In my latest Web wanderings I ran across this (paying) internship program with the American Horticultural Society. It's open to "any college-level student of journalism, English, horticulture or related fields, and to adults with relevant experience who are making a career change or seeking additional training."
Interns work with the staff of The American Gardener magazine, gaining experience "in all facets of the editorial and production processes for a national, four-color magazine. Primary duties include researching and writing short articles, proofreading and fact-checking, and coordinating author and photographer submissions."
Internships run for 3-6 months in spring, summer and fall. "Internas are paid $9.00 per hour and work a 37.5 hour week." Application deadlines are November 1 for winter/spring; March 1 for summer; and August 1 for fall.
For more information and application materials, click here.