I tend to think of rockeries as places for Alpine plants which need good light. It was somewhat surprising to find that in The Back Garden Beautiful by Harry Havart (1912) they were seen as a way of planting ferns in a damp shady area. He advocates construction with reused paving slabs, burr (over-fired) brick and clinker form the local gas works.
The raised beds along the west side of the garden at Honeywood are edged with burr brick and were significantly shaded by the trees on the land to the west. They are not a rockery but there seems to be a similarity of approach. It is possible that the raised beds – which are probably Victorian rather than Edwardian – were originally planted with ferns which were fashionable in the second half of the 19th century.
The rectangular pond in the northwest corner of the garden may have been planted in the same way. An excavation a few years ago produced evidence for a brick structure set in the ground close to both the pond and the culvert which carries a stream under the lawn. This might be the remains of a fern house although it does not appear on the 1868 Ordnance Survey map or on later editions.
If the beds were made wholly or partly for ferns it does not mean that they continued to be planted in that way into the Edwardian period. Fashions and gardener’s interest change.
The brick structure needs further thought – I will go through the excavation archive in the next few days.