Why your autoflower plants stay small

Many of us have experienced the feeling that we may have been cheated by a seed company when an order arrives and either the seeds do not germinate, they don’t make it past the seedling stage or we are disappointed with the harvest (different phenotypes, low yield, etc.). Granted, there are better quality seeds and seed companies than others, but if you have ever wondered why despite your best efforts your autoflower plants are not as big as you were hoping, you might want to keep reading as we will present below possible reasons as well as some solutions to the problem of undersized autoflowering cannabis plants.

How do genetics impact the size of your autoflower plant?

Cannabis seeds

Autoflowering plants grow quite differently to photoperiods, so it’s good to know a little something about your starting material. While autoflowers do have the reputation of being easier to grow than photoperiod plants, that doesn’t necessarily mean that you can just pop the seed into the ground and let time do the rest. Just like with photoperiod seeds, phenotypes and genetics as well as how you attend to your plants also play a crucial role with respect to how your plant will turn out. Some plant phenotypes (particularly indicas) are known for their short, bushy stature, others are known for being tall and lanky (sativas). No matter how much you might pamper them, their genetics will only let them reach a certain size before they fully mature.

Considering the fact that autoflowers have cannabis ruderalis (C. sativa sativa var. spontanea) as their genetic base, they will never achieve the stature of a tall, equatorial sativa. Most autos will clock in around 3 feet (1 m) in height, with the occasional XXL-sized plants going up to about 5 feet (1.5 m), provided their parents have been crossed with the genetics known for their larger size. Going with a trusted and respectable breeder is your safest bet to obtaining the genetics you want in a plant. Nonetheless, genetics can be a bit of a roulette and you still may get a short, squat plant despite the breeders’ intentions.

Different Life Cycle

Time (as well as timing) is of the essence with respect to autoflowering cannabis plants. By their nature or breeder’s design if you want to make that argument, they enter the flowering phase after about a month of vegetative growth and flower for at least another 6-8 weeks afterwards, sometimes longer depending on the variety, though they tend to max out between the 10th and 12th week from germination. Because of this fixed life cycle, they have less time to recover from potential setbacks, such as stress, pest infestations, nutrient issues, etc.

All cannabis species are quite robust and can recover well depending on the severity of the issue, however, autos have a limited amount of time to do so before they start flowering, after which they focus on bud production. If the issue for whatever reason stunts the growth of a given plant, the likelihood of that plant developing to its fullest potential becomes diminished. It is therefore of utmost importance to keep an eye on your plants on a regular basis and to resolve the issue as quickly as possible so as not to stunt growth any further.

How pot size impacts yield

Autoflower plants growing in air pots

The shape and size of root structures in many plants reflects the shape and size of the plant above ground, which means that the more space your roots have to grow and fetch nutrients and water, the bigger your plants will grow in general. Keeping your autos in small pots will lead to your roots being confined to a small space with very limited room to grow. As a result, they become root bound and their growth suffers.

Many growers prefer autoflowers for their smaller size but sometimes overlook the fact that to get those desired large yields, roots also need space for nutrients but also to breathe. Without proper air exchange, roots can also choke, resulting in stunted growth. The best way to deal with both of these issues is to find a proper-sized pot that additionally allows for root aeration. Fabric pots and/or Airpots work very well for autoflowers and are inexpensive. If growing indoor, aim for a pot size of at least 3 gallons (11 L), if growing outdoors 4 gallons (15 L) is a recommended minimum.

Nutrient Issues & pH

Autoflowering plants are easier to grow than photoperiod strains, however that doesn’t mean that growers are free to feed and water them as they please. In fact, autoflowers can be less forgiving due to their limited life cycle. As a result, the right balance of nutrients, as well as the right amount of water and pH levels, are the key to having a bountiful harvest.

Despite having the best intentions, many growers tend to overfeed and/or overwater their plants, thinking that by drowning them in nutes they will get everything they need and have a little leftover when the going gets tough. However, this approach can lead to an overdose of a given nutrient, leading to nutrient lockout and a pH imbalance, stunting growth and potentially even killing the plant. On the other end of the spectrum, some growers neglect their plants’ needs and let them go hungry and/or thirsty, resulting in smaller plants and lower yields.

Autoflowers generally do not like soil that is too ‘hot’ (i.e. overloaded with nutrients) as this can damage roots and affect growth. This can also result in various pH issues, such as an imbalance or fluctuations, which can wreak havoc on plants. The trick is finding a grow medium that is light enough on nutrients but with enough of them to cover the plant’s needs. Fertilizers, in general, should be used lightly and water should be provided on an as-needed basis. Slow-release organic, dry fertilizers provide plants with the necessary nutrients without causing them to overdose on nutes. A nutrient imbalance can also potentially knock your plants out of the recommended pH range (5.5-6.5), so be very tempered with feeding as well as watering to keep your girls happy.

Indoor vs Outdoor Lighting

autoflower growing under LED lights

The location of your garden may also play a significant role as to why your autos might not be as big as you would like them to be. Indoors you are most likely relying on artificial light and limited grow space, whereas outdoors your plants are getting plenty of sunlight and have much more breathing room. The better (and cheaper) option would be to grow outdoors in large pots, however not everyone has the luxury to do so, so if your only option is to grow indoors, try to give your autoflower plants enough space and enough lighting. LEDs are highly recommended as they provide a very good amount of light while drawing much less power than HPS fixtures. To get those big yields, an LED lamp of 400-600 watts should do the trick for a small indoor setup.

Pruning and training

Last but not least, there are several little tricks that you can try to naturally increase plant size and thus yields. Topping and/or fimming are tried and tested ways of maximizing yields that don’t require the use of additional nutrients to get bigger sized plants. However, considering that autos don’t have much time to recover from this type of stress, it is recommended that they be topped/fimmed by the 3rd week since germination or once the plant has developed at least 3 nodes.

Low stress training is another great way of exposing bud sites and increasing yields. This requires a little more attention than topping as you will be doing a fair amount of tying and/or bending, but the results are definitely worth it and the process can actually be a lot of fun.

How can you fix a stunted autoflower?

To fix a stunted autoflower, first diagnose the issue. Check for adequate lighting and adjust if necessary. Review your watering schedule to prevent overwatering or underwatering. Ensure proper nutrient levels and pH balance in the soil for optimal nutrient uptake. Investigate root health and provide sufficient space for root expansion. Maintain an environment with controlled temperature and humidity levels. Optionally, perform light pruning to redirect energy to essential growth areas. Lastly, exercise patience and closely monitor your plant for signs of recovery, making adjustments as needed to promote healthy growth.

Get the best results from your autoflowering seeds

Your autoflower plants don’t have to be small at all, steps can still be taken to maximize your yields. Some adjustments should be made when going from photoperiod to autos, but there still is a lot of overlap between the two. The best approach is to pay regular attention to your plants and give them what3 they need, no more, no less. By keeping it simple, you will let the plants take their natural course and that is when they are at their happiest, which translates to a very satisfying yield. Happy growing!

4 Replies to “Why your autoflower plants stay small”

  1. I want my plants to stay short sense I grow in a grow tent lambs breath from the king are short do you recommend any I have tried white widow and Jack Herer grow to tall

  2. I’m on second run seedlings auto. My plants are small seedlings and slow growing? Whatsup? IV got really good soil ,and have moved them outside wear they’ll growup! I hope ?
    Am I just impatient? Thinking short life fast growing?
    Confused. Brent TX

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