To Mulch or Not to Mulch?

BY JANICE F. BOOTH

JUN. 04, 2021

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This too-MULCH-uous topic comes up among gardeners seasonally: Is mulching really a good idea? It’s a lot of work and some expense. Why should we mulch? When? What kind of material? Where? How much? “Mulching or not” seems an issue with many reasonable points of view, depending on your tastes, your budget, and your sense of environmental responsibility. 

Professional landscapers and serious gardeners are strong advocates of mulching for very good reasons. However, there are pros and cons to all the methods and materials available for the job. This may be the year you want to investigate an alternative to traditional mulching, one that is effective, attractive, and inexpensive. So, here we go.

Why We Mulch Our Gardens

There are five excellent reasons to mulch, which means covering the soil with organic or synthetic material around plants, bushes, and trees. 

Mulch can… 1. Suppress weeds, easing the burden of maintaining a happy, attractive flower bed or vegetable patch. 2. Retain moisture in the soil when it’s dry and protect the soil from erosion when heavy rains pelt the earth. 3. Insulate the soil from the extremes of summer heat and cold winter weather. 4. Potentially improve the soil’s quality by adding nutrients and encouraging earthworms and oxygenation. 5. Contribute to a tidy, well-groomed appearance in the garden areas.

When Should We Mulch

For all the reasons just reviewed, mulch is best applied in the late springtime and late fall. It’s probably unwise to mulch too early, when the mulch could settle on top of emerging plants and seedlings. Heavy mulch could deform and even smother the new plants and new growth. Also, the compacted mulch may insulate the still-cold earth, keeping the warm, spring sunlight from penetrating to the dormant roots below. Waiting until May or even early June gives the garden lots of time to offer up its promising growth to be admired and protected by the careful placement of protective mulch. After a long summer and in preparation for the cold winter months, fresh mulch can be reapplied. A word of caution, however: In the autumn, wait to lay down the fresh mulch until the leaves have been blown, raked, and collected. If fresh mulch is applied too early, it may be raked up and blown away with the leaves, twigs, and detritus. (Note: If you compost your leaves, you may have the makings of an excellent, organic mulch for the coming spring. See below.) Expand

What Material Should be Used as Mulch

There are a few basic qualities that characterize good mulching material. It should be light-weight, free of bacteria or fungus, and clean (no weeds or seeds). That said, there are two basic types of mulch, organic and inorganic. 

The common inorganic varieties are rocks, stones, rubber, plastic sheets, and geotextile or landscape fabric. 

Organic mulch includes, straw, compost, bark, wood chips, leaves, and pine needles—natural materials. 

You might decide to use more than one variety of mulch in the garden. Or, you may decide to skip the mulch and go directly to ground cover, low-growing plants such as English ivy or Periwinkle, that provide the same benefits as mulch. (More on this later.) Expand

Professional landscapers and serious gardeners are strong advocates of mulching for very good reasons. However, there are pros and cons to all the methods and materials available for the job. This may be the year you want to investigate an alternative to traditional mulching, one that is effective, attractive, and inexpensive.

All of the organic mulches provide similar benefits, those five we discussed. A few additional points about organic mulch: Compost is delightfully “pollinator friendly,” encouraging bees and other insects to come closer—always good for the plants and flowers. A word of caution, however, as compost should be loose and only partially decomposed when applied. Otherwise, it can remove oxygen and leach nitrogen into the soil. Not good! “Sour mulch” as it’s aptly called can ruin your plants. 

All the wood products—bark, chips, leaves, and needles, afford an excellent source of nutrients for the soil. As they decompose photosynthesis occurs, cleaning the air of toxins, absorbing carbon monoxide, and releasing oxygen_. (Ground cover provides this same advantage.) Bark is often dyed, allowing for colorful flowerbeds. Be careful to check that the dye used in the bark is non-toxic. Leaves are readily available and easy to compost. They must be ground or broken up, however. If left unmodified, the leaves matt and may smother young plants and form a hiding place for insects and mice. 

Straw (not hay) is a byproduct of grain and provides an inexpensive, clean ground protection. However, it’s not appropriate for urban and formal gardens. It is inexpensive and often used for vegetable gardens. 

Cardboard and newspaper are useful secondary mulching materials. If the paper products are undyed and free of wax or gloss-finishes, they will serve well as an underlayment for another mulch, such as chips or bark. The wood fiber in these products breaks down slowly and smothers weeds. 

Inorganic mulch products include rocks, gravel, stone, rubber mulch, plastic, landscape fabric—all of which are easy to maintain and long-lasting. 

Stone, gravel, and rock are tidy and relatively permanent options. They are best used for paths, around trees, and, generally, in places where the weight of the stones will not harm plants or shrubs. Rocks and gravel are relatively permanent. It is a chore to place them, and an even bigger job removing them from a bed or walkway. In addition, rocks absorb heat. They may overheat the soil beneath and kill plants and even young trees. Plan carefully if you choose these forms of mulch.

Rubber mulch is durable and excellent for play areas, requiring little maintenance. It is unaffected by heat and humidity, and stays free of fungus and bugs. Since it’s rubber, it is heavy—which is the good news (won’t be blown away) and the bad news (potentially compacts the soil beneath). Rubber mulch does not enrich the soil and may leach heavy metals, such as zinc aluminum, and chromium, into the earth. It’s expensive, gives off a slight odor, and, in my experience, floats out of the flower beds in a serious downpour. (I watched my tidy mulched flowerbed washed clean of its expensive, fresh rubber mulch!)

Plastic and landscape fabric efficiently discourage weeds and help retain moisture. They’re excellent in early spring and fall as blankets, keeping the plants’ roots warm. They’re best laid in fresh, new flowerbeds and vegetable patches. It’s tough to install plastic or fabric in an established bed. 

Finally, a word or two in support of a mulch alternative—-ground cover. In our region Vinca minor, Myrtle, Periwinkle, and English ivy thrive. They provide an attractive, easily maintained protection for the ground. (Keep an eye on the ivy in case it tries climbing up a tree or wall.) Ground cover that is living carries on photosynthesis, cleaning the air of toxins, absorbing carbon dioxide , and releasing fresh oxygen. There are many color variations, and Periwinkle and Myrtle produce sweet, tiny, purple flowers. The only drawbacks are that they take a year or two to fill-in. (Which can be a boon if you’re adding them to a bed that has young plants that need to mature a bit before sharing space with ground cover.) Some of the groundcover may die, and you’ll have to remove that section and replant. 

So, lots of choices and a few cautions as you consider what you’ll do next fall—mulch…or maybe not.