Like Namvet said a trash bag is not necessary. Be careful when using certain organics however like blood or bone meal, as that could attract animals. When I did my outdoor grow I stopped by home depot and picked out some plastic netting for pretty cheap, found some sticks in the woods to put in the ground and put my netting around that. My reasoning is that if an animal like a deer, elk, moose or even a bear want to get to your plants for any reason, you're not going to stop them. The netting might make them question it and leave it, but that's all I wanted to achieve. This year I will not be doing that however, it stands out more.