Trees: Irrigating Newly Planted Trees

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 under-irrigated during the establishment period often develop undesirable, low, codominant stems and double leaders that can split from the tree later. Splits (so-called frost cracks or sunscald) along the lower trunk have also been associated with under-irrigation after planting. 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.

Size of nursery stock Irrigation schedule for vigor 1,3 (see notes below) Irrigation schedule for survival 2,3,4 (see notes below)
< 2 inch caliper Daily for 2 weeks; every other day for 2 months; weekly until established. Twice weekly for 2-3 months
2-4 inch caliper Daily for 1 month; every other day for 3 months; weekly until established. Twice weekly for 3-4 months
> 4 inch caliper Daily for 6 weeks; every other day for 5 months; weekly until established. Twice weekly for 4-5 months

Notes on Irrigation

  • Delete daily irrigation when planting in winter. Irrigation frequency can be reduced slightly (e.g. 2-3 times each week instead of every other day) when planting hardened-off, field-grown trees that were root-pruned during production. Establishment takes 3 (hardiness zones 10-11) to 4 (hardiness zones 8-9) months per inch trunk caliper. Never apply irrigation if the soil is saturated.
  • Irrigation frequency can be reduced slightly (e.g. to once or twice each week) when planting hardened-off, field-grown trees that were root-pruned during production.
  • At each irrigation, apply 2-3 gallons (warmest climates) per inch trunk caliper to the root ball. Apply it in a manner so all water soaks into the root ball. Do not water if root ball is wet/saturated on the irrigation day.
  • Trees take much longer to establish when not regularly irrigated. Irrigate during drought the following summer.

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