If you can attach it also to the raised bed that will definitely increase the strength, though I would also go ahead and burry it a few feet if possible. If you could do both, attach it to the bed, and burry it 3ft, I think it would be sturdy enough to trellis what you need.

I buried it 2 feet deep and attached it to my raised bed. I (~230 lbs) was able to hang from it without any deflection. I guess the only worry about it would be to have more weight on one side than the other... I guess its just an experimenting year, and I will hope for the best!