Why "na wiosnę" is used instead of "w wiośnie"?
As I know, unlike other seasons, "wiosna"(spring) is used with "na".
What is the reason of using "na" with "wiosna"?

Question

Why "na wiosnę" is used instead of "w wiośnie"?
As I know, unlike other seasons, "wiosna"(spring)  is used with "na".
What is the reason of using "na" with "wiosna"?

Answer

I don't know the reason, I believe it's like Amelia said - no reason but it's not the truth that's it's unlike other seasons because the same thing we have with autumn/fall. We say: "na jesień", not "w jesień". Or: "jesienią"

Answer

We use "wiosną"/"na wiosnę"/"podczas wiosny" . "Wiośnie" is other grammatical case (Dative/Locative). We don't know the reason. :)