I have a covered deck and I find alot of flies fly around in the centre of it and they are annoying, especially since we like to entertain there. Are there any outdoor plants that I could plant in a container on the deck that would ward off flies?

There are no plants we are aware of that ward off flies. Some plants are attractants, such as the Venus Fly Trap, but the number of flies controlled would be small. The use of fly strips or fly traps is recommended.