How to grow marijuana indoors, a beginner's guide.
We at LEDTonic love to create green life, no matter the plant species. Previously we’ve written an indoor vegetable growing guide, this time we’ll focus on marijuana as our lights are mainly designed for this plant type.
This is a beginner-friendly article. We’ll discuss the basics from start to finish, seed to harvest. We’ll go through what you’ll need for a basic but successful grow setup and what to consider before starting out. We’ll explain the process in a way that even a first-time grower with no previous growing experience will be able to get going.
With that said, this article is not for people who are already experienced growers and are looking for advanced growing techniques. We will not talk about pruning, bending, tying, low-stress-training (LST), diseases, pests, CO2 boost, optimization for maximum yield, and similar topics. Instead, we’ll focus on keeping this basic and simple to show that growing plants indoors really isn’t that difficult.
Where are you going to grow?
Cannabis is grown in plenty of different locations or spaces, all depending on your conditions. Some grow marijuana outdoors in open fields, gardens or on a balcony. The more common way is growing indoors. Large scale operations grow in massive warehouse-like buildings but the average hobby-grower usually has a grow room, grow closet, or, possibly the most common setup, an indoor grow tent. It’s the latter options, the ones that are indoors, which we’ll assume are true for you.
Growing indoors, in a tent for example, is easiest for first-time growers as indoor spaces are easier to control. The risk of your plants suffering from pests or diseases are lower, it’s easier to control temperature and humidity, the light from your grow lamp is confined within the tent, and the grow is easy to access as it’s within or near your living space. In short, if you’re new to growing and are considering your options, we recommend a grow tent. Further down we’ll talk about tent size and necessary accessories.
Growing medium (soil or hydro)?
Weed is grown in either soil (indoors or outdoors) or in a so-called hydroponics setup, without soil. Growing in soil is more beginner-friendly and requires less precise grow strategy (less likely to mess up). Soil is the grow medium we’ll focus on in this article. More on this below.
What you’ll need:
The seeds are what the plant will develop from. Different strains have different characteristics. Some strains grow very tall, others need a longer time to develop, some produce buds with high THC, others with high CBD, etc. Your seed bank will be able to give you specifics of each seed you’re considering. What’s important is to choose feminized seeds. These guarantee a female plant, which produces the maximum amount of flowers, or buds.
Nowadays “auto-flower” seeds are widely available and they are a good choice for beginner growers. Auto-flower plants do not need to be transplanted (from small to larger pot) but more importantly, they will transition from vegetative stage to flowering stage automatically, without any changes in light. More on this later. Auto-flower strains typically produce somewhat smaller yields but their grow-friendliness still makes them the ideal choice for inexperienced growers.
The time from seed to harvest for auto-flower strains is shorter than regular strains. Usually, around 2-3 months whereas non-auto-flowers usually need 3-4 months. Once again, the specifications for each strain will be available on the seeds’ package or in the shop.
The size of the pot has a big significance on how large your plant will grow. The plants’ roots need room to grow and the more room they have, the larger the plant will be. 3 gallons (10 liters) pots are usually considered the bare minimum. Twice the size is recommended if you have enough space.
It’s important there’s plenty of holes in the bottom of the pots to allow for excess water to drain.
Plastic pots are preferable to clay pots as clay soaks up water.
As mentioned above, auto-flower strains can be planted right into their “long term” pot. Regular strains will need to be planted in a small pot, around 8 oz (0.25 liters), and when they develop four sets of leaves, transplanted into their long term pot, 3+ gallons (10+ liters).
When choosing soil you’ll want a type of soil that has the right pH for your plants. Around 6 (+/-0.5) pH is ideal for marijuana. The soil also needs to retain water and have a texture where the roots can develop well. With that said, the soil needs to drain excess water to prevent root rot.
Sand (on its own), for example, would be a poor choice as it holds water and nutrients poorly which results in it drying out quickly; your plant won’t be able to extract water from it.
If you can, purchase soil from a physical gardening store and explain what you’re intending to grow. They will be able to recommend a good soil. If you don’t want to mention that you’re growing cannabis, tomatoes have similar preferences and you could say that’s what you need the soil for.
Purchasing soil online is a bit more difficult but generally speaking, organic potting soil, organic potting mix, or organic super soil are alright. Auto-flower strains also grow well in a light mix without much or any nutrients (as these should be added when watering).
An inch of hydroton (LECA/clay pebbles) at the bottom of the pot (below the soil) will help with drainage.
Some soil types come packed with nutrients. While this is good for somewhat developed plants (3+ weeks old), too much nutrients can hurt seedlings. It’s also important to remember that the nutrients in the soil will be consumed by plants. Typically in around four weeks. It’s preferable to choose a soil that isn’t fully loaded with nutrients and instead add nutrients separately as you water the plants. The supply of nutrients will be steadier and nutrients bought specifically for marijuana will give a better result than “general” nutrients.
Assuming you grow indoors, you’ll need a grow light. We’re, of course, biased so light is our favorite aspect of growing. Nutrients management, pruning, soil, to name a few, can be equally important. But since we manufacture and sell lights, this is what we’re passionate about. Check out our LED grow lights.
To keep this nice and short, we’ll only cover the very most basic aspects but we strongly encourage you to read our extensive article about LIGHT where we dive deeper into, well, pretty much everything about LED grow lights.
You, as a beginner indoor grower, need to know the following things when choosing a LED grow light and setting up your grow area:
- The grow lamp’s light output: Light particles are called photons and the light output from a grow light is called PPFD (also referred to as PAR) and it’s measured in umol/m2/s. Weed plants in their veg stage need 150-300 PPFD. During flowering, they need 500-700 PPFD, or more if you add CO2 (not recommended for beginners). The lamp manufacturer should list the lamp’s PPFD levels at various heights as the PPFD decreases the further the plant is from the lamp.
- Light footprint: This explains how the light from the lamp spreads. Some lamps have a very narrow footprint and may not be suitable for large or several plants. You want to make sure that the lamp you’re considering produces enough light to cover your grow space.
- Light spectrum: A trend with low-end LED grow lights in recent years is that they only, or mainly, produce blue and red colored light only. While these are the dominant colors used in photosynthesis, a plant needs a healthy balance of blue-green-red. Although green has less direct effect on photosynthesis, it helps the plant’s overall health and also boosts some processes. A small but important detail.
LEDTonic Z5's light spectrum; an optimized balance of blue-green-red.
- A word of warning: Do not fall for some of the ridiculous claims made by some brands. Browsing Amazon for “LED grow lights” will show plenty of results for “1500W” or similar lights. This value means very little at best. It either refers to which HPS equivalent lamp that particular grow light should replace or the total LED diode wattage.
There is no correlation between LED wattage and HPS wattage so any claim in this regard without supporting PPFD values and light footprint is more or less bogus.
The LED diode wattage doesn’t tell much about the lamp either. In fact, the larger the diode, the more heat it produces and the less efficient it becomes (more of the input electricity goes wasted through heat).
These “1500W” lights only draw about 200-300 watts. That means they are running at 20-30% of the maximum capacity. A LED grow light with smaller diodes, like ours, run at ~60% of max capacity so you’re still getting a high output despite “low” wattage.
Lumen and lux, commonly used to measure white light, do not paint the full picture when measuring LEDs with specific light color output. PPFD is far more accurate.
- In short: Look for a lamp’s PPFD output, spectrum, and light footprint. Any inflated wattage claims mean nothing if the electricity isn’t efficiently converted into light with a good spectrum.
Water, pH, pH tester
Water is one of three (light and nutrients are the other two) essentials for growth. Tap water, unless contaminated, can be used to water your plants. Depending on where you live, your tap water will have a certain pH level. Usually around 7 pH. Cannabis prefers water around 6 (+/- 0.5) pH. It’s easy to both test and regulate the pH level. A pH test kit can be purchased online or in a garden store. This would be a liquid which, when mixed with water, will turn into a specific color that indicates the water’s pH level. There are also pH meters that work just like a baby thermometer. Insert in water and it will read the pH level on the spot. This type of tool is not cost-efficient for small scale grow projects, though. See below how to regulate and control the pH level.
Plants typically need to be watered in small amounts 1-3 times a week. Water only when the top 1-2 inches of the soil is dry. Over-watering is a mistake that’s not uncommon and this can hurt our plants and its roots. The soil needs to dry up between waterings to avoid mold and root rot.
Nutrients & pH regulator
In addition to water and light, your plants will need nutrients. Consider these three elements (water, nutrients, light) the plants’ food. For your plant to develop, grow, and produce buds, it will need to “eat”. Nutrients typically come in liquid (or crystal) form and need to be mixed with water. There’s not just one nutrient mix that will be enough for the entire plant’s cycle. Typically, nutrients are sold as sets with 3-6 different flasks. One might contain nutrients that boost root growth, another one enhances plant growth, and a third might help with flowering (buds). Each nutrient brand/mix will have detailed instructions with the flasks. It’ll also explain how much nutrients to mix with the water. Typically, it’s a couple of milliliters of nutrients per liter of water.
While nutrients may seem like an expensive investment, it really pays off. Growing a plant indoors limits the nutrients (“food”) the plant can naturally absorb from the soil so the plant is depending on added nutrients to develop and flower well.
pH regulator, an acidic solution to bring the pH level down or an alkaline solution to bring the pH level up. As with nutrients, this solution is purchased in a flask or bottle and applied in very small amounts to the water after nutrients have been mixed. Nutrients can lower or raise pH in water so be sure to test and regulate the pH level after the nutrients have been mixed. Some soils have a bit of limestone mixed in which may affect the pH levels. If you want to be thorough, pH test the drainage water that runs out from underneath your pot.
Temperature & humidity
There’s a certain temperature span where cannabis grows well. Within this range there are better and worse temperatures but generally speaking, the plant will be able to grow. Too cold or too hot temperatures, however, can significantly limit or even stop the plant’s growth, regardless of stage. Certain strains also have their own preferences but, generally speaking, 65-82F (19-28C) are ideal temperatures for indoor grown strains. Day temperatures should be a few degrees higher than night temperatures.
Simply put, the higher temperatures a plant is subjected to, the higher is its needs for light and nutrients.
As for humidity, the plant develops well in humid environments during its early stages. As a seedling, 65-80% is a good range and then about 10-15% lower during its vegetative stage, and another 15-20% lower (RH 40-50%) during flowering.
During the plant’s early stage, when it’s a seedling, it prefers around 77F (25C) during day, and 3-5 degrees colder during night.
When the plant has grown and is in its vegetative stage, it has less specific temperature requirement. 70-80F (22-28C) will do during day and, once again, a couple degrees colder during night.
At the end of the plant’s life cycle, during its flowering stage, it’ll want 68-78F (20-26C) and possibly even a bit colder during its very final week.
Tent, fan, rope ratchet
As suggested above, growing plants inside a grow tent makes it easy to regulate temperature, humidity, light intensity, and also contain light. If growing at a large scale, a CO2 booster and air filter (for the smell) can be fixed to the tent.
Regardless of size, a fan is definitely needed within the tent to create air flow. Without a fan the air is still and mold will grow quickly. A small USB computer (a fan you could connect to your laptop’s USB port) is enough for smaller tents (32x32x60”) whereas a table top might be necessary for larger tents. Angle the fan so it blows air into open space, try to avoid blowing straight onto a plant or branch.
To fix and hang a light inside a tent at the appropriate height, rope ratchets are the go-to solution. One end of the ratchet is tied to the top of the tent and the lamp is hung in the other end. Adjust the height depending on your plants’ light requirements and the lamps’ light output. Seedlings and young plants require less light than a mature plant, thus the lamp should be further from the plant’s canopy.
Tents come in all shapes and sizes. Two rather small plants will fit in a 24x24x60” tent. Growing plants in hydro instead of soil will usually make for a larger plant and also require a larger tent.
Four small plants can fit in a 32x32x60” tent but that’s really the minimum recommended area.
To automate as much as possible of the grow process, digital timers are used to switch lights on and off. Weed plants require anywhere from 12-24 hours of light per day. Certain strains have their specific preferences but in general, indoor grow cannabis will want 18 hours to 24 hours of light during its vegetative stage (18 hours of light and 6 hours of darkness is arguably the most common choice). During its flowering stage, 12 hours of light and 12 hours of darkness is usually preferred.
Auto-flower strains typically require the same amount of light during both veg and flowering. Confirm your strains requirements when purchasing the seeds.
Lamps that emit a heavy BLURPLE (blue-red-purple) colored light (not white) are not easy on your eyes. Light with short wavelengths (gamma, X-ray), and in the case with the BLURPLE lights; UV, and deep blue, is more or less harmful to humans. The more time you spend with your plants and looking at BLURPLE light the more you’ll expose your eyes to these colors of the spectrum. Heavy red light is not considered dangerous but can still irritate your eyes.
Wearing appropriate eye protection should not be overlooked. Or better yet, choose a light that isn’t BLURPLE and thus easier on the eyes. Grow lights don’t necessarily have to have all white diodes but the total light emitted should appear white or pink-ish, not blue-red, for the sake of your eyes.
A watering can gives a nice and even water flow which is recommended when watering plants. Using a jug or glass for watering purposes is an option, but not a great one. A 2-3 gallon watering can which you can fill and let acclimatize to room temperature is the best way to go. It’ll last for a couple of waterings and you’ll only have to measure the amount of nutrients when you fill up the can.
Once you have all the items mentioned above, you’re ready to setup your tent or grow area and then begin your grow.
Start your weed grow!
Seeds need a humid and damp environment to start their development. A moist environment signals to the seed that it’s time to hatch and sprout. An easy way of germinating seeds is to put them between two damp paper towels and then put the paper towels in an enclosed space. Between two plates or in a zip-lock bag, for instance. Then put the entire package in a dark space at room temperature. The seeds will germinate in 2-3 days. Once a tiny root has shot out and grown to about an inch (2.5 cm), plant the germinated seed in soil.
Non-auto-flowering, strains need to be planted in a smaller pot and then transplanted in 1-2 weeks’ time, or when the plant has 4 sets of leaves.
Auto-flower strains can be planted straight into their long term pot but regular strains need to be translated once the plant reaches a certain size (or sets of leaves).
Poke a 1-2 inch deep hole in the soil with your finger and place the germinated seed with root downwards in the hole. Cover the hole lightly with soil and give it a little bit of water. Putting a layer of plastic film on the pot helps contain a humid environment until the tiny plant breaches the soil, which normally happens in 3-5 days. Make sure to only expose these fragile little sprouts to a tiny bit of light. A window sill without direct sunlight or a not-so-powerful lamp is recommended. Avoid direct sunlight and high light output. If you’re growing inside a tent, have plenty of space between lamp and plant. The distance is determined by the lamp’s light output. LEDTonic’s Z2 and Z5 lamps need to be about 3 feet (90 cm) from the young plant.
If you know your lamp’s PPFD output, aim for around 100 PPFD at the plant’s canopy.
Aim for a temperature of 77F (25C) and 70-80% RH (humidity).
During the first 1-2 months of the plant’s life it will be in a vegetative stage. In short, this means that the plant is growing and developing but not yet producing flowers (buds). Leaves will develop and grow on a daily basis and the first set of fan leaves grow to a decent size in roughly 2 weeks. It is around this time nutrients should be added into the watering mix. Make sure to let the top 1-2 inches of the soil dry out between waterings. Water in excess will create an environment where mold quickly grows.
As more and more leaves develop, the plant will be able to absorb more and more light (300-500 PPFD), which results in quicker growth. The leaves and roots of the plants can be compared to a person’s mouth. The plant absorbs its “food” (light and nutrients) through the leaves and roots.
During the vegetative stage a healthy plant will be short in length but bushy. They prefer a blue/white light at this stage which resembles the natural light spectrum of springtime.
Temperature of 70-80F (22-28C) during the day and a few degrees colder during night is ideal with around 60% humidity.
Two of the first signs of the flowering is stage is that the plant starts growing in length quickly, up to a few inches a day, and that the plant’s pistils (white little hairs) are shooting out. The plant requires more light and more nutrients to support its growth. At this time, the plant grows best when there’s plenty of warm white or red light in addition to the blue. Some grow lights come with so-called “veg” and “bloom” switches or buttons. These buttons control which diodes of the lamp are turned on. Normally the veg switch turns on “cold” white and blue diodes whereas the bloom switch also turns on warm white and red diodes. During flowering stage, all diodes should be lit and the lamp should ideally have a warm white or pink/red-ish color to stimulate growth.
Keep feeding your plant nutrients according to the instructions on the nutrient package. As your plants are progressing toward the end of their flowering stage they will need more and more nutrients and more and more light (~500-700 PPFD) to grow as many and as big flowers (buds) as possible. While nutrients are important, too much nutrients (or in incorrect ratios) can have an adverse effect on growth.
The plants will eventually develop trichomes which look like tiny little crystals on the leaves near the buds. As these trichomes turn from a clear, almost transparent color to cloudy or milk-like color, the THC is developing. The highest THC levels are reached just before the trichomes turn amber. If the trichomes are starting to turn amber, the resulting high will be more of a body high. Choose the time to harvest depending on your preferences.
The temperature during flowering should be slightly colder than during veg, 68-78F (20-26C) and around 40-50% humidity.
It can be difficult to clearly see the trichomes, especially without a magnifying glass. Using your phone's camera and taking a picture under white light then zooming in, is an okay workaround.
An alternative method is to look at the pistils. This is less exact but easier and can be seen with the bare eye. The white pistil hairs will eventually turn amber, orange, or red, depending on your strain. When over half of the pistils have changed color from white to orange, the THC is reaching its peak. Letting your buds develop further will increase the CBD to THC ratio which will result in more of body-high than euphoric high.
As your trichomes or pistils are getting within your desired range, cut the branches with buds with scissors or a knife and trim the leaves. Then hang the branches in a non-humid room and let them dry for 3-7 days.
In short, this is how you as a beginner can get started with your grow. You'll learn plenty of hands-on techniques as you go along. Eventually, you'll want to absorb more information to realize maximize your grow but with this guide, you'll understand the basics and can look forward to producing your own supply :-)!