21 days old auto started flowering. Why?

Very common for an autoflower to start flowering in 3 weeks. Looks great so far.

Everyone pretty much nailed it there. Autos can be quite unpredictable.

Some autos start to show sex early and still kind of freezes in vegetative stage while grows bigger. Some has midget gene inside. Some are just mismatch of environment or growers mistakes. I have now 3 Mimosas running , one is midget and will be harvested next week. Other two will need 4-5 weeks extra, but will beat that small ounce type plant like 5 times or so in weight... Even with photos you can have some slower developing or influenced badly girls. No stress, just prepare a small chair for her ;)

Lol thanks man. Yeah autos have their place but I rarely run em.. for a variety of reasons .

Autos are finicky sometimes, depending on the breeder and the strain, consistency among the pheno types can be drastic. But one thing I've noticed about some autos is, as soon as the roots touch the sides or bottom of the pot, they start too flower. This isn't Always true, but has been true more times than not for me. Sometimes things like this such. But every grow has a new Lear I ng experience for us. Good Luck 🤘

Ezzjaybruh, I guess so.. I know photos are more stable but this time I needed faster harvest so I took autos.. and I think this one will be the first, which will give me total 5 grams of supply :D Love your doggo btw 💚