If there is a white 'flower pot' icon in the garden, this means that you can plant the flowers in this very area.
Force click on the 'flower pot' icon, and you will see the list of flowers you can plant.
Choose the one you prefer the most, click on ✅ and see how the flower looks in the garden 😉

📌 NOTE:  If you change the choice of flowers and press ✅, the previous flowers will be replaced by a newly selected one and cannot be retrieved.