All species proposed for planting in exhibits must first be approved by the veterinarian to make sure none are toxic. The species and quantities of vegetation chosen can have a great deal to do with the degree of success. Certain cats seem to especially enjoy destroying certain species of plants. This can be employed to your advantage by using these species to distract the tigers from the plants you want to establish. Dead trees and other dead vegetation can be left in the exhibits as natural looking furniture, barriers to protect other living plants, and to be used and abused by the residents.
Weeds can be a gardener's best friend.
There are some plants that just cannot be killed. Care needs to be taken not to let them get out of hand and strangle other plants, and so they need to be somewhat contained. There is also a problem with exhibits looking too similar if these plants are used too much. Vegetation planted outside the enclosure and allowed to grow into it can have beneficial effects such as shade, visual barriers for the cats, and perceptually breaking up cement walls. There is a lot more flexibility in the selection of species used in these areas and the plants have a much better survival rate.