Mulch has many duties in the garden: It works to keep moisture in and weeds out during the summer, and it can give garden beds a cohesive, finished look, K-State says.
“Today’s landscape trends are making pebbles and gravel popular again. I recommend thinking of those minerals as decor, not mulch,” Dennis Patton, K-State Research and Extension horticulturist, said. “For plants to get the most benefits, they need an organic material — shredded hardwood, bark chips, dried grass clippings, cotton seed hulls or the like.”
Applied correctly, an organic mulch will prevent many weeds, Patton said. It will also slow down soil compaction and water evaporation, reduce erosion and moderate the growing season’s temperature extremes.
To be sure that organic mulch achieves these goals, Patton said:
• Applying a 2- to 4-inch layer, keeping finer mulches (e.g., dried clippings) on the lower end of the depth range and coarser ones (bark chips) on the upper end. “Anything less welcomes weeds,” he said. “Anything more promotes molds and diseases.”
• Top-dress as needed. “Organic mulches gradually decay, improving the soil’s nutrients and texture. The finer the mulch, the faster that happens,” Patton said. “So you need to add more mulch occasionally to keep the layer thick enough to do its other jobs.”
• Keep from piling mulch against stems and trunks, where it can foster diseases and provide cover to insects. Also avoid a year-round volcano of organic mulch that is replaced as it decays. Over time, this can make trees and shrubs think that their planting depth is changing, Patton said.
“Plants need a donut hole of bare space, the size of which relates to each plant’s size,” Patton said. “A big, old oak could use a foot left uncovered around its trunk. A pepper plant needs an inch or so of room.”