Planting too deep is No. 1 cause of root collar disorder

CHAMPAIGN, Ill. — The root collar of a tree is an important transition zone from the trunk tissue to the root tissue and the underground part of the plant.

“Xylem and phloem are present there, which is the conductive tissue inside the tree that conducts water, nutrients and energy up and down the plant,” said Ryan Pankau, University of Illinois Extension horticulture educator.

“Anchor roots arise from the root collar and there are photosynthetic cells in the bark,” said Pankau during an Illinois Extension webinar.

Many tree roots are very shallow in the top foot of soil.

“A lot of the roots extend beyond the drip line of the plant and some roots have been measured two to three times the drip line of the tree,” Pankau said. “Some studies have found the diameter of the plant is a better predictor than the canopy width for the size of a root system on a healthy tree.”

As trees age, Pankau said, the energy put towards root systems changes.

“More energy goes towards maintenance and less towards growth and expansion of the root system,” he said.

Impervious surfaces such as driveways or sidewalks will restrict root growth because roots need water and oxygen.

“Root systems are not uniformly distributed because they adapt to the environment,” Pankau said. “There are more roots on the uphill sides of trees, more in the direction away from the lean and more in the direction of the prevailing wind.”

Fine roots turn over quickly, which has a significant effect on soil.

“As they die, they leave channels, they leave behind nutrients and as they decompose, build soil structure,” Pankau said.

When someone has a tree question, one of the first things Pankau evaluates is if the tree has a root flare or if it looks like a telephone pole.

“If you see a telephone pole going in the ground there is a root collar disorder,” Pankau said.

“A root collar disorder occurs when conditions have created an unnatural environment that adversely impacts tree health,” he said.

“The No. 1 cause of root collar disorders is burying the root flare in the soil,” he said. “It can also occur from grade changes or mower and string trimmer damage.”

Signs and symptoms of a root collar disorder include stress symptoms such as yellow foliage, small leaves or small annual twig growth.

“Additional signs include sloughing bark, signs of decay or a red maple with fall colors in August,” Pankau said. “There may be small nicks around the base of the truck from mower damage that are hard to detect.”

In some cases there are few detectable symptoms before the tree shows health declines.

“So, to a home owner, it’s a perfectly fine tree and then all of a sudden during hot, dry weather you see leaf drop, quick fall color happens and the tree is in trouble,” Pankau said.

Once a problem is detected, Pankau said, tree owners should minimize the environmental stress.

“Do mulching, watering and improve the root zone by expanding the mulch area,” Pankau said.

“You should do a root collar excavation when you see the telephone pole appearance,” he said. “Dig down and find the first structural roots, which tells us where the root flare starts.”

The next step is to remove the excess soil and look for girdling roots.

“Look for signs of decay and leave the root flare at the soil surface so it is exposed to air,” Pankau said. “Consider removing the tree before the tree becomes a hazard.”

A study in 2000 showed that 93% of professionally installed plants had soil or mulch above the root collar.

“Another study in the ‘90s said 75% of nursery grown trees had root collars buried in the pot 3 to 12 inches deep,” Pankau said. “But that’s fixable at planting time.”

Before digging a hole, Pankau said, the first step is to find the root flare of the tree.

“Dig your hole three times the width of the root ball,” he said. “You want a wide and shallow hole because that allows the plant as it’s overcoming transplant shock nice, loose soil to expand its root system.”

Access the soil quality and look for natural soil horizons while digging the hole, Pankau said.

“If there is a mixture of subsoils, you might consider amending the soil with compost to get more organic matter,” he said.

Applying mulch helps to preserve moisture.

“The biggest mistake is piling the mulch on the root flare,” Pankau said.

For balled and burlapped trees, it is important to remove what is around the trunk to prevent restricting the trunk growth.

“I remove all the burlap because I think anything that restricts the root growth is a bad idea,” Pankau said. “If there’s a little burlap or wire basket at the bottom of the hole, I don’t worry about that.”