Hana no Mizo Shiru

An ongoing Boys Love manga created by Takarai Rihito (artist of Seven Days and The Sleepy Residents of Birdcage Manor), serialized in Craft magazine. In 2011 it was licensed by DMG under the name Only The Flower Knows.

Arikawa has an unexpected encounter with a student from his university, Misaki; he gives him a hand when he trips, carrying a bunch of potted plants. Shortly afterwards, he bumps into him again at the train station, and accidentally picks up his necklace, which seems to have sentimental value... Then he starts having recurring romantic dreams about him, although he doesn't actually remember him, since he didn't have his glasses on at the time.

The two end up working together doing agricultural research in the labs, under Professor Tsujimura, and gradually become friends. There's potential for more, but there are also some obstacles to romance (namely the fact Arikawa already has a girlfriend; the fact Misaki alternates between acting shy and cold/distant towards Arikawa; and a mysterious man who won't stop calling Misaki's phone, and seems to have some sort of history with him...).

Tropes used in Hana no Mizo Shiru include:

Big Damn Kiss: Full-page and lovingly-drawn in Chapter 4. In a field of flowers.
Bishonen
Blind Without'Em: Arikawa, hence why he doesn't recognize Misaki after encountering him outside and at the train station. His vision is a blur.
Boys Love
Cannot Spit It Out: Both boys about their feelings for each-other, but only up until Chapter 9.
Conveniently an Orphan: Misaki, who also loses his grandfather - which is what allows for his relationship with Kawabata, spurring a lot of the story.
Crazy Jealous Guy: Kawabata acts this way towards Misaki (over both Arikawa, and all his university acquaintances, apparently). As far as the trope goes, though, he's a pretty tame example...
Cry Cute: Misaki, whose tears over his grandfather's death prompt Kawabata to kiss him. Arikawa, too, thinks about how his teary face is adorable.
Cute Clumsy Boy: Misaki, a rare male example.
Dream Sequence: Arikawa's dreams about Misaki, in which he's "always lovingly touching and kissing" him.
- Homoerotic Dream
Even the Guys Want Him: Misaki. In addition to Arikawa and Kawabata, there's a rumor around the university that he catches men's attention with his feminine looks, and was sexually harassed by a male upperclassman.
Gayngst: Misaki frequently has this, wondering why he was born a man, since he can't seem to stop himself from falling for other men (men with girlfriends, too, to add insult to injury). Kawabata, surprisingly, seems to have this too, as it's implied that he only got a girlfriend because that's what society expects of him. In Chapter 11 he cancels their wedding preparations, however, saying he can "think for himself" now.
Flower Motifs: Obviously, given the title. There's talk about botany and floriography, flower imagery throughout the manga and in a lot of the Chapter pictures, Misaki's flower necklace...
It Was a Gift: Misaki's flower necklace, from Kawabata, to remind him that he isn't alone.
Jerkass / Bespectacled Bastard Boyfriend: Kawabata, although Chapter 11 attempts to humanize him some.
Love Confession: Arikawa to Misaki in Chapter 9, prompting a Relationship Upgrade.
Love Triangle: Subverted a couple of times. Arikawa starts out the story with a girlfriend, and kisses Misaki while they're still together, but they break up before it can go much further than that (and he only half-consciously kissed him, anyway). Then Kawabata enters the picture, who Arikawa assumes is Misaki's lover, but Misaki turns out to have moved on from him already.
Luminescent Blush / Crush Blush: Misaki, very frequently.
Raised by Grandparents: Subverted. Misaki moves in with his grandfather after his parents die in an accident, but then he dies, too, leaving him solely in Kawabata's care...
Red Oni, Blue Oni: Arikawa is extroverted, cheerful and completely open about his feelings (to the point where it creeps people out). Misaki is introverted, quiet and an enigma to his classmates.
Sexy Mentor: Kawabata to Misaki.
Ship Tease
Shrinking Violet: Misaki increasingly comes across this way, as he seems less cold and distant and more shy (and is also quiet and seemingly friendless). From Chapter 8 onwards he's shown to be more insecure.
Tsundere: Misaki initially comes across this way, since he's cold and suspicious towards Arikawa after he embarrasses him in public (by talking loudly about how much he loves Misaki in his dreams!), but gradually warms up to him over time, and gets easily flustered in his presence.
Uke / Seme: Misaki/Arikawa and Misaki/Kawabata both fit the archetypes, though not rigidly.
Visible Sigh: Used both when the characters actually sigh, and to show heavy breathing - particularly during, uh, Chapter 10...
Will They or Won't They?: Subverted. The main characters' relationship is teased at, but not dragged out. They do, in Chapter 9.