Proper Mulching

Daniel Gill  |  4/1/2015 9:21:56 PM

Redwood Rubber Mulch

If you currently are not utilizing mulches in you gardening efforts, you really should give them a try. You’ll be amazed at how much work they save you weeding and how nice they can make a garden look.

Organic mulches are an important part of sustainable gardening because they recycle yard waste, lessen the need for fertilizers, reduce the need for irrigation and minimize the use of herbicides.

Mulches are applied year round, whenever new beds (flowers, vegetable, shrubs) are planted or to replenish mulch in existing beds.

WHAT IS “MULCH”

Mulch is a material spread over the ground to cover bare soil areas that provides a variety of benefits to the garden.

Organic mulches, such as leaves, pine straw, ground pine bark, ground tree trimmings, dry grass clippings, newspaper and other organic matter, are all derived from once living materials. They are popular for their ease of use, attractive appearance (except for newspaper) and because as they decompose they add beneficial organic matter to the soil. They are the most popular mulches.

Organic mulches decay over time and must be regularly replenished, generally once or twice a year depending on what is used. Monitor the depth of mulch around trees and shrubs and maintain the proper thickness.

Inorganic mulches are derived from nonliving sources and include such materials as plastic sheeting, landscape fabric or weed barriers, stone chips or gravel, tar paper or even carpet remnants. Some of these mulches are not very attractive and are only suitable in more utilitarian situations such as a vegetable garden. For instance, carpet remnants work very well in walkways of vegetable gardens. In more decorative areas, unattractive inorganic mulches, such as landscape fabric, may be covered with a layer of organic mulch for appearances sake.

WHY WE USE THEM

Control Weeds

The first and foremost reason to use mulches is to control weeds. Whoever said, “A job well done doesn’t have of be done again,” never weeded a garden. Every time weeds are removed, new weed seeds germinate creating the problem all over again. Mulches work to stop this by blocking light from reaching the soil surface. Most weed seeds need light to germinate as this tells them they are close enough to the soil surface to sprout and grow. When covered over with mulch, it’s as if they are still deep in the soil and the weed seeds will not germinate.

To create this barrier to weed growth organic mulches have to be applied thick enough to do the job. Too often, gardeners spread out mulch as thin as possible just to cover the soil. This will be ineffective in preventing weed seeds from sprouting. Apply organic mulches in beds about 2 inches thick for effective weed control.

Organic mulches are not as effective in controlling persistent perennial weeds that grow from below ground bulbs or rhizomes or run into beds from surrounding areas, but they can help. Common perennial weeds include nutsedge (nutgrass, cocograss), oxalis, bermudagrass, torpedograss and dollarweed. Woven weed barriers or landscape fabric often do a better, though not perfect, job.

Improve Appearance

Many people apply mulches to beds simply because they feel it makes their landscape more attractive. In these circumstances the type of mulch selected may be chosen primarily based on its looks. There is nothing wrong with this as long as the mulch is put out sufficiently deep. A properly applied mulch, however, does much more than just look pretty.

Reduce Watering

Another important function of mulches is that they conserve moisture in the soil. By slowing down evaporation from the soil surface, mulches keep beds from drying out as fast. This is especially important in hot, dry weather. Your plants receive a more even supply of moisture and you save money on your water bill. Shallow rooted plants with limited root systems, such as bedding plants and vegetables in sunny areas, are particularly benefited.

Affect Soil Temperature

Organic mulches also insulate the soil and moderate soil temperatures – keeping the soil warmer in winter and cooler in summer – which helps the roots. Mulches can even reduce injury from freezing temperatures in winter to whatever part of the plant they cover.

Black plastic used in the vegetable garden during winter and early spring helps to warm the soil by absorbing the heat of the sun. This keeps winter vegetables growing vigorously and allows for earlier planting of spring vegetables. As the weather warms up in April, black plastic mulch should be covered with an organic mulch to shade it and prevent excessive heat build-up. Mulches also reduce certain vegetable disease problems by preventing soil dwelling fungi from splashing up onto the vegetables.

Prevent Soil Compaction

Have you ever worked hard to turn the soil in a bed until it is nice and loose only to watch rain and watering beat it down again until it’s just as hard and compacted as it was before? You will find that if you mulch as soon as you finish bed preparation and planting that the mulch will substantially prevent compaction. A looser soil is easier for roots to grow through and absorbs water faster. The longer the soil stays loose, the more good results you will see from your digging efforts.

WHAT TO USE

There is no best mulch for every situation. Which one you choose depends on a variety of factors including the gardening situation, your preference based on appearance, what’s available, cost and durability. I like to recycle yard waste such as leaves and dry grass clippings and use them as is or allow them to partially compost and then use them. It’s cheap (free), effective and attractive. This type of mulch generally needs to be replenished twice a year.

If you are lucky enough to have access to free pine straw, it makes an ideal mulch. You can also purchase bales of pine straw rather economically or chopped pine straw by the bag.

Ground pine bark works well, is durable and looks nice, but can float right away during heavy rains if water flows through the bed. Pine straw is recommended for those situations as it is very stable and will not wash away.

Ground up tree trimmings, branches or stumps can also be used for mulching purposes. Ground wood is generally fairly durable and will last longer than grass clippings or leaves.

The cypress mulch available these days is generally made from entire cypress trees that have been ground up, and is not the byproduct of milling cypress logs for lumber. This mulch is currently somewhat controversial as many people object to cutting cypress trees in coastal areas.

Mulching Guidelines

Around newly planted transplants, such as vegetables and bedding plants:

Generally apply no more than one inch at the time of planting. As the transplants grow larger, add enough mulch to bring the depth up to about 2 inches.

Around shrubs:

Mulches should be about 2 inches deep, and could be applied somewhat deeper around older, large shrubs.

Around young trees:

Newly planted trees should have an area about two feet out from the trunk cleared of lawngrasses and kept mulched. This will encourage root growth and speed establishment. It also prevents damage from lawn mowers and string trimmers. The mulch should be applied in an even layer over the area about three inches thick, pulled back an inch or two from the trunk. Do not apply much in a cone shape piled against the trunk (called “volcano mulching”). The mulch will trap moisture against the bark of the trunk and could lead to decay.

Around older trees:

As trees grow larger, shade often prevents lawngrass from growing under them. Although shade loving ground covers are often planted in these locations, a simpler and attractive solution is to just mulch the area. Mulches under older trees can extend out as far as needed to cover areas where the grass will no longer grow. Generally, mulches under trees are applied about 4 to 6 inches thick.

Dan Gill
Consumer Horticulture Specialist
LSU AgCenter

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