Mulch Mistakes | Garden Design

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Mulch Mistakes

We are happy to introduce another post from one of our Advisory Board members. We’ll be running regular columns about inspiration and gardening tips from our advisory board throughout the year. (If you missed it, some of our past columns have include how to plant dahlias, by Frances Palmer, creating seaweed art, by Karen Robertson, and creating a container cutting garden, by Saipua, aka Sarah Ryhanen.)

Today’s post is by landscape designer Paul Keyes, who helped create our James Beard garden makeover. Read more about his work on his Advisory Board member page!

The author, cultivating the Donald B. Lacey Display garden at Rutgers University in 1989.

I think that gardeners are often too reliant on mulch. I started in the landscaping business more than 30 years ago and I have very clear memories of professional gardeners who carefully cultivated planting beds. Recently, cultivating beds seems to have been replaced by mulching, or perhaps I should say over-mulching.

My favorite garden tool is my cultivator. When I work in my garden I look forward to cultivating my beds. After I cut my grass, I can get into my garden beds and pinch, prune, weed, and cultivate the soil. There is something so rewarding and almost therapeutic for me and my plants after I cultivate a bed—it’s like giving a great massage to the earth. When I’ve finished, I know I have helped the health and vigor of my plants and the garden looks and smells amazing.

Unfortunately, it seems to me that mulching or rather over-mulching, has replaced the very important garden practice of bed cultivation. So why should we mulch and what is the right mulch and method of application?

Pine needle mulch. Photo by Paul Keyes.

The Good Mulch:

1. Stabilizes soils and prevents erosion.

2. Helps soils retain moisture for plant use.

3. Improves soil structure and quality over time, if properly applied.

4. Looks great (sometimes).

5. Improves biological activity and mixes organic materials into soils.

6. Prevents weed growth. Keep in mind that the definition of a weed is “a plant out of place.” If we mulch to prevent weed growth, then what is it doing to the desirable plants?

7. Can be an effective herbicide in place of chemicals, cutting, mowing etc.

Leaves as mulch. Photo by Paul Keyes.

Types of Good Mulch:

1. Bark Mulch: It stays loose and does not bind. Bark mulch has a nice dark color and is a great background for plants and it does not fade over time. Bark mulch cultivates nicely into the soil and improves soil structure and drainage. It is usually innate and does not require nitrates to decompose. It is readily available and comes in easily handled 1 to 3 cubic foot bags in a variety of sizes from 4″ to 3/8″

2. Soil Conditioner: This is usually the 3/8″ and smaller screenings left over from sorting bark mulch. It is great for top-dressing beds and used as a component in planting mixes.

3. Straw Mulch: This can be either salt hay or pine needles and more commonly used in the southern part of the United States. Straw mulch is available in easily handled lightweight bales and it has a nice color and natural look. Salt hay (also known as salt marsh hay) is hay from salt marshes and spreads through rhizomes rather than seeds, so it eliminates the risk of contaminating the soil with weed seeds.

4. Cocoa Bark: Cocoa bark has a nice dark color, an interesting scent, does not bind, and mixes nicely into the soil and improves its quality. It is little on the expensive side.

5. Sweet Peet: This is the brand name of a specific type of mulch that is a combination of mulch, agricultural manure, soil conditioner, and humus. Look for it, I think it’s amazing. Their website is sweetpeet.com.

6. Leaves and other organic matter: Keep some leaves in the beds—plants shed leaves for a variety of reasons including as a way to feed and protect themselves. But for some reason, we spend too much time and energy removing them. I’ll never understand the fascination to keep our garden like our bathrooms. It’s okay to be neat, but don’t sterilize you garden by removing all the leaves. Find ways to hide them in your garden beds. They will improve biological activity and in many cases, it is much better than mulch. Go walk in the forest and uncover the duff layer (leaf layer) and take a look at what’s happening! It’s alive!

7. Living Mulch: Ground cover plants like ivy, Pachysandra, and Liriope are great. It’s better to invest in this mulch than something that needs replacing every season.

8. Peat Moss: A great material as long as you moisten it and mix it in with the soil and keep an eye on soil PH. It looks great, too.

9. Stone Mulch: This is a durable and long-lasting mulch that is good for areas where much can easily be washed away by heavy rains or in commercial applications such as parking lot islands.

Just say no to dyed mulch, like the stuff shown here. Photo by Paul Keyes.

The Bad Mulch:

1. Too much mulch that is improperly applied in too thick of a layer kills plants and/or prevents proper growth.

2. Some mulch like hardwoods and shredded bark actually bind together, which prevents penetration of air and water.

3. Bad mulch reduces the biological activity in the soil. Where are the bugs and the worms in this mulch? If they can’t live in it, how does a plant?

4. A badly chosen mulch can changes the chemical composition of the soil. Mulch that is not fully decomposed draws nitrogen from the soil as it breaks down. Some mulch also leach micronutrients, like magnesium, that are harmful to plants.

5. Bad mulch can changes the soil structure and chemical makeup of the soil. Productive soils have variable percentages of five equal parts, including clay, sand, silt, organic matter, and biological components. Too much organic matter is never a good thing.

6. Mulch that is not clean and that contains garbage, weed seeds, or harmful pathogens.

7. Consider the cost of mulch. Determine what your annual mulch budget is and spend half on living mulches that will spread, reduce mulching, and increase plant material in the garden.

Types of Bad Mulches:

1. Wood Chips: A by-product from arborists, this is essentially someone else’s waste. It is best used if allowed to decompose for two to three years and mixed with other garden compost and organic fertilizers to aid in decomposition.

2. Double-ground hardwood mulch: These are usually wood chips that are immediately processed as the byproduct of tree removal, dyed, and made available in bulk. It’s not the worst if the goal is to prevent weed growth or to stabilize soils and prevent erosion. But do not use it within the drip line of the plants or apply it around stems and trunks.

3. Cedar Mulch: Everybody loves it for the color and scent, but it has many of the same negatives as other hardwood mulches, with a tendency to bind together and mat down.

4. Rubber Mulch: Yes, I said it and I’ve seen it. It’s just bad and really needs no explanation, so don’t use it. It is sold as an environmental solution to reduce the mountains of discarded automobile tires in this country. Is it really a good environmental solution to grind up tires and put that in our gardens? (No. Obviously.)

5. Plastic sheeting and fabric weed barriers: This should only be used on limited basis. It is best used for commercial purposes and for small scale jobs. It does prevents weed growth, but it is also unsightly and prevents water and air from entering the soil and therefore reduces biological activity.

The Cone of Shame! Photo by Paul Keyes.

The Ugly Mulch

1. Cone of Shame: This is when mulch is piled around trees and plant stems to make a cone. It smothers the plant, looks horrible, and actually brings water away from the plant. Instead, use mulch to make a plant saucer just outside the drip line to keep water where the plant needs it.

2. Hot Stuff!: If you use mulch that is not fully decomposed (too green) or piled on too high, the decomposition process will generate heat and I have seen gardens literally cooked with green mulch.

3. Anaerobic (sour) Mulch: Mulch should normally smell like freshly cut wood or cultivated soil, but sometimes it develops a strong toxicity that can kill plants. This happens when organic material is not rotated or turned over enough. When this occurs, the process may become anaerobic and produce phytotoxic materials in small but toxic quantities.

4. Using mulch to improve the appearance of a garden or landscape instead of using plants. I often see commercial landscapers with little experience and training use mulch as a quick fix to make a garden look good. Great for their bottom line and profits, but a bad investment for homeowners.

5. Mulch that Binds: Most perennials and annuals need lots of air and the ability to spread to thrive. Over mulching or using the wrong mulch prevents good, productive growth when the mulch binds.

6. Garbage Mulch: One person’s garbage is another person’s mulch. Be wary of organic and inorganic materials recycled from the waste stream and made into mulch. Not all recycling is good for the environment.

Types of Ugly Mulch

1. Dyed Mulch: Ugh! Nothing takes away from the beauty of architecture, plants, or landscapes than red or orange dyed mulch. Just don’t do it.

2.Plastic or Fabric: Bad for plant growth, but also unsightly in the long run and does not decompose or improve soil.

3. Rubber Mulch: Just say no.

4. Straw Hay: Used as a construction site soil stabilizer, straw made from barley, oats, rice, rye, and wheat hay have seed heads that will germinate and create a major weed problem.

In summary, I think using good mulch in moderation is the most effective application method. Combine mulch use with good garden design, practices, and know the makeup of your mulch and its origin. Don’t fall into the mulch trap as a quick fix to make your garden look good. Choose plants over mulch and get yourself a good cultivator to get rid of those weeds and massage the earth!