USA, UK are among the reputable countries which are good for MSc Horticulture. Here are few basic requirements for further procedure -

1.) One should have a good academic background.

2.) One should have experience of internships and different short courses to provide you a edge over others.

3.) IELTS or TOFL are compulsory exams in order to secure a seat in foreign countries and one should have good scores in these exams.

4.)  Search for colleges relevant according to you and go to their websites and take a note of when their admissions starts.

Thank you.