At the end of each summer, before the worst frosts come along, the rock garden should receive its winter coverings. Some plants winter best if liberally top-dressed with stone chippings but otherwise unprotected. Other rock plants, particularly those with rough, hairy, or woolly, winter very badly in this climate, though they are perfectly hardy in alpine regions. They cannot stand the constant moisture of our fogs and rains. It is not always convenient to winter these in an alpine house’ and if they must remain in the open, they should be protected by glass. The erections called “alpine protectors” are specially valuable, because they are simple pieces of glass held over the plant so that most of the rains are diverted, and do not enter the heart of the plant and cause decay.
Ordinary bell glasses can be used, but must never remain closed for so long that they shed condensed water into the centre of the plant, or they will prove worse than useless. They should be lifted off daily in fine weather and replaced at night.
A well-made rock garden should not need frequent renovation, though in all rock gardens, certain pockets need to be cleared out now and again and refreshed with some new. If faulty or extension of the rock garden necessitates rebuilding, remove the large rocks one by one, and carefully lift out the plants. Pack them into boxes, and stand these in a sheltered shady corner while remodelling takes place. Lift all the soil possible with the , so that they do not suffer. Then rebuild as desired, and put back the plants at the earliest opportunity. If they are moved carefully, the plants will not suffer even if they are disturbed while in active growth; but the replanting must be firm, and afterwards the soil must be kept moist for a time.
Increase of rock plants is effected by the ordinary methods of increase. A number of the more vigorous subjects can be roughly pulled apart and replanted, or pieces can be pulled away and inserted without further preparation in boxes a sandy soil or in a shaded nursery plot. Arabis and cerastium are well-known plants that can be roughly handled in this manner without any apparent harm.