Regional Gardening Reports :: National Gardening Association

In the Garden:
April, 2012
Regional Report

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Many trees are planted too deep. Soil touching the bark can cause an early death.

Where's Your Tree's Root Flare?

The handsome paperbark maple (Acer griseum) anchors Marilyn's new front garden and patio. An expensive tree with exfoliating bark, the paperbark maple is a four-season beauty.

I dug down around the trunk expecting to remove four, maybe six inches of soil against the bark. Most trees are planted too deep. When a client gets a new tree, I routinely dig away the soil till I find the root flare, a must-do I learned at the Pennsylvania Horticultural Society's Tree Tenders Training many years ago.

Some 15 minutes later I was still digging the hole, now nearly two feet (24 inches!) deep. The highest buttress root flared at 26 inches below the soil line. Besides the paperbark, a professional landscape company had planted her other trees incorrectly.

What's the Problem?
Trees planted too deep will eventually choke and die prematurely, explained nurseryman Michael Colibraro. Bark should not be in contact with soil. "Keep the bark above the soil level. Soil interferes with air exchange. Moisture rots the bark," Colibraro continued. "That's why you shouldn't have mulch volcanoes. Keep mulch 4 to 5 inches away from the tree trunk."

Retired horticulture professor Dr. Rick Ray adds that roots growing above the root flare often girdle the tree. "My experience is that the roots come up from the bottom and start circling around. Adventitious roots form below the soil line and above the root ball. Roots circle the trunk, restrict fluid movement (food and water), and can girdle and kill the tree."

A tree planted too deep is "a stressed plant," Ray continues. "It's more susceptible to health problems. It won't grow as fast as it should. It's more likely to get scale, insects, diseases, and fall over and possibly kill someone."

Why Are So Many Trees Planted Too Deep?
Nearly 100 percent of trees are planted too deep, said Ray. Initially, seedlings are mechanically planted too deep. Through the growing and replanting processes, on average an additional 9 inches of soil accumulates against the tree trunk. Unless that extra soil is removed, the maturing tree will be subject to "girdling and strangling roots as well as a less healthy life."

Planting Correctly
Before planting a balled-and-burlapped tree, remove the burlap and string from the root ball. Remove a containerized tree from its pot. The next steps are for all nursery-grown trees.

Remove soil surrounding the trunk, being very careful not to scrape the soft bark or touch the trunk. I use a Japanese hand hoe that cuts through hard, dry soil. Gently pull soil away perpendicular to the trunk till you see the root flare -- a swelling on the bottom of the trunk where buttress roots enter the soil. Ray calls it the "shoulder."

Ray and Colibraro also suggested planting a large-balled tree high, then removing the excess soil. "If anything, I plant too high. I've never lost a tree," said Ray. "If you don't see the root flare, plant trees 9 inches too high. Remove as much of the wire basket as possible. Then remove soil till you reach the root flare."

What To Do?
In Marilyn's case, the landscape company returned, dug up and replanted the paperbark higher. Check on the tree in late March, I discovered it was still 6 inches too deep.

To raise a too-deep, newly-planted bare-root tree, Ray wraps several turns of burlap low around the trunk. With a friend, each takes an end. Together they lift the tree up, being careful not to damage the bark.

Professionals can raise a recently planted tree that has not grown into the soil with the right professional equipment -- a front-end loader, Ray noted. After five years though, a tree too deep in the ground can be a serious hazard that may need to be cut down, he advised.

My advice: Show this article to anyone planning on planting a tree -- before the tree goes in the ground!

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