How should I water my trees in winter?
Many plants shut down and go dormant for the winter to protect themselves from cold weather. As the days become shorter and the temperature drops in the fall, plants shift their energy from flowering and producing new growth to gradually hardening off their tissues.
The most important influence on the timing of dormancy is shorter daylight hours. For example, even during an Indian summer in autumn, plants continue to go dormant because of the change in light. If temperatures drop too suddenly before a plant has had time to shut down, the plant's tissues can be injured and it won't produce new growth in the spring.
The biggest culprit in winter damage is not the cold, it's the heat. Mid-winter warm spells create a cycle of freezing and thawing. This cycle causes frost heaves, which can expose fragile roots.
To protect from frost heaves and to retain moisture, surround newly planted trees with a 2 to 3 inch layer of mulch. Don't use more than 2 to 3 inches; mulch volcanoes can kill plants by causing cankers and disease on the lower trunk. Never mulch right up to the base of a tree or shrub. Likewise, keep mulch off the crown (the root/stem juncture) of a perennial.
Well established, deciduous trees do not need a lot extra attention in the winter, but make sure that they are well watered before winter sets in. This is particularly true of trees growing in containers which are more likely to desicate in the winter months. Do not over-feed these trees in the late fall as the new growth spurt will delay their dormancy. Water every 3 to 4 weeks during the winter, when the ground is not frozen.
Evergreen trees continue to take up moisture through the winter and need more careful oversight. The best way to prevent winter burn is to water them properly in summer and fall. Healthy plants have the best opportunity to successfully survive the winter. Water plants on warm days in January, February and March. Adding a 2 inch layer of mulch will reduce water loss. In extreme cases, create a windbreak with stakes and burlap. You can also try anti-desiccants. Apply in late November and again in early February. Spray when it is 40°F or warmer. However, we rarely use anti-desiccants at the Garden and make efforts to properly site our trees and shrubs so that they can fend for themselves.
Courtesy of the NYBG Plant Information Service