How do you grow great weed indoors?

Before you start this labor of green love, it is important to understand how a cannabis plant grows in any given grow space.
With marijuana plants in the germination phase, seeds sprout and roots emerge in as little as 12 hours or up to 8 days. The seed coat will crack open and root will emerge and grow downward. The root anchors itself after a few days and two leaves will then emerge.
Then, the seedling stage begins and lasts for about a month. This is when the plant is most vulnerable, so it is critically important to control the environment (light, heat, humidity, watering) at this stage.
Veg Stage
In the vegetative phase, an indoor plant has rapid vertical growth and produces new leaves. The root system greatly expands as well. The plant is in the midst of the vegetative phase when it has seven distinct sets of leaves. This takes about two months.
Pre-Flowering Stage
The pre-flowering phase is called “the stretch” and can take about 10 to 14 days. During this phase, growers switch to a 12 dark/12 light cycle. The plant rapidly develops and can double or even triple in size during this time. The plant develops many more branches.
Flowering Stage
Finally, the flowering stage and phase arrives. Depending on the strain (indicas, sativas or hybrids) this phase can last 6 to 22 weeks. The sex of the plant is finally revealed in this phase. Male plants produce flowers that look like grape clusters (panicles).
Female plants not pollinated with male pollen will produce sticky buds in the last ditch effort to catch any male pollen blowing around in the wind. These sticky resins are the sweet spot because they contain the largest amounts of THC (or other cannabinoids). A fertilized female plant can also produce the sticky resins, but the plant also produces seeds, which takes most of the plant’s energy, so the resins are not plentiful in a marijuana
Soil
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.
Hydroponics
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.

Setting Up Your Grow: Choosing a Space

Clean Spaces
Your space needs to be clean before you start and easy to clean once plants start growing. You probably shouldn’t have any type of cloth like carpeting or curtains because they’re hard to keep clean. It is also recommended to start with clean and new fabric pots for your marijuana plants.
Environmental Controls

It is imperative that you control your growing environment for conditions like humidity and temperature. Monitor your space before you make it a growing room.
What’s it like?
Is it cold and dry or warm and humid?
Is it easy to let fresh air in through a door or window?

The space you choose should be naturally cool and dry with easily accessible fresh air. If it’s not, you’ll have trouble controlling your growing environment down the road.

Temperature needs to be maintained from 70 to 85 degrees F (lights on) and 60 to 70 degrees (lights off). There’s a bit of variability in temperature depending on the strain you’re cultivating. Some strains like indica do better in lower temperatures, while other strains are more heat-tolerant.

It is important to choose climate control and lighting systems that can be automated. You don’t really need anything fancy (or expensive). You really just need a fairly simple 24-hour timer for your light system and a thermostat for your exhaust fan.

Creating the Ideal Environment: Lighting

The correct light spectrum for cannabis plants
When it comes to the to the colour temperature of the light spectrum, cannabis plants will benefit from receiving blue light (450-500nm) during their vegetative growth stage, and red light (610-750nm) during the flowering period.

When rooting clones and in the first stage of starting seedlings, many growers use simple fluorescent tubes or CFL lightbulbs with a blue spectrum. For plant growth and pre-flowering, many will begin to use lights with the same spectrum, but with greater power, such as Metal Halide lamps. This encourages the structure of the plant become stronger and hardier, preparing her for abundant flowering.

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 grow 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 grow 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.

Air Flow Indoors For Growing

If your room doesn’t have natural air flow, you may have to artificially create that steady stream of freshness that your new plants need to survive and thrive.

The fresh air is needed to counterbalance the copious amounts of carbon dioxide (CO2) that your plants are producing in a closed space. You might have to invest in a system of exhaust fans to move CO2 out and fresh air in. Typically they need to be replaced near the ceiling to remove the warmer air and CO2 that rise to the top.

Be sure to buy an exhaust fan big enough to handle the size of your space and robust enough to move out the heat that is going to be generated from all those lights. Because lighting systems vary widely in terms of the heat they produce, it’s best to decide on your lighting system first, then ensure that you have a proper fan.

Do some test runs. Set up your lights in the room before you’ve got the plants in. Monitor conditions throughout the day and night. This will help you ensure you’ve got the proper airflow.

Here’s a trick that some growers who live in warmer climates do—they run their light cycle at night to keep temperatures and electric bills low. If the pungent smell of blooming cannabis is too strong for you, add a charcoal filter to your fan or room as many hobbyist growers do.

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 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 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.