Strictly not horticultural therapy but I found this whilst scouring the internet. It is a transcript of Francis Bacon’s essay of gardens from 1625.
Francis Bacon (1561-1626) was Lord Chancellor of England, a philosopher and a pioneer of empirical science.
This essay inspired gardens as far a field as the Shakespeare Garden, Evanston, Illinois (much later than 1625 it should be said!).
You can find it on the excellent gardenvisit.com website, which has various information about gardens around the world and garden design and history. A valuable resource.