How to Grow Autoflowers: A Complete Guide From Seed to Harvest

To grow autoflowers, start the seed straight in its final container, give it 18 hours of light a day (anywhere from 18 to 24 works), use a light, airy growing medium and go easy on training: the plant flowers on its own at 3 to 4 weeks old and is ready to harvest in about 2 to 3 months. That speed and toughness are exactly why autoflowers are the go-to for beginners and for growers who can't babysit their plants. Here's everything you need to know to get a solid harvest.

Autoflowering strains are wired to flower based on age, not on a change in the light cycle. Regular cannabis plants, called photoperiod plants, need a specific light schedule to bloom and won't start flowering until the days get shorter, signaling that winter is on its way.

Autoflowers start flowering at around 3 or 4 weeks old no matter how much light they get, and they'll be ready to harvest in just two or three months. 

As a rule of thumb, autoflowers are ready to harvest way earlier than photoperiod plants: about 2 to 3 months after germination. As for yield, you can expect around 100-130 g (3.5-4.5 oz) per plant if you give it proper care throughout its life, though how much bud you pull really depends on how you grow it.

When you talk about yield, keep in mind that autoflowers can be harvested more times a year than photoperiod plants, simply because their life cycle is so short.

Despite that estimate, plenty of growers end up with just 20 g (under an ounce) per plant. That's usually down to inexperience or problems in the grow, especially low-quality genetics, weak lighting and poor feeding. 

On the flip side, experienced growers with solid genetics and dialed-in conditions can push past 150-200 g (5-7 oz) per plant. 

How many hours of light does an autoflower need? 

Autoflowers start building buds on their own from around the third week after germination, whatever light schedule you run. Photoperiod plants are different: you have to switch to a specific light schedule to tell them it's time to bud, 

Still, the question everyone asks is: what's the best light schedule for an autoflower? The short answer is 18/6, meaning 18 hours of light and 6 hours of darkness.

Most growers agree the sweet spot for autoflowers is somewhere between 18 and 24 hours of light a day. Some growers swear autoflowers need a dark period and won't stay healthy under 24 hours of light, but there's no evidence for that.

Another thing to think about with autoflowers is light spectrum. With photoperiod plants, growers typically use more blue light during the vegetative stage and more red light during flowering. You can do the same with autoflowers: use blue-heavy light before the plant shows its sex, then switch to red.

Any color in the spectrum will give you decent growth, as long as it comes from a proper grow light.

Training techniques for autoflowers

Believe it or not, you can “train” an autoflower during its short vegetative stage and it can pay off. 

Experience shows that, as long as the plants are healthy, autoflowers tend to respond well to a simple topping or to LST. The cool thing is that they can be trained to produce more and better colas, and the right training can boost your overall yield and results.

When it comes to training autoflowers, there are three main schools of thought, and growers tend to pick a side:

1- No training: since autoflowers only spend a short time in veg, stressing them with heavy training can leave you with a stunted plant and a tiny harvest.

2- LST only (low-stress training): the goal of LST is to shape the plant into a wide, flat canopy, kind of like a canoe, by bending new stems and tying them down. One of its big advantages is that it puts very little stress on the plant.

3- Topping plus other training: topping means cutting off the top of the main stem to force the plant to grow two colas instead of one. It usually doesn't stress a healthy, fast-growing plant much, but if you're careless it can stress it out or slow its growth.

Experienced growers recommend skipping aggressive training on autoflowers, like main-lining, because the plant needs several weeks of vegetative growth to recover from it. 

What are the best containers for autoflowers?

Autoflowers do best in big, white containers, for two reasons:

1- You want big containers because you don't transplant autos. They start flowering almost while they're still growing, and with such a short life cycle, it's best not to stress them so your yield doesn't take a hit. On top of that, autoflowers slow down their growth and start flowering when the roots hit the bottom of the container.

2- If you grow outdoors, go with white containers: they don't heat up in the sun, so the roots stay cooler and don't turn into a breeding ground for fungi. 

What growing medium should you use for autoflowers?

1- Airy mix: the medium should be fluffy and never compacted, so roots can grow and spread out freely and get the oxygen they need to develop properly. 

2- Perlite: your mix should include perlite, which keeps it loose and well drained so the roots stay comfortable.

3- Nutrients: autos usually don't need as much feeding as feminized photoperiod plants, so a lightly fertilized mix works perfectly. That said, you can also go with a pre-fertilized mix that provides all the nutrients they need.

If this is your first time growing autoflowers, germinate the seed, put it straight into its final container and skip training altogether, so you can see how the grow plays out. This type of strain is ideal for beginners.