Most of these gardens are open all year round, or during the flowering season for the relevant genera. A few, however, are only open occasionally, for example under the National Garden Scheme in the UK, or by appointment: these are identified in the lists (like this

). Most gardens will offer guided tours by prior arrangement.
Many of the gardens are either owned by members, or the gardens (or a significant employee) themselves are members. These are identified with a * in the lists.
Why not consider becoming a member of the Rhododendron, Camellia and Magnolia Group: it isn't just for experts, it is for anyone who is interested in the three genera. Go
here for information about the benefits you receive as a member.