The following was distributed at the 1995 Menninger Sunbelt Tree Conference By Roy A. Mecklenburg
Irrigating Newly Transplanted Trees
Newly transplanted trees in Central Florida require 1.5 to 3 gallons of water per inch of trunk diameter per irrigation. This water must be applied so that it penetrates into the root/soil ball. It does no good if it runs around the soil/root ball.
The water ring should be constructed so that it is directly over the edge of the root/soil ball not over the edge of the planting hole.
The water ring should be made of material that will hold water and force it to soak into the root/soil ball. Water must be applied to the root ball the day the tree is planted and continued each day thereafter until it is established.
The most effective method for applying water is a temporary above the ground ½ inch diameter Dura-pol polypipe / spray stake system attached to the normal overhead landscape irrigation system. Overhead irrigation is not needed so long as the root ball is kept moist for trees under 12 inch trunk diameter. Container-grown trees require more frequent irrigation after transplanting followed by freshly dug fabric container-grown trees. Hardened-off field- grown trees require the least frequent irrigation after transplanting.
Root Growth Rates
Tree roots of newly transplanted trees in central Florida will grow at a rate of 8 feet or more during the first year. This is 8 feet out away from the root ball. When established tree roots will extend well beyond the drip line of the tree, frequently more than 3 times the distance from the trunk to the edge of the drip line.