Young Trees Need Help to Thrive

If young trees aren't thriving in a home landscape, the reason may be the company they're keeping. They're hanging out with too much turf and not enough water.

"Many landscape trees evolved from forest species that had little competition from grasses, even though they were in fertile soil with lots of organic matter. The tree canopy kept sunlight from reaching the ground," said Emily Nolting, horticulturist with Kansas State University Research and Extension.

Trees' fibrous, water- and nutrient-absorbing roots are mostly in the top 6 to 12 inches of soil.

"Lawn roots take up so much of the room there that young trees can't compete," Nolting said.

So, she recommends mulching, rather than growing turf under young trees. The mulch layer should be 2 to 3 inches deep, start at least 2 inches out from the trunk, and extend to the sapling's drip line.

"Conifer bark, pine needles or organic compost are best because they resist rotting and remain porous," Nolting said. "They also help keep the upper soil aerated, conserve moisture, and insulate against temperature extremes. That's probably why young trees grow up to six times faster when mulched – that, plus the fact you never have to get near them with a trunk-damaging mower or whip."

Young trees need a deep soaking every seven to 10 days, Nolting added.

"If you irrigate the lawn and sapling together, you'll be encouraging shallow tree roots," the horticulturist warned. "You need to water trees slowly over enough time that the top 12 inches of soil can absorb moisture – whether you use a spiral of soaker hose or a slow-running hose that you move around."

The test for moisture depth is to push a long screw driver, piece of rebar or the like into the soil. A narrow metal piece will move fairly easily through moist soil and stop when it reaches dry dirt.

by Kansas State University Research and Extension