My plants are so small after a Month!

I have been growing 3 Auto Flowering plants outdoor for a Month now and the tallest one is 4 inches and the others are a little bit below 4 inches.
I water them every two to three days.
They get the maximum amount of sunlight per day and i'm very curious as to why they are so small compared to others i have seen on the internet.

Here is a picture of all 3

I'm a little noob-noob, but I'd say the size of your pots & amount of medium.

Odds are your medium wasnt right for em...too wet, too packed, too much nutes.