There is a full set of instructions for this in the watering box when you hover your mouse over a fully grown Bamboo plant in your own garden. I don't know whether people don't know that's there, or if they don't understand the instructions when they read them, but since it's clear that so many people seem to be having problems with this, I thought it might be useful to have a step-by-step set of instructions.
1. You must have a fully grown Bamboo plant in your garden.
2. You must also have an empty plate. Make sure that the plate is completely cleared, not just empty, otherwise the bamboo food has nowhere to go.
3. To get the bamboo food onto the empty plate, you need to spot black and white wildlife in other gardens (for example, Panda, Badger, Skunk, Raccoon, Penguin, Magpie, etc). The garden you spot the wildlife in must also have a fully grown bamboo.
4. If you spot a Panda but the bamboo has become RTH since the Panda was programmed in, you will get the Panda but not the bamboo.
5. Pandas give double organic food (10 feedings). Any other black and white wildlife gives organic (five feedings).
Courtesy of Tracey And Cobweb
https://www.fairylandgame.com/fbfairy/forums.php?tid=108294 
