How to grow marijuana indoors, a beginner's guide. As weed legalization spreads so does growing it. You can grow your own supply in the comfort of your home. Cannabis needs plenty of light, water, nutrients, and good soil. We'll walk you through the process step by step and explain in a beginner friendly way how to. Growing weed indoors is a great option for new homegrowers. Learn everything you need to know about growing weed indoors, including how to set up your grow room and climate control.
Grow Weed Indoors: Guide for Beginners to Cultivate Cannabis
This is a beginner-friendly article. We’ll discuss the basics from start to finish, seed to harvest. We’ll go through what you’ll need for a basic but successful grow setup and what to consider before starting out. We’ll explain the process in a way that even a first-time grower with no previous growing experience will be able to get going.
With that said, this article is not for people who are already experienced growers and are looking for advanced growing techniques. We will not talk about pruning, bending, tying, low-stress-training (LST), diseases, pests, CO2 boost, optimization for maximum yield, and similar topics. Instead, we’ll focus on keeping this basic and simple to show that growing plants indoors really isn’t that difficult.
Where are you going to grow?
Cannabis is grown in plenty of different locations or spaces, all depending on your conditions. Some grow marijuana outdoors in open fields, gardens or on a balcony. The more common way is growing indoors. Large scale operations grow in massive warehouse-like buildings but the average hobby-grower usually has a grow room, grow closet, or, possibly the most common setup, an indoor grow tent. It’s the latter options, the ones that are indoors, which we’ll assume are true for you.
Growing indoors, in a tent for example, is easiest for first-time growers as indoor spaces are easier to control. The risk of your plants suffering from pests or diseases are lower, it’s easier to control temperature and humidity, the light from your grow lamp is confined within the tent, and the grow is easy to access as it’s within or near your living space. In short, if you’re new to growing and are considering your options, we recommend a grow tent . Further down we’ll talk about tent size and necessary accessories.
Growing medium (soil or hydro)?
Weed is grown in either soil (indoors or outdoors) or in a so-called hydroponics setup, without soil. Growing in soil is more beginner-friendly and requires less precise grow strategy (less likely to mess up). Soil is the grow medium we’ll focus on in this article. More on this below.
What you’ll need:
The seeds are what the plant will develop from. Different strains have different characteristics. Some strains grow very tall, others need a longer time to develop, some produce buds with high THC, others with high CBD, etc. Your seed bank will be able to give you specifics of each seed you’re considering. What’s important is to choose feminized seeds. These guarantee a female plant, which produces the maximum amount of flowers, or buds.
Nowadays “auto-flower” seeds are widely available and they are a good choice for beginner growers. Auto-flower plants do not need to be transplanted (from small to larger pot) but more importantly, they will transition from vegetative stage to flowering stage automatically, without any changes in light. More on this later. Auto-flower strains typically produce somewhat smaller yields but their grow-friendliness still makes them the ideal choice for inexperienced growers.
The time from seed to harvest for auto-flower strains is shorter than regular strains. Usually, around 2-3 months whereas non-auto-flowers usually need 3-4 months. Once again, the specifications for each strain will be available on the seeds’ package or in the shop.
The size of the pot has a big significance on how large your plant will grow. The plants’ roots need room to grow and the more room they have, the larger the plant will be. 3 gallons (10 liters) pots are usually considered the bare minimum. Twice the size is recommended if you have enough space.
It’s important there’s plenty of holes in the bottom of the pots to allow for excess water to drain.
Plastic pots are preferable to clay pots as clay soaks up water.
As mentioned above, auto-flower strains can be planted right into their “long term” pot. Regular strains will need to be planted in a small pot, around 8 oz (0.25 liters), and when they develop four sets of leaves, transplanted into their long term pot, 3+ gallons (10+ liters).
Coco coir is our preferred choice of soil. Its biggest advantage is that it will not contain any bugs or eggs. Certain types of soil can come with unwanted pests as bugs like to deposit their offspring in organic matter. Coco coir is sterile in that regard. Also worth adding is that coco coir can come with or without added nutrients. It’s preferable to choose a coco coir without nutrients and instead add the necessary nutrients manually when watering. This gives the grower better control of what substances the plant can consume. Adding extra nutrients to an medium that already contains nutrients can cause nutrient burn, especially for young plants.
Some soil types come packed with nutrients. While this is good for somewhat developed plants (3+ weeks old), too much nutrients can hurt seedlings. It’s also important to remember that the nutrients in the soil will be consumed by plants. Typically in around four weeks. It’s preferable to choose a soil that isn’t fully loaded with nutrients and instead add nutrients separately as you water the plants. The supply of nutrients will be steadier and nutrients bought specifically for marijuana will give a better result than “general” nutrients.
Here’s a soil that has nutrients added as indicated by the EC and NPK ratio.
Assuming you grow indoors, you’ll need a grow light. We’re, of course, biased so light is our favorite aspect of growing. Nutrients management, pruning, soil, to name a few, can be equally important. But since we manufacture and sell lights, this is what we’re passionate about. Check out our LED grow lights.
To keep this nice and short, we’ll only cover the very most basic aspects but we strongly encourage you to read our extensive article about LIGHT where we dive deeper into, well, pretty much everything about LED grow lights.
You, as a beginner indoor grower, need to know the following things when choosing a LED grow light and setting up your grow area:
– The grow lamp’s light output: Light particles are called photons and the light output from a grow light is called PPFD (Photosynthetic Photon Flux Density) and it’s measured in umol/m2/s. Weed plants in their veg stage need 150-300 PPFD. During flowering, they need 500-700 PPFD, or more if you add CO2 (not recommended for beginners). The lamp manufacturer should list the lamp’s PPFD levels at various heights as the PPFD decreases the further the plant is from the lamp.
– Light footprint: This explains how the light from the lamp spreads. Some lamps have a very narrow footprint and may not be suitable for large or several plants. You want to make sure that the lamp you’re considering produces enough light to cover your grow space.
– Light spectrum: A trend with low-end LED grow lights in recent years is that they only, or mainly, produce blue and red colored light. While these are the dominant colors used in photosynthesis, a plant needs a healthy balance of blue-green-red. Although green has less direct effect on photosynthesis, it helps the plant’s overall health and also boosts some processes. A small but important detail.
LEDTonic Z5’s light spectrum; an optimized balance of blue-green-red.
– A word of warning: Do not fall for some of the ridiculous claims made by some brands. Browsing Amazon for “LED grow lights” will show plenty of results for “1500W” or similar lights. This value means very little at best. It either refers to which HPS equivalent lamp that particular grow light should replace or the total LED diode wattage.
There is no correlation between LED wattage and HPS wattage so any claim in this regard without supporting PPFD values and light footprint is more or less bogus.
The LED diode wattage doesn’t tell much about the lamp either. In fact, the larger the diode, the more heat it produces and the less efficient it becomes (more of the input electricity goes wasted through heat).
These “1500W” lights only draw about 200-300 watts. That means they are running at 20-30% of the maximum capacity. A LED grow light with smaller diodes, like ours, run at ~60% of max capacity so you’re still getting a high output despite “low” wattage.
Lumen and lux, commonly used to measure white light, do not paint the full picture when measuring LEDs with specific light color output. PPFD is far more accurate.
– In short: Look for a lamp’s PPFD output, spectrum, and light footprint. Any inflated wattage claims mean nothing if the electricity isn’t efficiently converted into light with a good spectrum.
Water, pH, pH tester
Water is one of three (light and nutrients are the other two) essentials for growth. Tap water, unless contaminated, can be used to water your plants. Depending on where you live, your tap water will have a certain pH level. Usually around 7 pH. Cannabis prefers water around 6 (+/- 0.5) pH. It’s easy to both test and regulate the pH level. A pH test kit can be purchased online or in a garden store. This would be a liquid which, when mixed with water, will turn into a specific color that indicates the water’s pH level. There are also pH meters that work just like a baby thermometer. Insert in water and it will read the pH level on the spot. This type of tool is not cost-efficient for small scale grow projects, though. See below how to regulate and control the pH level.
Plants typically need to be watered in small amounts 1-3 times a week. Water only when the top 1-2 inches of the soil is dry. Over-watering is a mistake that’s not uncommon and this can hurt our plants and its roots. The soil needs to dry up between waterings to avoid mold and root rot.
Nutrients & pH regulator
In addition to water and light, your plants will need nutrients. Consider these three elements (water, nutrients, light) the plants’ food. For your plant to develop, grow, and produce buds, it will need to “eat”. Nutrients typically come in liquid (or crystal) form and need to be mixed with water. There’s not just one nutrient mix that will be enough for the entire plant’s cycle. Typically, nutrients are sold as sets with 3-6 different flasks. One might contain nutrients that boost root growth, another one enhances plant growth, and a third might help with flowering (buds). Each nutrient brand/mix will have detailed instructions with the flasks. It’ll also explain how much nutrients to mix with the water. Typically, it’s a couple of milliliters of nutrients per liter of water.
While nutrients may seem like an expensive investment, it really pays off. Growing a plant indoors limits the nutrients (“food”) the plant can naturally absorb from the soil so the plant is depending on added nutrients to develop and flower well.
pH regulator, an acidic solution to bring the pH level down or an alkaline solution to bring the pH level up . As with nutrients, this solution is purchased in a flask or bottle and applied in very small amounts to the water after nutrients have been mixed. Nutrients can lower or raise pH in water so be sure to test and regulate the pH level after the nutrients have been mixed. Some soils have a bit of limestone mixed in which may affect the pH levels. If you want to be thorough, pH test the drainage water that runs out from underneath your pot.
Temperature & humidity
There’s a certain temperature span where cannabis grows well. Within this range there are better and worse temperatures but generally speaking, the plant will be able to grow. Too cold or too hot temperatures, however, can significantly limit or even stop the plant’s growth, regardless of stage. Certain strains also have their own preferences but, generally speaking, 65-82F (19-28C) are ideal temperatures for indoor grown strains. Day temperatures should be a few degrees higher than night temperatures.
Simply put, the higher temperatures a plant is subjected to, the higher is its needs for light and nutrients.
As for humidity (%RH), the plant develops well in humid environments during its early stages. As a seedling, 65-85% is a good range and then about 10-15% lower during its vegetative stage, and another 15-20% lower (40-50%RH) during flowering.
During the plant’s early stage, when it’s a seedling, it prefers around 77F (25C) during day, and 3-5 degrees colder during night.
When the plant has grown and is in its vegetative stage, it has less specific temperature requirement. 70-80F (22-28C) will do during day and, once again, a couple degrees colder during night.
At the end of the plant’s life cycle, during its flowering stage, it’ll want 68-78F (20-26C) and possibly even a bit colder during its very final week.
Tent, fan, rope ratchet
As suggested above, growing plants inside a grow tent makes it easy to regulate temperature, humidity, light intensity, and also contain light. If growing at a large scale, a CO2 booster and air filter (for the smell) can be fixed to the tent.
Regardless of size, a fan is definitely needed within the tent to create air flow. Without a fan, the air is still and mold can grow quickly. A USB computer fan (a fan you could connect to your laptop’s USB port) is enough for smaller tents (32x32x60”) whereas a table top fan might be necessary for larger tents. Angle the fan so it blows air into open space, try to avoid blowing straight onto a plant or branch with too high wind intensity.
To fix and hang a light inside a tent at the appropriate height, rope ratchets are the go-to solution. One end of the ratchet is tied to the top of the tent and the lamp is hung in the other end. Adjust the height depending on your plants’ light requirements and the lamps’ light output. Seedlings and young plants require less light than a mature plant, thus the lamp should be further from the plant’s canopy.
Tents come in all shapes and sizes. Two rather small plants will fit in a 24x24x60” tent. Growing plants in hydro instead of soil will usually make for a larger plant and also require a larger tent.
Four small plants can fit in a 32x32x60” tent but that’s really the minimum recommended area.
To automate as much as possible of the grow process, digital timers are used to switch lights on and off. Weed plants require anywhere from 12-24 hours of light per day. Certain strains have their specific preferences but in general, indoor grow cannabis will want 18 hours to 24 hours of light during its vegetative stage (18 hours of light and 6 hours of darkness is arguably the most common choice). During its flowering stage, 12 hours of light and 12 hours of darkness is usually preferred.
Auto-flower strains typically require the same amount of light during both veg and flowering. Confirm your strains requirements when purchasing the seeds.
Lamps that emit a heavy BLURPLE (blue-red-purple) colored light (not white) are not easy on your eyes. Light with short wavelengths (gamma, X-ray), and in the case with the BLURPLE lights; UV, and deep blue, is more or less harmful to humans. The more time you spend with your plants and looking at BLURPLE light the more you’ll expose your eyes to these colors of the spectrum. Heavy red light is not considered dangerous but can still irritate your eyes.
Wearing appropriate eye protection should not be overlooked. Or better yet, choose a light that isn’t BLURPLE and thus easier on the eyes. Grow lights don’t necessarily have to have all white diodes but the total light emitted should appear white or pink-ish, not blue-red, for the sake of your eyes.
A watering can gives a nice and even water flow which is recommended when watering plants. Using a jug or glass for watering purposes is an option, but not a great one. A 2-3 gallon watering can which you can fill and let acclimatize to room temperature is the best way to go. It’ll last for a couple of waterings and you’ll only have to measure the amount of nutrients when you fill up the can.
Once you have all the items mentioned above, you’re ready to setup your tent or grow area and then begin your grow.
Start your weed grow!
Seeds need a humid and damp environment to start their development. A moist environment signals to the seed that it’s time to hatch and sprout. An easy way of germinating seeds is to put them between two damp paper towels and then put the paper towels in an enclosed space. Between two plates or in a zip-lock bag, for instance. Then put the entire package in a dark space at room temperature. The seeds will germinate in 2-3 days. Once a tiny root has shot out and grown to about an inch (2.5 cm), plant the germinated seed in soil.
Non-auto-flowering, strains need to be planted in a smaller pot and then transplanted in 1-2 weeks’ time, or when the plant has 4 sets of leaves.
Auto-flower strains can be planted straight into their long term pot but regular strains need to be translated once the plant reaches a certain size (or sets of leaves).
Poke a 1-2 inch deep hole in the soil with your finger and place the germinated seed with root downwards in the hole. Cover the hole lightly with soil and give it a little bit of water. Putting a layer of plastic film on the pot helps contain a humid environment until the tiny plant breaches the soil, which normally happens in 3-5 days. Make sure to only expose these fragile little sprouts to a tiny bit of light. A window sill without direct sunlight or a not-so-powerful lamp is recommended. Avoid direct sunlight and high light output. If you’re growing inside a tent, have plenty of space between lamp and plant. The distance is determined by the lamp’s light output. LEDTonic’s Z2 and Z5 lamps need to be about 3 feet (90 cm) from the young plant.
If you know your lamp’s PPFD output, aim for around 100-150 PPFD at the plant’s canopy.
Aim for a temperature of 77F (25C) and 70-80% RH (humidity).
During the first 1-2 months of the plant’s life it will be in a vegetative stage. In short, this means that the plant is growing and developing but not yet producing flowers (buds). Leaves will develop and grow on a daily basis and the first set of fan leaves grow to a decent size in roughly 2 weeks. It is around this time nutrients should be added into the watering mix. Make sure to let the top 1-2 inches of the soil dry out between waterings. Water in excess will create an environment where mold quickly grows.
As more and more leaves develop, the plant will be able to absorb more and more light (300-500 PPFD), which results in quicker growth. The leaves and roots of the plants can be compared to a person’s mouth. The plant absorbs its “food” (light and nutrients) through the leaves and roots.
During the vegetative stage a healthy plant will be short in length but bushy. They prefer a blue/white light at this stage which resembles the natural light spectrum of springtime.
Temperature of 70-80F (22-28C) during the day and a few degrees colder during night is ideal with around 60% humidity.
Two of the first signs of the flowering is stage is that the plant starts growing in length quickly, up to a few inches a day, and that the plant’s pistils (white little hairs) are shooting out. The plant requires a higher intensity of light and more nutrients to support its growth. At this time, the plant grows best when there’s plenty of warm white or red light in addition to the blue. Some grow lights come with so-called “veg” and “bloom” switches or buttons. These buttons control which diodes of the lamp are turned on. Normally the veg switch turns on “cold” white and blue diodes whereas the bloom switch also turns on warm white and red diodes. During flowering stage, all diodes should be lit and the lamp should ideally have a warm white or pink/red-ish color to stimulate growth.
Keep feeding your plant nutrients according to the instructions on the nutrient package. As your plants are progressing toward the end of their flowering stage they will need more and more nutrients and more and more light (~500-700 PPFD) to grow as many and as big flowers (buds) as possible. While nutrients are important, too much nutrients (or in incorrect ratios) can have an adverse effect on growth.
The plants will eventually develop trichomes which look like tiny little crystals on the leaves near and on the buds. As these trichomes turn from a clear, almost transparent color to cloudy or milk-like color, the THC is developing. The highest THC levels are reached just before the trichomes turn amber. If the trichomes are starting to turn amber, the resulting high will be more of a body high. Choose the time to harvest depending on your preferences.
The temperature during flowering should be slightly colder than during veg, 68-78F (20-26C) and around 40-50% humidity.
It can be difficult to clearly see the trichomes, especially without a magnifying glass. Using your phone’s camera and taking a picture under white light then zooming in, is an okay workaround.
An alternative method is to look at the pistils. This is less exact but easier and can be seen with the bare eye. The white pistil hairs will eventually turn amber, orange, or red, depending on your strain. When over half of the pistils have changed color from white to orange, the THC is reaching its peak. Letting your buds develop further will increase the CBD to THC ratio which will result in more of body-high than euphoric high.
As your trichomes or pistils are getting within your desired range, cut the branches with buds with scissors or a knife and trim the leaves. Then hang the branches in a non-humid room and let them dry for 3-7 days.
In short, this is how you as a beginner can get started with your grow. You’ll learn plenty of hands-on techniques as you go along. Eventually, you’ll want to absorb more information to realize maximize your grow but with this guide, you’ll understand the basics and can look forward to producing your own supply :-)!
How to grow weed indoors
Growing weed indoors is great because you can grow it any time of year and you’ll have complete control over the plant and what you put into it. Live in an apartment or a small house? Don’t worry, you can grow weed practically anywhere, even if you don’t have a backyard or a lot of extra space.
Benefits of growing weed indoors
Although it’s more resource-intensive than growing outdoors and you will likely have to spend more money on utilities to power equipment, you can control every aspect of your grow environment and what you put in your plant, allowing you to dial in your setup to grow some primo weed.
Unlike outdoor growing, you aren’t tied to the sun and the seasons. You will be providing the entire environment the plants need to grow, including the grow medium—soil, rockwool, etc.—and regulating the amount of water and nutrients they receive, as well as controlling temperature, humidity, and more for them.
You can let your plants get as big as you want, and can control when they flower and when you harvest, and you can start another batch right away or whenever you want. You can grow any time of year, even straight through winter or summer, and you’ll get consistent crops each time.
Privacy and security
Even in legal states, you may want to conceal your crop from judgmental neighbors and definitely from potential thieves. Growing indoors allows you to grow discreetly behind a locked door.
How to set up an indoor grow room
Below is a list of things to consider and equipment you will need to purchase to get started growing marijuana indoors.
You’ll need a dedicated space for your marijuana plants—you won’t be able to move them around. Ideally, the space is next to a window so you can vent air from the grow space outside. Growing weed plants smell! Especially when flowering kicks in, you’ll want to redirect air so your house doesn’t reek of weed.
A lot of people these days buy grow tents for their weed, but they aren’t necessary. You can grow in a closet, tent, cabinet, spare room, or a corner in an unfinished basement. Just keep in mind that you’ll need to tailor your equipment (and plants) to fit the space.
It’s a good idea to start small—the smaller the grow, the less expensive it is to set up. Newbie mistakes will be less costly if you only have a handful of plants. Additionally, most state laws only allow for growing six plants, but some allow up to 12.
When designing your space, you’ll need to take into account room for your plants, as well as space for lights, fans, ducting, and other equipment. You’ll also need space to work on the plants. Cannabis plants can double in size in the early stages of flowering, so make sure you have adequate head space!
Every space is different and there will be a learning curve to growing in yours.
Cannabis, like all plants, prefers certain environmental conditions in order to thrive. Temperature, humidity, light intensity, and airflow are all factors that will need to be monitored and regulated in order to keep cannabis healthy through its different phases.
Although you’ll be controlling the climate inside the grow space, climate outside the grow space will affect your plants. If the environment outside your grow space is very warm or humid, you’ll have issues controlling your grow space. Choose a cool, dry area with ready access to fresh air from outside.
If you’re growing in a cold, wet basement, you might have to run a dehumidifier or heater to stabilize the environment. Conversely, if your space is too hot, you might need to add extra fans or an AC to cool the plants down.
One trick to avoid hot temps is to have the grow lights on during the evening, when it’s cooler outside, and leave the lights off during the day when it’s hot. This may help bring down the temps, but you’ll only be able to work on the plants at nighttime when the lights are on.
Weed plants need different amounts of light during their vegetative and flowering stages. You don’t have to worry about this in an outdoor setting—the sun and the season dictate this—but when growing indoors, you will be controlling it.
Plants need 18 hours of light a day when in the vegetative stage and 12 hours a day when flowering. The reduction in light from 18 to 12 hours a day is what triggers the flowering cycle—when weed plants start to grow buds.
Because the amount of light a plant receives is so important, you’ll need to make your indoor grow space light-tight. Light leaks during dark periods will confuse your plants and can cause them to produce male flowers or revert to a different stage.
Different lights produce different colors of light. Here’s a brief rundown of the most popular types of cannabis grow lights used for indoor growing.
Can you grow weed indoors without grow lights?
Just about all indoor weed growers use grow lights for their plants. Grow lights ensure your weed plants will grow healthy and strong, while maximizing yields.
In theory, as long as a cannabis plant can get at least 6 hours of full sun a day, whether inside next to a window, or outside, you don’t necessarily need a grow light, but pretty much all indoor growers use them.
HID (high-intensity discharge) lights are the industry standard, widely used for their combination of output, efficiency, and value. They cost a bit more than incandescent or fluorescent fixtures, but produce far more light per unit of electricity used. Conversely, they are not as efficient as LED lighting, but they cost much less.
The two main types of HID lamp used for growing are:
- Metal halide (MH) produces light that is blueish-white and is generally used during vegetative growth.
- High pressure sodium (HPS) produces light that is more on the red-orange end of the spectrum and is used during the flowering stage.
In addition to bulbs, HID lighting setups require a ballast and hood/reflector for each light. Some ballasts are designed for use with either MH or HPS lamps, while many newer designs will run both.
If you can’t afford both MH and HPS bulbs, start with HPS as they deliver more light per watt. Magnetic ballasts are cheaper than digital ballasts, but run hotter, are less efficient, and harder on your bulbs. Digital ballasts are generally a better option, but are more expensive. Beware of cheap digital ballasts, as they are often not well shielded and can create electromagnetic interference that will affect radio and WiFi signals.
Unless you’re growing in a large, open space with a lot of ventilation, you’ll need air-cooled reflector hoods to mount your lamps in, as HID bulbs produce a lot of heat. This requires ducting and exhaust fans, which will increase your initial cost but make controlling temperature in your grow room much easier.
Fluorescent grow lights
Fluorescent light fixtures, particularly those using high-output T5 bulbs, are quite popular with small-scale cannabis growers because:
- They tend to be cheaper to set up, as reflector, ballast, and bulbs are included in a single package.
- They don’t require a cooling system since they don’t generate nearly the amount of heat that HID setups do.
The main drawback is fluorescent lights are less efficient, generating about 20-30% less light per watt of electricity used; space is another concern, as it would require approximately 19 four-foot long T5 bulbs to equal the output of a single 600 watt HPS bulb.
LED grow lights
Light emitting diode (LED) technology has been around for a while, and they are getting more efficient all the time. The main drawback to LED grow lights is their cost: well-designed fixtures can cost 10 times what a comparable HID setup would.
But the benefits are great: LEDs last much longer, use far less electricity, create less heat, and the best designs generate a fuller spectrum of light, which can get bigger yields and better quality.
Check out our buying guide on indoor lights for more info.
Plants need fresh air to thrive and carbon dioxide (CO2) is essential to the process of photosynthesis. This means you will need a steady stream of air flowing through your grow room, which will allow you to move hot air out of the space and bring cool air in.
This is easily achieved by placing an exhaust fan near the top of the space to suck out warm air—warm air rises—and adding a port or passive fan on the opposite side of the space near the floor to bring in cool air. A complete air exchange throughout the entire grow space should occur once every minute or so.
Without proper airflow, a grow space can experience rapid changes in humidity or develop pockets of CO2 depletion, neither of which are good for plant growth. CO2 depletion can lead to nutrient lockout, and areas of high humidity are prone to pest infestation, mold, or mildew.
It’s also a good idea to have oscillating fans to provide a constant breeze in your grow room as it will strengthen your plants’ stems, making them stronger and healthier.
Setting up fans
For small spaces or tents, clip-on fans can be attached to structures like walls, corners, or support beams. For larger grow rooms, use medium-sized oscillating fans or big floor models.
Fans should be positioned to provide direct, even airflow throughout the garden. This typically involves using multiple fans that work together or fans that have oscillation capabilities.
There should be a comfortable airflow both above and below the canopy, and fans shouldn’t blow air directly onto plants—this can cause wind burn, which makes leaves recede into a claw-like deformation.
Dehumidifiers and ACs
If your space is too humid, you may need to invest in a dehumidifier—also known as “dehueys.” However, keep in mind that while dehueys will reduce humidity, they typically increase temperature—you may need more fans or an AC when adding a dehumidifier.
Getting the right climate for your plants can be a delicate balance involving multiple pieces of equipment and also lots of electricity. This is part of what makes growing weed indoors more expensive than growing outdoors.
Fans are a must in a grow space to move air around, so buy some of those before an AC unit. If you find that fans aren’t bringing down the temperature enough, then you may want to invest in an AC.
You will definitely want to invest in a timer for your lights. Because the amount of light a plant receives dictates its vegetative or flowering stage, it’s important to give it a consistent amount of light every day, and that’s done with a timer. It’s a good idea to check your timer at least once a week to make sure it’s working properly.
You can also use a timer for your fans, but a thermostat is better—you can set it to a specific temperature, and the fans will turn on when it’s too hot and turn off when it’s too cold.
Most dehumidifiers and ACs have built-in thermostats, but if they don’t, you’ll want to buy an external one.
For growers who have a little extra money to spend and want full control over their indoor garden, environmental controllers will allow you to automate the process. These devices are essential for if you’re away from the garden for a long period of time.
You can connect a controller to fans, dehumidifiers, humidifiers, heaters, or air conditioners, and set thresholds whereby each device will power on and off based on your ideal environmental settings. Some units run autonomously, making changes based on set parameters, while others allow you to control each element via an app on a phone, tablet, or computer.
How to regulate temperature and humidity when growing weed indoors
You’ll need to ensure that temperatures remain within a comfortable range for your plants, between 70-85°F when lights are on and between 58-70°F when off. Some varieties of cannabis—generally indicas—prefer the colder side of the range, while others—typically sativas—are more tolerant of high temperatures.
For the most part, weed prefers these temps at each growth stage for optimal health:
- Seedlings/clones: 75-85°F; ~70% relative humidity
- Vegetative growth: 70-85°F; 40-60% relative humidity
- Flowering: 65-80°F; 40-50% relative humidity
The two factors you need to control to dial in the environment are temperature and humidity.
Inevitably, there will be fluctuations of temperature and humidity in your cannabis garden. These fluctuations can occur both throughout a grow space as well as within pockets inside a given room. They can also occur at different points within a given day or throughout a season as conditions change in the environment outside your grow space.
It can be tricky getting the right balance of temperature and humidity because they affect each other—turning up your dehumidifier will lower the humidity of your grow space, but it will also increase the temperature of the area. This in turn may require you to turn on an AC unit—everything’s connected!
Tools to measure temperature and humidity
Equip yourself with these cheap and easy-to-use tools to take measurements in your indoor cannabis setup:
- Thermometer: A basic one will allow you to measure how warm or cool the environment is inside your garden.
- Hygrometer: This measures humidity, or more specifically, water vapor content in the air.
- Infrared thermometer, or IR thermometer (optional): IR thermometers use a detection device called a thermopile to measure surface temperatures. Although not necessary, these are helpful in finding out leaf temperatures, which will give you an extra layer of knowledge on how to properly regulate environmental conditions.
Controlling temperature in your indoor grow room or cannabis garden can be achieved by manipulating these factors:
- Lights: Different grow lights will give off different heat signatures. Hot lights such MH, HPS, and fluorescents produce much more heat than LEDs. Also, lights can be raised or lowered to change temperature at the canopy level.
- Airflow: You can remove warm air (up high) out of the garden and bring in fresh cool air (down low) with fans and ducting. Fans can also help exchange air throughout your canopy, cooling leaves in the process.
- ACs: You may need to bring in an air conditioner to rapidly cool the overall temperature of your grow space if it’s too hot and fans aren’t enough.
- Heaters: Some gardens may require warm air, especially during times when lights are off and not generating heat.
How cold can weed plants handle?
When temperatures fall below 50°F, it can slow a weed plant’s growth and negatively impact the plant. Colder still and the plant could freeze.
Humidity is the amount of water vapor in the air. Here are some ways to control it in your marijuana grow room:
- Dehumidifiers: Dehueys remove moisture from the air but also increase temperature.
- Airflow: As with regulating temperature, regulating airflow will allow you to move moisture in and out of your grow space and control humidity—simply opening up a space, i.e., opening the door to your grow room or tent, can bring down humidity.
- Humidifiers: A humidifier can add water vapor to a grow space and increases moisture levels if it’s too dry.
- Water: In the absence of a humidifier, you can mist plants with a spray bottle to create extra moisture.
Soil and other media for growing weed indoors
There are many different media to choose from, including good ol’ fashioned pots full of soil, rockwool cubes, a hydroponic tray, and more.
Soil is the most traditional medium for growing marijuana indoors, as well as the most forgiving, making it a good choice for first-time growers. Any high-quality potting soil will work, as long as it doesn’t contain artificial extended release fertilizer—like Miracle Gro—which is unsuitable for growing good cannabis.
Good soil for cannabis relies on a healthy population of mycorrhizae and soil bacteria to facilitate the conversion of organic matter into nutrients that a plant can use. Alternately, you can use a regular soil mix and then supplement your plants with liquid nutrients.
Finding the right soil for cannabis
For most first-time gardeners, we recommend buying a quality potting soil that will provide your plants with enough nutrients to get them through most of their growth cycle without having to add many amendments or liquid nutrients. This pre-fertilized soil—often referred to as “super-soil”—that can grow cannabis plants from start to finish without any added nutrients if used correctly.
You can make this yourself by combining worm castings, bat guano, and other components with a good soil and letting it sit for a few weeks, or it can be purchased pre-made from a local nursery or grow shop.
While shopping for soil, you might be overwhelmed by the options available at your local garden store. The soil type is the basic structure of your soil. From there, look at nutrients, microorganisms, and other amendments that improve the soil. Your choices will be flooded with words like:
- Worm castings
- Bat guano
- Peat moss
- Fish meal
- Bone meal
- Glacier rock dust
- Plant food
These are just some examples of amendments commonly used in different types of soils. Heavily amended soils will have long lists that break down all organic nutrients they contain. Some companies create soils that offer a great structure with base nutrients, but allow you to fill in the gaps as you desire.
Soil temperature for cannabis
Soil should be in the 65-75°F range, or about the temperature of your grow space. If it seems like soil is getting too hot under grow lights, add some water on the cold side next time you water.
What soil temperature is too hot for weed plants?
A soil temperature above 80°F for a plant isn’t ideal. When soil gets that hot it can be difficult for roots to uptake nutrients.
Hydroponics is a system of growing weed without soil. Plant roots are suspended in water, which is constantly recycled throughout the system. One of the main benefits to growing hydro is that roots have easy access to nutrients. Many argue that you can grow bigger, more potent buds with hydroponics.
Can you grow weed indoors without hydroponics?
Hydroponics is an advanced form of growing that experienced growers may take on, but indoor growing can be done with soil and pots for all levels of growing experience, and is much cheaper and easier than dealing with hydroponic systems.
What type of container you use will depend on the grow medium, the system, and the size of your plants.
Inexpensive options include standard plastic pots or cloth bags, while some growers choose to spend more on “smart pots” or “air pots”—containers designed to enhance airflow to the plant’s root zone.
What size pot do I need?
Many growers will start plants in a one-gallon pot and then transplant up to a bigger pot as plants get bigger. A lot of growers will transplant once, from a one-gallon to a five-gallon pot, and harvest from there. If your plants get bigger, they may need a seven- or ten-gallon pot.
What to look for in a pot
Your cannabis wants a safe, healthy place for root development. Without healthy roots, your cannabis will never thrive. Roots are in charge of water retention, nutrient absorption, anchoring the plant, and they also facilitate vegetative growth.
Drainage is key, as cannabis plants can get waterlogged and develop root rot. If you repurpose containers, be sure they have holes in the bottoms and set them in trays.
For a root system to develop and thrive, they will need the following:
- Drainage: Water retention is paramount for healthy plants—without it, your cannabis will wither and die. But too much water will waterlog your plant and lead to root rot, killing roots.
- Oxygen: Plant roots require oxygen to function properly. Choose a container that facilitates enough oxygen for root development without overexposing them to the elements—containers do this though various styles of perforation.
- Nutrients: Roots require optimal conditions for nutrient absorption to occur. This includes pH balance, optimal temperatures, and nutrient availability.
- Space: Roots need plenty of space to branch out. A container that is too small will cause it to become rootbound and choke the plant.
Traditional plastic containers
Standard plastic containers are a popular option for growers operating on a budget. These pots are inexpensive and provide the essentials for your plants.
- Low overhead costs
- Solid drainage (plus it’s easy to add more holes)
- Transplanting is easy and inexpensive
- Can’t protect root systems from temperature fluctuations as well
- Lack of durability which can cause cracks and structural damage over time
- May have airflow issues depending on the grow medium
These are quickly becoming the standard. Roots in fabric pots grow to the outer edges and attempt to bypass the porous fabric wall but are cut back, allowing new growth to occur. This process, called “air pruning,” results in a denser root composition which promotes healthy growth and development.
- Promotes dense, healthy root systems
- Increased airflow to roots
- Excellent drainage
- Require more attention and maintenance because they dry out quickly. Note: You can use larger pots to help slow drying.
- Flimsy structure can make plant support challenging
Terra cotta pots offer a unique set of benefits to growers in hot climates.
- Absorb moisture and retain lower temperatures during hot days
- Heavy weight helps to anchor larger plants
- Less than optimal drainage; drilling holes into clay pots is possible but requires special tools and is labor-intensive
- Heavy weight makes it difficult to transport plants
Caring for your indoor cannabis plants
When starting with clones or seedlings, you’ll want to check your plants every day because they’re delicate and sensitive to environmental conditions. You may need to adjust temperature and humidity levels in your indoor grow space at first to hit the sweet spot for your plants.
As your indoor weed plants grow, they’ll need less attention, but you’ll still need to check up on them every 2-3 days.
Best water for growing weed
The cleaner the water, the better for your plants, but you don’t need to buy a bunch of distilled water. Generally speaking, if you’re only growing a few plants and your tap water is good enough to drink, it’s probably fine for your weed plants.
You can invest in an EC (electrical conductivity) meter, which measures the dissolved salts of your water, to be sure. Plain water should be between 50-300 ppm.
Ideal water temperature for growing weed
Water shouldn’t be too hot or too cold—keep water temperature between 65-75°F. Cold water can shock the plant and make it difficult for roots to absorb. Excessively hot water can damage plants.
When growing weed indoors, you’ll likely have to add nutrients to your plants. You won’t need to add nutrients every time you water, but get on a schedule where you water every other time, or two on, one off.
Before watering, check the pH of your water and add pH Up or Down if needed.
Do weed plants like warm or cold water?
If anything, use water on the cold side, rather than the hot side. Under 65°F will slow nutrient uptake, but water above 75°F can damage a plant.
If using nutrients, estimate how much water you’ll need for all of your weed plants so you can measure out and mix in the appropriate amount of nutrients.
Remember, a common mistake newbie growers make is to overwater plants.
Check out our Guide on nutrients for more info.
Check for pests, mold, or nutrient deficiencies
You’ll also want to take this time to check over your weed plants for pests, mold, or nutrient deficiencies.
Examine the tops and undersides of leaves for pests or discoloration—spider mites live on the underside of leaves—as well as stalks and branches. Also, check the soil for pests.
Make sure all equipment is on, no breakers have flipped, and everything is running smoothly. Check lights, timers, fans, dehueys, ACs, and anything else that plugs into the wall or has a battery.
Think of all the equipment in your grow space as organs in the body—if one fails, the others will have to work a lot harder for a bit, and then will fail in a matter of time.
Daily maintenance checklist for your indoor marijuana grow
- Water plants
- Check pH of water
- Measure and mix nutrients
Indoor marijuana grow timeline
The growth stages of marijuana can be broken down into four primary stages from seed to harvest:
- Germination (3-10 days)
- Seedling (2-3 weeks)
- Vegetative (3-16 weeks)
- Flowering (8-11 weeks)
Generally speaking, it takes anywhere from 10-32 weeks, or about 3-8 months, to smoke what you’ve grown. (It’ll be quicker if you start with a clone or an autoflower seed.)
That’s a big variance, but it really depends on how big you want your plants and how often you want to harvest—you can have multiple harvests of smaller plants, or less harvests of bigger plants.
For example, it takes less time to grow 3′ weed plants than 5′ plants; in the span of a year, you can maybe grow four harvests of 3′ plants, or two harvests of 5′ plants.
You’ll likely yield about the same amount of weed in both cases, but more harvests mean you’ll have fresh weed to smoke more often and have more opportunities to grow different strains. But more harvests also means more work in cleaning up the space between harvests, trimming, etc.
The biggest variability in how long a marijuana plant takes to grow will happen in the vegetative stage—after the seedling phase and before flower.
The flowering stage will always take about eight weeks—some strains take seven, some nine, some even more, it depends on the strain.
So when growing weed indoors, you can control the size of your plants by flipping them into flower whenever you think they’re big enough in the vegetative stage.
Odor control in your indoor marijuana grow
As much fun as growing marijuana indoors is, having a home that perpetually smells like fresh weed can be a serious inconvenience, if not to you than possibly your neighbors. Although weed odor from a small indoor grow in a closet is much easier to manage than a large grow with several flowering plants, both can produce pesky odors that will permeate an entire home if left unattended.
Plants in the vegetative stage maintain a low odor as they haven’t begun to produce terpenes, the plant’s aromatic compounds. As weed plants transition into the flowering phase, trichomes will start to develop and produce terpenes, causing them to smell more.
Here are some ways to mitigate odor when growing weed indoors.
Check temperature and humidity levels
The first step in odor control is making sure temperature and humidity are under control in your grow space—high temperature and humidity will perpetuate odors.
As your plants get bigger and especially when they start flowering, they’ll start to smell more. Outfitting your grow with a dehuey or AC can help bring odor down.
Make sure air is circulating through your garden
Proper air circulation will help maintain temperature and humidity, and also bring down odor. Ideally, air needs to move through a garden every few minutes, and you should create a vent to the outside. Oscillating fans, and intake and exhaust fans can move air through your garden quickly, taking odors out with them.
Odor absorbing gels may help
Odor becomes much more difficult to manage in the final six weeks of a marijuana plant’s life, when trichomes and terpene production ramps up. You can also get odor-absorbing gels, which replace weed smells with other scents. Keep in mind that odor gels don’t eliminate odors, but simply mask them.
Activated carbon filters
These come in different shapes and sizes and are a great way to get rid of odor in an indoor weed grow. Also known as “carbon scrubbers” for their ability to get contaminants out of the air, these employ activated and highly ionized carbon to attract particulates responsible for carrying odor, such as dust, hair, mold spores, and volatile organic compounds, and traps them in a filter.
Carbon filters usually work best when positioned at the highest point in your grow space, where the most heat accumulates.
Patrick Bennett and Trevor Hennings contributed to this article.