In the first part of our series on mulch, published in Green on May 27th, we talked about the different types of organic mulch. The Frederick County Forestry Board strongly recommends using organic mulch over all others because, in addition to structure and porosity, only organic mulch adds essential nutrients and allows water, oxygen, and roots to burrow and penetrate the soil. All of this is necessary for plants and trees to grow and thrive, produce our food and oxygen, and pull carbon from the atmosphere.
Before we dive into inorganic mulches, let’s share some best practices for all mulching applications.
First, determine where you want your flower bed or mulch ring to go, and use an edger or planting spade to dig a 2- to 3-inch-deep demarcation edge. Remove any grass or plant matter from the bed. Most landscapers apply a pre-emergent herbicide at this point to discourage future weeds. However, if you want to keep weeds at bay and don’t want to add chemicals to the soil, we recommend applying a biodegradable geotextile layer prior to applying the mulch, which allows water to drain but blocks light from entering. For existing beds and mulch rings, remove old mulch from existing plantings to about 1/2 to 1 inch, then apply the new mulch on top according to the following specifications: We recommend installing mulch in plant beds and tree rings at a depth of 2 to 2 1/2 inches. Individual trees should have a saucer formed around the outside of the root ball of new or existing soil with a raised lip at the drip line about 3 inches. Do not place new soil on top of the root flare and leave a 2 to 4 inch gap between the log and the newly applied mulch ring. We’ve seen too many “mulch volcanoes” around the bases of trees because old mulch hasn’t been removed or mulch has been stacked against the trunk, preventing air, water and nutrients from moving in the soils and damaging the tree.
Older organic mulches lose their color over time and should be incorporated into the soil. Otherwise, they can develop some unusual unwanted organisms. Have you ever seen small black spots on areas of the house or patio that resemble tar stains? These are fungal spores of a shotgun fungus that form in the mulch and are released onto nearby surfaces. Another organism called Dog Vomit is a slime mold that looks horrible but does no harm to your plants, pets, or family. Other fungi and mold can also appear over time, but they usually dry up and disappear.
Colored mulch has also become popular over the years as artificial color enhances the visual contrast between plants and lawn. While there are some mulches that use organic dyes (primarily yellow and brown plant dyes), most colored mulches actually contain less organic matter because it doesn’t retain color as well. For this reason, many colored mulches are made from wood chips from old pallets that may be used to ship toxic chemicals, demolished wooden structures, and even old pressure-treated lumber, which isn’t good for our soils and food. Black-colored mulch, in particular, can become toxic to the environment if the dye comes from heavy petroleum products like tar and coal tar. These products are known as soot and they can potentially find their way into soil and eventually our water. So please read mulch labels and look for Mulch Soil Council (MSC) certification to ensure it does not contain pressure treated – also known as chromated copper arsenate (CCA) treated – wood.
There are many inorganic mulches on the market. Many are only used for aesthetic reasons and add no nutrients to our soils. For example, rubber mulches are often made from recycled tires, which then contain chemical pollutants such as volatile organic compounds, polycyclic aromatic hydrocarbons, benzothiazyl disulfide, and latex. The EPA has determined that these chemicals cause cancer, headaches, nausea, contact dermatitis, allergies, and other health problems. The zinc from caoutchouc lye is also harmful to plants. In other words, check the composition, durability, and source of rubber mulch if you decide to go this route.
Another popular flooring in our area is geotextile weed barriers, landscape fabrics, and floor dividers made of non-woven and woven polypropylene. However, we strongly encourage you to look for biodegradable geotextiles as we certainly don’t need to add any plastics or polyprenes to our soil. If you decide to use a geotextile cover make sure you are aware of its special drainage potential to avoid flooding the area and do not place the material too close to trees as plastic can get very hot the summer and can literally cook off the roots of nearby plants. Landscape fabric, on the other hand, is porous and shouldn’t pose a problem if it’s biodegradable unless blocked. Over time, Mother Nature will manage to plant weeds on all textiles.
Since most newspapers do not use toxic dyes, newspapers can also be used for mulching. We have used moist papers to keep the roots of plants moist for years as they have good moisture retention abilities. Additionally, papers suppress weeds (in fact, you can smother grass with layers of newspaper) and they control soil temperature if you put four to eight layers of paper around your plants to keep them moist.
Finally, there are many sizes and shapes of crushed stone, gravel, river rock, shale, rock and boulders. Most of these are attractive and protect soil from wind erosion and compaction, but rocks don’t hold moisture, reduce weeds, or disperse high and low temperatures as well as organic mulches. Some may also require a special edge to hold them in place. Gravel and rock work well as mulches in areas that need good drainage or beds with plants that like a little extra warmth, such as gardens. B. Mediterranean herb gardens and rain gardens. Stone is difficult to remove, so plan for the long term when using it.
When it comes to mulch costs, it can be difficult to compare apples to apples. Pay attention to the source, sale, size of the container, and quality and type of product. The Frederick County Division of Solid Waste and Recycling has an affordable program that offers double-shredded hardwood mulch at $10 per ton to anyone who comes and picks it up at 9031 Reichs Ford Road in Frederick. This is part of the county’s effort to recycle local yard waste, branches and tree stumps and is perfect for landscapers and neighborhood groups. Unless you buy by the ton, you can buy mulch in bulk in cubic yards or in 2 or 3 cubic foot bags. If you buy mulch in a 3 cubic foot bag, you will need nine bags to give you one cubic yard. Mainstream prices for bagged mulch can range widely, from $24 per cubic yard of hardwood chips to about $40 per yard for dyed mulch to $100 per cubic yard of cedar shavings or even $150 for rubber mulch.
To summarize our mulch suggestions, we recommend planning ahead, delineating and measuring where you want to add what type of ground cover and mulch, and then exploring availability and cost. The Forest Service recommends using organic mulch as it is the only one that provides nutrients and structure to our soils.The Frederick County Forestry Board promotes the conservation, stewardship, and sustainable use of our forest resources and urban landscapes. We educate the public and work vigorously to maintain or improve the integrity of our local, regional and national forest ecosystems. Trees promote our physical and mental well-being; improving the quality of our streams, lakes and bay; help cool the environment; preserve and improve soil; produce oxygen while consuming carbon dioxide; and provide shelter and food for wildlife. Please visit frederick.forestryboard.org for additional information and resources or to sign up for our free weekly Nature Note articles, tree planting, second Sunday tree walks, treehouse exchanges and more.