Much ado about mulch

By KIM COWHERD Extension Agent for Horticulture Published:

Mulching your trees and shrubs in your landscape is a very important part of your routine maintenance to ensure the health and well being of your valuable landscape plants. Mulches help retain water in the soil, keep the roots cool in the summer and warm in the winter, keep weeds at bay, control soil erosion, and keep the dreaded Mower Weevils from slowly killing your trees! Some mulches also can help with soil composition, help protect from some plant diseases, and give your lawn a well-manicured appearance.

There are two basic types of mulch organic and inorganic. Organic mulches are generally any type that is derived from plants. Organic mulches include various types of shredded or chipped bark, pine needles or compost. Inorganic mulches are generally man-made products. Inorganic mulches include chipped rubber products, mats made of various geotextile fabrics, and various rock products.

Selection of a type of mulch is based on the type of plant you are applying mulch to; cost and availability of the mulch; desired end-use appearance; and personal preference.

Organic mulches are readily available, relatively inexpensive, and fairly easy to handle. These mulches will decompose over time, and can contribute positively to the health of the soil by adding nutrients and improving the soil quality. Organic mulches may need to be replenished and reapplied generally every year or so, a thin top dressing will usually be sufficient. Be sure you are using high quality mulch that is free from weeds and does not have a sour or vinegar-type odor.

Inorganic mulches are also available. These mulches do not decompose, and can be in your landscape for years. Inorganic mulches can be expensive and more difficult to apply, and must be removed when replanting or replacing entire beds.

Mat-type mulches must be cut to fit the area, and cut to ensure that valuable tree and shrub trunks will not be girdled or damaged by rubbing of the material. Mat-type mulches will need to be pinned down to prevent them from migrating from the area they are originally placed.

Inorganic mulches can hold more heat and water under them and must be placed where excess water can drain adequately. If they are in full sun, you must be careful that the plants they surround can take the extra heat and reflected sun. On the plus side, inorganic mulches can provide additional color to your landscape, and do not have to be replaced. They can be very effective in weed control.

Black plastic is not recommended as a mulch material for landscape plants. While plastic will help control most weeds and conserve water, it does not allow water, nutrients, and air to move freely to the soil below. Plants often develop a very shallow root system that is more subject to damage during severe drought or cold weather.

Steps for mulching

The steps in mulching trees and shrubs are simple.

First define and outline the area you wish to cover with mulch by placing a hose, string, or marking with turf paint. Second, remove the sod by applying appropriate herbicide such as one containing glyphosate to the grassy area, then cutting and removing the sod after it has died; or cut and lift the sod while it is still alive. Simply covering the weeds or grass with mulch is not a good practice!

Next, apply a weed pre-emergent herbicide. You may apply a geo-textile fabric at this point. Finally, apply your mulch. Organic mulches should be applied at a rate of 2 to no more than 4; inorganic mulches can be applied at 1 to 2, depending on the type of mulch you use.

Remember- too much mulch can be more detrimental than no mulch at all.

You should lay the mulch in a bowl-type fashion higher on the outer edges away from the trunk, and gradually decreasing the thickness of the mulch toward the trunk. You should never pile the mulch around the trunk of the tree or shrub! This is called volcano mulching. This is very detrimental to the health of the plant by causing excess moisture around the trunk.

Mulch can be applied any time of the year. However, the best time to mulch is late spring after the soil has warmed. Early spring application will delay soil warming and possibly plant growth. It is not necessary to remove the mulch when you fertilize. Apply the fertilizer over the mulch nutrients will move with water to the roots below.

Any weeds that emerge in the mulch should be pulled. Careful application of a glysophate type-weed killer can be done for large populations of weeds, but extreme care must be taken not to damage valuable landscape plants. Always read and follow all directions on pesticide containers!

Information for this article was gathered from the Alabama Cooperative Extension Service, Virginia Cooperative Extension Service, NC Cooperative Extension, and International Society of Arboriculture/Trees Are Good.

For further information regarding this topic ask for publication HO-78. For other horticultural questions, contact Kim Cowherd at the Franklin County Extension Office, call 502-695-9035.

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