Mulch helps cut down on weeds, but this most basic and essential of gardening tasks also has lots of other benefits.

Mulch helps maintain moisture in the soil and reduces the amount of water lost to evaporation, which decreases the amount of time we spend watering and the amount of water we use.

Mulch also helps buffer the soil temperature by trapping radiant heat from the soil in the winter and insulating roots from the heat of the summer.

Aesthetically, it provides a neat and uniform appearance to landscape beds.

As part of your routine gardening maintenance, it’s a good practice to check mulched areas every spring and fall.

Mulch should be layered between 2 and 4 inches thick. If an area has become too thin, replenish it with fresh material. However, too thick a layer can reduce the amount of oxygen reaching the soil.

There are two main types of mulch: organic and inorganic.

Natural, organic mulches include wood chips, shredded bark, pine needles, leaves, compost, straw, grass clippings and even paper or cardboard. Inorganic mulches can be rocks, plastic and landscape fabrics.

Each type of mulch offers benefits and, sometimes, drawbacks. What you choose ultimately depends on the design, intended use of the area and the types of plants growing there.

Some of the advantages of organic mulches are that they decompose and improve soil fertility, aeration, structure and even drainage. All of these will improve plant growth and health.

Bark is one of the most commonly used mulches. It's readily available and often the least expensive. Available in larger nuggets or shredded, bark mulches come from several types of trees, including pine, cedar and cypress.

Nuggets break down much slower than shredded bark but do not stay in place well. Heavy rains can carry them away, and if not layered at a good depth, they leave large gaps where weeds can grow. Shredded bark provides good coverage and stays in place well but breaks down more quickly than nuggets.

When choosing the tree source from which the mulch is made, consider avoiding cypress. Such mulches made from bald or pond cypress are not as sustainable or environmentally friendly as other types. The harvesting of cypress trees can increase the loss of coastal wetlands and wildlife habitat — a situation we are desperately trying to stop.

Bark mulches are great for landscape beds, but are not recommended for vegetable gardens because they can make nitrogen from the soil less available to the plants. However, leaves, pine needles and straw are ideal for vegetable gardens.

Straw mulches, including pine needles, are excellent for both vegetable and ornamental landscape beds. They have the benefit of slower breakdown than leaves or grass clippings, and you can find them in small, shredded options in addition to larger sizes. They are readily available and affordable. Both help prevent soil from splashing up onto fruits and vegetables when laid properly.

Fallen leaves are economical because they are free. You’ve got to get them cleaned up, so why not put them to work for you? It is a sustainable landscape practice to use fallen leaves to make compost and use it as mulch. 

One other organic option is paper and cardboard. Place a thick layer down and use a few rocks to hold in place, or cover it with a thin layer of another type of organic mulch. You are reusing and reducing waste. Paper mulch rolls also are now being produced and can be purchased online and sometimes in stores.

Inorganic options, such as landscape fabric and plastic mulches, can be very effective, especially when growing vegetables and in rows. They are readily available but are often more expensive and labor intensive to install. They do a great job of suppressing weeds, retaining moisture and preventing soil from splashing up onto plants. But black plastic mulches get very hot during the summertime, take time to pull up and are persistent, meaning they don’t break down and are not environmentally friendly.

Rocks also can be used as an inorganic mulch. They don’t break down, so you won’t have to reapply, but they do not improve your soil and they can get very hot in the summer. If they are not laid thickly enough, they allow weed growth.

You will likely need to use a landscape fabric underneath rocks to help prevent weeds, making this one of the most expensive options. However, rocks are uniform and add aesthetic interest to the landscape.


Email questions to gardennews@agcenter.lsu.edu.