2021 Guide to Cannabis Auto-Flowering Strains

Published Sep 23, 2021

by Nebula Haze

It’s 2021, and there’s never been a better time to grow an auto-flowering strain. Autoflowering cannabis plants tend to stay small and are ready to harvest in 2-3 months, which is several months faster than standard (photoperiod) cannabis strains. While photoperiod cannabis strains need daily dark periods to start making buds, auto-flowering strains start making buds automatically after a few weeks. This simplifies the home grow process because growers don’t need to put grow lights on a timer or think about light leaks.

Auto-flowering cannabis plants are like houseplants on steroids. Unlike standard cannabis strains, they tend to stay small and are ready to harvest just 2-3 months from germination.

Auto-flowering plants usually don’t get enormous due to their short lifespan, but they can produce multiple ounces of bud per plant when grown in optimal conditions with lots of strong light.

This Ultimate Auto in a 2-gallon fabric pot was harvested 65 days from germination and produced almost 4 ounces of prime bud on one plant.

Ultimate Auto buds at harvest

Why auto-flowering strains are great:

  • Grows like a regular house plant (on steroids) – Just germinate the seed and keep plants alive until harvest. Voila, you’ve got buds! Auto-flowering plants don’t need special light periods to make buds like photoperiod strains. Even a sunny window can produce a few grams of buds from an auto-flowering plant. However, it’s important to remember that light is the plant’s “food”. More light equal more buds (up to a point) and you need more than a sunny window to produce a lot of weed. One of the best options for home growers to produce multiple ounces of bud per plant is a cannabis-specific LED grow light.
  • Ready to harvest in 2-3 months – While standard photoperiod strains typically take 3-5+ months from seed to harvest, autoflowering strains are ready to harvest in just 2-3 months from germination.
  • More harvests per year – The ability for a 2-month grow period let you harvest up to 6 times a year compared to 3-4 harvests a year with photoperiod strains.
  • Hundreds of strains to choose from – There are auto-flowering strains with almost any combination of THC and CBD to suit your personal needs. There are also auto-flowering versions of popular and legendary strains.

Cons to auto-flowering strains

  • Reduced strain choice – Auto-flowering strains do have lots of options, but they are a relatively new (and boutique) type of cannabis so there are not as many options as photoperiod strains. You also need to be extra careful who you buy auto-flowering seeds from because some breeders sell questionable auto-flowering genetics.
  • Plants stay small if you run into major problems – An auto-flowering plant gains its full size within about 6 weeks from germination, then the plant stops growing any bigger and focuses all its energy on fattening buds. This short growing period means a plant may stay small forever if itgets stunted during the first 4-6 weeks of life. This is opposed to photoperiod strains which need dark periods to start making buds, which gives you as much time as you want to grow plants to the desired size.
  • No advanced training techniques – Plant training techniques like manifolding or schwazzing aren’t suitable for auto-flowering strains due to the shorter grow period.

Want to give auto-flowering strains a try? Continue reading this article to learn how to grow auto-flowering plants so they produce potent, high quality weed.

Autoflowering plants stay very small when grown in small pots with a small grow light

Example of Nebula's Microgrow - this mini grow tent was 2'x2'x3' with 4 autoflowering plants and used a HLG 100 LED grow light

Autoflowering plants get much bigger when given plenty of light plus room for plants and roots to spread out. A 2’x4′ grow tent can produce up to 1 pound of cannabis if you fill it with auto-flowering plants.

Example of 8 different autoflowering cannabis strains grown in a grow tent

The final size / yields of auto-flowering plants is determined by their genetics, their care (how well you treat them), and how much light they get. These plants were the same strain, but the smaller plant was grown under a much less powerful grow light.

If you give your auto-flowering plants water, nutrients, and a good environment, you can produce a surprising amount of bud in 2-3 months.

The biggest downside to auto-flowering plants is plants stay stunted and small if you run into major problems during the first several weeks of life. That can dramatically reduce yields since a small plant can’t support a lot of buds.

Here’s an example of an auto-flowering plant that was overwatered as a seedling and stayed small. At 6 weeks old, it stopped growing any taller and was only a few inches tall at harvest.

This auto-flowering cannabis plant was stunted by growing problems, and as a result it will produce lower yields that its potential

Auto-flowering Window Plants?

Auto-flowering cannabis strains are kind of like a regular houseplant in their care, except they need much more light and nutrients.

A long as you keep an auto-flowering plant alive and healthy (and ensure it gets several hours of bright light every day) it will produce buds that are ready to harvest in 2-3 months.

An auto-flowering plant in a window can be a fun way to get started growing weed without investing in a grow light.

Even a window auto-flowering plant can produce a few grams if you take care of it.

The above plant produce 3.5 g after being grown in a sunny window.

In contrast, a photoperiod strain can’t be grown in a window because it needs 12-hour dark periods every day for 8-12 weeks in order to make buds. A photoperiod plant that gets light during its dark period will re-veg, which makes buds wither away and die.

Side Note Based on the Cat in Picture: Never leave a dog or cat alone with a cannabis plant or you may find nibbles on the leaves. Cannabis leaves are generally well-tolerated by cats or dogs (and some pets find cannabis leaves calming), but pets can harm or knock over your plants. This particular cat (my calico) will methodically take a bite out of every leaf if left alone with a plant for even a second.

Many cats and dogs love eating cannabis leaves. I collect extra leaves and feed them to my kitty separately 🙂

What Auto-Flowering Strains Should You Get?

If you want to get great results with auto-flowering cannabis plants, you must choose great genetics. Auto-flowering strains were developed from cross-breeding a type of hemp and the first commercial strain (called “Lowryder”) was released in the 2000s. In the beginning, all auto-flowering buds were small and relatively non-potent compared to their photoperiod counterparts.

All auto-flowering plants descend from the humble Ruderalis cannabis plant from northern Siberia. These tiny hemp plants developed the auto-flowering characteristic as an adaptation to the short 2-month summers near the arctic circle. Cannabis breeders have crossed these hemp plants with standard cannabis strains to create auto-flowering strains that produce potent fat sticky buds.

These adorable Ruderalis hemp plants are the ancestors of all auto-flowering strains

A ruderalis cannabis plant in the wild - pic taken in Russia

Dedicated growers have slowly created auto-flowering strains that produce buds as big and potent as photoperiod strains. As of 2021, many auto-flowering buds match or in some cases even exceed the quality of photoperiod buds.

However, due to this breeding history, there is incredible variation between the worst and best auto-flowering strains. Unfortunately, some breeders still sell older or subpar genetics. It’s especially important when ordering auto-flowering strains to choose a trustworthy breeder that uses modern auto-flowering genetics. Here are some examples of trustworthy breeders and auto-flowering strains.

Recommended Auto-Flowering Breeders

There are many great breeders, but this list is based on my personal experience. These are the breeders I have ordered my auto-flowering seeds from so far in 2021.

  • Ethos Genetics – also specializes in photoperiod strains but has been extensively working on their auto-flowering line since 2020 (sparkly smelly genetics)
  • Seedsman – Offers excellent in-house versions of popular auto-flowering strains at lower prices (their photoperiod strains are good too)
  • Seed Supreme –  a great variety of excellent modern genetics adapted into stabilized auto-flowering seed form (also ships from US)

Honorable mentions (I’ve ordered from these companies in the past and had great experiences)

  • Bomb Seeds – I especially like their THC Bomb Auto for both yields and potency
  • Dutch Passion – excellent yields though not necessarily the highest potency on their autos
  • Fast Buds – auto-flowering plants grow fast and get consistent results
  • G13 Labs – they’ve been in the auto-flowering game for a while and have some real winners in their strain library
  • Mephisto Genetics – been developing great auto-flowering strains since 2012 (one of the first great auto-flowering breeders)
  • Sweet Seeds – colorful strains with relaxing effects and delicious flavors

Recommended auto-flowering strains

High THC (25% or higher) – high potency with strong physical and mental effects

High CBD (Over 15%), Low THC (Under 1%) – anti-anxiety with subtle mental and physical effects (won’t get you “high”)

Above-Average Yields

Relaxing and Uplifting Bud Effects

Purple Auto-Flowering Strains

Get a trustworthy autoflowering strain to make sure you’re happy with your results at harvest.

Here’s a Zkittlez Auto by Seedsman I grew.

The buds grew big, fat, and sparkly

After harvest, the bud quality was excellent

Pink Kush CBD 30:1 Auto is one of the highest-CBD auto-flowering strains available today (almost no THC so it won’t get you “high”)

I hope that helped give you some ideas on strains to grow . Now it’s time to learn how to grow your auto-flowering seeds so you get great results.

How to Grow Auto-Flowering Plants

Here are simple directions on how to grow a cannabis auto-flowering plants from seed to harvest.

1.) Get seeds (recommended strains above)

This one is easy. All auto-flowering plants are started from seeds and any of the choices above will work great. Check out our seeds page for recommendations on where to buy seeds online.

A main thing to keep in mind when choosing auto-flowering seeds is to look at the breeder information and match the strains for a similar amount of flowering time. Avoid growing “tall’ and “short” strains at the same time. The more similar plants grow to each other, the easier it will be for you. Sometimes growing different strains together can cause unexpected problems. I tend to get strains that take 9-11 weeks from seed to harvest and grow to a medium size, which means all my plants tend to “play well” with each other.

Cannabis seeds - ready to be sprouted and grown!

2.) Prepare grow light, grow medium, and nutrients

Before you get started growing, you need to make sure your plants have light, nutrients, and a home for their roots.

Not sure what to get? For beginner growers, I recommend getting an LED grow light, using soil or coco as a grow medium, Dyna-Gro Foliage-Pro and Bloom nutrients (can be used in any grow medium) and choosing a 2, 3, or 5-gallon fabric pot as your container.

The Spider Farmer SF-2000 is a great 200W LED grow light that doesn’t make much heat and can produce over 10 ounces per harvest (here’s my review)

I personally believe soil or coco are the best choice for first-time growers. These mediums tend to be more forgiving than hydroponics.

Example of great cannabis soil

3-gallon fabric pots like the ones here let an auto-flowering plant get big enough to produce big yields, but plants usually won’t get much bigger than this

Dyna-Gro (Foliage-ProBloom) are inexpensive nutrients that work great for growing cannabis in any grow medium including soil, coco, or hydro. Use “Foliage-Pro” during the vegetative stage, and “Bloom” during the flowering stage. Just follow the instructions on the bottle.

Dyna-Gro "Foliage-Pro" is a proven cannabis nutrient option for the vegetative stagePlusDyna-Gro "Bloom" is a proven cannabis nutrient option for the flowering stage

Learn more about what you need to start growing.

3.) Germinate seeds

Once you get set up, it’s time to start growing. There are many ways to germinate seeds. Here’s the technique I use to get nearly 100% germination. But at its simplest, you can stick seeds in a pot about half a knuckle deep.

Germinate your autoflowering seeds and you’ll soon have seedlings. Remember, bigger pots let plants get bigger while using small pots or solo cups will keep plants small.


4.) Water plants

Basically the idea is to give your plants water when the top starts drying up. Young seedlings only need a little water in a circle around their base at first. Wait until your plants are growing fast before giving enough water to get runoff out the bottom.

Learn how to water plants perfectly every time.

Seedlings only need a few cups of water at first. Notice how we only gave these plants a little water in a circle.

Once plants are growing fast, you can give them enough water for runoff (remove the runoff immediately). Wait until the top is dry before watering plants again.

5.) Adjust grow light as needed

As plants get taller, raise the light to keep it the recommended distance away from plants. When in doubt, start lights about 24″ away, though many lights can be kept closer.

How far should I keep my light from my plants?

Adjust lights as needed to keep them the proper distance from plants as they grow

6.) Harvest (learn when to harvest)

Buds are ready to harvest when the white hairs have darkened and curled in!

The hairs on buds darken and curl in as buds mature. Buds should look solid by the time they’re ready to harvest.

Here’s the full “When to Harvest” guide

Don’t forget to dry and cure your buds!

Keep the leaves after harvest to turn into edibles or hash!

7.) Enjoy!

You earned it.


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