A garden cannot be healthy. A garden is not an organism. Only the plants and animals in the garden can be healthy.

A garden is an ecosystem. Ecosystems can be healthy or not.

You miss the point of semantics. The word I use does what I want it to do. Nothing that you said is an argument that I didn't succeed in communicating what I wanted to communicate.

Regardless I think that healthy is an adjective that applicable to biosystems. I went to multiple community organisation barcamps and the related professionals do speak about the health of online communities.