It’s officially Spring (after the winter that never was.) Gardeners and landscapers alike have been spreading mulches of shredded bark and/or wood chips around trees and shrubs and over emerging perennials, an annual event as regular as the swallows returning to Capistrano. Unfortunately, eruptions of mulch “volcanoes” are more predictable than the real things, as they are found an nearly every street and in every neighborhood. More about these in just a moment.
The widespread us of mulches is a relatively new phenomenon – shredded bark, which is removed from logs prior to their being milled or processed into pulp, was considered waste until the late ‘60’s or early ‘70’s, and it accumulated in massive piles surrounding lumber mills. If gardeners mulched at all, it was usually with peat moss, a less than perfect option for many reasons. Sometimes grass clippings would be used, or perhaps composted leaves.
Eventually though, a use for those piles of slowly decomposing bark was found, and a huge market was created – bark mulch. Because today’s log de-barking machines are even more efficient, it’s inevitable that some wood ends up in the mix, so bark mulch is less pure than it used to be. Somewhere along the way, an entrepreneur decided that inferior wood, old pallets, construction debris and the like (with no bark at all) could be chipped and ground up into small pieces, colored with dyes (brown, black, or red) and then sold as “bark” mulch. This product is inferior to the real thing, and should actually be called “colored wood chips”.
Using organic mulches (I’m leaving aside stone mulches for the moment) have many benefits, if properly applied. They help to modulate soil temperatures in cold or warm weather and slow down the evaporation of soil moisture. They help prevent soil-borne weed seeds from sprouting (but serve as a good incubator for those that land on the surface.) By offering themselves up as a food source, they help foster a healthy community of microbes which break them down by composting them into less complex substances that are released to the soil, increasing its nutrient and organic content as well as its tilth. Earthworms and other organisms are good recyclers of soil organic matter, which benefit plants even more. Further, microbes also become intimately associated with root hairs in the soil, and form an immense extension of a plant’s root system. Many plants cannot exist without these microbial populations.
However, if improperly applied, mulch can lead to plant distress or death. Over the past few years I have come to find that overmulching is a leading cause of plant death – especially of perennials. If you are applying more mulch yearly than is being broken down by the natural decomposition process, you are applying too much. Try to maintain an even layer about 2- or 3-inches thick from year to year. When mulches approach 4-inches in depth or more, they can actually repel water and reverse one of the benefits of mulch. If the surface needs to be refreshed, a very thin layer (sufficient to barely cover the ground and no more) may be spread, and never over the tops of perennials, for it can smother them over time.
Back to mulch volcanoes, those tall mounds of mulch around the trunks of trees and even shrubs. Where they originated is anybody’s guess, but the practice continues to be spread by uninformed landscapers as well as homeowners. Why are they bad? Bark respires by exchanging oxygen and carbon dioxide, and as mulches tend to hold excess moisture, they interfere with this respiration if piled against the trunk. Another consequence is the development of tree diseases which are favored in moist conditions. Follow nature’s model: walk through any forest, and you will not see the decaying leaf litter up against tree trunks. The natural flare of the trunk is clearly visible, and should be around your own trees as well.
As to what sort of mulch to use, I prefer the true aged (or partially composted) darker mulches, which have a softer and finer texture than more freshly-ground bark. I also like the dark color, as it resembles the color of soil and shows plants off well against it. I avoid the use of any mulches which are basically chipped and colored wood chunks – and especially those that are dyed red or orange to resemble true hemlock mulch (which, when fresh, is reddish, and is hardly ever available anymore.) I find this color disturbing in the landscape, but that is a personal preference.
I also like to use pine needles, shredded leaves and even compost in the garden whenever available. These are freely available and beneficial to the soil (and pine needles do not increase its acidity, despite popular belief.) “Weed barrier” fabrics do nothing to control the spread of weeds that originate from wind-blown seeds, and inhibit the growth and spread of desirable plants, particularly ground covers.
In any case, mulches should not be a dominant garden theme, but a helpful solution to make gardening easier while improving the soil at the same time. Vast barrens of bark mulch are often created and maintained, but do nothing to enhance the landscape. Even a meager lawn can look better, with scarcely more time needed to manage it. Dense plantings of shrubs, perennials and ground covers, topped with a light layer of organic mulch every other year or so, will require little mulch and maintenance over time – the best combination of beauty and function for today’s gardeners of whatever ability.
