By Marilyn Loser
2014 October 29
I was amazed to hear about the recent relocation of an older-than-our-country, 65-foot tall Bur Oak on the University of Michigan (UM) campus in Ann Arbor. According to npr.org, the root ball had a 44-foot diameter and the estimated weight of tree and root ball was 700,000 pounds.
The venerable old tree stood in the way of an expansion of the university’s Ross Business School. I, for one, would have designed the addition without disturbing the tree. But, then, I’m a tree hugger!
In Alamosa, when the new City Complex was under construction, two Blue Spruce were moved to the viewing area just northeast of the Cattails Golf Course entrance. I took a look today and they have fairly healthy new growth. In their new location they don’t receive as much water as when they were in a lawn, but I believe they are adapting. The Alamosa Dept. of Parks and Recreation Crew did the transplanting and it didn’t cost $400,000 as did the UM transplant.
I wondered how they prepared and moved the huge Michigan tree. And what are its chances of surviving? We don’t have any trees that large or old in the San Luis Valley. But maybe you have a tree you need to relocate and are wondering the steps to take.
Root pruning turns out to be an important part of the process. I didn’t know what root pruning was until State Forester and Alamosa Tree Board member Adam Moore described the process this summer. The Tree Board and Parks and Recreation Director Heinz Bergann toured the new city complex looking at trees that were planted after construction and might need to be relocated as they are too near a light pole or another tree.
As Adam described the process, a year or several months before transplanting, dig a circle around the tree at the drip line about a foot deep with a sharp shovel. This method is called spading. This cuts the roots and encourages new root growth. When you are ready to transplant the tree, dig up the root ball outside of the cuts so you capture the new feeder root growth.
For Michigan’s Bur Oak a crew dug a three and a half feet deep trench around the tree 20 feet from the trunk and backfilled it, probably with good organic material. This method is called trenching. The trench was much closer to the trunk than the drip line which appears in photos to be about 60 feet from the trunk.
Most folks will move much smaller trees. The Penn State Extension (PSE) website suggests a minimum root ball diameter of 16 inches for a 1-inch caliper tree. For larger caliper trees add 8-10 inches in root ball diameter for each 1-inch increase in caliper size.
Trenching is more appropriate for trees (or plants) that have been located in the old site for several years or more. Trenching can be done all the way around the plant or only part of the way around the plant, followed by further trenching later in the season.
The PSE website states, “To root prune using trenching, dig a trench 8 to 12 inches wide or wider, 12 inches deeper or deeper with the outer edge of the trench corresponding to the outer edge of the future root ball. Next, fill the trench with soil high in organic matter, made by mixing two parts topsoil with one part compost. If conditions are good, the plant will grow new feeder roots in the trench of rich soil by transplanting time. These feeder roots will give the tree added ability to withstand transplant shock. Be sure to move as many of these new, young roots as you can when you move the plant.”
It’s important that the tree develop a good net of fibrous roots before transplanting. “Digging a root ball larger than originally planned may assure that all of the new roots go with it,” the PSE website finishes.
I’ll skip the rest of the details regarding the move of the Michigan tree --visit NPR’s Morning Edition website if you’re interested.
How viable is the move? “If it's done properly, chances of survival are fantastic," says Paul Cox of Environmental Design, the company that moved the Michigan tree. For the next three to five years, the tree will be on a strict maintenance program which will include close monitoring of pH and moisture levels according to UM’s newspaper. A horticulturalist will monitor leaf size and color, as leaf health is indicative of overall tree health.
"One can build a palace in a few months. A great tree requires hundreds of years. But even a great tree doesn't last forever." Attributed to Hirohito in the docudrama Hiroshima