Well, mine has the bumper with the ball mount, and it's got a what appears to be a factory frame hitch/receiver under it. I *believe* it's the factory tow package, I haven't run the VIN to find out exactly what it came with.
I'd go for a frame hitch - a class 3 is not that expensive and they should be predrilled for reasonably easy installation. This will also let you tow stuff bigger than your landscaping trailer if you ever need to. I believe the only F-150's that are not certified for a full class 3 (500/5000) are the 4.2 and 4.6 with the 5 speed manual M5OD, those are good to 350/3500.