A Guide to Growing Auto-Flowering Cannabis Outdoors in 2025

Auto-flowering cannabis plants are different from traditional photoperiods because, as their name states, they will flower automatically! There are many benefits to working with autos, especially when it comes to growing an outdoor crop, maintaining a low-profile garden, and the opportunity to harvest continuously throughout the year. 

In this article, I explain all you need to know about auto-flowering genetics when growing them outdoors, the benefits associated, and what to expect when planting autos outdoors in 2025.

What are auto-flowering genetics?

Royal Queen Seeds states that the term “auto-flowering” originates from the fact that these varieties don’t rely on light signals to initiate flowering, unlike photoperiod varieties. Instead, it happens automatically after a few weeks into the vegetative process.

Photoperiods will begin to transition to flowering once the daylight hours approach 12 to 14 hours of sunlight. Autos, on the other hand, will have a short vegetative state, typically lasting 28-35 days, depending on the variety. Auto-flowering cannabis plants will then begin flowering regardless of the time of year, resulting in a seed-to-harvest time of usually around 11-12 weeks. 

The Benefits of Growing Autos Outdoors

• Auto-flowering cannabis plants are short to medium-sized plants.
• They will grow to a final height of 90-120 cm.
• Autos can be planted year-round and will not be dependent on the 12/12 cycle.
• Autos are tough and resilient plants ideal for all types of weather.
• Growers can achieve a perpetual harvest with autos when planted outdoors.
• The buds an auto produces are often top quality in terms of resin and terpenes. 
• Autos can be planted on a roof terrace, garden, patio, or sunny balcony.

How Much Light Do Autos Need When Growing Outdoors?

Indoors, being able to bloom under 20-24 hours of daylight already offers a tremendous advantage to the most vigorous auto genetics, according to Dutch Passion. However, outdoor autos will only receive 14-15 hours of sunlight, so planting during the Summer months will produce the largest and best plants, as well as the highest yields. Autos can still be planted, and flowers require 9-12 hours of light; however, this may result in low-quality yields and short plants.

The Best Nutrients to Use for Autos

When it comes to feeding autos, for the first 4 weeks of vegetative growth, you should feed them with a vegetative nutrient as you would use for photoperiod genetics. This means a nutrient that is higher in Nitrogen with a lower ratio of Phosphorus and Potassium. During the first four weeks, autos will focus only on producing a prolific root base and growing the stem, leaves, and side branches.

Once an auto-flowering cannabis plant passes day 28 and begins to transition to flowering, you should feed it a mixture of vegetation and flowering nutrients to aid in the transition process. By day 35, a flowering nutrient that is higher in Phosphorus and Potassium is optimal and will kick start the blooming phase. This is the time when female auto-flowering cannabis plants produce bright white pistils that will develop into calyx and bracts and, later on, dense buds.

The Best Growing Medium for Autos

When deciding the best-growing medium for your autos, consider the importance of a medium that has plenty of air pockets inside, does not become too heavy when saturated, and contains the right balance of primary and secondary nutrients and trace elements. Many growers enjoy using soil mixes or creating their super soil by adding perlite and vermiculite. Adding 30% coco coir to the soil will help boost root development and create an air-rich environment for the roots to grow. 

Do Auto-Flowering Cannabis Plants Stretch When Flowering?

M.S.N.L advises that some auto-flowering strains are naturally stretchier than others. Sativas tend to grow taller and stretch more, while indica plants stay shorter and bushier. Autoflower genetics are a mix of both, but you’ll still notice some variations. You will not need to worry about auto-stretching and growing as tall as photoperiods, as most autos typically reach a height of around 120 cm in the most extreme cases.

Potential Problems That May Occur When Growing Autos

Autos that are grown in small pots (2 gallons or less) will not have the opportunity to develop an extensive root base. They will be reflected in a short-sized plant, typically around 50-60 cm tall. As a result, yields will be minimal, and a grower may expect to harvest 10-15 grams of dry buds.

Auto-flowering cannabis plants that do not receive a high amount of intense sunlight during the first 4-5 weeks will also become small and less productive. All you need to remember with autos is to give them the best start in life, especially when it comes to P.A.R levels.

Applying plant training techniques to autos can be problematic. There is a set time frame for when you should use training to allow the plants to recover and bounce back fully, due to their short life cycle.  Ideally, all plant training should be done from weeks 3-4; however, using the low-stress technique and defoliation will be the most viable option without inducing high levels of stress before the transition stage begins.

Repotting autos can promote stunted growth, so it is best to start auto-flowering seeds in a large pot (3 gallons or larger). Allowing the roots to grow freely without becoming agitated or disturbed will produce the best results, and plants between 100 – 120 cm tall.

My Final Thoughts on Growing Autos Outside

Growing autos outdoors in 2025 can be an excellent way to produce a crop with a short turnaround time of only 11-12 weeks from seed to harvest. As a beginner grower, you can learn a great deal about how cannabis plants grow, especially if you have a photoperiod plant nearby. Growers living in a hot and sunny climate can plant autos outside from May until the middle of October, achieving fantastic results and a perpetual harvest. 

Feature photo: Amaretto Tarmac Auto is ready to harvest from Seed Stockers. Photo credit: Seed stockers.