Bill Quade, horticulturist at the Biltmore House, Ashville, N.C., uses three different types of mulch: pine straw, tub grindings and leaves.
Photos courtesy the Biltmore House.
Using mulch on clients' properties is beneficial landscape management practice. Generally mulch is applied to beds and around valuable trees in either the fall or in the spring. The availablity, selection and use of mulch varies by region.
"Our main emphasis on mulching begins in the fall after the leaves have finished falling and after the perennials are cut back," says Bill Quade, horticulturist at the Biltmore House, Asheville, N.C. "This gives us an opportunity to remove the fallen leaves if necessary and then mulch the beds. Mulch is very beneficial to help retain soil moisture, reduce weed competition, reduce soil runoff by breaking up the rain droplets, increase soil fertility by decomposition of the mulch, improving soil structure and provides us a better appearing landscape bed."
The main benefit of winter-cover in the northern states is protection from wide temperature fluctuations in the soil. Soil may "heave" when subjected to wide temperature variations, and plant roots might then be forced up out of the ground exposing them to the elements.
Kyle Daniel, Purdue University, commercial nursery and landscape specialist, further explains: "The temperature mediation in the soil is aided by the addition of mulch around the root system of plants. In environments that frequently experience extreme cold or hot, mulch can assist in regards to temperature. It has been frequently cited in literature that roots are much less cold-hardy than aboveground portions of plants, so extra protection from cold can be beneficial."
Daniel adds that organic mulches, such as chipped leaves, pine straw, various hardwood nuggets and shredded bark all contribute to those positive effects of protection and help retain moisture in the soil, along with substantially reducing weeds during the growing season.
"When applying mulch, 1 to 3 inches is recommended," says Daniel. "Three inches is optimal for most of the benefits to be realized. When applying mulch, it is important not to place it up to the bark of the plants, as this will be detrimental. Mulch 'volcanoes' may look nice, but they will absolutely harm the plants, especially trees. If applying mulch in the spring or fall, an application of preemergence herbicide is recommended to aide in reducing winter- annual and summer-annual weeds, respectively."
After a bed is prepared for the winter, applying a thin layer of mulch provides a finished look and offers added protection for plants from bitterly cold temperatures.
Don't overdo it
Rebecca Finneran, Michigan State University Extension, adds, "Over-mulching is the most common mistake landscapers make. If the mulch is covering the crown, then it is too much mulch. Likewise, lawn care pros should watch out for mulch build-up and discard or, at least, turn over excess amounts of old mulch. My preference is to utilize leaves as an effective mulch and to add compost or shredded bark as a topdressing. And leaf mulching is also an effective way of adding nutrients into lawns."
Quade says that at the Biltmore Estate they'll mulch new areas 2 to 4 inches deep, but reduce that amount to 1 to 2 inches around perennials and just 1 inch around annuals. For more established beds they simply touch the bed up for appearances, if and when the mulch is adequate enough to retain moister and provide good cover. However, North Carolina doesn't always see the wild temperature extremes that are sometimes found in the upper Midwest.
The Biltmore also has the luxury of supplying its own compost and some of its own mulch; nothing goes to waste.
"We use three different types of mulch here at Biltmore: pine straw, tub grindings and leaves," says Wade. "The pine straw is much quicker to apply (especially in difficult to reach locations), tends to retain less moisture than other mulches and adds more acidity to the soil during decomposition. The tub grindings are produced on property from the silviculture waste, the yard trash and the yard waste we accumulate on the property. It's used in the beds where we want a more finished look. The leaves are composted for a minimum of one year before we use them. This is a much courser mulch than the other two so it is used in a majority of our wooded landscape beds."
Kyle Daniel, Purdue Nursery & Landscape Extension, recommends just 1 to 3 inches of mulch for landscape beds and around landscape trees.
Both Daniels and Finneran concur that it is best to wait until after the first few frosts, when temperatures are constantly below freezing, before applying mulch. Applying mulch too early can smother herbaceous plants and encourage disease development. Quite often in young trees, bark splitting may occur as the sun warms the bark considerably and then is affected by sudden drops of temperatures, commonly referred to as southwest injury.
All the experts agree that 'volcano' mulching serves only to damage plants and especially trees. Bark decay occurs when mulch is left against tree trucks or stems of shrubs for extended periods of time. The mulch causes continuous dampness that will encourage decay, attract insects, fungi and bacteria to feed on the rotting wood. Wood rot can develop and cause the eventual death of woody plants.
Rodents have also been known to nest in excessive mulch. In addition, when over-mulching, feeder roots can grow into the thick layer of mulch, making them highly susceptible to water stress during dry periods and cold injury during freezing temperatures.
Trees should have an asymmetric trunk that narrows as it climbs. Often those trees that have grown to resemble a telephone pole were subject to volcano mulching techniques. Mulch should be applied in a donut shape around trees, and not more than 2 to 3 inches thick to avoid disfiguration.
Although differences in temperature extremes and in rainfall/moister amounts in the air are important to consider when choosing the type and amount of mulch to apply, soil type is also a factor that should be observed.
Organic mulches decompose in time and enrich and improve soils. Silt and clay loam soils derive aeration benefits from proper mulching, as well as effective reduction of compaction. Mulch increases the water holding capacity of sandy loam soils.
Volcano mulching creates conditions that lead to disease and insect problems. This is a common mistake.
Be aware that soil pH levels can also be affected by the types of mulches used. For example, most composts will be slightly alkaline, so they're excellent for use in regions with acidic soils. However, continuous use of oak leaves, pine needles, pine bark and peat moss will increase acidity. The breakdown products of leaves, including oak leaves, will however, be alkaline, but continuous use of oak, pine and peat moss products will keep the soil surface acidic.
Organic mulches contain various mineral elements essential for plant growth, but should not be considered substitutes for fall fertilizer. Of course, inorganic mulches such as crushed stone, gravel, volcanic material, plastic and recycled rubber are less expensive, but offer no organic benefits to the plants.
Careful consideration, planning and educating clients on the advantages of fall/winter mulching will make their properties look much better this spring and increase their property values and their enjoyment of the warm seasons to come.
Mike Ingles is an experienced researcher and writer who lives and works in Columbus, Ohio. Reach him at firstname.lastname@example.org.