Grow: An Intro to Indoor Cannabis Cultivation

What You’ll Learn in This Article

 

  • The goal of indoor cultivation is to artificially create the ideal environment for your plants at all growth stages.
  • Specialized indoor cultivation equipment allows cultivators to achieve multiple harvests per year.
  • The two main grow medium options for an indoor garden are soil and hydroponic media. There’s much to consider when deciding between the two.
  • Feeding your plant is the process of giving it the chemicals and compounds it needs to grow out its leaves, roots, and heavy, trichome-covered colas.
  • When it comes to cultivating indoors, you must also provide your plants with the optimal temperature, humidity, air circulation, CO2, and nutrients.

Indoor cannabis cultivation is a rewarding endeavor that basically can be done in any climate. It takes detail orientation, the right equipment, time, and money, but the benefits reaped from growing your own weed is more than worth the duration and expenditure. 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.

The practice of indoor cultivation is chosen over outdoor cultivation primarily for its 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 grow space.

Indoor cultivation of cannabis began in the 1970s as a direct response to marijuana prohibition. As law enforcement officials cracked down on outdoor cannabis grows, cultivators responded by moving many of their operations indoors — not only allowing them to hide their valuable plants from prying eyes, but also freeing them up from limits and challenges imposed by being exposed to nature and authorities.

While techniques were being worked out and environmental controls tweaked, the practice of growing high-end, craft cannabis began to really find its footing in the 1990s. Master growers dialed in personal growing methods and utilized high-performing nutrients on top of prime genetics from a surge of seed banks. The genetics of the 1970s were bred and crossbred into the countless cultivars we enjoy today. Those techniques have now been folded into standard indoor grow practices.

Ultimately, the costs of equipment and recurring utility bills are more expensive than 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.

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 out and then flower the plants. This includes horticultural lighting, fans to recreate a gentle breeze, dehumidifiers to maintain the proper humidity, heating, ventilation, and air conditioning (HVAC), 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 grow.

Setting Up Your Grow: Medium and Feeding Methods

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 depending on its composition and your chosen irrigation method is the way 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 grow 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 grow medium options for an indoor garden are soil and hydroponic media. Here’s what to consider when deciding between the two:

Soil

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 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 their water and nutrients.

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 mechanical support. Media such as rockwool, coco coir, and hydroton can drastically increase the control that you maintain 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 monitoring systems to ensure a stable pH is maintained.

Soilless Mediums

Rockwool, also known as mineral wool, is one of the most common forms of hydroponic grow 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.

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, especially when used on its own.

Coco Coir, or coconut fiber, 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, as they allow them to quickly change the pH and nutrients that a plant is exposed to. 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 either be used by itself or added to soil or hydroton to improve drainage and growth capability.

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 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 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.

Electrical Power

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:

Amps = Watts/Volts

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

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.

Odor Control

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.

Security

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.

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.

Nutrients

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 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 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 Circulation

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.