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Over the Garden Fence

Mulch Madness

Calls to the Master Gardener Help Desks about using bark mulches in the home landscape and gardens has prompted a Q&A column this week. Organic mulches are used on new plants to help them establish and lessen transplant shock. Mulches conserve soil moisture; keep weeds and grass from encroaching and moderates soil temperatures, making it easier on the limited root system. On older established plants, mulches really are there more for aesthetics.

Q: When will I know it is time to add mulch?

A: Bark mulches are organic and will break down over time releasing nutrients into the soil for uptake by the plants. Organic matter also improves water retention and soil structure. It is time to re-mulch when you begin to see bare soil and weed seedlings showing up through the remaining mulch.

Q: How deep should mulch be in my landscape beds and are there precautions when I have mulch installed?

A: Once settled, the mulch should be 2 to 3 inches deep in a landscape bed or a mulch ring around established trees. Caution should be used if applying bark mulch in perennial beds (see next questions for more on that). Mulch should not be piled up around the trunk of trees in a "volcano" fashion. Tree bark is intended to be exposed to the air and sunlight. Mulch piled up softens the bark of the trunk inviting fungal decay and insects.

Q: Since the last time I mulched our fine textured shrubs, they have grown poorly, what did I do wrong?

A: Fine textured shrubs, like Potentilla and Spirea, and some groundcovers cannot be mulched into the crowns because of the way the new growth emerges each year. Those young tender shoots cannot make it through the compacted mulch. You can mulch right up to the crown area, but do not put mulch in the crown.

Q: Which bark mulches last the longest?

A: Cedar and Cypress mulches followed by hardwood bark mulches last the longest. They also can be the more expensive ones as well, as Cedar and Cypress mulches are not locally produced.

Q: What does double- or triple-screened mean?

A: Mulches are run over a screen to provide a consistent product. The more it is screened, the more uniform the material. A very consistent product will be easier to handle and to spread and will look more even after you are done.

Bark mulches were originally used or intended to be temporary to prevent weed growth while the landscape plants grew and matured, covering the bed by themselves. As the plants grew in size, less mulch would be needed and any mulch still exposed once the plants reach canopy cover became the aesthetic element of the overall bed design becoming the transition between the lawn and bed or sidewalk. What can be seen currently are landscape beds that have a "sea" of mulch with a few plants "floating" along. Consider the addition of more plants combining woody plants, herbaceous plants, evergreens and spots for annuals for continued color all summer long.

Richard Hentschel is a Horticulture Extension Educator with University of Illinois Extension, serving DuPage, Kane and Kendall counties. Stay tuned to more garden and yard updates with "This Week in the Garden" on Facebook at The 2017 Kendall County Master Gardener Help Desk currently is open Monday, Wednesday and Friday from 9 a.m. to 12:30 p.m. at 630-553-5823 or at

About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.