Earth-covered caves are used often by nurserymen to store grapevines and fruit trees and for storing grafts of the orchard fruits (85. Packing Away the Grafts). The few who have tried it on a large scale also find it a desirable place for storing winter apples. For apple storage it should have ample ventilation. When the apples are put in from the orchard in the fall the days are usually warm and the nights cool. During the night keep doors and ventilators open, and during the day keep all closed, putting in each day's picking early in the morning. Even in winter the cave is opened at night for a longer or shorter period, depending on the temperature, to let in cold air, which is held during the day by keeping every aperture closed. Those who have had experience with the cave method prefer it to all others except ammonia cold storage. But it must be kept in mind that when the cellar air is near freezing in winter, if it is opened at midday, when the air outside is much wanner and loaded with moist air, it will rush in and precipitate its moisture.