Hi Susan, We have experimented with this some and had some success for a community garden. However we must be mindful that if the tree dies...what do you tell the sponsor?
It'd good to have a clear idea of what the expected goals are.
Does the community garden need financial assistance with purchasing plants? Do you want to be able to show sponsors the plants/gardens?
it might be worth considering requesting potential donors to sponsor a garden plot/area. the garden could still post a thank you sign. Or tag the donor in social media posts to say thanks.
We decided on garden areas and requested gift cards to local nurseries. There are so many options.
Hopefully more peoples will offer additional insights.