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Bark Mulch

by James B. “Jim” Kea
Area Extension Forestry Agent – now retired
Thursday, February 9th, 2006

Bark mulch can make your landscaping more colorful, more beautiful, and is more beneficial for your plants. Bark mulch can be used on your flower beds, around your trees and shrubs, on walkways, in playgrounds, or anywhere you can think of to use one of nature’s most versatile and abundant materials – bark – for your benefit. By applying bark mulch on top of your plant soil, you protect your plant’s delicate roots from excessive heat and draught in summer.

Mulching with bark also helps improve your soils’ texture by enriching it with natural humus. Bark mulch can improve the drainage of heavy clay soils and improves the water-holding capacity of sandy soils. And it won’t crust, blow away, or wash away if properly applied.

The initial application of four (4)-inch layer of bark mulch can save you yard-maintenance time. Because it smothers weeds, you do less weeding and you won’t have to trim grass along borders. It reduces evaporation so you won’t need to water as often. Another advantage of bark mulch is that it breaks the force of rain which prevents mud splattering on the side of your house. Bark mulch will last 3 to 6 years after your initial application and needs only the addition of a minimum amount of new material each year to maintain the proper depth of 4 inches and renew that rich brown color.

Bark mulch is made from a wide variety of forest tree species – both hardwood and pine. It is relatively inert and non-toxic. Tests show that bark mulch will not affect the acidity of your soil in any appreciable way. Nor will it use your soil’s nitrogen if you follow normal fertilization practices.

The bark is removed from logs by a debarker before they are sawed and processed into lumber products. The bark is then processed through an industrial hammermill or shredder. Next, the material is screened into different types and sizes of bark mulch.

The largest-size pieces are called chunks; the next size particles are referred to as nuggets; and the smallest pieces are called mini-chips or chips. The remaining fines are packaged and sold as a soil conditioner. The cambium layer, a zone of living cells between the bark and woody stem, is long, stringy material which is sold as bark shreds. This material is more suitable for mulching on steep slopes.

Some persons question whether to use pine or hardwood bark for mulching. The following key points explain the difference.

Pine Bark. Most people are more familiar with this product because a much larger supply of this material is being processed, packaged, and sold, especially locally. The bark of pine trees is much thicker. Therefore, a much higher percentage of it can be bagged and sold either as chunks or nuggets for decorative purposes.

Hardwood Bark. A much wider variety of bark comes from hardwood tree species being processed and packaged for mulch. These barks are platey, fissured, thin, or stringy. When hammer milled and screened, most fall into the smaller size categories of mini-nuggets or mini-chips, soil conditioner (fines) or sheds. These barks are used more for utility rather than for decorative purposes.

There is little or no difference between the usefulness of either pine or hardwood bark. Both perform adequately to conserve moisture and reduce weeding around plants. Also, none are toxic to plants. Some hardwood barks are more acidic, but the addition of nitrogen can offset this property.

Bark mulch is carried in garden centers, nurseries, discount stores, hardware stores, and food markets in a range of types and sizes. It is generally packaged in 3 cubic-foot plastic bags containing enough material to cover 18 square-foot area with 2 inches of mulch. It can also be bought from local processors in bulk quantities at much lower prices.

You should keep in mind your planned uses when selecting the type and size of bark mulch you will need. When making an initial application of bark mulch on bare soil, you should use the soil conditioner or mini-chips types for the first 2-inch layer. These grades of bark mulch are the least expensive to use and will decompose the fastest adding useful organic humus to the soil.

Remove grass and weeds from around your plants and loosen the soil before applying your mulch. It would be useful to add a layer of newspaper on the bare soil before applying the bark mulch. This holds the moisture in the soil and prevents weed growth. After the first 2 inches of bark mulch are applied, you can then add another 2 inches of the nugget or chunk bark. These are the most expensive sizes of bark mulch.

Weed and grass control around trees may double growth by reducing competition for nutrients and increasing available moisture. Many diseases caused by lawnmower damage can also be eliminated.

Bark mulch can be used for landscaping around any kind of living plant in your yard. It is a very attractive material which adds to the beauty of the landscape. It also provides a useful function for plants and trees by conserving moisture and adding organic material once it decomposes.

Bark mulch may also be used in many other ways. Some examples are: 1) for borders along fences, driveways, and sidewalks, 2) in pet enclosures, 3) in picnic and barbecue areas, and 4) for ground cover, planting beds and on seeded steep slopes. Bark is also composted and mixed with fertilizers, nitrogen, and other additives for use as a soil conditioner and potting media.

Bark will not provide food for termites. Termites found in or under pine bark are there for buried wood. Treating bark is a waste of money and may be hazardous to pets, children, and beneficial wildlife. If slugs are a problem, use beer traps or commercials baits. Roaches found outside in bark or woodpiles are not the type that breed in the house. The woods roach needs moist conditions to survive.


Revised 2/16/2006, 10/13/2011.