Forgive me if this appears twice! Somehow the first one evaporated.
Anyway the best thing I did was to join Garden Writers Association. It is not cheap and the meetings are reasonably priced until you count the getting there and staying! BUT... the networking is invaluable. You cannot beat getting to meet the editors face to face and getting a feel for what they want. Or plant people from university research places that are a great resource for articles.
However, even with such networking, it still comes down to finding the right angle and article to reach an editor at the right time - networking can only get you introductions, not outright work!
Which ever way you choose, network locally with freelance writers, and garden writers and enjoy what you do - we are gardeners first and writers second! Good luck!

Here is a link that might be useful: Garden Writer's Association

Some of us are writers first and gardeners second, but I'm quibbling.

This reminds me of the two books I just bought on songwriting: Idiots Guide To Songwriting and Songwriting for Dummies. When I got through reading them I was truly thankful that I had written my songs BEFORE I read those books, otherwise I might have been so intimidated and confused that they would have never been written. That's my way of saying to just go ahead and do it (write the articles) then shop them around to the editors of gardening books that you see on the newsstand or bookstores. About the Garden Writers Association, If I was forced to reduce my membership in gardening organizations to just one - GWA would be the one I would keep. It means a lot to me to read their newsletter, go to their symposia, visit out-of-this-world gardens and meet the greatest garden people on the face of this earth.

I echo KatyCopsey and Eddie - Join Garden Writers and come to the meeting this September! You are fortunate - you'll be able to drive from where you live. You'll connect with editors and other writers. The GWA has an on-line directory of publishers (book AND magazines) that you can download as a member. Contact names and addresses. See you in Canada in September?

I've had good luck in other magazine genre with finding writer's guidelines online. Often I have to do a site search to find them, but what a treasure trove when you do. Just go to the magazine's site and explore. Don't be afraid to pick up the phone and ask which editor to send submissions to.

Good Luck!

Happy

You're welcome to email me for the guidelines for the online magazine I edit. My email address is linked in my profile.

Thank you all for the fine advice about garden writing. Jerry