Нет не о розах, о всех цветах:)
Вот цитата
For many years, it was believed that only an uneven number of flowers was acceptable. This tradition comes from France. At one time, people wanted to prove that their flowers had not been bought from the market. While markets always offered flowers in even numbers, shops sold them in odd numbers.
Вот тут по разным странам
https://myglobalflowers.com/blog/lifestyle/traditions-of-flower-gifting-in-different-cultures