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Backyard Gardener: Let’s talk about mulch

Hello Mid-Ohio Valley farmers and gardeners. October is here! That’s right, football, picking pumpkins and making apple cider. Well, a lot more goes on in the fall but I do enjoy some good apple cider, maybe with some pumpkin muffins or doughnuts. They do make pumpkin flavored doughnuts, yes?

Fall is a busy time on the farm and around the garden. Harvest season is in full swing as we look to shorter days, cooler nights and around the corner we can see old man winter. October is the time to plant garlic in the valley, but maybe I will discuss that next week.

Fall is a great time to apply mulch and other soil amendments. First and foremost, you need a soil test to know what your current nutrient levels are and what the soil is lacking. This is the best time of year to take a soil test for the garden, lawn, or field crops. If you have questions, contact me at the Extension Office. Don’t guess, soil test.

This week I want to focus on the importance of mulch. Any homeowner or landscaper knows the crucial role which mulch plays, so taking the time to spread mulch around flower beds, trees, and in the garden. Especially around new plants or ones which need protection this winter.

Applying mulch or mulching serves many purposes for the backyard gardener. It helps to prevent weed growth, conserve soil moisture in the heat of summer, cool soil surface and stabilize soil temperature. Research shows that two inches of bark mulch will reduce moisture loss in the summer by 21 percent and lowers soil temperatures during summer in the upper four inches of soil by 10 degrees F.

Mulch also reduces heaving of small plants (plant roots being forced upward out of soil) as a result of alternate freezing and thawing of the soil in the winter. It reduces soil erosion and keep fruits, vegetables and flowers cleaner. Finally, it can improve the overall look of the landscape.

One of the major benefits of applying mulch is you are adding organic matter to soil. Many gardeners ask me “Where does all the mulch go? I keep having to apply it every year.”

The faster the mulch is breaking down, the healthier your soil is. Your soil is alive with beneficial bacteria and fungi. The billions of microbes in the soil are breaking down the organic matter in the mulch to be used by vegetables, flowers, shrubs and trees.

The two most common questions homeowners ask about mulch is what kind of mulch to apply and how much. Let’s start with the easy one. The recommended mulching depth, depending on the material selected, is about 2 to 2.5 inches. At this depth, most mulches will accommodate the primary objectives of weed control, soil moisture conservation, adding organic matter and temperature modification. If a site already has mulch from last year, a thin, 1-inch top-dressing is more than adequate.

However, too much of a good thing can be bad. Mulch applied 3 to 6 inches deep or more may lead to serious problems for landscape plants. A mulch that is too thick may severely reduce or eliminate drying and lead to water-logged soil, particularly during wet seasons or in heavy clay loam soils.

Extended periods of wet soils in spring are most damaging to a number of perennials including azalea, rhododendron and conifers in general. Excess mulch, particularly if applied right against the stem or trunk of landscape plants, also leads to constantly wet bark and invites disease development.

Now we can talk about what kind of mulch to apply. It depends on what your goals are and what plants you are mulching. Most organic materials such as shredded or ground bark, ground wood chips or shredded leaves can provide the key benefits we want out of mulch including conserving moisture, controlling weeds, and adding organic matter. Cost, aesthetic appearance and availability are often factored into your decision-making process.

For general weed control and other benefits go with shredded bark. This material is by far the most popular landscape mulch due to appearance, availability and cost. This includes shredded hardwood in addition to cypress bark, chipped and chunk pine, and fir.

Compost is also an option. Commercially purchased composted manure, mushroom compost or leafmold can add lots of slow-release nutrients to the soil. You can also make your own compost with grass clippings, leaves and kitchen waste.

For new garden beds, apply a 3- to 4-inch layer of compost to the soil surface. You can add other amendments such as lime and fertilizer as needed. Incorporate these materials with a digging fork, spade or rototiller. For existing garden beds, apply a layer of compost about 1-inch deep to the bed surface each year.

Dried animal manure can be used if you live close to a farm. Free organic matter and all those nutrients, of course it can be used as a fertilizer. However, weed seeds are often introduced with manure and if it is not fully composted it can burn the roots of small plants. The best plan is to compost animal manures.

The pH of the soil can be changed depending on the mulch selected. For example, most composts will be slightly alkaline or sweet (pH greater than 7) and are excellent for use around flower beds and gardens.

Continuous use of oak leaves, pine needles, pine bark and sphagnum peat moss will increase acidity. The breakdown products of leaves, including oak leaves, will be alkaline, but continuous use of oak, pine and sphagnum peat moss products will keep the soil surface acidic (pH less than 7).

If you have blueberries, azalea, rhododendron and conifers sphagnum peat moss may be a good choice for mulch. It will add organic matter and is acidic so it will keep the Ph low for these acid loving plants. The needles of pine trees as well as shredded cones make an excellent mulch particularly for evergreens and plants that thrive in acidic soils. Pine needle mulch, formerly available only in the southern states, is available now.

Historically, straw and hay have been used for winter protection of perennials, small plants and of course strawberries and small plants. My only caution is weed seed can be introduced from these sources. These materials decomposes readily so you will have to reapply.

Lawn clipping are a poor choice for mulch since they tend to mat together and impede water penetration if they dry out. In addition, they are unsightly and can produce an unpleasant odor as they decompose. A much better option is to compost your lawn clippings and then use the compost in your garden or as a top-dressed amendment before you apply mulch.

May and June are good times to apply mulch, but another application is often needed in autumn. For established plants, timing of the mulch application may not be as important as it is on new plantings, especially shallow rooted shrubs and evergreens, herbaceous perennials, or strawberries.

Mulching slows the freezing/thawing cycle which causes soil heaving. Heaving of small plants, especially those newly planted, occurs following alternate freezing and thawing of the soil.

To reduce heaving, which breaks roots and leads to winter injury, apply mulch following the first indication of frost in the ground. For established plants, water thoroughly in late autumn if the soil is not already moist, then mulch.

Fall mulching may prevent seed germination of several spring enemies of raised flower beds and gardens. Weeds such as henbit (Lamium amplexicaule), purple deadnettle (Lamium purpureum), chickweed (Stellaria media) and hairy bittercress (Cardamine hirsuta) germinate in fall and early spring.

As the soil starts to warm up, they grow rapidly and produce conspicuous blooms. Mulches serve a physical barrier that affects seed germination, conserves soil moisture and reduces the incidence of soil-borne diseases.

Contact me with questions at the WVU Extension Office at 304 424 1960 or at jj.barrett@mail.wvu.edu. Good Luck and Happy Gardening!

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