Issue: January 22, 2000
Trees trying to grow too early?Question:
I have only lived in New Mexico for one year. Last year we planted about 17 trees and today they are trying to sprout. We have not watered them. Since we live in the middle of the desert, have not watered our trees, and they are sprouting, should we water them even though it is going to freeze again, or should we leave them alone? Will they die if they do not get any water?Answer:
At this time of the year the buds on some trees begin swelling, though the leaves will not appear for several more weeks. It is possible that the trees will leaf out too early and suffer freeze injury, but what you are seeing is probably just the swelling of the flower buds. This is especially evident in the silver maples, cottonwoods, apricots, and elms.
For most trees, in most years, there is no problem. If we do see a freeze after the leaves form, the damage is usually minimal. The buds which had sprouted are killed, but the tree has smaller dormant buds at the base of the larger buds. These buds are insurance to allow the tree to survive freezing of the larger bud. Usually these accessory buds remain dormant and never grow, but occasionally they get the chance. If this happens, there may also be some damage to the "wood" (the newly forming xylem and phloem) and the cambium. These tissues are just under the bark and, as the tree begins to grow, these tissues also become subject to freeze injury. If the cambium or xylem and phloem or injured, the branches may grow for a while, then the ends of the branches will die. Only in extremely rare situations will trees and shrubs be killed because they began growth too early.
Another consideration is that once the buds begin to swell, they become active producing auxins (hormones) which translocate to the roots and stimulate the growth of new roots. At the time the buds begin to swell, then it is time to irrigate and be certain that there is moisture in the soil so that the new roots do not desiccate and die as they are formed. Should the roots die now, they will not be present to provide moisture and minerals to the leaves which form several weeks from now. If that happens, the tree may appear to grow normally at first but, after a few weeks as the weather gets warmer, injury may become apparent.
Dry winters are very common in New Mexico, and tree irrigation is necessary during most winters for the shade trees most commonly grown. Irrigation once a month is sufficient because the air is cool, evaporation is reduced, and the plants are dormant. If the winter has been cold, shady locations may have frozen soil which won't absorb water. The soil is frozen because there is moisture in the soil, so those locations may need less irrigation. In other areas, winter irrigation is essential if plant roots are present. It is important to irrigate deeply but not too often at this time of year. Irrigation will not stimulate early flowering and leaf development which are under the influence of temperature. Failure to irrigate will cause injury to the trees.
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: firstname.lastname@example.org, office: 505-865-7340, ext. 113.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!