The Right Stuff

Having a hard time growing trees in your subdivision or near your new home? Wish you could find a magic vitamin to give your trees? This summer, Arboretum researchers found something that helps. While it's not quite magic, it's proven, it's inexpensive, and it's hot off the presses!

The back story

New housing subdivision soil often is destroyed by common construction practices.

• When developers prepare the land for houses, they scrape off all the rich, good topsoil.
• During construction, large machines press down on the earth, squeezing out the spaces that hold air and water in the remaining subsoil.
• After houses are built, builders typically add a few scanty inches of topsoil, which can't make up for what was lost and damaged during construction.

The result? Newly planted trees have trouble growing roots in the compacted, thin soil. They die early. Homeowners plant new ones. Those die, too. Homeowners get frustrated. Repeat. Repeat. Repeat. Eventually, people give up on achieving their ideal of a green, shady yard. Sound familiar?

Well, there's hope for all you frustrated suburban tree-huggers out there. In a three-year experiment by the Arboretum's Soil Science Lab, led by Dr. Bryant Scharenbroch, researchers set out to find out what we can add to soil around trees to help the grow better in new subdivisions. First, they scraped the land and prepared the research site as if they were builders getting a fresh plot of land ready for a new subdivision. They skipped the house building, though, and cut to the chase by planting 120 trees. Then they applied different soil treatments over three years. Researchers tested:

• Hardwood mulch
• Organic compost
• An inorganic fertilizer product
• A commercial product with bacteria and fungi
• The latest trend in soil care: compost tea

Read more about the experiment.

And the winners are...

Compost and hardwood mulch! Both these solid organic materials improve soil physical, chemical, and biological properties of the soil. Trees growing on mulch and compost plots had greener leaves and grew faster, both below and aboveground. If you want to get the best of both worlds, apply a mix. Read our Plant Clinic leaflet on mulching trees and shrubs, which contains information about the kind of hardwood (chips) mulch Scharenbroch tested, as well as other kinds of organic materials often used in compost.

Want to hear the kicker? These materials are inexpensive or even free! Some towns give away free wood chips—check with forestry departments in the towns near you. And, you can make your own compost using fall leaves and kitchen scraps. Visit U of I Extension for ideas on building your own compost pile or bin.

Scharenbroch says these results weren't that surprising. "Soil quality is imperative for tree health. If you want a healthy tree, you should strive to preserve or recreate the soils found in our forests. Mulch and compost resemble freshly fallen woody debris and decomposing organic matter," he says. "I apply wood chips in the spring and fallen leaves to my own trees every autumn."