Being planted too deep is the main reason why trees in South Valley fail. Is your tree failing to thrive? Does it seem overly susceptible to pests or diseases? Are leaves smaller, scorched, or otherwise discolored? Have wilting, early leaf drop, or twig dieback been occurring?
It may be that your tree is planted at the incorrect depth.
A properly planted tree shows a flare at the base of the trunk. If a tree looks more like a fence post, it is probably planted too deep. Trees planted too deep cannot breathe properly. Trees planted too shallow dry out quickly and can be unstable.
The easiest way to tell if an established tree is planted at the correct depth is to dig down an inch or two, with your fingers, next to the trunk. You should come across four to 11 substantial roots. If all you find are delicate feeder roots, the tree is planted too deep. If the roots are visible from the surface, it is too shallow.
Trees planted too deep should be dug up, the roots inspected, and then replanted at the proper depth. This can be a huge project, best done by professionals. Trees planted too shallow need more soil added around the trunk. You can prevent all this work by planting trees properly in the first place.
New trees may or may not have been planted at the proper depth at the nursery. You need to take them out of their contain and wash soil off the roots to see what they look like. Remove any roots that look diseased or damaged. Spread them out and look at the overall shape. If they are growing in a spiral, see if you can unwind them. If you can’t unwind them, cut them back to where they can be straightened out somewhat. Identify the root crown (or root collar), where the trunk flares outward and joins the root system. This is not the same thing as the swelling seen where trees have been grafted onto rootstock. The different bark textures and colors can help you identify the root collar.
Dig a planting hole that is two or three times wider than the spread out roots, and slightly shallower than the roots or the root ball. As the soil settles, so will the tree. Do not “spin” roots into a too small planting hole, as this can lead to girdling roots, another common cause of tree death. Amendments are not needed at planting time.
Proper planting depth is critical to tree health. Trees planted above or below grade will never thrive. It is much easier to do it correctly the first time.
Kate Russell is a UCCE Master Gardener in Santa Clara County. For more information, visit mgsantaclara.ucanr.edu or call (408) 282-3105 between 9:30 a.m. and 12:30 p.m., Monday through Friday. Be sure to stop by the Spring Garden Market between 9 a.m. and 2 p.m., April 13 at Martial Cottle Park for your spring planting needs.