The size of  these autoflowering cannabis plants is directly related to the post size, light intensity, spectrum and cycle, fertilizer, growing medium(soil) , training(topping, LST-low stress training, SCROG-screen of green), PH level, watering and other stresses like transplanting, temperature changes, bug problems, diseases and even humidity levels.

The typical auto-flower plant size is from 7 to 20 inches (17cm to 50cm) but it may be smaller if the conditions are harsh or exactly the opposite if they are perfect.

Basically all of these previously mentioned conditions can affect the plant size but some may affect it more than others and there are also those SUPER autoflowers that grow huge so be careful what strain you get!

Here are the most common environmental factors that can influence your plants size the most:

Pot size

Pot size is very important aspect for your autoflowering plants size and if the pot is too small then your plant will become root bound and it will stun the growth. For regular plants the rule of thumb is to get a gallon (3,7 liters) of dirt per foot (30,4 cm) of the plant height. That means if you are planning to grow your plant 60 centimeters then you need at least a 7 liter pot. In general you can grow your autoflower plant to its fullest potential in 1 to 3 gallon (3,7 to 11.1liter) pots but be sure to read more about pot sizes before getting the right one.


Light is the plants elixir of life and cannabis loves the intense natural summer sunlight, but if you are growing indoors you have to replicate the Suns light artificially and that can be a problem. Autoflowering cannabis size is affected very tremendously by the light you have and how close or far it is from your plant. If the light is too far away your green friends will stretch and will become weak so they won’t be able to produce dense buds. But if the light is too close your cannabis plant can get heat burns that will stunt the growth and it could either become a dwarf plant or just wont be able to give you the yield you are expecting.

The light cycle also affects these day neutral plants and if the majority of the day it is dark in the growing room then your plants will also stretch and won’t be able to produce dense and huge buds, but if they get the proper amount of light (18 to 24 hours a day) then they will grow like real weeds and you will be able too see height changes every single day!

Fertilizer and nutrients

Autoflower plant size can also be affected by the amount of fertilizer – if the amount of nutrients is too small then your plant will struggle to grow and will show nutrient deficiency symptoms but if the fertilizer concentration is too high autoflowers will also struggle to absorb other elements and will become a small sick plant that shows signs of nutrient toxicity. If you manage to get the right nutrients concentration then your plants will grow strong and can produce up to 3 ounces (85 grams) of dried bud, but know that the harvest can be even more larger if you grow Super autoflower strains or use some advanced growing methods like hydroponics or CO2 enrichment.

The nutrients or if I am precise the elements that are found in the fertilizer are your plants food and it can’t grow without them, but too much of them can kill your precious plants so check out the nutrient post for more information!


Auto-flower plants have a very short life cycle and any stress can greatly affect them. Topping autoflowering plants is completely useless, because the plant needs recovery time but the short life cycle will not allow it to fully recover and that will dramatically reduce the plants size and end yield. Even LST and SCROG are not that recommended because they can stress your plants if you do it wrong but with proper knowledge on training methods you can train them to any size you want.


Even transplanting your ruderalis plant can reduce its size and it is better to plant them in one container and let it grow untouched. But if you really need to move it to a different growing container you need to get the best tips for transplanting autoflower plants and even then there can be some stress and lost yield as well as reduced size.

After examining all these things that affect autoflower plant size we can see that they are very delicate and do not like to be stressed in any way and even the smallest stress can reduce the plants height so be careful and always be prepared to nurture your autos at any given time.


  1. I’m growing a blueberry strain of the ruderalis and they re very accepting to being tied over as opposed to them being topped and if you let them revegitate through the year you can have a five foot indica looking ruderalis than a twenty inch stick with a bud on it they are great plants I’ve been growing them for two years now

    • Becky Herring on

      Hi Jimbob! I’m a rookie, and growing my first auto-flower. You said in your post you can revegitate these plants? I didn’t think you could do that. Could you give me some instructions on “revegitating” my auto-flower? Thanks!

  2. terry mckibbins on

    My 4 week old bubblicious is 25 inches and growing 2 in. a day under a 250w cfl grow light 19/5 in a 5 gal.cloth pot, the light is giant and I keep it 3 inches above the plant, it has over 30 branch’s on a thick main stalk I feed it 1/4 teaspoon of 0-50-30 fert. in a gal of water weekly and a quart of water every other day, I boil tap water for 10 min. then let it sit in a big open bowl for 3 day’s this is my first grow is this normal growth or is she a beast? thank you

  3. I was wondering about pruning autoflowering plants. This is my first indoor grow, and my first autoflower grow. I Have grown regular feminized (not autoflowering) seeds outdoors before, and i’ve had to remove some of the larger shade leaves, so that the buds would get more light. Should i be doing the same thing with an indoor autoflowering plant? My friend says no. But i think yes, because they are so damn bushy. Your advice is appreciated.

    • My opinion is that by cutting off leafs you are damaging the plant and reducing its energy consumption so in general I avoid pruning. But if the plants gets too bushy or the lower fan leafs don’t get enough light they can wilt and that can introduce mold and fungus so in this case it is necessary to prune.

  4. Probably a strange question Harvested one of my Lemon autos and the sun of a gun continued sprouting new shoots put it back under lights and its growing again never heard this before is it possible or did I just get lucky or am I wasting my time ???

    • I have also seen something similar on an autoflower plant. How did the plant grow? Did it produce more flowers and how much yield you got from it?

  5. Hello I’ve been growing an auto flower Northern Lights ouside for about 8 weeks now. The flowers have appreared very quickly and now there are brown threads coming out of the flowers. Does that mean it’s time to harvest ? The plant is only 12 inches tall. Is that possible ?

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