Spring gardening and landscaping often means mulching. Mulch is a layer of material spread on top of the soil to protect plants. It helps keep the soil warmer during the winter, and cooler in the summer. It reduces
soil erosion and compaction, amends the soil, helps control weeds, and protects plants during droughts. Texas A&M AgriLife Extension states that a “well-mulched garden” can produce up to 50 percent more vegetables than one of similar size that’s unmulched. Mulching benefits do not end there; it can also be used to create landscape design elements, such as forming a dry creek bed, defining uncluttered borders, creating patterns, or highlighting trees or other plants. Although it sounds simple enough, it’s useful to understand the different types of mulch and their benefits and limitations, so the right material can be used to maximize its advantages.
Mulches are categorized as organic and inorganic. Organic mulches include any natural material that easily decomposes. Wood chips, grass clippings, nut shells, compost, straw, newspaper, and sawdust are all examples of organic mulches. A benefit of organic mulches is when it decays, some nutrients will make their way into the soil. Sawdust, however, can inhibit nitrogen, so fertilizer must be applied to the soil (or mixed into the sawdust before using it as mulch).
Of all the mulch types, organic is probably the least expensive and easiest to find with the least negative consequences except for the need to replace it more frequently.
Wood chips and nut shells are commonly used. They allow for air and water circulation, and organic material helps clay soil, which is common in Ellis County, to be more crumbly instead of hard-packed. AgriLife Extension recommends a 4-inch layer of mulch; it will not only allow the ground to absorb more water, but it also reduces water loss. Preventing this loss is essential during Texas’ hot summers. When mulching around trees, do not pile the mulch up and around tree trunks, which can lead to disease and pest infestations. Sawdust and compost have a finer texture than chips and shells. With deep layers they can control weeds, but water and air circulation will be inhibited.
Organic materials decompose quickly and require frequent replenishing. AgriLife Extension advises applying enough organic material that when settled, it will be 4 inches thick. Coarser materials, like straw, may
need as much as 8 inches or more, and newspapers should be at least eight layers thick. Further, AgriLife Extension recommends adding more mulch during the growing season to keep weeds at bay as the materials break down.
Dyed mulches, such as black wood chips, are not toxic to use, according to the Cooperative Extension at the University of Maine. However, they caution buyers to know the supplier and wood source, so recycled pressure-treated wood can be avoided because it might be contaminated with copper arsenate. The Environmental Protection Agency (EPA), advises that wood treated with chromate arsenicals should not be used for mulch. According to that agency, chromated arsenicals, which include chromated copper arsenate, have been used to treat wood as a pesticide since the 1940s but no public health risks have been found. However, it can be a risk for plants and aquatic invertebrates.
Inorganic or synthetic mulch refers to man-made materials and those that do not decompose quickly. These mulches include plastic, recycled rubber mats, rocks and rock chips as well as landscape fabric. A benefit of synthetic mulches is it breaks down slowly and does not require frequent replacement. On the other hand, synthetics’ shortcomings relate to its artificial composition. As it decomposes, it may release chemicals into the ground. It can also create a barrier for rain and air circulation, which may be good for weed control but also negatively affect desired plants.
AgriLife Extension notes that plastic is the only inorganic mulch used in vegetable gardens. Black plastic helps to warm the soil in early spring and summer, and it can help to reduce weeds. The downside to using it is that at the end of a growing season it must be removed because it cannot be turned back into the soil.
Rocks and stones can add depth and dimension to a landscape. Although it may seem contrary, rocks do not increase ground temperature. While rocks do prevent weeds for a while, they are not a good permanent solution without using herbicides.
An alternative mulch is ground cover, often called living mulches. Lush ground covers are gorgeous to behold for spaces that otherwise might be bare. They fill spaces under trees and in open, sunny areas. Some
produce flowers, bringing color into an area that may be plain. Some popular ground covers are ajuga, Asian jasmine, Carex/sedge, periwinkle, ivy, horseherb, liriope, mondo grass, purple wintercreeper, and Texas frogfruit. The downside to living mulches is competition. It competes with other plants for everything — water, light, nutrients and space.
AgriLife Extension offers some tips for mulch selection. The first is cost — if you have appropriate material already available, use it. For example, cut branches and trees can be chipped in a wood chipper. Next is to never mulch with the same crop material as what is planted. To illustrate the point, if cucumbers are grown in the spring, do not use those same plants as mulch for an autumn cucumber crop. This simple rule will avoid spreading diseases from one season’s crop to the next. The last tip is to consider the mulch color. Light color mulches reflect heat and are better in the summer and fall, but dark mulches will warm the soil for spring planting.
by Teresa Brown, ECMG
Sources
Environmental Protection Agency. (n.d.) Ingredients Used in Pesticide Products. Chromated Arsenicals.
https://www.epa.gov/ingredients-used-pesticide-products/chromated-arsenicals-cca
Texas A&M AgriLife Extension. (June 2014.) Easy Gardening: Mulching. PDF Hort-PU-110
https://cdn-de.agrilife.org/extension/departments/hort/hort-pu-110/publications/files/easy-gardening-mulching-1.pdf
Texas A&M AgriLife Extension. (n.d.) WaterSmart Landscapes for the Upper Texas Gulf Coast. https://watersmart.tamu.edu/mulching
University of Connecticut, College of Agriculture, Health and Natural Resources. (n.d.) Mulch Basics. https://homegarden.cahnr.uconn.edu/factsheets/mulch-basics
University of Illinois Urbana-Champaign, Illinois Extension (March 27, 2023). Make the most of Mulch by choosing from living, synthetic, inorganic, or organic.
https://extension.illinois.edu/news-releases/make-most-mulch-choosing-living-synthetic-inorganic-or-organic
University of Maine. Cooperative Extension. Ask the Expert. (June 15, 2022). Is black mulch harmful to plants? Is the dye in the mulch toxic?
https://extension.umaine.edu/gardening/2022/06/15/is-black-mulch-harmful-to-plants