Indoor cultivation is utilized primarily for its control, reproducibility, and risk mitigation. The goal is to artificially create the perfect environment for your plants at all growth stages. This is achieved through precise control over the lighting, temperature, humidity, carbon dioxide content, and air movement within each indoor grow room — all of which make indoor cultivation a viable option not unique to cannabis.
Indoor cultivation of cannabis began in the 1970s prohibition era. As law enforcement officials cracked down on illegal outdoor cannabis grows, cultivators responded by moving many of their operations indoors — not only allowing growers to hide their valuable plants from prying eyes, but also freeing them up from limits and challenges imposed by location.
The costs of equipment and recurring utility are more expensive than that of outdoor and greenhouse settings. However, specialized indoor cultivation equipment allows growers to achieve multiple harvests per year and a more reproducible product. For the detail-oriented and technologically inclined, indoor gardening can be fun and rewarding.
To set up an indoor garden, you will need equipment to help create a stable environment that mimics the outdoors. This includes special lighting, fans to re-create the wind, dehumidifiers to maintain the proper humidity, and all the basic supplies that a plant needs to survive from water to grow media and nutrients.
Planning, designing, and implementing an indoor garden can be daunting, but having a firm understanding of the basics can go a long way in helping a new indoor grower get started on the right path to a healthy, successful grow.
The first step in creating a proper indoor growing environment is to identify the medium and irrigation method you’ll be using to supply your plants with the proper nutrients throughout the growth cycle. Think of a medium as a house for your plants roots and your chosen irrigation method as the vehicle through which you feed your plants their nutrients.
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 easy to work with, while others offer more control over the finer details. Different media will retain moisture at different rates, which in turn determines how often plants need to be watered. Some media harbor beneficial microbes that can help plants eat nutrients. Others create environments that, while less stable, allow for more control over a plant’s metabolism.
The two main grow medium options for an indoor garden are soil and hydroponic media. Level of expertise is the main factor to consider when deciding between the two.
Soil is a great choice for beginners. It can be much more forgiving and requires less precision when watering and feeding plants additional nutrients. Less-frequent waterings 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 can also create favorable conditions for pests to spread. Working with soil and hand-watering plants can be messy, but it will allow you to get familiar with the pace in which your plant consumes its water and nutrients.
Hydroponic media are a viable indoor alternative to soil, but they’re considered advanced media because they bring with them a set of challenges that may prove difficult for beginners.
Hydroponics is a blanket term that for the growing of plants in a nutrient solution with or without an inert medium to provide mechanical support. Mediums like coco coir, rockwool, and hydroton can drastically increase the control that a grower maintains over a plant’s growth. With a plant’s roots system exposed, hydroponically grown cannabis can grow faster and more efficiently, requiring less water and nutrients but also requiring extensive monitoring systems to ensure a stable pH is maintained.
Advanced Soilless Mediums
Coco Coir, or coconut fiber, is the fibrous material found inside of 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 experienced growers as they allow cultivators to quickly change the pH and nutrients that a plant is exposed to. Coco coir can either be used by itself or added to soil to improve drainage capability and allow for more aeration.
Rockwool, also known as mineral wool, is one of the most common hydroponic grow media. Similar to coco coir, 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. Generally recognized as an advanced growing medium, rockwool will quickly expose any watering or feeding mistakes. Missing even one day of watering could be detrimental when using rockwool.
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 does provide plant roots with equal levels of oxygen. Similarly to rockwool, the biggest issue is that it can dry out very quickly, so you have to be extra careful to keep it hydrated.
Other common soilless mediums used by hydroponic growers include perlite, vermiculite, coarse sand, and gravel. Advanced growers frequently mix these mediums to create custom blends that suit their specific grow style and environment.
Cannabis Feeding Systems
Feeding your plant is the process of giving it the chemicals and compounds that it needs to grow its leaves, roots, and ultimately produce the trichome-covered flowers we call buds. 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 that are used, replenishes them with a smaller amount of fresh nutrients, then reapplies the solution to the plants the next time the plant is fed.
When using soil as your primary medium, drain-to-waste is the only possibility. In soilless hydroponic systems, it is up to the growers’ discretion. Most hydroponic growers will opt to maintain a drain-to-waste system because it affords them full control over the 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 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 a 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.
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 both electricity and water. Some local jurisdictions may also ask that indoor gardens mitigate odors that may arise from 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 and provide a clean, reflective, and enclosed environment for your plants to grow. As a general rule of thumb, 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.
Grow tents also make it possible 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 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 a maximal harvest each year.
Whether you are growing two (2) or 30 plants in your house, grow equipment requires a significant amount of electricity, primarily from 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 necessarily need to be an electrician to design an indoor grow, but a having basic understanding of the relationship between watts, volts, and amps is essential. The equation below can be used to determine if your property has the minimum amount of power for an indoor garden:
Amps = Watts/Volts
Always make a list of the power requirements for every 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, or 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. Knowing these contents will help you determine the correct amount of nutrients to feed your plants.
Most local jurisdictions require you mitigate the odor from your plants so as to not disturb your neighbors. Activated charcoal filters absorb plant odor in your grow tent. Adding a charcoal filter to your heating, ventilation, and air conditioning (HVAC) system or placing one within your grow area is a great way to drastically reduce the smell. The size of the filter is largely dependent on the size of your room. Make sure it is sized and installed correctly and keep track of the life of the filter as their effectiveness diminishes over time.
Even when growing cannabis legally, it’s still a good idea to minimize your public visibility as a grower and take some mild to moderate precautions. Simple things such as not tagging 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.
Choosing the right horticultural light for your indoor grow can mean the difference between success and failure. Correct lighting is important, as it drives photosynthesis. In other words, your plants will not grow without proper lighting. Lights also control 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 6 hours of darkness. To initiate flowering, plants need a shorter day, with 12 hours of light and 12 hours of darkness.
The intensity of light and placement within your grow room are important aspects to consider when choosing a light. 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. If your light is too close it can damage the plant and ruin your buds.
There are several different types of grow lights that serve different purposes, each with their own set of pros and cons.
Fluorescent lights are affordable lights that 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) light that works by igniting a gas in a tube with a spark of electricity. Metal-halide bulbs emit a spectrum of light that is beneficial during the vegetative phase. They emit more usable light for a plant than a fluorescent bulb, but tend to cost substantially more.
High-pressure sodium (HPS) bulbs are highly efficient HID lights that produce the perfect spectrum 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, thereby increasing the air conditioning (AC) requirements.
Light-emitting diode (LED) lights are another form of high-intensity lighting that are growing in popularity. LED lights produce a spectrum suited for all phases of plant life. They typically cost more than other grow lights, but they last longer, are more efficient, and give off less heat than other HID lights.
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 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 he amount of heat the lights and other equipment produce. 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.
While AC systems maintain temperature, they also dehumidify rooms. Fluctuations in humidity can negatively 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, dehumidifier, sensors, temperature, humidity, etc). These environmental controllers can be worth the hefty price tags for the peace of mind they provide.
With lighting and AC in place to control the environment, indoor cannabis plants will require large amounts of fertilizer or nutrients. Hydroponic systems lack the base nutrients that come with in soil, which leaves it up to growers to feed their plants with nutrient concentrations — the exact formula of which depending on 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.
Carbon Dioxide Supplementation
Controlling the amount of available carbon dioxide (CO2) in your garden is another aspect of indoor growing. 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’ stage of growth. 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 into your garden 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 day 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 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.
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 mistakes.
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 easiest and cheapest 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.