- Special Sections
- Public Notices
Every year, I write about mulch but no one seems to care! Mounds of mulch still choke the trunks of trees everywhere you look this time of the year. Trees in landscapes look like telephone poles sticking out of soon to be crusted over black mulch.
How’s that for a foreboding tale?
Here’s the message, too much mulch is a bad thing. I know, some people have been liberated but we still have some more work to do. The bottom line: 2 inches of coarse mulch that is not piled around the trunk of the tree or shrub is the desired goal.
Mulching is like comfort food for people; the more they pile around their plants the better they feel. But, just like food, too much mulch is definitely not a good thing for one’s overall health.
Ohio State University states that, “excess mulch, especially if applied right next to landscape plants, leads to constantly wet bark and conditions favorable for disease development. In addition, there have been some reports of an increase in girdling roots developing in the excessively mulched areas.”
OSU further supports what other researchers and professionals practice: use 2 to 2.5 inches of mulch to achieve weed control, moisture retention and temperature moderation.
I believe that the aesthetic use of mulch is where its over-use has become standard practice, so think about mulching in different terms. We are advised to mulch for weed suppression, moisture retention, temperature moderation. As a result we also create a clean, aesthetically pleasing planting bed or provide a buffer zone between plants and power equipment.
Fact: to achieve all of these things 2 to 2.5 inches of mulch is all you need. Problems begin to occur with anything over 2.5 inches. Additionally, the coarser the mulch the better; a coarser mulch like pine straw or bark chips allows for water and air movement and lasts longer in place.
Mulching for weed suppression is straight forward enough. Only 2 inches of mulch adequately suppresses weeds. That is, until weed seed lands on top of the mulched areas. Use common sense and keep your mulched areas weeded when the pests appear. Most mulch is organic material and as we all know weeds will grow in the crevices of a sidewalk. You can be sure that they will grow in mulch, too.
Mulching for moisture retention is particularly important during the summer months. Cool, moist soil can increase root growth and development, however, if you have heavy clay soils where drainage is poor, over-mulching can harm roots and slow their development because of over saturation. (Be mindful of automatic watering systems. Nightly watering from an automatic irrigation system may make it easier for you but it may also kill some of your landscape plants).
If over saturation due to heavy soils is a problem for you, use a mulching material that includes some compost such as worm castings.
Partially decomposed materials will help to improve the condition of the clay soil and add tilth over the years.
Over mulching can also deprive the plant’s roots of the necessary oxygen requirements for healthy growth. Just like humans, a plant’s root system needs oxygen in order to properly function.
Too much mulch, especially fine-textured mulch, can eliminate oxygen penetration, which causes the finer feeder roots to grow into the mulch (thus defeating the goal of moisture retention because during drought conditions the mulch dries out more quickly than the soil).
I have seen mulch piled in 10” to 12” volcanoes around newly planted trees, which, in effect, smothers the roots and discourages healthy, deep root systems. You want to see the natural flare of the trunk where it meets the soil surface, if you don’t scrap away the mulch until you do!
Mulch is also useful in preventing the #1 killer of landscape trees: power lawn equipment. Creating a “no-mow-zone” around the base of trees and other ornamental plants means that lawn equipment can stay a safe distance from our plants.
It also prevents soil compaction under the canopy of the plant from repeated runs of heavy lawn equipment.