I became interested in the above post about Berlin Tierpark. Many zoos have lush gardening and tending all the plant life in general spaces and in animal exhibits probably takes lots of time and money. Gardening, at the same time, is a rather routine task and zoo people are not the best in it. Do zoos search or use donations of gardening centers and companies? Plants, work, maintaining or even designing and executing whole parts of the zoo? Are volunteers sought specifically for gardening?
Most zoos won't say no to free labor if people are willing- while I don't know how much zoos seek volunteers specifically for gardening, I have seen zoos using one-time volunteers for gardening and/or other ground-keeping around the site.
Good question. We outsource a lot of our day to day gardening stuff, things like mowing and general upkeep. We do have a good size in-house Horticulture team though that does a lot for us. I believe we also have several volunteers to help with the plants on the grounds, and in our halls.