Natsu, Kimi ga Saku.

From Storm in Heaven:

1)You Blossom in the Summer
Shinobu grew up in a town so small that he didn't even have any classmates in elementary school. Without any friends his age, he spent his time learning about flowers with a local horticulture expert. Now that he's moved away to a city, he still sticks to himself, since he never really learned how to make friends. That is, with the exception of Yukihito, who came up to him one day and became his friend. The trouble is, now Yukihito means the world to Shinobu, and he doesn't know what to do about it.

2)The Language of Flowers

3)The Insightful Florists

4)Strawberry Concerto

5)Cafeteria Love

6)Thermidor Fireworks