How about Longwood Gardens? And the much bally-hooed Arnold Arboretum? I hear Arnold like to think they're pretty good (ahem).

Do a google search for horticulture employment and browse the listing. There should be a link in the top few results that has a number of jobs and internships listings.
If you need help, let me know.

What school are you going to? Most I know of have a rather extensive collection of internship programs available to their students.

It is my recollection that everybody wanted to see the letters after my name until I get them. After I got letters nobody cared, they were only interested in experience.

It is my recollection that experience is more difficult to get than letters behind the name. So were I doing it, I would go for the internship and then figure out some way to finance the degrees.

Will the military still pay for the education? That is how I got mine. Scholarships are such a bother.