I'd say it's nature-flavored restoration magic. Since restoration deals with healing and "life force" it seems plausible that magic that makes plants grow is part of the restoration school.
It could be argued that it is alteration if existing plants are reshaped and given new properties and such. So it could be a mix of both.
Do note that the schools of magic haven't been established yet in ESO's time if that is in any way relevant to the reason behind you asking that question. At the end of the day they are just made-up to better categorise magic.
dragonflame wrote: »Yea, that why I asked I didn't know that the schools hasn't been established yet
At the end of the day they are just made-up to better categorise magic.