How to Grow Medical Cannabis Indoors

If you’re looking to grow your own cannabis – whether that’s because you don’t have access to a reliable, legit source of cannabis in your area; because you’re disabled and you can’t always get to a dispensary; because you’re looking to save a little money over time by going DIY; or just because you have a green thumb and you want a new challenge – you’re part of a huge community of indoor growers.

But if you’ve never grown so much as a houseplant before, starting to grow marijuana for the first time can seem like an overwhelming prospect. Have no fear! There are tons of resources online to answer your every question – and we’ve put together this beginners’ guide to help you get started.

Step 1: Choose a strain

The strain of cannabis you choose to grow will depend on a number of factors. Probably the most important of these is space, but you also need to consider the purpose for which you’re growing the weed.

Sativa strains of cannabis produce a high that users describe as ‘uplifting’ and ‘creative’. More prosaically, sativa takes up a lot of space. However, if vertical space isn’t a problem but you don’t have a lot of width to work with, a sativa strain with fewer branches might work for you.

Indica strains have a higher ratio of CBD to THC than sativa, so this is the more usual choice if you’re growing for medical use. If you’re just growing it to get stoned, expect a dreamy, all-over body buzz. These are shorter, denser plants than the sativa strains, and they also grow more quickly, all of which adds to their popularity for indoor growing.

Step 2: Obtain seeds or clones

mmj seedsThere are two ways to start growing your cannabis plants: you can purchase seeds and grow them from scratch, or you can create clones. All you need to do to create a clone is identify a donor plant, take some cuttings from it, and grow these cuttings in a separate medium. This has the advantage of saving money and quite a lot of time – you don’t need to buy seeds or wait for them to germinate and grow – and it also means that all your plants will be females, which is what you need.

However, cloning means that you’re very dependent on the donor plants. If you take cuttings from a plant that is flawed in any way, your clone will have those flaws. Clones are also very sensitive and can die easily if they’re mishandled.

For this reason, experts tend to recommend that you start by growing from seeds if you’re a beginner weed grower: you’ll have a higher rate of success, and might find it easier to obtain feminized seeds than to access a plant you can clone from. Use a reputable seed-buying site and check the reviews before you buy.

Step 3: Choose your growing method


There are a wide range of budget options available to you under the heading of ‘soil’ – from whatever is in your garden to organic, pre-fertilized ‘super soil’ full of all the nutrients your plants need – but they’re all going to work out cheaper than hydroponics, along with using less water. However, a lot of growers prefer to seek alternatives that are cleaner, and guarantee a faster, more controlled grow.


There are a whole range of different hydroponic systems out there, but they all refer to a method of growing plants in nutrient-rich water, rather than in soil. This can be expensive, and leaves you little room for error when you’re making up the chemical solution your plants need – but if everything goes right you’ll likely get a higher, healthier cannabis yield in a shorter time than you would with soil.

Step 4: Set up the grow environment


If this is your first grow project, you’re going to want to start small, to avoid wasting money on trying to grow more plants than you can take care of. You can use a spare room, part of your basement, a closet…the smaller the space, the easier it is to control the grow conditions, so if you’re planning to grow in a full-size room or basement, think about using a grow tent or grow box as described below. Just be sure to leave enough space not only for your plants (including enough vertical space for them to double or even triple in size) but also all the other equipment described in this section – and don’t forget you’ll need space for yourself while you’re working.


Cannabis needs a lot of light: 250 watts per square meter at the very least, close enough to the plants to maximize light intensity without being so close that the heat from the lamps causes damage to the leaves.

There are four main varieties of lights used in grow rooms. Full spectrum LEDs, as the name suggests, these lamps give off the full spectrum of light that plants use as they grow, meaning less light waste, lower bills and better plant yields. These lights are increasingly popular with growers, but as a result there are many dodgy products out there: read some reviews before you buy.

High Intensity Discharge (HID) grow lights are much less expensive, but not as energy-efficient: they do give off a lot of heat so you’ll have to be sure not to skimp on your ventilation. You’ll also need different varieties for different stages of the growing process: the bluish-white metal halide lights are generally used for the vegetative growth stage, while the orange-red high pressure sodium lights are better for the flowering stage.

Fluorescent lights are cheaper than either of these, as the reflector, ballast and bulbs are all included, plus no cooling system is required – however, these use up more energy and more space. The electrodeless version of fluorescent lamps – also known as induction grow lights – are a more efficient kind, but more expensive and harder to find.

Temperature and ventilation

Plants need fresh air to live and carbon dioxide to photosynthesize, so you’ll need to create a constant stream of fresh air by means of a filtered air inlet to let fresh air in and an exhaust fan near the top of your grow room to let the warmer air out. Combined with a charcoal filter or an ionizer this will also help deal with the strong marijuana odor. An alternative is to use a combination of an air conditioner, a dehumidifier and supplemental carbon dioxide, but we wouldn’t recommend this expenditure for your first small grow.

The size of the fan you’ll need depends on the size of your space but also the kind of lights you’re using and how much heat they put out, and the ambient temperature in whatever part of the world you’re growing. Switch your lights on for a trial run for a while to get an idea of how much airflow you’ll need to get it down to the right temperature.

Depending on the strain, cannabis plants can tolerate temperatures between 58 and 92F, but ideally they will want to be between 70-85F when the lights are on, 58-70F when they’re off – the drop in temperature at ‘night’ will improve the flavor.

You’ll also want a wall-mounted fan to circulate a light breeze in your grow room: it cuts down on mold and pests, and helps your plants grow stronger stems. Make sure the fan isn’t pointed right at your plants, as this could damage them.

Monitoring and control

Finally, you’ll need a way to automate the functions of this equipment: the timing of the light/dark cycle is particularly important as your plants will need a period of darkness at the same time every day. As a beginner, all you’ll likely need is a 24-hour timer for the light and an adjustable thermostat to control the extractor fan.

You should also monitor the pH level of the medium in which you’re growing: cannabis needs a pH of between 6 and 7 if you’re growing in soil, 5.5-6.5 for hydroponics.

Grow tent or grow box

growing cannabis in a grow box
Example: Grobo cannabis grow box

If you don’t have the resources to dedicate an entire room to your grow, one of these products might work for you. You can buy them in a huge range of sizes, from one single plant up to 30. Grow tents are pretty simple affairs with a basic metal and canvas frame, so you’ll need to purchase all the same grow equipment you’d need for a full-size grow room (albeit on a smaller scale). Automated grow boxes are a lot more hi-tech (and thus a lot more expensive): you can buy boxes that come with lights and hydroponic systems all ready to go, along with separate chambers for different stages of the growing process so you can have multiple plants on the go at one time – some even have monitors that link to phone apps so you can check on your plants wherever you are!

Step 5: Grow!

If you’re growing your plants from seed you’ll need to germinate the seeds first: you can find out how to do that here. When they grow to seedlings – a quarter-inch sprout with a pair of leaves – you can replant each into your chosen growing medium. At this stage they’re very vulnerable and you need to be careful not to over-water them. They also need around 16 hours of light per day.

If you’re growing from clones, you’ll start at this stage. This is what’s called ‘vegetative growth’. This stage varies in length depending on your growing method – and the longer this period is, the bigger your plants will be – but generally it lasts 4-5 weeks.

After 4-5 weeks, reducing the daily lighting period to 12 hours triggers the plants’ ‘flowering’ phase (autoflowering strains will, as the name suggests, do this without the light trigger). During this phase the plants need bright light and more nutrients (see below). After about 8-10 weeks in the flowering phase, your plants should be ready to harvest. A good sign that it’s harvesting time is when the trichomes become cloudy: you can find out more about trichomes here.


Your plants will need to be fed with essential nutrients – this is essential for hydroponic growing, but even if you’re growing in soil the nutrients will soon be depleted. The plants need nitrogen, phosphorus, potassium, and a little calcium, magnesium, iron and copper. Find a well-reviewed nutrient solution that is formulated for each stage of the growing process: the nutrient levels your plants need during the flowering stage would likely damage them with nutrient burn during the vegetative phase.

Feed your plants at least once a week. For the first ‘feeding’, use a half-strength solution to see how they take it: you can always add more later.

If your plants are healthy, they’ll be perfectly green: discoloration, particularly yellow or brown tips to the leaves, means that the nutrient levels are too high.

Water and drainage

Your plants will generally need watering every other day. Water at the base, not over the top: you can mist lightly during the vegetative phase to keep pests away, but do not do this once the plant is flowering, otherwise you risk moldy buds. Some growers used distilled water, but this is not strictly necessary in most areas: if you’re concerned, try boiled water. Just be sure to let it cool before watering: your plants need room temperature water. It’s easy to over-water your plants so make sure your plants are in a well-draining medium, and keep an eye out for signs of over-watering, like stunted growth and discoloration. The soil should never be either soggy or completely dry.

There is a lot to remember: but the more you grow, the more this stuff will become second nature to you. Just start small, don’t spend too much money right away, and keep experimenting to get a feel for what works. Go grow!

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