How to grow marijuana indoors: a beginner’s guide
Congratulations, you’re interested in growing your own cannabis plants for the first time! But before you flex that green thumb of yours, understand that growing marijuana indoors presents a unique set of challenges for the new hobbyist, and the sheer volume of information available on the subject can be overwhelming.
Our clear, easy-to-digest guide to indoor growing will help even first-time growers get started.
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Benefits of growing weed indoors
- High-quality weed: Although it’s more resource-intensive than growing outdoors, you can control every aspect of your environment and what you put in your plant, so growing indoors will allow you to dial in your setup to grow some primo weed.
- Adaptability: Live in an apartment or a small house? You can grow weed practically anywhere, even folks who don’t have a backyard or a lot of extra space.
- Multiple harvests: Unlike outdoor growing, you aren’t tied to the sun and the seasons. You can let your plants get as big as you want, flip them into flower, harvest, and then start another batch right away. You can grow whenever you want, even straight through winter.
- 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.
Step 1: Designate a cannabis grow room or space
The first step in setting up your personal cannabis grow is creating a suitable space in which to do it. This space doesn’t even need to be a typical room—it can be 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.
When tackling your first grow project, you’ll want to start small for multiple reasons:
- The smaller the grow, the less expensive it is to set up
- It’s much easier to monitor a few plants than a large number
- Your mistakes as a first-time grower will be less costly
Remember, most new cannabis growers will experience setbacks and lose plants to pests or disease. A failed grow of two plants will put a far smaller dent in your wallet than a lot more plants.
…But think big
When designing your space, you’ll need to take into account not only the amount of room your plants will need, but also your lights, ducting, fans, and other equipment. You’ll also have to leave enough room for you to work. Cannabis plants can double in size in the early stages of flowering, so make sure you have adequate head space!
If your grow room is a cabinet, tent, or closet, you can simply open it up and remove the plants to work on them; otherwise, you’ll need to make sure you leave yourself some elbow room.
Cleanliness is crucial
Make sure your space is easily sanitized; cleanliness is important when growing indoors, so easy-to-clean surfaces are a must. Carpeting, drapes, and raw wood are all difficult to clean, so avoid these materials if possible.
Keep it light-tight
Another crucial criterion for a grow room is that it be light-tight. Light leaks during dark periods will confuse your plants and can cause them to produce male flowers.
When deciding where to grow your cannabis, keep the following variables in mind:
- Convenience: You’ll need to monitor your plants carefully. Checking on them every day is important, and beginners will want to check in several times per day until they have everything dialed in. If your room is hard to access, this crucial step will be difficult.
- Temperature and humidity concerns: If your grow space is already very warm or very humid, you’ll have issues controlling your grow environment. Choosing a cool, dry area with ready access to fresh air from the outdoors is highly recommended.
- Stealth: You’ll most likely want to conceal your grow from nosy neighbors and potential thieves, so be sure to pick a place where noisy fans won’t garner any unwanted attention.
Step 2: Choose your cannabis grow lights
The quality of light in your grow room will be the number one environmental factor in the quality and quantity of your yield, so it’s a good idea to choose the best lighting setup you can afford.
Here’s a brief rundown of the most popular types of cannabis grow lights used for indoor growing.
HID grow lights
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 as little as one-tenth as much for comparable units.
The two main types of HID lamp used for growing are:
- Metal halide (MH), which produce light that is blue-ish white and are generally used during vegetative growth.
- High pressure sodium (HPS), which produce light that is more on the red-orange end of the spectrum and are 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 the temperature in your grow room much easier.
Fluorescent grow lights
Fluorescent light fixtures, particularly those using high-output (HO) T5 bulbs, are quite popular with small scale hobby growers for the following reasons:
- 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 near the amount of heat that HID setups do
The main drawback is that 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 HO 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, but only recently has it been adapted to create super efficient light fixtures for indoor growing. The main drawback to LED grow lights is their cost: well designed fixtures can cost 10 times what a comparable HID setup would. The benefits are that LEDs last much longer, use far less electricity, create less heat, and the best designs generate a fuller spectrum of light, which can lead to bigger yields and better quality.
Unfortunately, there are many shoddy LED lights being produced and marketed towards growers, so do some research and read product reviews before laying down your hard-earned cash.
Induction grow lights
Induction lamps, otherwise known as electrodeless fluorescent lamps, are another old technology that has been recently adapted to suit the needs of indoor growers. Invented by Nikola Tesla in the late 1800s, the induction lamp is essentially a more efficient, longer-lasting version of the fluorescent bulb. The main drawback of these fixtures is their price and availability.
Step 3: Give your cannabis plants air
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, easily achieved by means of an exhaust fan placed near the top of the room to remove the warmer air, and a filtered air inlet on the opposite side near the floor.
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 they are off. Some varieties of cannabis (generally indica strains) prefer the colder side of the range, while others are more tolerant of higher temperatures.
The size of your exhaust fan will depend on the size of your grow space and amount of heat generated by your lighting system. HID systems put out a ton of heat, especially if they aren’t mounted in air-cooled hoods. People who live in warmer regions will often run their lights at night in an effort to keep temperatures in their grow down.
It’s advisable to set up your lights, turn them on for a while, and then determine how much airflow you’ll need to maintain a comfortable temperature for your plants. This will allow you to choose an exhaust fan suitable for your needs. If the odor of cannabis plants in bloom will cause you problems, add a charcoal filter to your exhaust fan.
Alternately, you can create a sealed, artificial environment by using an air conditioner, dehumidifier, and supplemental CO2 system, but this is quite expensive and not recommended for the first-time grower.
Finally, it’s a good idea to have a constant light breeze in your grow room as this strengthens your plants’ stems and creates a less hospitable environment for mold and flying pests. A wall-mounted circulating fan works well for this purpose — just don’t point it directly at your plants, because that can cause windburn.
Step 4: Pick your climate controls and monitors
Once you have selected your lights and climate control equipment, you’ll want to automate their functions. While there are sophisticated (and expensive) units available that control lights, temperature, humidity, and CO2 levels, the beginner will generally need a simple 24 hour timer for the light and an adjustable thermostat switch for the exhaust fan.
The timing of the light/dark cycle is very important when growing cannabis; generally you will have your lights on for 18 hours per 24 hour period while the plants are in vegetative growth, then switch to 12 hours of light per 24 hour period when you want them to bloom. You need your lights to turn on and off at the same times every day or you risk stressing your plants, so a timer is essential. You can use a timer for your exhaust fan as well, but spending a few extra dollars on a thermostat switch is a much better option.
With the most basic models, you simply set the thermostat on the device to the maximum desired temperature for your space and plug your exhaust fan into it. Once the temperature rises to the level you set, it will turn the fan on until temperatures fall a few degrees below the set threshold. This saves energy and maintains a steady temperature.
Since you’re probably not spending most of your time in your grow space, a combination hygrometer/thermostat with high/low memory feature can be very handy in keeping tabs on conditions in your room. These small, inexpensive devices not only show you the current temperature and humidity level, but the highest and lowest readings for the period of time since you last checked.
Step 5: Decide on a cannabis grow medium
Growing indoors means you have many different media to choose from, and whether it’s good old fashioned pots full of soil or a rockwool slab in a hydroponic tray, every medium has its benefits and drawbacks.
Here we’ll examine the two most popular methods and the media they employ.
Soil is the most traditional medium for growing cannabis 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.
A very good choice for beginners is organic 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. This can be made 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 few different suppliers.
As with all organic growing, this method relies on a healthy population of mycorrhizae and soil bacteria to facilitate the conversion of organic matter into nutrients that are useable to the plant. Alternately, you can use a regular soil mix and then supplement your plants with liquid nutrients as the soil is depleted.
Soilless (aka hydroponics)
Indoor growers are increasingly turning to soilless, hydroponic media for cultivating cannabis plants. This method requires feeding with concentrated solutions of mineral salt nutrients that are absorbed directly by the roots through the process of osmosis.
The technique for quicker nutrient uptake leading to faster growth and bigger yields, but it also requires a higher order of precision as plants are quicker to react to over or underfeeding and are more susceptible to nutrient lockout and burn.
Different materials used include rockwool, vermiculite, expanded clay pebbles, perlite, and coco coir, just to name a few. Commercial soilless mixes are widely available that combine two or more of these media to create an optimized growing mix. Soilless media can be used in automated hydroponic setups or in hand-watered individual containers.
Step 6: Pick a container
What type of container you use will depend on the medium, the system, and the size of your plants. A flood-and-drain, tray-style hydroponic system may use small net pots filled with clay pebbles or just a big slab of rockwool to grow many little plants, while a “super-soil” grow may use 10 gallon nursery pots to grow a few large plants.
Inexpensive options include disposable perforated plastic bags or cloth bags, while some choose to spend more on “smart pots,” containers that are designed to enhance airflow to the plant’s root zone. Many people grow their first cannabis plants in five gallon buckets.
Drainage is key, as cannabis plants are very sensitive to water-logged conditions, so if you repurpose other containers, be sure to drill holes in the bottoms and set them in trays.
Step 7: Feed your cannabis plants nutrients
Growing high-quality cannabis flowers requires more fertilizer, or nutrients, than most common crops. Your plant needs the following primary nutrients (collectively known as macronutrients):
- Nitrogen (N)
- Phosphorus (P)
- Potassium (K)
These micronutrients are needed as well, albeit in much smaller quantities:
If you aren’t using a pre-fertilized organic soil mix, you will need to feed your plants at least once a week using an appropriate nutrient solution. These nutrients are sold in concentrated liquid or powder form meant to be mixed with water, and generally formulated for either vegetative or flower (“bloom”) growth. This is because cannabis has changing macronutrient requirements during its lifecycle, needing more nitrogen during vegetative growth, and more phosphorus and potassium during bud production.
Most macronutrients are sold in a two-part liquid to prevent certain elements from precipitating (combining into an inert solid that is unusable by the plant), meaning you’ll need to purchase two bottles (part A and part B) for veg, and two bottles for grow, as well as a bottle of micronutrients. Other than these basics, the only other nutrient product you may need to purchase is a Cal/Mag supplement, as some strains require more calcium and magnesium than others.
Once you’ve purchased the necessary nutrient products, simply mix them with water as directed by the label and water your plants with this solution. You should always start at half-strength because cannabis plants are easily burned. It’s almost always worse to overfeed your plants than to underfeed them, and over time you will learn to read your plants for signs of deficiencies or excesses.
It’s important to get a pH meter so you can check the pH level of your water when mixing nutrients. Cannabis prefers a pH between 6 and 7 in soil, and between 5.5 and 6.5 in hydroponic media. Letting the pH get out of this range can lead to nutrient lockout, meaning your plants are unable to absorb the nutrients they need, so be sure to test your water regularly and make sure the nutrient mix you are feeding your plants falls within the desired range.
Step 8: Water your cannabis plants
Most people won’t think twice about the water they use on their plants; if you can drink it, it must be fine, right? Well, it may not be an issue, depending on your location, but some water contains a high amount of dissolved minerals that can build up in the root zone and affect nutrient uptake, or it may contain fungus or other pathogens that aren’t harmful to people but can lead to root disease.
Additionally, some places may have high levels of chlorine in the water supply, which can be harmful to beneficial soil microbes. For these reasons, many people choose to filter the water they use in their gardens.
The most important thing to remember during this phase is to not overwater. Cannabis plants are very susceptible to fungal root diseases when conditions are too wet, and overwatering is one of the most common mistakes made by the beginning grower.
How often you water your plants will depend on the medium used, size of the plants, and ambient temperature. Some people will wait until the lower leaves of the plant start to droop slightly before watering.
As you gain experience and knowledge, you will alter your grow room and equipment to better fit your particular environment, growing techniques, and the specific strains you grow, but this article will give you a solid foundation of knowledge to get started on the right foot.
And remember, growing marijuana is a labor of love, so spend a lot of time with your plants and have fun!
This post was originally published on June 6, 2016. It was most recently updated on April 2, 2020.
Our indoor cannabis growing guide will help simplify the process for you into clear, easy-to-digest sections to help the first-time grower get started.
An intro to indoor cannabis cultivation
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- What are the basics of growing weed?
- How to start growing weed
- What Is the best way to grow marijuana indoors?
- Cannabis feeding systems
- Setting up your grow: choosing a space
- Creating the ideal environment: lighting
- Creating the ideal environment
- Tips for success
- Frequently asked questions
What are the basics of growing weed?
Indoor cannabis cultivation is a rewarding endeavor that basically can be done in any climate. Growing pot takes attention to detail and the right equipment, time, and money, but the benefits reaped from growing your own weed are more than worth the time and expense. Not only is the practice of gardening itself therapeutic, it also lends a connection to the plants that cannot be experienced outside of a hands-on approach. Having trained and grown out a favorite cultivar to fruition is one of life’s great joys for a marijuana enthusiast.
Indoor cultivation provides many benefits compared to outdoor cultivation, including control, reproducibility, and risk mitigation — not to mention location, location, location. The goal is to artificially create the ideal environment for your plants at all growth stages. This is achieved through precise lighting, temperature, humidity, carbon dioxide content, and air movement within each indoor growing space.
Ultimately, the costs of equipment and recurring utility bills are more expensive than in outdoor and greenhouse settings. However, specialized indoor cultivation equipment allows cultivators to achieve multiple harvests per year and a more reproducible product. If you’re detail-oriented and technologically inclined, indoor gardening is a fun and rewarding pastime, or could even be a full-time job.
How to start growing weed
To set up an indoor garden, you will need equipment to help create a stable environment that mimics the necessary periods of light and darkness to grow plants through the flowering stage. This includes horticultural lighting, fans to recreate a gentle breeze, dehumidifiers to maintain the proper humidity, HVAC (heating, ventilation, and air conditioning), and all the basic supplies that a plant needs to survive, from water to grow media to nutrients.
Planning, designing, and implementing an indoor garden can seem daunting, but having a firm understanding of the basics goes a long way in helping a new indoor grower get started on the path to a healthy and bountiful harvest.
What Is the best way to grow marijuana indoors?
The first step in creating a proper indoor growing environment is to decide on the medium and irrigation methods you’ll be using to supply your plants with the proper nutrients throughout their growth cycle. The medium is a shelter for your plants’ roots that retains moisture. The irrigation method is the way you deliver nutrients to the plants.
Unlike outdoor cultivation — where you almost always use soil to grow your plants — growing indoors offers several different options for growing systems and media. Some media are easier to work with than others, while some are a little trickier, but offer more control over the finer details. Different media retain moisture at different rates, which in turn determines how often plants need to be watered. Some media harbor beneficial microbes that can help roots absorb nutrients better.
The two main options for an indoor garden are soil and hydroponic media. Consider the following:
Soil is a great choice for beginners. It can be much more forgiving and requires less precision when watering and feeding plants. Less-frequent watering and a stable pH foundation can drastically increase the likelihood of a successful first harvest. Soil also contains beneficial microbes and nutrients that help keep plants healthy, though it also creates favorable conditions for pests, mold, and mildew to spread. Working with soil and hand-watering plants can also be messy, but it will allow you to get familiar with the pace in which your plants consume water and nutrients.
Soil can be much more forgiving and requires less precision when watering and feeding plants additional nutrients. Photo by: Gina Coleman/Weedmaps
Hydroponic media are viable indoor alternatives to soil, but they’re considered more advanced because they bring with them a set of challenges that may prove difficult for beginners. Then again, if going hydroponic is in your plans, it’s best to learn the method from the beginning.
Hydroponics is a blanket term for the growing of plants in a nutrient solution, with or without an inert medium to provide physical root support. Media such as fused basalt rock and chalk (known as rockwool), coconut fiber (coco coir), and clay pellets (hydroton) can drastically improve nutrient delivery. With a plant’s roots system exposed, hydroponically grown cannabis can grow faster and more efficiently, requiring less water and fewer nutrients but also requiring monitoring systems to ensure a stable pH.
Rockwool , also known as mineral wool, is one of the most common forms of hydroponic media for the beginning stage of a plant’s life. Rockwool is an inert substance, and its composition of mineral or rock fibers provides a relatively sterile environment with a unique capacity to hold water. Rockwool will quickly expose any watering or feeding mistakes. Missing even one day of watering could be detrimental when using rockwool, especially for tender young plants.
Coco Coir is the fibrous material found on and in coconut shells. As a byproduct of the coconut industry, it is favored by growers as a sustainable and renewable medium. Coco coir is an inert medium with a neutral pH that does not provide or maintain any nutrients. These qualities are great for growers who know how to appropriately adjust pH, allowing for quick pH and nutrient changes. There may be a learning curve, but if you’re numerically inclined, it’s not too hard to get a grip on the process. Coco coir can be used either by itself or added to soil or hydroton for improved drainage and growth capability.
Coco Coir is the fibrous material found on and in coconut shells. Photo by: Gina Coleman/Weedmaps
Hydroton is a lightweight expanded clay aggregate composed of porous clay pebbles that can be used alone in a hydroponic system or blended with soil or other soilless mediums. Hydroton does not retain water to the extent of coco coir or rockwool, but it does provide plant roots with equal levels of oxygen. Like rockwool, the biggest issue is that it can dry out very quickly, so you have to be extra careful to keep it hydrated, especially when used on its own.
Other common soilless mediums used by hydroponic growers include perlite, vermiculite, coarse sand, and gravel. Advanced growers frequently mix these media in custom quantities to create blends that suit their specific growing style and environment.
Cannabis feeding systems
Feeding your plant is the process of giving it the chemicals and compounds that it needs to grow out its leaves, roots, and ultimately produce the heavy, trichome-covered flower clusters called colas. There are two main types of feeding systems: drain-to-waste and recirculating.
A drain-to-waste system applies fresh nutrient solutions to the grow medium every time the plant is fed. Any nutrients that drain through the medium are then disposed of and not reused.
A recirculating system collects the nutrients and water that are used, replenishes them, but with a smaller amount of fresh nutrients, then reapplies the solution to the plants the next time the plant is fed. A grower will check the solution’s pH before and after adjusting the nutrients.
When using soil as your primary medium, drain-to-waste is the only possibility. In soilless hydroponic systems, it is up to the growers’ preferences. Most hydroponic growers will opt to maintain a drain-to-waste system, because it affords them full control over the application of nutrients. Recirculating systems are typically reserved for the most advanced and efficient cultivators.
Top feed drain-to-waste systems can be as simple as putting your plants in a soilless medium and watering them from the top of the container, either with a drip system or by hand.
Ebb and flow systems, also known as flood and drain systems, are a popular type of recirculating system that uses a pump to bring water and nutrients from a reservoir into a flood tray where the plants are positioned in their grow medium. The nutrient solution floods the tray and gets absorbed by the roots and medium before slowly draining back into the reservoir. This process repeats itself on a timer to ensure that plants are properly hydrated.
Nutrient Film Technique (NFT) is another recirculating system in which plants are suspended by net baskets or neoprene collars that run along a trough. A thin film of water and nutrients continually circulates through the bottom of the trough, providing food to the tips of the roots, while leaving a majority of the root mass exposed to air.
Deep Water Culture (DWC) is a modular bucket system that suspends the plant’s main stem in a net basket while the roots are completely immersed in a highly oxygenated nutrient solution. An air pump supplies the oxygen to the nutrient solution which circulates through 3-5 gallon, or 11.4-18.9 liter, pots. DWC buckets can be configured to run in a stand-alone drain-to-waste system, or all of the buckets can be connected together to run in a recirculating manner.
Aeroponics are hydroponic systems in which the roots are suspended in air and lightly misted with a nutrient solution on regularly timed intervals. This method can achieve faster growth rates while using less water and nutrients than other hydroponic systems, though this is considered of the most advanced methods of growing hydroponically.
Setting up your grow: choosing a space
Before you purchase any equipment, it is important to understand the possible limitations of an indoor garden. Consider the height of the ceiling, how much insulation your space offers, and your ease of access to electricity and water. Some local jurisdictions may also ask that indoor gardens mitigate odors during the flowering phase.
If you’re a beginner, prefabricated grow tents are a great option, as they allow for minimal wear and tear on your property. Instead of renovating or building a new room, grow tents can be set up and taken down in a matter of minutes while also providing a clean, reflective, and enclosed environment for your plants to grow. As a general rule, your ceiling height should be at least a height of 8 feet, or about 2.4 meters; this is the typical height of a tent. Check your prospective tent’s measurements before committing to the purchase.
Grow tents also make it easier for home growers to maintain two separate environments: one for vegetative growth, and the other for flowering. This allows you to keep a perpetual harvest going by propagating and growing young plants in one tent and flowering another set of plants in the other tent. Maintaining a balanced rotation like this can result in maximized harvests year over year.
Whether you are growing two or 30 plants in your house, grow equipment requires a significant amount of electricity, primarily from your lighting and air conditioning units. Make sure that all electrical equipment is installed by a trained professional to reduce the likelihood of an electrical fire. You don’t need to be an electrician to design an indoor grow, but having a basic understanding of watts, volts, and amps is essential. The equation below can be used to determine whether your property has the minimum amount of power for an indoor garden:
Always make a list of the power requirements for each piece of equipment and make sure your electrical panels can support the electrical load before you make any big equipment purchases.
Water quality is another key aspect of indoor gardening. It’s important to determine water acidity and general mineral content prior to planting. Checking the pH, the acidity or alkalinity of the water, is easy to do with a handheld water quality meter. The same device can be used to check the total mineral or chemical content of your water as well. Knowing these things will help you determine the correct amount of nutrients to feed your plants or if fresh water needs to be introduced.
Most local jurisdictions require you mitigate the odor from your plants to avoid disturbing your neighbors. Activated charcoal filters absorb plant odor in your grow area. Adding a charcoal filter to your HVAC system or placing one within your grow space is a great way to drastically reduce the odor. The size of the filter is largely dependent on the size of your grow. Make sure filters are sized and installed correctly. Keep track of the life of the filter, as their effectiveness diminishes over time.
Even when growing cannabis legally, it’s a good idea to minimize your public visibility as a grower and take some mild to moderate precautions. Simple steps, such as not geotagging your location when you post grow pictures or hiding the glare from your grow lights when you run them at night, can go a long way in keeping your prized indoor garden secure.
Creating the ideal environment: lighting
Choosing the right horticultural lighting for your indoor grow can mean the difference between success and failure. Correct lighting is crucial, as it drives photosynthesis. In other words, your plants will not grow properly without proper lighting. The duration of your lighting controls the photoperiod, or the times in which a grow is exposed to light. During the vegetative growth phase, plants need a minimum of 16 hours of light. The most common schedule during this phase is 18 hours of light and six hours of darkness. To initiate flowering, plants need a shorter day, with 12 hours of light and 12 hours of darkness.
Correct lighting is crucial, as it drives photosynthesis. In other words, your plants will not grow properly without proper lighting. Photo by: Gina Coleman/Weedmaps
The intensity of light and its placement within your grow space are important aspects to consider when choosing what kind of light to grow with. Low light levels will slow photosynthesis, delay growth, and result in poor yields. If your light is too far away the plant will not receive enough of it and will grow spindly. If your light is too close it can damage the plant and ruin your colas.
There are several different types of grow lights that serve different purposes, each with their own sets of pros and cons.
Fluorescent lights are affordable and use minimal wattage to produce a low-intensity light. They are available in strips or larger arrays of multiple bulbs, and are most commonly used during the germination and propagation of seeds and clones. They should not be used during the flowering phase.
Metal-halide (MH) lights are a type of high-intensity discharge (HID) lights that work by igniting gas in a tube with a spark of electricity. Metal-halide bulbs emit a spectrum of light that is most beneficial during the vegetative phase. They emit more usable light for a plant than a fluorescent bulb does, but tend to cost substantially more.
High-pressure sodium (HPS) bulbs are highly efficient HID lights that produce a very effective spectrum of light to promote growth during the flowering phase. Most HPS bulbs are double-ended and can last 10,000 hours without losing efficiency. While these lights are the workhorses of most grow rooms today, they produce a significant amount of heat that needs to be removed, increasing air conditioning requirements.
Light-emitting diode (LED) lights are another form of high-intensity lighting that have been growing in popularity as their technology has advanced. LED lights produce a spectrum suited for all phases of plant life. They typically cost more than other grow lights, but they last much longer, are more energy efficient, and give off a lot less heat than HID lighting.
Creating the ideal environment
When it comes to cultivating cannabis indoors, you need to be sure to provide your plant with the optimal temperature, humidity, air circulation, CO2, and nutrients.
Temperature and Humidity
Maintaining the ideal temperature and humidity at all times is crucial to the health of your plants. Some plant varieties prefer hot and humid climates, while others like it cool and dry. Keeping them alive and healthy means controlling the temperature and humidity when the lights are on or off.
Air conditioning (AC) and humidification systems are used to control the temperature and relative humidity of an indoor grow room. The size of each unit is based on the amount of heat the lights and other equipment produce in relation to the size of the space. In an open grow room, intake and exhaust fans are used to constantly exchange the air within the room to maintain a consistent temperature. In sealed rooms, mini-split AC systems are used because they circulate the air in the room without bringing in fresh air.
AC systems maintain temperature and also dehumidify rooms. Fluctuations in humidity can affect plant health and should be controlled using a dehumidifier or humidifier, depending on conditions.
Advanced growers use digital environmental controls to monitor all equipment responsible for maintaining a stable environment (i.e., fans, AC, dehumidifiers, sensors, thermostats, etc.). These environmental controls can be worth the hefty price tag for the peace of mind they provide.
With lighting, AC, and other environmental controls in place, indoor cannabis plants will require large amounts of fertilizer or nutrients throughout their lifespans. Hydroponic systems lack the base nutrients that occur within soil; that leaves it up to you, the grower, to feed their plants with nutrient concentrations — the exact formula of which depends upon plant variety and phase of cultivation. With hydroponics, salt-based nutrients typically come in the form of a concentrated liquid or dry soluble powder that can be mixed with water.
As a cannabis plant develops, its nutrient needs change. That’s why different nutrient lines are available for different growth phases. Most nutrient lines come with recommended feeding charts. If you’re just starting out, be sure to get to know your nutrients and their ratios.
Carbon dioxide supplementation
Controlling the amount of available carbon dioxide (CO2) in your garden is another aspect of growing marijuana at home . During photosynthesis, CO2 converts into sugar, which the plant uses as energy for growing its vegetation and, ultimately, its seeds or flowers. Adding CO2 to your indoor garden can drastically improve your yields. While the atmosphere naturally has an average CO2 concentration of around 400 parts per million (PPM), most indoor growers try to maintain a range of 800 to 2,000 PPM, depending on the plants’ growth stage. Levels above 2,000 PPM can damage plants, and anything above 3,000 PPM can be dangerous to humans.
The amount of CO2 you supplement your garden with depends on how much light your plants are receiving, the growth phase they are in, and their overall size. CO2 should only be used during the “daylight” period, as plants are unable to utilize CO2 at night or in the dark. Sealed grow rooms are ideal when supplementing CO2, as open rooms tend to exhaust the CO2 more quickly than the plants can use it.
CO2 can be supplemented into an indoor garden using compressed gas tanks or generators. Using compressed CO2 tanks is the most common method because they’re readily available, easy to set up, and do not add any extra heat to your room the way a CO2 generator does.
Air movement is the least expensive component of creating an ideal environment for your plants. Even a gentle breeze can help keep pests and microbes from landing on your plants, move oxygen and carbon dioxide around the leaves, and create a uniform environment throughout your room. One of the easiest ways to maintain sufficient air circulation is by hanging oscillating fans on the walls or ceiling/grow tent corners and placing a small box fan on the floor. The goal with air circulation should be to mimic a light breeze and avoid powerful gusts that may harm your plants.
Tips for success
The health of your garden is completely dependent upon the environment you create and the equipment you select. It is easy to buy a new line of nutrients, but much more difficult to replace an undersized air conditioner. Careful planning prior to your grow will go a long way in saving you from expensive mishaps.
Cleanliness in an indoor garden cannot be overstated. Clean your entire grow room before your first grow cycle and after every harvest. The walls, floors, trays, irrigation lines, reservoirs, lights, and fans should be cleaned using a three to five percent (3%-5%) hydrogen peroxide solution, an efficient sterilizing agent that leaves no dangerous or toxic residues behind. Be careful what you bring into your grow room. Pets, dirty clothes, and contaminated clones can introduce unwanted pests and diseases.
Maintaining a grow journal and logging all major aspects of your grow is one of the cheapest, easiest things you can do to become a better grower. Logging daily temperatures along with water and feeding amounts will help you pinpoint problems, and may give you something to show other growers who can help you resolve issues, increase your yields, and save a troubled crop.
Remember, not everyone was born with a green thumb or an affinity for setting up and maintaining equipment. But with practice, passion, and an attention to detail, you can ready yourself for an amazing growing experience that has the potential to change your views of and interaction with cannabis for good.
Frequently asked questions
Should you grow cannabis with distilled water or reverse osmosis water?
Distilled and reverse osmosis water are fairly comparable. It’s the process of distilling that differs from the reverse osmosis process. Distilled water has been boiled to a vapor and cooled back into liquid to filter out contaminants. Reverse osmosis (RO) filters pressure water through a filtration membrane and produce wastewater as a byproduct. They’re generally better than distillers at removing volatile chemicals such as chloramines.
RO filters can remove 95% or more of contaminants, and typically increase in efficiency when pre-filters are placed before them in a filtration system. Carbon or sediment filters remove chlorine and chloramines as well as larger solids such as sediment and dirt. Water softeners exchange calcium and magnesium for sodium chloride so it can be purified and softened through the RO filter.
There are big differences when you grow cannabis indoor versus outdoor. Learn everything you need to know about growing weed indoors.