USA TODAY National
I think I’d be hard pressed to find a gardener unaware of mulch, that stuff you put under plants to help keep down weeds and make your landscape beds look more defined. But there’s more to mulch than you might realize.
Mulching your lawn
You might not consider that lawns profit from mulching, but unless you use a leaf catcher each time, you are mulching your turfgrass as you mow. As shredded tree leaves and blades of grass decompose, important nutrients are added to your lawn.
It is estimated that a year’s worth of leaf clippings left on a lawn is equivalent to one chemical fertilization of your lawn. It’s best to use a mulching blade or adjust the angle of your mower’s blade to shred as finely as possible and to return the shredded debris back to the surface of the lawn.
Mulching your landscaping beds
Home gardeners often think of mulch as being something you add to landscape beds to discourage weed growth and retain soil moisture. While mulch not only provides these important functions, it also helps define your landscape beds, can serve as a border next to driveways and sidewalks, and provides contrasting color. In addition, mulch can act as a buffer around the base of trees and shrubs to prevent damage from mowers and string trimmers.
Placing mulch around trees, shrubs, and planted beds provides additional benefits. In areas that are difficult to mow, irrigate, or otherwise maintain, you can use mulch to replace turf or other plants. Consider placing mulch in shady areas where turfgrass may struggle. Mulch is a nice aesthetic addition to gardens and landscapes and helps tie the landscape together.
Applying mulch to prevent weeds
While bed areas should be weeded prior to mulching, putting down an appropriately deep layer of mulch is a highly effective way to control future weed germination and growth. Mulch both prevents light from penetrating to weed seedlings and stresses existing weeds. This benefit does wane as mulch breaks down but will return as mulch is refreshed.
Some organic mulches, especially certain types of wood chips, can control weeds through emission of allelopathic, or growth-inhibiting, chemicals naturally occurring in the wood. Pine and eucalyptus mulches can suppress germination of several common weed species. To prevent weeds, pine straw mulch is effective at a depth of three to four inches, while a layer of two to three inches of pine bark mulch is sufficient.
The use of landscape fabric under mulch is not only unnecessary, but it actually can work against you in establishing and maintaining plants. See the UF/IFAS blog, Consider Landscape Fabric Carefully for more information about the use of landscape fabric.
Encouraging root growth and plant performance
Roots covered in mulch expand far past the trunk or stem compared to roots in bare soil, thus stabilizing the plant and increasing the chances of survival. Mulch has also been shown to help plants survive transplanting in harsh conditions.
Many studies have shown that organic mulches allow trees, shrubs, and other plants to thrive. Researchers have found that a mulched tree grows 67% better than one planted in bare soil. Increases in plant height, stem and trunk diameter, leaf size and number, and flower, fruit, and/or seed production have all been shown to improve with the use of mulch.
However, an exception to this is citrus, which grows best without mulch on the surface above the roots.
Controlling disease and enriching the soil
Mulch helps maintain soil moisture, slowing evaporation and reducing plants' water needs. It moderates soil temperature by keeping plant roots warmer in winter and cooler in summer.
Organic mulches help gradually build soil organic matter as they decompose, improving nutrient-holding capacity and thus available nutrients for landscape plants. All these factors indirectly provide an optimal environment for healthy plants to grow, lowering the plants’ susceptibility to pathogens.
Research has shown that organic mulches also promote soil health by supporting a diverse community of beneficial microbes and insects, both in the mulched area and in the larger landscape.
Organic mulches are the best
The best choice is always an organic mulch because it contributes nutrients to your soil as it decomposes. Avoid any bagged mulch that contains cypress (check the label), as the wood may have come from whole trees that have been harvested from wetlands. As you have no way of knowing where the cypress came from, it is best avoided.
Another popular bagged mulch is shredded wood from pallets and other scrap lumber, usually dyed red, brown, or black. The potential problem with such mulch is that it may have been made from lumber that was treated with chemicals harmful to the environment.
Look for bags that are certified safe from these harmful chemicals. This mulch product settles quickly and requires frequent renewal.
Pine products – either straw or pine bark – are very commonly used in our area and are considered environmentally friendly. Pine straw does not wash away very easily in heavy rains, as the needles tend to knit together, so this may be a preferred product for a slope. However, pine straw settles and breaks down relatively quickly and requires frequent refreshing. A consistent three- to four-inch layer of pine straw is optimal.
Pine bark nuggets are a byproduct of the forest industry. They come in ground and nugget forms, have a rich brown color, and settle slowly. One study by UF/IFAS found them to maintain two-thirds of their original depth after two years. Consider the mini nuggets to put around smaller plants. The most effective depth of pine bark nuggets is two to three inches. Bark mulch deeper than that can actually preclude water from reaching the soil.
It’s possible to obtain shredded tree mulch from utility companies or tree services, but since unidentified plants, weed seeds, and/or soil may be mixed in, this mulch type may be better utilized along driveways and sidewalks than in your flower beds.
Avoid inorganic mulches
Gravel or pebbles used as mulch do nothing to hold in moisture and do not add any organic matter to your soil. Light colored gravel also may reflect so much light and heat back to your plants as to cause damage. Pebbles and gravel also don’t look good with leaves and other yard debris on top of it, thus requiring a lot of maintenance, So these are best left for garden paths (with landscape fabric underneath) and under downspouts.
Rubber mulch made from recycled tires is not recommended by UF/IFAS. It is generally less effective than organic mulches in suppressing weeds. This recycled material also absorbs heat, leading to extremely high temperatures in the ground beneath. There is also the concern about the possibility of toxic chemicals leaching into the soil as the material slowly degrades.
Where you don’t want mulch
Mulch should be pulled away from the base of shrubs for a few inches, and you should keep mulch 12 to 18 inches from the trunk of any size tree. For aesthetic reasons, a thin, one-inch layer of mulch can be placed over the root ball; otherwise, a thicker layer will block irrigation and rain from reaching the roots.
Outside of the root ball, provide a two- to three-foot diameter circle of mulch for newly planted trees. During the establishment of the new tree, use the mulch – and herbicides, if necessary – to keep turf as far away from the tree trunk as practical. The mulched area around the tree will also help prevent mower and string trimmer damage to the trunk and avoid soil compaction. Mulch should extend all the way to the drip line under larger trees.
Piling mulch against the trunk of a tree is called “volcano mulching” and should be avoided. It holds moisture against the lower bark and encourages rot. Additionally, it creates a habitat for rodents, which tend to chew on the tender bark of trees.
Appropriate mulches add to the organic matter in the soil, retain water, regulate soil temperatures, and contribute to the beauty of the landscape.
There’s no other single gardening practice that adds so much to your landscape with such ease.
Susan Barnes is a Master Gardener Volunteer with UF/IFAS Leon County Extension, an Equal Opportunity Institution. For gardening questions, email AskAMasterGardener@ifas.ufl.edu.
This article originally appeared on Tallahassee Democrat: Everything you always wanted to know about mulch and more
Reporting by Susan Barnes / Tallahassee Democrat
USA TODAY Network via Reuters Connect
Cover Media
ABC News US
The List
The Week
IMDb TV