Tree establishment refers to the point a newly transplanted tree has grown roots into the surrounding soil a distance equal to approximately 3 times the distance from the trunk to the branch tips. During the establishment period, shoots and trunk grow slower than they did before transplanting. When their growth rates become more or less consistent from one year to the next, the tree is considered established. It is important to consider establishment time when planting trees in any landscape.
In moist climates, by the end of the establishment period a tree has regenerated enough roots to keep it alive without supplemental irrigation. Trees provided with regular irrigation through the first growing season after transplanting require approximately 3 months (hardiness zones 9-11) per inch of trunk diameter to fully establish roots in the landscape soil. Trees that are underirrigated during this establishment period are likely to require additional time to establish because roots grow more slowly. Most trees are underirrigated during the establishment period. Because roots are not fully established, be prepared to irrigate through the entire establishment period, especially in drought. Since most root growth occurs in summer, be sure soil moisture is appropriate during this crucial season.
Irrigation capabilities at the planting site should be considered before selecting trees. It is virtually impossible to plant and establish a thriving tree in our climate without an irrigation system in place. Regular irrigation after planting encourages rapid root growth that is essential for tree establishment. Irrigation helps maintain and encourage the desirable dominant leader in the tree canopy on large-maturing trees. Instead of a dominant leader, trees that are underirrigated during the establishment period often develop undesirable, low, codominant stems and double leaders. Since most root growth occurs in the summer months, irrigation during this time is crucial. You could loose almost an entire year’s root growth if you under-irrigate the first summer.
Unlike established plants, research clearly shows that recently transplanted trees and shrubs establish quickest with light, frequent irrigation. For trees planted in spring or summer, provide one (cooler hardiness zones) to three irrigations (warmer hardiness zones) each week during the first few months after planting. Daily irrigation in the warmest hardiness zones provides the quickest establishment.
Following the initial few months of frequent irrigation, provide weekly irrigation until plants are fully established. At each irrigation, apply about one (cool climates) to two (warm climates) gallons of water per inch trunk diameter (e.g. 2 to 4 gallons for a 2-inch tree) over the root ball only.
In most landscapes that receive more than 30 inches of rain or irrigation annually, if the mulch area is maintained weed-free, irrigation does not need to be applied outside of the root ball. Never add irrigation if the root ball is saturated.
Water twice per month in warm weather in spring, summer, and fall and once or twice per month in winter in the first three to five years. Between years five and seven, water once every three weeks in warm weather and once every six weeks in winter.
Water Restrictions and Drought
Water restrictions are often implemented throughout Florida during times of decreased rainfall or drought. A common restriction during this time is to give a 30 day grace period for newly planted landscapes. This usually means that a new landscape can be irrigated daily during this time period with the irrigation system. As the establishment information above indicated this 30 day period is not enough time to establish a tree in Florida. While most restrictions allow for hand watering with a hose as much as needed the large size and scope of many landscape jobs does not make this a realistic option. Low volume irrigation systems with drip or bubbler heads are often exempt from watering restrictions as well. This is because low volume systems enable trees to be watered on separate zones without the need to water surrounding shrubs or turf. Experience shows that the investment required to install a low volume system is small because drip or bubler systems can dramatically increase tree transplanting success.
Some of the information in this article is from Dr. Ed Gilman’s website at hort.ifas.ufl.edu/woody/planting.html