Yes you can :) When you "edit" your grow weed you can choose for it to be vegetation or flowering ! You can do it 2 ways you can click on your profile then select the diary you want to edit and click edit week and fix your mistake or you can click on the plus symbol at the top right of the screen and do it just as tho you were on your profile select the diary you want to edit and click the edit button and fix what you need to fix :)
-Happy Growing!