The pros and cons of mulch

Marion Shier

You may not find the phrase “mulch volcanoes” in the dictionary, according to University of Illinois Extension horticulture educator Martha Smith, but the concept has been gaining ground and can create problems.

“To landscapers, arborists and gardeners, this is a phenomenon that wasn’t so prevalent years ago,” said Martha Smith.  “In recent years, people have begun mounding mulch around the base of trees creating the ‘mulch volcano.’  New problems have emerged because of this practice,” said Smith. 

“Tree bark is meant to protect the trunk.  It works best in the air and light.  If you pile mulch onto the bark, it is now exposed to dark and moisture.  Bark will begin to rot, and rotted bark cannot protect the tree from insects and diseases.  In fact, diseases grow better in this type of environment.”

Smith said mulch breakdown can produce heat—with a compost pile reaching temperatures above 140 degrees Fahrenheit.  Mulch piled high around the tree trunk can get hot.  This heat may directly kill the inner bark/phloem layer of young trees, or may prevent the natural hardening-off period that plants must go through in the fall in preparation for the winter.

“Mulch piled around the trunk promotes the growth of secondary roots, which can encircle the trunk and choke off the trees main roots,” she cautioned.  “Some trees, such as maples, have shallow roots and deep mulch encourages these roots to grow into it.    

“A mountain of mulch piled high against a tree trunk will not kill the tree immediately – it results in slow death.  Homeowners don’t associate their actions with tree decline several years after they overmulched a tree.”

There are positive reasons to mulch, Smith added.

“Mulching helps maintain moisture. Evaporation is reduced, and the need for watering can be minimized,” she said. “It also helps control weeds.  A mulch layer will suppress weeds from germinating at the soil line.  Remember, lawn mower clippings blown onto mulch and animals may bring in weed seeds that may germinate on top of the mulch.”

Mulch serves as nature’s insulating blanket. Many organic types of mulch can improve soil aeration, structure (aggregation of soil particles) and drainage over time as they decompose.

“Mulching also lowers maintenance needs and can reduce the likelihood of damage from lawn and weed trimmers when the equipment gets too close,” she said. “Mulch can give planting beds a uniform, well-cared for look.”

Mulch should be between 2 to 4 inches deep.  Often, when applied, it appears deeper, but after settling you should end up with a 2-inch matted layer. 

“Organic mulches include wood chips, pine needles, hardwood or softwood bark, cocoa hulls, leaves, compost mixes, and a variety of other products usually derived from plants,” said Smith. “Organic mulches decompose in the landscape at different rates, depending on the material. 

“Those that decompose faster must be replenished more often.  Herein lies the problem.  Some mulches, such as cypress mulch, remain intact for years, but they turn a gray-tan color.  People prefer the “fresh” look of new mulch and top dress annually, not considering the existing mulch depth,”  she said.

Deep mulch, she added, can lead to excess moisture in the root zone, leading to root rot and insect and disease problems.  If mulch is too heavy, you can deprive the roots of oxygen and greatly reduce the soil’s ability to dry out. Thick layers of fine mulch can become matted and may prevent the penetration of water and air, whereas anaerobic “sour” mulch may give off odors. 

Early spring gardening

Early spring gardening is a challenge for gardeners who gamble that the weather won’t be too cold, too wet, or both, said a University of Illinois Extension horticulture specialist Richard Hentschel.  

“There are some strategies that a gardener can try in order to come out on top and have a great garden, starting with your earliest plantings,” said Richard Hentschel.

“Learning when to plant is a matter of reading each seed packet or understanding the catalog lingo.  No matter where you garden in Illinois, there can be an early garden planted.  In the southernmost tip of Illinois, the planting date could be as early as the first week in April.  The same planting date for early vegetables in northern Illinois can be closer to the first week in May.  The difference in growing days from southern Illinois to northern Illinois is typically about 40 days.” 

Hentschel said another thing to consider is whether you’ll be planting seeds or transplants. “If you would like the additional challenge, try growing the transplants,” he said.

“Another bit of needed information is the historical and somewhat mysterious frost-free date for the area you live in.  Everything is referenced to that date for your first planting.  These are very specific dates, yet each year the gardener will have to decide if it is better to postpone the planting one day or several,” he said. 

“Southern Illinois has about 200 frost-free days wheras northern Illinois only has about 160 days and the rest of Illinois has something in between,” he said.  “This information allows gardeners to choose vegetables that will germinate, grow and produce before the first freeze kills the plants.”

The usual lists of vegetables for the early garden are those that can survive evenings when you can still get a freeze.  “The seeds in the ground won’t know if the air temperatures are below freezing or not.  These early spring vegetables prefer to germinate and grow in the cooler temperatures, or, like the potato, tubers prefer the cooler soil temperatures to get started and the tops come up a bit later when the air temps are warmer. 

“Some of the earliest vegetables grown from seed are leafy vegetables like kale, leaf lettuces of all kinds and spinach,” he said.  “Transplants that can handle the cold air are broccoli and cabbage.

“Vegetables that prefer colder soil to start growing include asparagus, onion sets, rhubarb and potatoes.  This group of seeds and transplants go in the ground 4 to 6 weeks before the average frost-free date.”

Two to three weeks after planting very hardy vegetables, you can plant frost-tolerant vegetables, which can survive a frost but not a freeze, Hentschel said.  “Beets, carrots, Swiss chard, radishes and parsnips are good examples.  Transplants that are available by then include herbs, cauliflower and Chinese cabbage.”

Planting both very hardy and frost-tolerant vegetables can be a bit of a job as the garden soil is often still too wet.  Sometimes it means digging an individual hole for the transplants and using dry soil set aside just for this purpose or using some bagged potting soil if your ground is too wet.

A similar strategy can be used for the rows of vegetables you are planting.  You can also use sand to cover the smallest of seeds if you feel the soil you have is too heavy,” he said.

“For vegetables like potatoes and asparagus, the plantings have to go in a lot deeper to accommodate tuber development for the potatoes and to establish a permanent planting of asparagus,” he said.