What is mulch?
Garden tasks like weeding, fertilizing, and watering get all the attention, but mulching is important too. You probably have it all throughout your garden, but what actually is mulch? Simply put, mulch is a material applied to the surface of the soil found around your lawn and in your garden. There are two main types of mulch: organic mulch and inorganic mulch.
What is mulch used for?
Beyond just helping your lawn and garden look good, mulch serves some important purposes, too. Adding mulch to your garden beds can improve their health by helping prevent weeds, protecting your soil and plants against erosion and runoff, and even by helping your soil to better retain water. But mulch doesn’t just protect your garden during the hottest months. In fact, once the weather starts to get cold, mulch can protect your gardens from the chilly temperatures by aiding in overwintering plants (protecting them from snow and freezing conditions).
Types of mulch
As mentioned before, the two main types of mulch are organic and inorganic. Within those two categories, there are many different options that you can choose from, each with their own list of pros and cons.
Organic mulch
Organic mulch is made from natural materials and is used not only to protect the surface of the soil, but also to help add nutrients back in. If you’re using an organic, carbon-based mulch, you can expect it to slowly break down over time. While this does mean you’ll need to add more mulch as it decomposes, it’s busy adding rich nutrients back into the soil. Some examples of organic mulch include newspaper, cardboard, and sawdust as well as the following:
Dry grass clippings
Pros
- Easily accessible—just save and dry out clippings when you mow your lawn
Cons
- Can bunch together and develop a bad odor if they become wet
- Will decompose quickly, so must be frequently reapplied
- May spread weed seed or herbicide residue if clippings are from a lawn that has been treated with herbicides or is heavily weed infested
- Removing clippings from the lawn means you won't have the benefit of grasscycling
Sunday Tip:
If you have a lot of weeds in your yard, or use heavy herbicides, avoid using your grass clippings for mulching.
Tree bark
Pros
- Available in a variety of sizes and colors
- Long lasting/takes awhile to break down
Cons
- Because of the high carbon content of bark, it may deplete the nitrogen content of the soil as it decomposes
Wood chips
Pros
- Long lasting
- Available in a variety of colors
Cons
- Can form a waterproof layer, making it difficult for soil to absorb water
Straw
Pros
- Good as a temporary mulch for overwintering perennial plants
Cons
- May provide overwintering habitat for rodents
- May blow around easily
Pine needles
Pros
- Good for plants that require a more acidic soil
- Easily removed if necessary
- Long lasting/slow to break down
Cons
- Can be expensive
- Not very high in nutrients for the soil
Leaves
Pros
- Easily accessible—just save piles when you rake your lawn
Cons
- Can bunch together when wet
- Will decompose quickly, so must be frequently reapplied
Inorganic mulch
Inorganic mulch, on the other hand, is made up of materials that won’t decompose, and it works mainly to protect the soil’s surface. Some examples of inorganic mulch include landscape fabric or materials like:
Rock
Pros
- Can retain heat (which can be beneficial in winter)
- Long lasting
Cons
- Can retain heat (can be a con in summer)
- Doesn’t always prevent weeds
- Doesn’t retain water
- Doesn’t add nutrients to soil
Plastic
Pros
- Good for weed control
Cons
- Expensive
- Not eco-friendly
- Can retain excessive amounts of heat
- Hard to dispose of
Sunday Tip:
Want to support pollinators? Avoid using plastic mulch, fabric mulch, or chemically treated organic mulches. Why? Ground-nesting bees can’t penetrate these types of mulches on their journey to the soil.
How to add mulch to your garden
Once you’ve determined the type of mulch that’s right for you and your garden, follow these steps to properly install it.
- Weed the area. Before you actually lay the mulch, it’s important to first prepare your garden. Take some time to thoroughly weed the area.
- Mulch around beds and plants. Next, apply a two- to four-inch layer of your chosen mulch material around your garden beds and individual plants. If you’re using a smaller material, like pine needles, apply a thinner layer, but if you’re using a larger or thicker material, like rocks or wood chips, apply a thicker layer. The thickness of this layer matters. If you make it too thin, the mulch may not be able to effectively prevent weeds or retain heat or moisture. However, if you make it too thick, the mulch may retain too much moisture, leading to waterlogged, anaerobic soils.
- Reapply as needed. For both plants and trees, be sure to reapply your mulch to maintain the proper mulch depth and function. The cadence of reapplication will vary depending on the type of mulch that you choose.
Mulch-free zones
There are areas in the garden where you shouldn’t put mulch. Specifically, avoid directly touching the stems of plants and the trunks of trees with mulch. Leave about three inches of mulch-free space around trunks and stems to help prevent excessive moisture retention and, in turn, prevent plant rot or disease.
For trees in particular, it’s recommended to mulch as far out as the dripline (the width of the canopy), or as far out as you can tolerate visually. That said, it's critical to avoid piling mulch high against a tree trunk—this is sometimes called a mulch volcano!—to protect the trunk from rot.
Common mulch issues and how to address them
Depending on the climate in your area, and the type of mulch that you’ve chosen, there are some common mulch issues that you may encounter.
Mushrooms, fungus, slime, molds, etc.
While this may be an alarming sight, it’s important to note that seeing fungus, mold, or slime in your mulch isn’t always a bad thing. While this sometimes can be an indication that your mulch is too wet, it can also signal that the mulch is decomposing, and therefore, providing nutrients to your soil. If you do notice mold, fungus, slime, or the like in your mulch, simply use a shovel to gather the affected areas and discard it, and then use a rake to fluff up the rest of the mulch to help air it out.
Insects
There’s no denying that insects are annoying, but seeing them around your mulch isn’t a red flag. In fact, it’s pretty common as mulch can create an ideal habitat for insects, and most won’t do any harm to your garden. (They may actually be beneficial to have around!) That is, with the exception of snails, slugs, earwigs, and ants. If you see any of these pests, it may be time to utilize some natural pest control methods, also known as Integrated Pest Management (IPM).
Nitrogen deficiency
If you're noticing that your plants are becoming pale or if the leaves are yellowing, this could be a sign of a nitrogen deficiency. Some organic mulches, like wood chips and straw, have a naturally high carbon content, and as they start to decompose, they may deplete the nitrogen in your soil. That said, composted mulches can help reduce the carbon-to-nitrogen ratio of your soil, so if this becomes an issue, consider incorporating some composted solids in your garden.
Stem rot
As mentioned before, when mulch is placed too close to the stem or trunk of plants or trees, you may start to notice rotting, which is caused by excessive moisture. If this is the case, be sure to create a mulch-free zone around the base of the plant to prevent moisture and rot.
Cited sources
Mulches for Home Grounds. Colorado State University Extension.
Mulching Trees and Shrubs. University of Maryland Extension
Using Mulch in the Garden. Iowa State University Extension and Outreach.
