I need to get advice about what to plant in south Florida as a hedge or palm screen between houses.
As you know, we really concentrate on Mid-Atlantic gardening, not Florida gardening. But we do have some resources. We checked some of the books we have here in the PHS McLean library. One of them, Native Florida Plants, is an eBook that you should be able to access online, since you are a member.
To do this, click on the above title link and log in to our eBook collection by using the number that is on your PHS membership card. This book mentions two native shrubs suitable for screens, Vallesia antillana (Pearl-Berry or Tear Shrub) and Chrysobalanus icaco 'Horizontalis' (Horizontal Cocoplum).
Pearl-Berry grows to a height of 10-12 feet in full sun to part shade. It is native to south Florida, zones 10-11.
Hortizontal Cocoplum grows to 6 feet in sun to part shade, also native to south Florida and the Caribbean.
Another book you may want to look at is Landscaping for Privacy. It is an eBook, which you can access by logging on with your PHS membership number. Look for plants that are hardy for south Florida, and of course it covers design tips that you can use anywhere.
I've uploaded a page from Betty Mackey's book, A Cutting Garden for Florida. It is a list of flowering trees and shrubs. Note that the recommendations cover north, central and southern Florida. Shrubs on this list that can be grown as hedges include Azaleas, Copper leaf or chelille plant, Gardenias, and Hibiscus, but you can research the others on this list as well.
See also the list of large shrubs on the web site South Florida Plant Guide
Hope these suggestions help.