MANHATTAN, Kan. -- Leaf-dropping trees and shrubs may need extra care this spring.

Landscape plants ended the 2000 growing season under stress, said Charles Barden, Kansas State University forester. Summer kept Midwest soil moisture in short supply. Then fall brought early freezes.

"Under normal conditions, trunk and roots reabsorb a lot of nutrients as leaves change color and dry out. Those nutrients become part of the plant’s winter food supply," added Barden, the tree specialist for K-State Research and Extension horticulture. "But drought limited the amount of nutrients available from tree leaves. Early freezes also interrupted the reabsorption process."

That’s why fertilizer and mulch are particularly important now, to help landscape plants prepare for upcoming summer weather extremes.

"Don’t overdo either application, though. You can make things worse, not better," the forester warned. "For example, trees basically need the same amount and kind of fertilizer you apply on your lawn. Anything heavier will cause lots of twiggy growth and over-large leaves that don’t do well in Midwestern winds and heat. Excess fertilizer also can worsen drought conditions because fertilizer essentially is a type of salt."

For trees growing in alkaline soils, lawn fertilizers containing iron or sulfur can be a good idea.

"The bag will say something like ‘formulated for the Midwest’ or ‘acid-forming,’" Barden said. "Or, it will have four, rather than three numbers. For example, the bag’s list may be 20-10-10-4."

The application zone is a circle, extending from near the trunk to as far as the branches spred.

"You won’t accomplish much if you just fertilize close to the trunk," he said. "Trees don’t have many feeder roots there."

Many fertilizers will then require watering, to jump-start their active ingredient.

Mulching around trees can not only conserve that kind of soil moisture but also even out soil temperatures, eliminate weed competition, and reduce the trunk’s odds for mower injury.

"You need to keep the mulch layer about 4 inches thick, adding more only to replace what you lose over time to decay or erosion," Barden said. "We’ve all seen young seedlings with a foot-deep pile of mulch around their trunk. They may look good for awhile, but they’re literally being buried alive."