Answer: If the fan on your air conditioner is on top, you won't have to worry about hot air being blown onto your plants; if it vents out the side or front, you may have difficulty finding plants able to withstand the blasts of hot air. A two-foot space seems minimal to me; if you impede air flow, your AC unit will work harder, which will cost you more in energy bills. Three feet should be a minimum when planting anything to hide the unit. If it vents out the top, your trellis idea is a good one, providing you keep it at least 3' away from the unit. If the unit vents out the sides or front, I don't think there are any plants that would endure the blasts of hot air. In this case, I'd build a pony wall at least 4' away from the unit, and plant in front of the wall.
Good luck with your project.
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