature, humidity, airflow, and light.

Selecting Your Grow Method

Soil is the most common medium for growing cannabis because it’s easy to find and comes with some nutrients already in it.

Weed grown in soil tends to taste better and have a stronger aroma. For the best results, use high-quality potting soil and consider adding extra nutrients designed for cannabis.

You can also create your own “super soil” by buying soil mixtures and choosing reputable brands with a good mix that includes earthworm castings and alfalfa meal.

You also have the option of using hydroponics as your growing medium. Hydroponics involves growing cannabis plants in a medium like coco coir or directly in a water reservoir, where you add all the nutrients to the water.

With this method, you don’t have to worry about watering your plants, overwatering, or dealing with runoff.

Hydroponics is more advanced than soil growing and requires more equipment, such as basins, oscillating fans, and lights, unlike a simple outdoor setup.

Also, hydroponics demands a lot of work and attention. You need to regularly check the water’s pH, monitor nutrient levels, maintain the water basins, and keep the equipment clean.

So, if you’re just starting, it’s best to consider soil as your medium.

Setting Up Your Indoor Grow Environment

After choosing your growing space and medium, the next step is to prepare the medium for planting your cannabis seeds.

However, before planting, ensure your indoor growing environment is set up correctly. This includes ensuring proper lighting, ventilation, airflow, temperature, and humidity control.

Lighting

When it comes to lighting for indoor cannabis growing, many enthusiasts suggest lights like plasma and CDM. While these additional lights can boost bud production, they aren’t really necessary for smaller grow rooms.

Different lights work better at various stages. Metal halide lights suit the vegetative stage because they emit more blue light.

Sodium lights are better for flowering as they produce more red light. Fluorescent lights are great for young plants and seedlings or for starting new plants.

Meanwhile, LED lights are popular among indoor marijuana growers since they use less energy, don’t need to warm up, and can be used throughout the growing process, though they can be expensive initially.

Quick Maths: An 800W LED Grow Light uses 800 watts of power each hour. If it’s on for 12 hours a day, it will use 800W x 12 hours = 9.6 kWh daily. At a rate of $0.12 per kWh, the daily cost is $0.12 x 9.6 kWh = $1.15. In a month, the total cost will be $1.15 x 30 days = $34.50.

Meanwhile, here is what you need in terms of lighting for growing cannabis indoors:

Lightning equipment	Purpose
A ballast	To control the energy for the light.
A reflector	To direct the light downward toward your plants
A sturdy chain or other strong material	To hang your lights.

Remember, you need a lamp with the correct wattage. For smaller grow rooms with limited space, keep it between 250 and 400 watts. Too high a wattage can make the room too hot and less effective.

Quick Tip:

For the vegetative stage of growing plants, you’ll need a grow light of about 100-125 watts. When your plants start to flower (usually after 4-6 weeks of growing), switch to a grow light of around 250 watts or more.

Ventilation and Airflow

Good air circulation is key for indoor weed plants, and that’s where extractor fans and intake fans come in.

An extractor fan’s job is to remove the warm air from the room, so it should be placed high up where warm air collects.

On the other hand, the intake fan brings fresh air into the room and should be placed on the opposite side of the extractor fan.

How many fans you need and what size will depend on the size of your growing space.

Where your growing space is located (the humidity level) will also determine if you need a dehumidifier or air conditioner to control the humidity or temperature in the room.

Temperature and Humidity Control

Temperature and humidity are controlled for indoor plants at each stage of life to ensure healthy growth.

You will need digital hygrometers to measure and monitor temperature and humidity accurately.

Germination Stage: Cannabis seeds need warmth and humidity to sprout. The ideal temperature is between 21-26°C (70-80°F), and humidity should be around 80%. You can achieve this with a heat mat and by placing your seeds in a water tray.
Vegetative Stage: After sprouting, your plants will grow leaves and roots. The ideal temperature for this stage is 18-24°C (64-75°F), and humidity should be between 50-70%. Use a fan to help with air circulation and monitor humidity levels.
Flowering Stage: When plants start producing buds, they need a slightly different environment. The ideal temperature is 21-26°C (70-80°F), with 40-50% humidity levels. To maintain these conditions, a dehumidifier and temperature monitoring are used.

Quick tip:

Place the hygrometers at the height of the plant canopy to get an accurate reading of the environment.

Preparing Your Grow Medium

Depending on your growing medium, you may need to put in some work to ensure your cannabis seeds germinate well and thrive.

Soil Preparation

If you’re new to growing marijuana plants, it’s best to start with a high-quality potting soil fondly called “super soil.”

This pre-fertilized soil gives your plants the nutrients they need for most of their growth, so you don’t have to add extra nutrients or amendments.

You can make your own super-soil by mixing worm castings, bat guano, and other ingredients with good soil and letting it sit for a few weeks. Alternatively, you can buy it ready-made from a local garden store or grow shop.

Meanwhile, your container type depends on your growing method and plant size.

Standard plastic pots or cloth bags are budget-friendly options, but air pots are better for improving airflow to the roots.

Start with a one-gallon pot and transplant to a larger one, like a five-gallon, as plants grow. For larger plants, you might need seven- or ten-gallon pots.

Quick tip:

Ensure containers have good drainage to prevent root rot. If using repurposed containers, check they have holes and use trays to catch excess water.

Hydroponic Setup

Growing hydroponically might seem complex, but it’s as easy as growing in soil with the proper setup.

A popular hydroponic method is Deep Water Culture (DWC), where roots are submerged in a nutrient-rich water reservoir with oxygen provided by an air pump. However, the Kratky Method makes hydroponic growing affordable and simple.

You can use various containers like buckets or plastic boxes for this setup. Plants are placed in net cups inserted into a lid, with roots reaching down into a nutrient solution below.

An air gap between the solution and the lid provides oxygen to the upper roots, eliminating the need for an air stone.

As the nutrient level drops, roots grow deeper into the solution. Just remember to top up the container before the plants use all the fluid.

Germinating and Planting Seeds

You have ticked the boxes of choosing the suitable growing space, ensuring the right temperature and ventilation, and setting up your growing medium.

Now, it’s time to do the actual planting of the cannabis seeds. It all starts with selecting the best weed strain for indoor growing.

Seed Selection

What makes an ideal cannabis seed for indoor growing? For starters, it should produce compact plants that suit micro-growing conditions, and a faster flowering time would be a plus.

Meanwhile, the seed should be high-quality and from a reputable seed bank. HomeGrown Cannabis is one such trusted seed bank.

When buying seeds, you can choose between feminized and non-feminized options. But feminized seeds are the best preferred for growing.

For indoor grows, consider strains bred for such environments, like

Wedding Cake, Purple Haze, Blue Dream, Bubba Kush and Sour Diesel.

If you’re a beginner, you may want to consider auto-flowering seeds, which are easier to grow and don’t rely on light cycles to mature.

Germination Methods

To germinate your seeds, the popular method— paper towel—involves placing them on paper plates or between paper towels and waiting for a taproot to appear. This can take a few days.

Once seedlings emerge, transfer them into your growing medium, like fabric pots with soil, and plant them about 10 mm deep. Keep the medium damp but not waterlogged.

For a simple method, soak seeds overnight in lukewarm water, then plant them directly in the ground or containers the next day.

Alternatively, you can plant seeds 1/2 to 1 inch deep in moistened soil or medium. This direct planting method avoids transplant shock since seedlings grow in their final environment from the start.

Generally, the growth stages of marijuana are:

Stage	Duration	Progress
Germination	3-10 days	Seeds begin to sprout.
Seedling	2-3 weeks	The plant develops its first leaves.
Vegetative	3-16 weeks	The plant grows larger and develops more foliage.
Flowering	8-11 weeks	The plant produces buds.

In the following sections, you will learn about each stage in detail. But overall, it takes about 10-32 weeks (3-8 months) to grow cannabis indoors from seed to harvest, though starting with a clone or autoflower seed can speed up the process.

Vegetative Growth Stage

The vegetative stage is when your cannabis plant experiences significant growth and typically lasts 3-16 weeks.

You should have transplanted your plant into a larger pot during this time. The roots and foliage will grow quickly. This is also the ideal period to start topping or training your plants.

Transplanting seedlings

Transplanting seedlings is straightforward but varies based on how you started them.

Once seedlings develop cotyledons, move them to a larger pot. Ensure the first true leaves are above the soil.

Let the soil dry, then gently remove the seedling by turning the pot upside down and transplanting it into a new pot.

Feeding and watering

After transplanting, you need to help the seedlings adjust to their new environment, or they can wilt and die.

Start by giving them a thorough watering to settle the soil around the roots. This helps establish a good connection between the roots and the medium.

But be careful not to overwater, though. Young roots need oxygen to thrive. Maintaining a consistent watering schedule keeps the soil evenly moist but not saturated.

You can adjust the watering based on the drying rate of the medium and the plant’s growth stage. Only water if the top inch of soil is completely dry.

Training and pruning

Plant training isn’t a do-or-die affair when it comes to growing cannabis plants, but it can maximize yields, especially with grow lights.

Training is most effective during the vegetative stage, as there’s limited training possible during flowering. If you have specific space needs, learn about plant training before your plants get too large.

The common techniques include:

Low-Stress Training (LST): Bending unruly branches and using gardening wire or soft ties to hold the branches where you want them.
Supercropping: Increasing a plant’s growth and productivity by subjecting it to high-stress levels.
Sea of Green (SoG): Densely planting cannabis seedlings and transitioning them to the flowering stage early.
Screen of Green (ScrOG): Setting up a horizontal screen or trellis above the plants and training the branches to grow horizontally through the screen.2
Topping: Cutting off the top of the plant’s main stem to promote lateral growth and increase yield
FIMing: Pinching or cutting off around 75% of the tip of a plant.
Defoliation: selectively removing leaves at the right time to optimize plant health, promote better light penetration, enhance airflow, and increase overall yields.

The screen of Green (ScrOG) is ideal for indoor cannabis grows with limited space. This technique maximizes indoor space and increases the likelihood of growing plants with dense, fat buds.

Flowering stage

The cannabis flowering stage is when female plants develop buds (while male plants produce pollen sacs that look like small balls).

Plants start flowering based on the amount of light they receive daily (that is, not autoflowering strains).

Light Cycle Adjustments

As long as the plants get a 12+ hour dark period each day, they will remain in the flowering stage until harvest.

During this stage, female plants develop wispy white hairs (pistils) at the plant’s joints.

Flowering nutrients

As cannabis plants enter the flowering stage, their nutrient needs will change significantly.

Early on, they benefit from nutrient solutions with more phosphorus and potassium. Choose an NPK formula (nitrogen, phosphorus, and potassium) that suits you, but avoid overfeeding to prevent plant burn. It’s best to increase nutrients around week two.

As buds grow, your plants will require more nutrients. Pay close attention to their response to changes in feeding.

A standard NPK ratio during mid-flowering is 6-10-15. Weeks 5 and 6 are peak flowering times, so monitor your plants closely for signs of nutrient issues. You may need to adjust nutrients to maximize your harvest.

By this stage, nitrogen should be reduced since it is more important for vegetative growth, and phosphorus, potassium, and calcium should be focused on for healthy flowering.

Managing Plant Health

Low-stress training (LST) helps manage plant stretch during early flowering and creates an even canopy, allowing light to reach lower buds.

Avoid stressing your plants during weeks 4 to 6 of flowering to prevent bud stunting or triggering hermaphroditism (the development of male sex organs within the buds themselves).

Stress can cause female plants to produce pollen and self-pollinate in a last-ditch effort to reproduce before dying.

Harvesting and Post-harvest

Harvesting too soon is a common mistake that can greatly lower your yields. In the last few weeks before harvest, cannabis plants increase bud size significantly, adding substantial weight to your final yield.

Determine harvest time

One major sign your plant is ready for harvest is when the trichomes—tiny, bulbous structures that produce THC—change from white to brownish amber.

Using a jeweler’s loupe can help you see them clearly. When more than 50% of the trichomes are amber, it’s time to harvest.

Harvesting marijuana too early usually results in a buzzed, heady high but can also cause anxiety and headaches for some people.

If you harvest later, the buds tend to provide a more relaxed, stony effect. Harvesting past the peak ripeness may lead to overly sleepy effects and weaker buds.

Fortunately, there’s a broad window for harvesting, varying by strain. Some growers harvest after 2 months of flowering, while others wait up to 4 months or longer. The ideal harvest time depends on the strain and personal preference.

Harvesting techniques

When it’s time to harvest, we recommend cutting down the entire plant using a PVC pipe cutter, which helps during drying.

Cut as close to the bottom of the stalk as possible. If you can’t cut the whole plant, cut it into branches but keep them intact. You can use this technique to prune cannabis plants efficiently.

Drying and curing

Dry the plant in a dark, cool space (around 56°F and 60% humidity) for 10 days to two weeks.

If drying inside the grow tent, remove the pot and lights, keep the fan running, and hang the plant from the top to avoid shape changes.

Quick tip:

The plant is dry when it makes a snap sound as you try to bend the stalk or branches.

After the initial drying, trim the bud-bearing branches from the stalk using the PVC cutter, and then cut the buds from the branches with spring-loaded pruning scissors.

Trim the protective sugar leaves from each bud, leaving a few to prevent oxidation. Gloves aren’t necessary but can help with the sticky resin.

After drying, place the dried buds in tightly sealed jars, filling them about 70-80% full. Store the jars in a cool, dark place.

Although, you’ll have to open the jars once a day during the first two weeks to release moisture and allow fresh air in.

Continue this process until the buds feel dry on the outside. The curing process generally takes 2-4 weeks, but some growers extend it up to 6 months for enhanced potency.

Quick tip:

Check buds regularly for moisture and mold. If they feel wet or smell unpleasant, adjust ventilation and discard any moldy buds.

Troubleshooting Common Issues With Indoor Cannabis Growing

When growing marijuana indoors, you might run into a few common issues. Knowing about these problems and how to prevent them can save you from surprises. Here are the common ones that new growers encounter:

Over or Underwatering

Cannabis plants need just the right amount of water. Too much water can drown the roots, while too little can dry them. To get watering right:

Water when the soil feels dry up to your first knuckle.
Make sure your pots have good drainage.
Bigger pots need less frequent watering.
Smaller pots need more frequent watering.
Aim for 20-30% extra runoff each time you water.

Too Tall Plants

Tall plants can be caused by not enough light. In this case, you have to move lights closer or get a stronger light)

If it’s due to the genetics of the strain you’re growing, then you must learn about your strain to understand its growth habits.

Improper Plant training can also be responsible. In this case, you can use LST, supercropping, or ScrOG to control plant height)

Nutrient Deficiencies

If you suspect a deficiency, follow this checklist:

Check for overwatering or underwatering.
Investigate proper environmental conditions (temperature, humidity, ventilation).
Make sure your plants are getting enough light (at least 100W for small grows).

Wrapping Up

Growing cannabis indoors can be very rewarding if you know the basics and follow the routine. We hope this guide helps you plant your weed inside hassle-free.

Meanwhile, make sure you’re using a high-quality seed strain suitable for indoor grow, too.

Many experienced growers recommend HomeGrown Cannabis for top-notch seeds, mainly because they have high-quality cannabis strains. Plenty of learning resources are also available on the platform to help you along the way.