As one of the most impactful variables affecting plant height, you need to think carefully about container size. If you’re aiming for particularly small and compact plants that will happily fit into a small grow tent or concealed area of your garden, opt for a pot size of no more than 11l. If you want your plants to reach their maximum height, try your hand at a 20l container alongside the right genetics.

The vast majority of autoflowering strains are naturally small and compact compared to their photoperiod counterparts. However, they do range in size. Carefully check the data sheet of each strain you’re considering growing to make sure they fit your size preferences. Some will top out at just 60cm under the right conditions, whereas others have the potential to surge up to 150cm.

Certain training techniques will limit the height of your plant without negatively impacting yields. While topping can stress autos and stunt their growth, techniques such as **LST are perfectly suited to these strains. This method involves tying down the growing tips of plants, which creates a flat and uniform canopy. Some strains will top out at just 30–40cm when subjected to LST.

Light Exposure & Intensity

You’ll need to illuminate your plants as soon as their shoots emerge from the soil to avoid leggy, lanky, and generally weak plants. Outdoors, place your plants in the sunniest position you have available. Indoors, run your lights for at least 18 hours per day to ensure quick and healthy growth and to eliminate the risk of stretching. If you’re willing to make the investment, you can measure **PPFD to make sure your plants are receiving enough photosynthetically available radiation for optimal growth throughout the entire growing cycle.

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The RQS Blog

How Tall Do Autoflowering Weed Plants Get?

Autoflowering weed strains are favoured for their rapid growing time and compact size. But how tall should you expect your indoor and outdoor plants to get? A range of factors influence the height of autos, including genetics, container size, lighting, and more. Find out what you need to know about autoflower plant height!

19 Jun 2024

By Luke Sumpter

Contents:

How tall do autoflowers get?
How tall do autoflowering cannabis strains get?
How tall do autoflowers get indoors?
How tall do autoflowers get outdoors?
How pot size affects plant size
Factors that influence the height of autoflowering weed strains
Cultivation tips: how to manage plant height
Why autoflowers are perfect for tight spaces
F1 hybrids: the fastest among autos

How tall do autoflowers get?

We'll consider all autoflower strains from the RQS catalogue to give you a general idea. Indoors, these strains range from 40 cm for the most compact varieties to 160 cm outdoors. Although these plants can be considered tall, they are much more compact than their feminised counterparts. On average, RQS's autos grow to a height of 65–105 cm indoors and 85–125 cm outdoors. This includes a wide range of genetics, from more Sativa-dominant to more Indica-dominant strains, and encompasses all families, such as Kush, Gelato, and Haze.

While some plants may exceed these heights, it is uncommon. Under optimal conditions, your autoflower plants should generally stay within this range.

Besides, many factors influence the final height of these compact and stealthy strains. Genetics, container size, temperature, and lighting all play important roles. Dive deeper into these factors below and find out how to use them to determine the height of your autoflowering weed plants.

How tall do autoflowers get — Indoor vs Outdoor height

How Tall Do Autoflowering Cannabis Strains Get?

Autoflowering strains are among the most compact and stealthy genetics available. They maintain a small stature throughout the entire growing cycle, and race from seed to harvest faster than photoperiod cannabis varieties. But how tall can autoflowers get? While most varieties stay relatively small, factors including container size, genetics, location, light intensity, temperature, humidity, and other variables will determine the final stature of your autoflowering cannabis plants. You can then tweak these variables in order to grow the smallest and stealthiest plants possible, or to push your plants to their maximum height, resulting in large yields.

As mentioned above, autos typically max out at anywhere from 40cm all the way to 160cm in height. All autos will reach a height of 5–10cm and develop several sets of true leaves before transitioning from the seedling stage into the vegetative stage. During veg, autos typically grow at a rate of around 5cm every 24 hours when nutrient, water, and light demands are met.

Genetics plays perhaps the largest role in determining the final height of an autoflower strain. Generally, those with a sativa-dominant genetic profile will grow taller, whereas those with indica-dominant genetics will remain stout and bushy. Autos in the Sativa-dominant Haze family can grow to around 100–120 cm before switching to bloom, during which the flowering stretch can add another 40–60 cm. Those belonging to the indica-dominant Kush and Gelato families will peak around 80cm before moving into the flowering phase.

Here are the average sizes of RQS auto strains, categorized by family:

Gelato

Gelato autoflower strains are known for their robust growth and impressive resin production, with a predominance of Indica strains in the catalogue resulting in mid-size plants.

Indoor Height: 75–115 cm
Outdoor Height: 90–130 cm

Haze

Haze autoflowers are renowned for their Sativa-dominant characteristics, resulting in taller plants.

Indoor Height: 75–115 cm
Outdoor Height: 110–150 cm

Cookies

Autoflowering Cookies strains are known for their dense buds and strong aroma, exhibiting a slight Indica dominance that results in plants of medium size.

Indoor Height: 75–115 cm
Outdoor Height: 85–125 cm

Kush

Kush autoflower strains exhibit Indica-dominant traits, producing compact and bushy plants.

Indoor Height: 65–105 cm
Outdoor Height: 90–130 cm

Afghan

Afghan autoflowers are known for their resilience and hardiness, resulting in robust plants with a shorter stature, making them the most compact of the RQS catalogue.

Indoor Height: 55–95 cm
Outdoor Height: 65–105 cm

Now, differentiating between broader categories:

Indica

Indica-dominant autoflowers generally grow shorter, with maximum heights of 120 cm indoors and 130 cm outdoors, making them ideal for compact spaces. They are renowned for their dense buds and robust structure.

Indoor Height: 70–120 cm
Outdoor Height: 90–130 cm

Sativa

Sativa-dominant autoflowers are taller and more slender, with indoor plants reaching heights of up to 120 cm and outdoor plants growing as tall as 150 cm. Due to their larger flowering stretch, they can surprise even the most experienced grower if not closely monitored.

Indoor Height: 80–120 cm
Outdoor Height: 110–150 cm

How Tall Do Autoflowers Get Indoors?

In most cases, growing indoors means cultivators have less space to play around with. Moreover, by growing in small pots, the roots of the plants are restricted. However, autos are naturally small and will reach their maximum height even in somewhat modestly sized containers. Untrained, you can expect autoflowering seeds such as Royal Runtz Auto to grow to 70–100cm indoors, Royal Haze Auto to 65–85cm, and Diesel Auto to 40–70cm.

How Tall Do Autoflowers Get Outdoors?

All cannabis strains typically grow taller outdoors. Gardens often provide more space, allowing growers to use big containers, and the power of the sun helps to push growth to the max. If you don’t want to grow in containers, consider transplanting into raised beds or directly into the ground to give the root system much more room to spread. These factors can result in some autos reaching upwards of 150cm. To provide some examples, Cookies Gelato Auto grows to 140cm outdoors and Granddaddy Purple Auto peaks at 120cm.

How Pot Size Affects Plant Size

As previously addressed, pot size plays an important role in controlling the size of autoflowering cannabis plants. The aerial parts of a plant will only grow in proportion to the size of the root system below the soil. Smaller containers limit the amount of room that plant roots can expand into, resulting in smaller plants overall. Many growers find that cultivating in an 11l pot produces easily manageable and healthy plants. If you want to maximise the size of an auto, consider a 20l container, or bigger.

Factors That Influence the Height of Autoflowering Weed Strains

Apart from pot size, several other important variables will impact how tall your autoflower cannabis plants get. Genetics certainly has a large influence, but lighting, planting density, and climate also dictate plant height. Let’s dive deeper into these influential factors below.

Genetics

Genetics partially dictates the vertical fate of your auto weed plants. Therefore, selecting the right strain from the get-go will help you control the height of your plants later down the line. Some auto strains are inclined to grow much larger, such as Cookies Gelato Auto, while others, such as Triple G Auto, will grow to just 60cm when managed correctly.

Lighting

Light helps plants build tissues; their cellulose structures are made from carbon, which they extract from the atmosphere with the help of light during photosynthesis. Not only does optimal lighting help to achieve bigger yields, but it’ll influence plant height. Those starved of light will grow tall and spindly as they desperately stretch to find a light source. Those grown in a sunny spot or with ample light indoors, on the other hand, will remain compact, healthy, and strong. If growing indoors, make sure to dial in your PAR levels.

Planting Density

Planting density refers to the number of plants per unit of growing area. Some trials indicate that growing cannabis plants closely together can trigger competition for light, leading plants to stretch dramatically taller. If you’re just growing one or two plants, however, aim for sufficient spacing of around 100cm in beds or containers outdoors. Indoors, growing single autos plants in separate 11l pots should provide ample space.

Temperature and Humidity

Both temperature and humidity can impact the height of autoflowering cannabis strains. Maintaining a temperature of around 25°C will spur optimal growth, helping your plants grow quicker. If temperatures drop too low, plants will become stunted. Meanwhile, humidity plays an important part when it comes to transpiration, helping plants to draw up nutrients from the soil, which facilitates growth. Aim for a humidity of 70%, 50–60%, and 40% during the seedling stage, vegetative stage, and flowering stage, respectively.

Cultivation Tips: How to Manage Plant Height

Now that you’re aware of the factors that influence the height of autoflowering strains both indoors and outdoors, it’s time to put that knowledge into practice. Check out some quick tips below to find out how to effectively manage the size of your autos.

Container Selection: As one of the most impactful variables affecting plant height, you need to think carefully about container size. If you’re aiming for particularly small and compact plants that will happily fit into a small grow tent or concealed area of your garden, opt for a pot size of no more than 11l. If you want your plants to reach their maximum height, try your hand at a 20l container alongside the right genetics.
Strain Selection: The vast majority of autoflowering strains are naturally small and compact compared to their photoperiod counterparts. However, they do range in size. Carefully check the data sheet of each strain you’re considering growing to make sure they fit your size preferences. Some will top out at just 60cm under the right conditions, whereas others have the potential to surge up to 150cm.
Training: Certain training techniques will limit the height of your plant without negatively impacting yields. While topping can stress autos and stunt their growth, techniques such as **LST are perfectly suited to these strains. This method involves tying down the growing tips of plants, which creates a flat and uniform canopy. Some strains will top out at just 30–40cm when subjected to LST.
Light Exposure & Intensity: You’ll need to illuminate your plants as soon as their shoots emerge from the soil to avoid leggy, lanky, and generally weak plants. Outdoors, place your plants in the sunniest position you have available. Indoors, run your lights for at least 18 hours per day to ensure quick and healthy growth and to eliminate the risk of stretching. If you’re willing to make the investment, you can measure **PPFD to make sure your plants are receiving enough photosynthetically available radiation for optimal growth throughout the entire growing cycle.

Why Autoflowers Are Perfect for Tight Spaces

Whether you only have room to set up a small grow tent or have nothing more than a balcony for a garden, autos will make your horticultural hobby exceptionally easier. Their inherent compactness makes them perfect for growing in small spaces, with modern hybrids still capable of producing fruitful yields with plenty of THC and tasty terpenes. Throw correct strain selection, container size, and lighting into the mix, and you'll end up with a compact and stealthy plant that meets all of your growing preferences.

Trainwreck Auto

	Trainwreck x Big Skunk Auto
	450 - 500 gr/m2
	80 - 130 cm
	8 - 10 weeks
	THC: 19%

	Sativa 80% Indica 15% Ruderalis 5%
	90 - 175 gr/plant
	130 - 160 cm
	12 - 13 after sprouting
	Clear, Motivating , Uplifting

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F1 Hybrids: The Fastest Among Autos

Autoflowering cannabis has come a long way over the years. Once known for their poor yields and low THC content, modern autoflowers have solved both of these issues. However, breeders here at Royal Queen Seeds have taken things a step further by creating the world’s first autoflowering F1 hybrids. The result of crossing highly pure inbred parent lines, auto F1 hybrids boast superior yields, higher levels of THC, better uniformity, and increased resistance to pests and disease. On top of this, these varieties are especially compact, often peaking at just 50–70cm without training.