Mulch (why, how, and so much more)

This article probably contains more information than you ever wanted (or cared) to know about mulch. However, if you mulch your gardens by yourself or even hire someone else to do it, shouldn’t you know why you’re expending energy or dollars to keep up with this age-old garden tradition?

Described below are some of the benefits of mulch, problems caused by improper mulching, types of mulch, as well as notes on how to finally mulch properly.


Benefits of natural mulch

Weed suppression: When applied and maintained to the appropriate depth of 2-4 inches, mulch acts as a sufficient weed barrier, particularly in new plantings. There is always opportunity to for weed seeds to blow in and germinate on top of mulch, but weeds in the soil layer are less likely to germinate, partly due to lack of sunlight and partly due to difficulty growing up through the resistant barrier.

*Note on Weed Barrier Fabrics- Fabrics are inferior to natural mulch because they prevent the broken down mulch from incorporating into the soil, which adds organic matter. Fabrics also deal with the same issue of mulch, in that, weed seeds settle on top of the fabric and germinate. Fabrics are costly, short-lived and should not be used with mulch.

Moisture regulation: Mulch allows water to infiltrate into the soil, but protects it from evaporating. Particularly in new plantings, a sufficient layer of mulch will reduce the amount of water needed to establish new plants and save time from repeated applications. If hand-watering, make sure to water thoroughly so that the water reaches the entire root-ball of your new plant.

Added organic matter: Natural mulches breakdown and provide beneficial organic matter to the soil. Organic matter improves soil texture, moisture retention, and a slow release of nutrients. It is important to maintain mulch at the 2-4 inch level to receive the many benefits of mulch, but do not become accustomed to adding 2-4 inches of mulch every year. Some years you may only need one inch of mulch, other years you may need two or three. The end result should be 2-4 inches over top of the soil.

Soil cover: To prevent soil erosion, mulch acts as a protective cover. Soil sediment is a major contributor to water pollution, plus the top layer of soil is usually rich in organic matter, so there’s no sense in letting that wash away. Shredded hardwood mulch locks together as it settles (usually 24-72 hours) and resists movement from wind, water, and foot traffic.

Plant protection: I see it all too often- trees in the middle of lawn with gashes in the trunk or surface roots in lawn that have been repeatedly run over by lawn mowers and aeration machines. Trees are not invincible and mechanical damage can create wounds that invite infection, weakening and possibly killing the tree. A layer of mulch around your plants provides an excellent physical barrier between the plants and maintenance equipment.


Problems caused by improper mulching
Improper mulching

“Mulch volcanoes” are a result of improper mulching. Excess mulch invites disease and these trees will likely die prematurely. No one should ever be paid to preform such inferior work.

Mulch is beneficial in moderation, but can cause many problems when used incorrectly.

It may seem obvious that plant roots prefer to be underground where it is moist; when you expose roots to sun and lack of moisture, the plant suffers. Similarly, plant stems and trunks prefer to be aboveground where they can dry quickly and receive sunlight.  When excess mulch is piled around the crown of a perennial or the trunk of a tree, that aboveground part stays moist for excessive periods.

Excess moisture, where it is not warranted, can cause a number of problems including disease, rot, adventitious root growth (roots that grow from confused plant cells), and even vole damage.

Also, mulch commonly gets an annoying little fungus called “Artillery Fungus” (Sphaerobolus sp.). As the mulch decomposes, if the spores of this fungus are in mulch, they may develop into little cups that project very sticky black spore packets. These tiny black packets stick to siding, windows, cars, etc. They are virtually impossible to remove too. The best solution is to work with nature- fill your beds full of plants so the spores stick to the undersides of leaves, just as nature intended!

Types of mulch (described by my professional experience)

Shredded hardwood- This is the GreenWeaver favorite. Shredded hardwood is readily available, reasonably priced, spreads and smoothes easily, “sets” after a day or two (the finely shredded hairs kind of lock together), and breaks down over a couple years. Its functional, tasteful, and an all around good choice for the garden.

Dyed hardwood- Black mulch? Red mulch? How about purple or green? (Yes, they unfortunately exist.) Dyed mulch is usually marketed as better than shredded hardwood because it has dye that keeps it looking fresh longer. Unfortunately, my experience has differed. Dyed mulch is generally more expensive to start. I’ve been on sites where the dye gets washed off the top pieces, only to expose chipped press-board and other post-construction debris- not something I want in my gardens. The dye is actually the most annoying part of the mulch. It’s messy to apply; it stains sideswalks; and the dye can even be tracked inside on shoes. In the horticultural hot-bed in which we live, there’s a reason display gardens never use dyed mulch.

Leaf mold- A great choice for sustainable gardens! Leaf mold is the partially decomposed leaves collected in autumn. It’s often available through townships and boroughs that do fall leaf collection, and then sold back to the community. Homeowners can also make their own or simply spread fall leaves through the garden in fall. Here at GreenWeaver, we would use it much more; however it is not commercially available in our area. It’s important to note that leaf mold breaks down much faster than shredded hardwood. Still, it replicates the natural forest process of decomposition, and adds all of the benefits to a garden listed above.

Pine needles (non-dyed)- Pine needles are commonly used in the south, but not as much in the mid-Atlantic. Personally, I like the style and texture. They are light and very easy to apply and, surprisingly, they don’t blow away. Pine needles even protect the soil from washing away. They are particularly good around ericaceous plants (acid-loving) since pines tend to have a low pH. My only real issues with pine needle mulch is that it does little for weed suppression and the pine needle mulch we use up here is usually transported up from the Carolinas. Mulch is a personal choice for the garden, but I honestly think pine mulch quite beautiful.

Licorice root- A beautiful, but rather stinky, mulch. Licorice root mulch is about 2-3 times more expensive than shredded hardwood. The reason why so many people like it is that licorice root is known to have anti-fungal properties which can help prevent the artillery fungus mentioned before. Nothing is a sure bet though, so just be aware. When the roots are shredded, there tend to be a lot of curly string pieces that, in time, lock together well, but during application may leave the surface lumpier than shredded hardwood. I was concerned about the carbon footprint of licorice root mulch, but it’s a by-product of the licorice industry, which makes me feel a little more at ease. I’m not sure where it is being shipped from, but there are manufacturers as close as Camden, New Jersey.

Proper mulching technique

Cut a sharp edge to define the mulch area. Four inches deep is standard. Please be careful not to cut roots to desirable plants.

Spread 2-4 inches of shredded hardwood mulch through the open areas.

Taper the mulch down to a minimal layer approaching the base of perennials, shrubs, and trees.

Smooth out any bumps and lumps.

Maintain mulch annually. Do not allow more than four inches of mulch from soil to mulch surface level. If the goal is aesthetics and there is already enough mulch, either remove the old mulch and compost it, or sprinkle a very light decorative layer over the old mulch.

Now that you’re an expert on mulch, get out there this spring and mulch for the benefit of your plants!