Does the botanical garden in Cologne look more beautiful in March or April?

I'm asking about the flowering times of the plants in this garden. Spring begins in March, and the flowers can already be seen at that time. I'm not familiar with the flowering times of plants. Can I go to the Botanical Garden in Cologne in March, or should I wait until April because it should look even more beautiful then?

I was in the Botanical Garden once four years ago in April. The flowers were already in full bloom.