May 8, 2020
As summer approaches, it’s time to prepare our plants for the potentially hotter and drier months of July and August, which are typical of the Illinois prairie. If you have not already done so, one of the best things you can do for your plants is to apply mulch.
So why mulch? Past springs have provided excessive amounts of rain and even flooding. As a result, plant roots have not had to go very far to reach moisture. But when the rains stop and the soil begins to dry out, roots near the surface will have a much harder time taking up moisture and may dry out and die. These fine roots are extremely important, as they are the ones that take up moisture and nutrients.
Benefits of mulch
By mulching, you mitigate extremes by conserving soil moisture and moderating soil temperatures. This provides a favorable environment for roots and those all-important microbes. Microbes such as bacteria, viruses, nematodes, fungi and earthworms play a huge role in breaking down organic matter and releasing nutrients for plant growth.
By applying mulch, you protect your plants from weed trimmers and “lawnmower blight,” help keep the weeds down, and give the landscape a tidier look. Additionally, as the mulch begins to decompose, it contributes organic matter and valuable plant nutrients, which improve soil structure. Good soil structure allows for better water infiltration and aeration — yes, roots need oxygen just like we do! And, mulch provides habitat for soil critters.
What not to do
However, like all good things, too much mulch can be detrimental to your plants. Do not “volcano” mulch, or pile it up around the base of the plant. Too much mulch can keep the bark constantly wet, which can lead to disease issues, provide habitat for rodents, and may become encrusted and not allow water to infiltrate. Nature does not volcano mulch, so why should we?
Two to 4 inches of mulch is plenty, and should be evenly spread out in a circle or “donut,” preferably out to the canopy drip line. If that is not possible or desired, minimally, try to create at least an 18- to 24-inch mulch ring, and be sure to leave a small gap between the trunk and the mulch.
If mulch is still present and is at the proper depth, there is no need to add more — just “freshen up” what is already there.
What types of mulch are good?
Look for any organic properly composted material such as wood chips, leaf compost, pine needles, bark chips or leaves. Avoid “green” sawdust because of its nitrogen deficiencies, straw because it carries weed seeds, and grass clippings because they may carry herbicide residue.
If you are growing plants that like acidic soils, such as rhododendrons, azaleas, conifers or blueberries, pine straw or pine bark chunks will help acidify the soil naturally. Also, do not remove the dead needles under existing trees for the same reason.
Inorganic materials such as lava rock, gravel or pulverized tires can be used, but these are not recommended around trees, as they can heat up air temperatures, killing the bark of thin-barked trees. Plus, they do not add any nutrients to the soil and do not break down. Further, if you already have alkaline soils (pH greater than 7), using limestone-based products will raise the pH over time, making most micro- and macronutrients unavailable.
For further information on proper mulching and mulching materials, contact your local Cooperative Extension office, professional landscaper or arborist, or garden center.
Miller is a horticulture professor at Joliet Junior College, Joliet, Ill., and a senior research scientist in entomology at The Morton Arboretum in Lisle, Ill. Email your tree questions to him at [email protected]. The opinions of this writer are not necessarily those of Farm Progress/Informa.
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