How to Grow Autoflower Cannabis Indoors

Starting your first grow? Fast Buds runs down all you need to know before you start.
Author Ryan
20 June 2018
5 min read
How to Grow Autoflower Cannabis Indoors

  • 1. Light
  • 1. a. Fluorescent
  • 1. b. High-intensity discharge
  • 2. Growing medium
  • 3. Nutrients
  • 4. Water
  • 5. Carbon filter

Autoflowering seeds grow, well, automatically when cultivated outdoors. Plant, water, and fertilize them, then let the sun and mother nature do the rest. Indoor growing is more technical, but just a bit. Whereas the Earth and the sun provide abundant soil and light, you'll have to provide those for your plant. You'll also need to pay a bit more attention to plant nutrition, as well as install a carbon filter to keep the smell away unless you're like us and want your home to smell like fresh marijuana all the time. Here's all you need to know to get started growing autoflower weed indoors.


With no sun to rely on you'll need to provide light for your plants. There are many different lighting options to choose from, and knowing which one is best for you can be tricky.


Fluorescent lights are cheap, easy to find, and fit nicely in even the most cramped grow environment. They don't generate a significant amount of heat relative to other options and can be kept close to plants without burning them. Compared to other options like HID (see below) fluorescent lights will grow plants of slightly lower yields. The tradeoff here is the grower takes a small impact to their yield but sees massive savings in electricity and heat management. Fluorescent lights come in a few varieties, each with their respective pros and cons.


Compact Fluorescent Light Bulbs

You've probably seen Compact Fluorescent Light bulbs in your own home. They're easy to find anywhere light bulbs are stored. They're cheap, small, and easy to find, making them perfect for private-minded growers with limited space to grow. Unlike other fluorescent bulbs, you'll want to keep CFLs close to your plants to make sure light reaches lower leaves and bud sites.


A T5 fluorescent light

These long tubular lights often plug into panels of four or five lights and take up significantly more space than CFLs, but they produce a light spectrum slightly better suited for cannabis growth. You can find them at any garden center or home improvement store. When growing seedlings or clones, be sure to keep the light far away. While you can keep T5 lights closer to mature specimens, their light is too intense to stay close to more fragile, younger plants.

High-Intensity Discharge

These large bulbs produce massive amounts of light at the perfect spectrum for growing cannabis, and they're more efficient than fluorescents in terms of weight of bud per watt of power used. That doesn't mean growers will see lower electricity bills using HIDs. Producers using smaller spaces can generate more than enough light using T5s or CFLs at lower wattages than even the most miniature HID bulbs.

HID lights generate a lot of heat, and you will have to manage your grow space's temperature when using them. If you don't have a good exhaust system, it's better to stick with a low heat option like CFLs or LEDs.

Like CFLs, HIDs also come in a few varieties.

Metal Halide

Metal halide lamp

Metal Halide lights are usually used during the vegetative phase of growth, but can also be used during flowering. Their bluish light is perfect for vegging plants, and while this will get the job done, many dedicated growers switch to another lighting solution once buds start to form.

High-Pressure Sodium

A High Pressure Sodium Light

High-pressure sodium lights serve as counterparts to Metal halide lights. If efficiency is your goal, you can't beat a combo of MH during veg and HPS during flowering. The yellow light produced by HPS enhances bud production.

LED Grow Lights

For the grower looking to cultivate discreetly, or for just their personal use, LEDs are the ideal middle ground between the efficiency of HPS lights and the low power consumption of CFLs. LEDs produce a more favorable spectrum than fluorescent lights, generate less heat and use less power than HPS lights.

COB Light from

You can recognize pictures of plants under LED lights through their purple hue. For many years these purple boards of diodes were the only option if you wanted to grow with LEDs.

However, recently, chip-on-board LEDs or COBs have made the lives small growers much easier. If you're only growing a couple of plants at a time, you can't go wrong with COB lights, which produce a much more photogenic white light compared to the harsh purples of traditional LEDs.

Growing Medium

You've got space, you've got light, but what are you going to plant your seeds in? There are seemingly endless choices for growing mediums, ranging from hydroponics and aeroponics to dollar store gardening soil. We'll tackle hydro and other high tech mediums in another article, for now, we want to keep things easy for new growers. After removing the high-maintenance, high-tech options, we're left with three choices: soil, soilless, or a combination of the two.


Soil is what millions of years of evolution trained cannabis seeds to grow in, and there's nothing wrong with germinating, planting, and trusting the plant's genetic to take care of the rest. The only caveat we have to add is that you find high-quality soil, either on the internet or your local hardware store. Cheaper, low-end soil is meant to grow small flowers, not giant cannabis bushes. In our experiments with bargain brands, we've found that plants grow quite well through the vegetative stage, but the once flowering starts our plants quickly exhaust the available nutrients and begin showing signs of malnutrition. This problem can be corrected with the addition of outside nutrients, but it's just easier to buy high-quality soil in the first place.


Fast Buds' Rhino Ryder growing in a soilless medium

There are a variety of soilless options to choose from, but the most popular for growing Cannabis is Coco Choir. Made from coconuts, Coco looks like soil at a glance but is ideally suited for growing friendly bacteria that will give your plants nutrients. You don't have to use it by itself; you can also mix it with traditional soil to create an ideal blend.


You'll need at least a little bit of fertilizer to get the most out of Fast Buds seeds. Some strains, like our Blue Dream'Matic, require just a bit and are easy to overfeed, while other strains like our Green Crack will take all the nutes you can give it.

In general autoflower strains are almost always hungry for calcium and magnesium, so you should get a brand that provides those vital nutrients. Beyond that, don't stress over it. The growing environment and medium, more than strain, determine what kind of nutrients you need to provide your plants. Since those are unique to each grower, it's hard to give generalized advice.


Of course, your plants will need water. A general rule of thumb is to water whenever the soil is dry from the top to two centimeters or an inch down. Depending on your setup you might water once every two days during vegging, but once in-flower Fast Buds' plants will drink and drink. For example, a mid-flower Stardawg in an 11-liter pot can take two liters of water a day without leaking anything through drainage. It drinks it all.

Carbon Filter

If you're trying to grow without alerting the neighbors, you'll want a carbon filter to take care of the smell of growing marijuana. Buying a filter and fan might be the most expensive part of your setup, but you'll more than make it up in the peace of mind you get in return.

That's all you need to get started growing indoors. Of course growing cannabis cup winning ganja takes a bit more, but a simple setup can net you 1.5 to 2 ounces of high-THC dried bud a month. While your researching be sure to check out our rundown of The Top 5 Best Indoor Autoflower Strains, and don't forget to follow us on Facebook and Instagram to stay up to date on all the latest strains, deals, and giveaways from Fast Buds.

Author Ryan
20 June 2018