The longan tree (Dimocarpus longan) is subtropical and will only grow in regions with warm, humid summers and dry, cool winters. Technically, longans thrive in U.S. Department of Agriculture plant hardiness zones 10 through 12, which makes them intolerant of cold and heavy frost. The success of your longan tree, however, depends mostly on choosing the right site with the appropriate soil and then planting it properly. Since the tree needs plenty of water after planting, choose the rainiest part of the year to put it in the ground.
The Planting Site
Maximize fruit production by planting the longan tree in the sunniest spot in the garden. The longan tree can grow to 100 feet in height but typically top out at around 30 to 40 feet, so choose a spot well removed from other trees and structures. The tree does best in sandy loam or sandy soils in spots where water doesn’t puddle after a heavy rain.
As the young longan tree becomes established, it sends roots out in all directions. To make it easier on the tree to reach out, dig a large hole, at least 3 times the diameter and 3 times the depth of the pot in which it is currently growing.
Planting the Longan
Always handle the longan tree by the root ball, not the trunk. Remove the longan from the pot by tipping it over and gently sliding it out. If the roots are tightly packed, use your fingers to gently pry them loose. Use the excavated soil to fill in the hole until the longan tree will sit at the same depth as it did while in the container. After placing the tree’s roots in the hole, shovel in the excavated soil until the hole is half full. Run water into the hole until it is full, allow it to drain and finish filling the planting hole with the excavated soil. The water removes air pockets from around the roots as it drains.
Water the tree – slowly -- right after planting until the soil is wet to the depth of the planting hole and 1 foot wider. Stick a long screwdriver into random areas of the soil around the base of the newly planted tree to ensure that the root ball and the surrounding 1 foot of soil are moist. Let the soil dry out somewhat before watering again and when you do, ensure that the root ball and surrounding 1 foot of soil have become moistened. Use the screwdriver or other long, sharp instrument to test the soil. Continue keeping the soil moist while the tree becomes established during the first year.
If you’re planting more than one longan tree, space them at least 40 feet apart for maximum fruit production. If you lack space in the garden, you can safely space the trees 25 feet apart but production will suffer and you may need to prune the trees more often.