Department of Agriculture hardiness zone 10 or warmer. As its name implies, the Christmas cactus blooms at Christmas. Keeping it healthy and blooming properly requires an understanding of its needs, such as how often to water it.
When and How Often to Water
Water your Christmas cactus when the top inch of the soil is dry. Always take into consideration the climate and time of year.
If your cactus is outdoors in a hot, dry climate, you might need to water every two to three days, especially if the plant has been in the sun. If you keep the cactus indoors where it is cool or humid, it might need water only once a week. Water less during the fall and winter to help stimulate blooming.
Avoid Over-watering and Under-watering
Over-watering is a problem for the Christmas cactus just as it is for other kinds of cactus. Over-watering can lead to fungal rot diseases such as white rot and can cause leaves to drop. White rot disease is easily recognized by the white spots on the leaves. Because Christmas cactus is not a desert cactus but a tropical one, it cannot take as much under-watering as other cactus species.
If a Christmas cactus does not receive enough water, it will wilt and its flower buds will drop. Unlike a desert cactus, a Christmas cactus cannot tolerate completely dry soil. To avoid problems with fungus, avoid overhead watering.
How to Maintain Humidity
The Christmas cactus does best in a humid environment. This is particularly important for gardeners living in a dry climate or whose homes have a dry indoor climate.
The easiest way to provide humidity is to place a tray of water near your plant. The water evaporates into the atmosphere, providing the needed humidity. Another way is to put gravel in a dish and fill with water before placing the potted plant into it. Misting your cactus with a spray bottle can also provide humidity.
Other Growth Requirements
The Christmas cactus prefers bright indirect sunlight. If growing them indoors, protect them from direct southern or western sun exposure. They do best in warm temperatures, 70 to 80 degrees Fahrenheit, and will form buds when evening temperatures are 50 to 55 degrees.
Throughout the winter, try to keep nighttime temperatures around 60 to 65 degrees. Avoid placing Christmas cactus in cold drafts and keep them away from sources of hot air such as heating vents or fireplaces. Fertilize in the spring as soon as tender growth appears. Use a liquid houseplant fertilizer every two to three weeks up to a month before the first blooms are expected to appear.
Source: sfgate.com
