7 Reasons Why Your Autoflower Cannabis Grew to a Small Height

01. 03. 2026

In our previous article, we discussed the average flowering time for autoflowering cannabis seeds. We will continue with this seed type, but this time we'll focus on the issue of size. Have you grown autoflowering cannabis that doesn't match the expected size? We'll tell you what are the main reasons for stunted growth.

Average Height of Autoflowering Cannabis Varieties

Just like autoflowering cannabis varieties have their average flowering time, they also have a typical height they usually grow to. This is typically a 50 to 100 centimeter height. The final height also depends on conditions and genetics. Sativa genetics are generally slightly taller than indica genetics. Simultaneously, sativa genetics mature slightly later than indica. The maximum height you can expect from autoflowering varieties is 1.75m.

There are several reasons why your autoflowering cannabis is short

Main Reasons Why Your Autoflowering Cannabis is Small

1.) Short Growth Phenotype

Every cannabis seed carries encoded information that influences its further growth. It's possible that small plant size might not solely be the result of insufficient optimal conditions. Sometimes it's simply a phenotype that grows to such a small height. Despite this, it can still produce solid buds and appreciable yields.

2.) Cannabis Lacks Root Space

Insufficient height can be caused by a small space where the autoflowering cannabis grows. Such a confined space means the plant is restricted by its roots. These can become tangled and reduce nutrient flow to the plant. Avoid this problem by using a 15-20 liter pot.

3.) Incorrect Conditions During Seed Germination

Seed germination is the first step where the plant begins to show growth elements. Be particularly careful that the soil is not too humid. In such conditions, the cannabis root cannot grow quickly and may even die completely. A hygrometer will help you precisely monitor soil moisture.

4.) Lack or Excess of Nutrients

Many growers want to provide maximum nutrients, which can result in unnecessary nutrient excess. This can burn the root system, which cannot handle excessive nutrient amounts. Double nutrient doses are dangerous as they can stop growth and shock the cannabis plant.

5.) Lack of Light

Correctly set light conditions are crucial for cannabis growth. Without proper lighting, it's impossible to grow taller autoflowering cannabis. For a typical 1.2m x 1.2m indoor growing space, we recommend 600W HPS diodes or LED lights (400-600W). We definitely do not recommend lower-performance lights as they won't produce enough light for your cannabis to grow.

6.) Incorrect Soil Type

Think you can't go wrong with soil? You can, if you choose an unsuitable soil type for cannabis. Select soil that is only slightly mixed and doesn't have too high a nutrient content. Adding coconut fiber is a good tip to aerate your soil.

7.) Incorrect pH and Insufficient Control

If you grow hydroponically or in coconut fibers, pH value must be strictly controlled. The optimal pH in these cases is 5.8. What happens if you don't maintain the ideal pH? Cannabis roots simply stop absorbing nutrients, which later impacts plant height.

These are the most common reasons why your autoflowering cannabis isn't growing to sufficient height. Prevention is always better than late problem-solving. Don't forget to check our seed selection, including autoflowering, feminized, and regular seeds. Start growing - that's how you'll gain the most experience.