December 19, 2009

1 - Should we irrigate in the winter?

Yard and Garden December 19, 2009


We are having a debate regarding the need for irrigation of trees and shrubs in the winter versus the risks of having a garden hose attached to the outdoor faucet. Should we irrigate in the winter?

- Kay S.



Trees and shrubs (and dormant herbaceous plants such as bulbs, peonies, etc.) need water during the winter. These plants are still alive and living organisms requires water. Deciduous trees and shrubs, dormant herbaceous ornamentals, and many other plants need much less water during the winter than during the growing season because their metabolism is slowed and because water loss is less under conditions of winter temperatures. Evergreen trees and shrubs are also using less water than in the summer, but their water requirements are higher than those of the deciduous plants. In general, one good irrigation every 4 weeks during the winter is adequate to sustain most trees and shrubs. If the plants are growing in a clay soil (which holds greater quantities of water) irrigation may be somewhat less frequent (once every 5 to 6 weeks). Sandy soils will hold less water, so they need to be watered once every 4 weeks. Some plants, especially plants native to the lower elevations in our arid environment can tolerate very infrequent irrigation, but even these plants may exhibits some symptoms of injury after a very dry winter. However, many of our landscape plants are native to regions with higher levels of moisture in the winter and will be injured by winter drought.

If there has been substantial precipitation, the need for irrigation may be reduced, but our typical winter precipitation is not adequate for many landscape plants. Each precipitation event or irrigation should moisten the soil the same depth to which soil is moistened during the growing season to sustain roots throughout the root zone. Since water cannot penetrate a layer of ice in frozen soil, and because it is water that freezes when the soil freezes, irrigation is not advised if the ground is frozen. In areas where the ground is not frozen irrigation can be effective. Our winters are often dry in January and February.

This is a time when tree roots prepare for spring by producing many small absorptive roots. If there is no moisture in the soil at this time, injury is likely to appear in the plants in late spring. At the time you see buds swelling in late winter the plants are preparing this root system and need moisture in the soil. If there is no precipitation during this time, irrigation is important.

When irrigating in the winter, it is important to remember that hoses attached to outdoor water faucets can cause pipe breakage. Irrigate only during warm days. The hoses should be detached from the water faucets before dark. This is extremely important. If you are concerned about forgetting to remove the hoses, an alarm with a reminder note should be set in an obvious place indoors to prompt you to remove the hose.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email:, office: 505-865-7340, ext. 113.


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