There are many types of mulch for garden use; each one has its own benefits and could be the best type of mulch for your future project. At Wellfield, we utilize different mulches, but there is one type in almost every garden bed. With the exception of the Peace Garden, every mulched garden bed has a shredded hardwood mulch. The Peace Garden contains composted pine bark mulch due to some of the properties of the mulch and the botanical composition of the space. The aspects of mulch that will be discussed here are inorganic versus organic, dyed versus natural, and the different compositions of each.
Rock mulch has been considered for a blog post for quite some time; it is commonly used in commercial landscapes, but not as much by botanic gardens. It is a fantastic low maintenance (short-term) solution for many businesses that do not have a focus on plants. No one goes to a gas station to check out the landscaping! There are a fair amount of downsides that accompany this “low maintenance” mulch though. Weed barriers are placed between the soil and the rock mulch in order to stop anything from growing out of the soil and through the rocks. This works well for a season or two. Eventually, the weed barrier will degrade and no longer do its job. The weeds will start popping up through the rocks from the soil layer below, and any organic matter that collects between the cracks of the stones will be capable of growing any seeds that blow into mulch. Sometimes, this is dealt with by using pre-emergent herbicides to lower the weed pressure and using a post-emergent, such as glyphosate, for anything that was missed. Another solution is to remove everything from the garden bed and replace the weed barrier and put the rock mulch back in place. It is extremely labor intensive (especially if it is a large area). It is definitely a benefit for many businesses to hire a landscaping company to install and restore this type of mulch every few years instead of upkeep throughout the season.
Termites are a commonly mentioned factor when homeowners are considering mulch and opt for rock mulch over wood, because they are worried the termites will be attracted to it. It seems intuitive that termites eat and are attracted to wood, and you’d invite the insects to your garden mulch and into your house. Research has suggested this is not the case, and the types of wood most often used for mulch are not preferred wood types for their diet.
Organic mulches do not always use weed barriers, and are often used for different reasons than rock mulch. Although it can still be used with an under layer of weed barrier, it often is not. One of the benefits of natural mulches is their ability to break down into the soil. The mulch breaking down can lead to soils with a higher ability to retain moisture and can increase the cation exchange capacity. Unlike with rock mulch, it is best to add a fresh layer of mulch every year since it will break down over time. Weeds also do not struggle quite as much when there is no weed barrier unless the mulch is very thick. If a small area is being mulched, it would be best to use over three inches of mulch. For a garden as large as Wellfield, we limit our layer of mulch to two inches. We still get the soil benefits and it does well to suppress the weeds. Most of our gardens have substantial amounts of shade, which helps.
There are pros and cons to each type of organic mulch. The shredded hardwood mulch used at Wellfield was chosen because it has a smooth appearance and a natural wood color. A big design goal of the Gardens is to maintain the Gardens in a “naturalistic” way. This type of mulch helps keep the garden beds looking nice while maintaining that design goal. Dyed mulches usually have a more eye-catching color and can work especially well for a landscape that is desired to stand out. The main downside of dyed mulches is the wood they use is sometimes a result of wood that had been scrapped and chipped. Occasionally this will lead to chunks of dyed plywood or other scraps in your garden beds, and the potential of chemicals from those woods affecting the plants in a garden bed.
Organic mulches include wood chips but also encompass cut grass, fallen leaves, and pine straw. Pine straw can give a bed a different aesthetic due to its texture and color compared to more standard options. Some research suggests that it can acidify soil, but not at the rates that it is normally applied. The acidifying effects of pine are one of the reasons that composted pine bark mulch was chosen for the Peace Garden. Aesthetics and its tendency to not break down quickly, were important factors as well.
Many other mulch options are available, but these are the most common. For people highly involved in their own garden who enjoy tending to it, natural wood mulches will make a better choice. The additions to soil help cannot be overlooked, even if they need to be reapplied each year. Rock mulches can work well when a higher intensity, less frequent maintenance is ideal for the space. They both have their tradeoffs that must be considered when making a garden plan. Sometimes the best option is to just use what is available. Many cities will provide free wood chips from trees they chip throughout the year; check with your local municipality!
And on your next visit, see how many different mulch beds you can find at Wellfield. Here are some photos from our Peace Garden to see our applications there. See you at the Gardens!
Cody Hoff Horticulture Operations Manager
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