Perhaps the reason we don’t see many bare spots in the wilderness is because Mother Nature knows uncovered ground is bad for business. When we manipulate our environment by growing something (plants, trees, flowers, vegetables), we can improve the ecosystem by covering up the resulting bare spots with mulch.
Mulch will suppress weeds, protect roots from fluctuating and extreme temperatures and retain soil moisture. It prevents compaction from our footsteps as well as erosion by wind or water. Conversely, when the sun is shining, it prevents evaporation from the soil surface while slowly releasing moisture into the soil. As a bonus, the right type of mulch looks fantastic.
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Inorganic mulch, such as ground-up tires, plastic nuggets or gravel, can last indefinitely, but organic mulch in the form of wood chips, leaves, bark and pine needles increases soil nutrients and biodiversity when it decomposes. Organic mulch slowly gets broken down by microbes into humus, a group of natural organic compounds, and increases the organic matter content of the soil. Humus has an incredible ability to hold onto lots of water, fend off pests and control weeds. Many people opt to mulch in early spring to ward off the weed-sprouting season, but mulch has year-round benefits.
You can buy mulch in bulk loads or in more manageable bags. If you want to save money in the long run and know the exact ingredients of your mulch, you can buy or rent a wood chipper to make your own mulch pile.
Know Your Mulch
All mulches are not created equal. Be sure to opt for the mulch that best suits your needs. Below is a list of some characteristics of most types of organic mulch.
Shredded Bark: Bark mulch is viewed as aesthetically pleasing because of its uniform color and texture. It only falls short as the ideal mulch because it often repels water instead of absorbing it.
Sawdust: Sawdust is also considered an eye-catcher, but due to its fine texture, sawdust creates an impermeable barrier that repels rain. Sawdust can be hard to find in large quantities, and it must come from clean, untreated lumber.
Wood Chips: Wood chips appear to have all of the benefits and none of the problems associated with bark or sawdust. Wood chip mulch will break down a lot faster than shredded bark while retaining moisture better.
Leaves: Some might prefer the aesthetics of other mulches, but a rainbow of autumn leaves can be stunning. Big, wet leaves can restrict air and water movement to the soil, so it is best to shred them a little and restrict the depth to about 2 inches. Aside from breaking down quickly (often in less than a year), leaves make for outstanding mulch.
Cypress: Some commercial cypress mulch now comes from immature trees rather than the bark of mature trees, which makes the mulch not as effective. In some areas, cypress trees are being overharvested. For more on the “cypress crisis,” go to vnps.org.
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Compost: Whether you think mulch and compost are the same thing or completely different, you are right!
Pine Straw/Needles: Although you’ll need a thick layer of pine straw to suppress weeds, you won’t need to apply it very often since it lasts a long time. Pine straw can also be used on slopes or anywhere there is a problem with wood chips floating away. The needles become entangled and stay in place better than other mulches.
Straw: Straw provides a great home for mice, voles and other harmful pests. It can contain weed seeds, and since it usually doesn’t completely block out the sun, it won’t act as a weed suppressant like other mulches unless it is piled high.
Grass: Grass can become too dense and matted, blocking moisture from the ground. Be wary of grass coming from chemically treated lawns. Grass clippings may be better suited for your compost pile.
Compost Vs. Mulch
It’s easy to confuse compost and mulch because they can sometimes be interchangeable. Each serves as a time-release fertilizer and insulator. In general, mulch is made up of organic matter that hasn’t yet broken down, whereas compost consists of organic matter that is fully decomposed. Mulch provides a protective cover for your plants or soil in the short term and then eventually breaks down and becomes the equivalent of compost.
Always apply mulch on the surface of the soil. Compost, on the other hand, is often worked into the topsoil as an amendment. Because mulch is denser than compost and takes longer to integrate into the soil, mulch doesn’t need to be re-applied as often as compost.
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Can compost be used as mulch? Absolutely! Compost is fantastic at holding moisture in the underlying soil. It also releases a bevy of nutrients, making it the ultimate fertilizer. Unfortunately, because compost is so rich and fine, it doesn’t work well as a weed suppressor.
Another consideration is availability. It often seems as if there’s just not enough compost to go around. Mulch is cheaper and more readily available, even if you make your own. But if you’ve got an ample supply, compost can definitely be used as mulch and can even do both jobs at the same time.
Mulch Myths Debunked
Misinformation about mulch has been passed down for generations, but science is finally catching up and revealing its benefits. Studies have debunked most of the following mulch myths.
Mulching starves your plants of nitrogen: This is perhaps the biggest mulch myth, and the explanation is more complicated than space allows. The research tells us that unless you’re working with container plants, mulch will not affect the pH or nitrogen levels enough to harm your plants’ root systems.
Pine needles/pine straw will make the soil more acidic: The truth is that any organic mulch will make the soil slightly more acidic. Azaleas, rhododendrons and blueberry plants love acidic soil, and other plants can tolerate the negligible increase in acidity. If you are leery, add some fertilizer or lime every few years.
The chemicals in wood chips will poison your plants: Recycled wood products like old pallets, demolished buildings and railroad ties have no business in your garden. But most other types of wood contain no harmful chemicals or only slight amounts of allelopathic chemicals, which should have no effect on established plants. They will be diluted to harmless levels after a heavy rainfall.
Pile mulch high at the base of trees or shrubs: “Volcano mulching” keeps moisture in constant contact with the tree bark, which promotes decay fungi. Once the protective bark has rotted away, decay can spread into the trunk and kill the tree. Volcano mulching prevents water from getting to the soil and promotes the development of surface roots. Mulch should always be pulled back a minimum of 6 inches from tree trunks. In most cases, there should be bare ground at the trunk out to about 6 inches. Then, the thickness or depth should be gradually increased to a maximum height at the drip line of the plant or tree or even well past it.
The more mulch, the better: Coarse-textured mulches like pine bark allow good air movement through them and can be as deep as 4 or more inches. But optimal depth is about 3 inches or less if you are using a denser medium like mulched leaves or grass. You want oxygen and water to be able to travel to plant roots, so don’t pile it on too thickly.
Mulch will attract termites and mice to your house: Termites may feed on mulch if they are already at the location, but in general, termites are attracted to higher-quality wood such as construction debris. Even if the wood you are chipping has some termites in it, the insects probably won’t survive the mulching/chipping process. Mice don’t really care for chips either. Mice like to burrow, but mulch tunnels collapse.
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You need to mulch annually: It depends on the type and depth of mulch. It’s best to give mulch a chance to completely break down and not prematurely pile on more layers.
Mulch made from diseased trees can infect healthy trees: There is no evidence that chips from a diseased tree will infect a healthy one. Just don’t backfill the tree’s hole with diseased wood chips. This can transmit disease.
Dyed wood mulch is harmful to your soil: According to the EPA, there’s nothing to fear from the colorants used in wood mulches. The dyed (especially the reds and greens) varieties are stunning at first but can quickly fade and even end up with an uneven appearance. The blacks and browns hold their color better.
Make Mother Nature happy. Whether to protect and nourish your garden beds and trees or just for landscaping aesthetics, cover up the myths with mulch!
How Much Mulch
Determining how much mulch you need requires some simple calculations. It’s important to know that there are 27 cubic feet in a cubic yard, and 1 cubic yard will cover a 324-square-foot area with a 1-inch layer of mulch.
First, figure out the surface area (square footage) of the space. For a square or rectangular bed, that’s width times length. In order to figure out the area of a triangle with two equal sides, multiply the base times height and divide by two. For a circular bed, you finally get to use your high school geometry. The square footage of a circular bed is the distance from the middle of the circle to the outside, multiplied by itself (squared), and then multiplied by 3.14 (which is pi).
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Now, you need to determine how deep you want your mulch. Multiply the depth in inches by the surface area (square footage). Divide your answer by 324 (because 1 cubic yard of mulch will cover 324 square feet 1 inch deep). Buy this amount of bulk mulch.
BY THE BAG: If you are buying bagged mulch, make one more calculation to convert cubic yards to cubic feet. One cubic yard equals 27 cubic feet, so multiply the total cubic yards from the previous step by 27 to get the number of cubic feet.
Purchase the number of bags containing the amount of cubic feet you need.
Here’s an example:
- 30 feet (width) x 10 feet (length) = 300 square feet
- 300 square feet x 3 inches (depth) = 900 cubic feet
- 900 cubic feet divided by 324 = 2.78 cubic yards of bulk mulch
- 2.78 cubic yards x 27 = 75.06 cubic feet of bagged mulch
Note: For those allergic to math, there are a myriad of online coverage calculators where you can just plug in your measurements to determine the amount of bulk mulch you need.
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This article was originally published in The NEW PIONEER™ Fall 2015 issue. Subscription is available in print and digital editions here.