Do lemon slices need to be treated before using them in a vase?

Yes, lemon slices should be treated before using them in a vase to prevent bacterial growth that can harm the flowers. You can soak the slices in a mixture of water and lemon juice or vinegar for a short period, then rinse them before placing them in the vase. Additionally, it's advisable to change the water regularly to keep both the lemons and flowers fresh.