Just when you thought you’d heard all the arguments for using mulch in the garden, here comes the Morton Arboretum’s Dr. George Ware with yet another benefit.
Using double-ground mulch around trees helps their health because it “degrades at a favorable rate to return nutrients to the soil,” but also, it manages water runoff more effectively than grass, according to Dr. Ware in a newly published report.
“Mulching around trees creates mini water-detention systems,” says Ware, dendrologist emeritus.
Ware observes that anyone concerned with “greening” the earth recognizes the need for water conservation. “Rain barrels and rain gardens are gestures in the right direction,” he says. But with enough double-ground mulch, water is held like a sponge and released back into the earth in quantities that will really make a difference.
The key is learning how to mulch a tree properly. This finely ground mulch, available in most garden centers and home improvement stores, appears shredded, as opposed to chips or chunks.
Of course mulch helps to protect tree roots from lawn mower blades and weed whips, but it also fortifies the tree. As the mulch decomposes, it adds organic material with needed nutrients to the soil.
“All gardeners can tell you their complaints about our region’s clay soil,” Ware chuckles. Not only does it produce rapid rain runoff, and lessen needed water from reaching plants’ roots, but it also may create basins for standing water in the wrong places. “The challenge is to get spongy soil,” Ware says.
With double-ground mulch, spread three-to-four inches thick, the porosity of the soil will be greatly improved in time. This allows oxygen and water to permeate to the plant’s roots. About every two years, you will need to replenish the mulch to compensate for decomposition and any displacement.
Ware says the type of mulch, that is, oak vs. pine vs. cedar, is less important than using a double-ground variety. “One of the best ways to get mulch is to rake up your own leaves and run the lawn mower over them,” he advises.
Mulch should be spread as far as possible to the drip line of the tree (the circle circumscribed by outer branches). Visit The Morton Arboretum website at www.mortonarb.org and get more details through Plant Clinic.
There is no need to remove grass under the area to be mulched. Just mow it closely before applying mulch and the grass will become part of the decomposed matter.
Ware suggests creating conditions in your yard that mimic the forest floor, where leaf litter naturally collects. “Let’s make the tree think it is back in the forest where its ancestors lived,” he says.
Glad You Asked
Q. Is mulch really that effective?
A. One study at the Morton Arboretum showed that young sugar maples that had been mulched at a three to four inch depth achieved crown growth (after five growing seasons) nearly twice that of controls where grass had returned. All evidence points to the benefits of mulch.
Q. What is the difference between the contributions of winter and summer mulch?
A. In summer, mulch is effective for conserving water, controlling weeds, preventing soil erosion, and encouraging root growth. Winter mulch acts as insulation to protect roots, and sometimes promote growth of tiny roots.
Q. What is “volcano” mulch?
A. “Volcano” mulch refers to the inappropriate practice of mounding mulch up around the trunk of a tree. This can tempt burrowing animals to nest there and damage the tree, or promote potentially lethal disease growth on the trunk’s base. It is far better to spread the mulch in a donut shape, with a thinner layer nearest the trunk of a tree.