Irrigation of newly planted street trees

"It is widely recognized that water stress is the fundamental cause of poor postplanting performance of street trees. Branch dieback is a common sight as transplanted trees begin their second season (Figure 1). Because a transplanted tree has so much of its root system removed (some say as much as 98%) when it is dug, it can quickly become drought stressed. Although the tree in Figure 1 is alive and appears to be establishing, effects of this dieback will be felt for years to come. This tree has essentially been topped by water stress, just as if had received a haircut from a fly-by-night "arborist." Some extensive corrective pruning will be required if it is to become a desirable street tree. Dieback can be so severe that no amount of pruning will correct the "topping" (Figure 2). This tree probably just dried out soon after it was planted. By the time drought symptoms were noticed and the rootball was irrigated, the dam-age was already done. This reactive style of irrigation may keep a tree alive, but establishment will be slow and dieback will probably occur. This is easy to dismiss this dieback as "transplant shock," and inevitable consequence of transplanting. However, dieback such as this is usually preventable. What is needed is a proactive, not a reactive irrigation plan." [Abstract]

[San Francisco, Mar. 5-6, 1998]

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