If you're looking for manga similar to GREEN - I Wish to be a Farmer’s Wife, you might like these titles. All recommendations are made by Anime-Planet users like you!
Kuze Shunpei, a high-school student, is on spring break going to Hokkaidou when he loses his wallet. Stranded in the mountains with no money and his motorcycle having run out of gas, he passes out in the snow on the side of the road. When he wakes up he finds that he's been saved and brought to the Watarai farm, a horse ranch that breeds race horses. There he meets a host of various people, ranging from stable hands to the owner and his family (which includes four daughters). Shunpei is completely unsuited for the farm life, and his city upbringing contrasts sharply with the hard labor required to help the farm out. Yet despite all this, he tries his best to become accepted.
In both series a city person comes to countryside and gets involved with farming. Main characters in both series represent their respective target audiences (teenage guy in Ja Ja Uma Grooming UP! and woman in her early 20'ties in GREEN). Both series feature a fair amount of comedy and some romance. Speaking of which, GREEN has inversed proportion of romance and farming in compare to Ja Ja Uma Grooming UP!
Anyway, if you liked the themes I mentioned earlier interesting, then both of those manga should prove satisfying.