The story start with a boy bringing flowers to school and it is mentioned that the flowers in his Garden grows faster than anyone else. when he go home, he find a guy in a back yard. Eventually he travels to the other desolate world with the man.

In this other world. There is no blue sky and he along with a group of people make their way towards the capital. Along the way, he finds seeds and makes plants grow, bringing back the greenery and fight against abyss(?) Monsters (not sure about the name) that live in the desert (as there is currently no greenery)

I believe the only women known as "saotome" (name could be incorrectly spelled) can make plants grow as this guy could. Turns out his mother was a saotome and the prince in the capital was his twin. Saotome are Born from trees, a closely guarded secret by one clan (before they were exterminated).

The the plants in this world is interested because there are seeds for "wall" or "barriers" or "bridge" or "well" the plant would grow into the shape of the item.

There's a lot of other plot items such as beasts that are given life with blood and rock, a guy who was blinded because he was born of a family that should have only given birth to girls (I think this is related to the clan with saotome)

I would be grateful if anyone can identify the name of this manga as I would like to re-read it