5 min readMulch is one of the most valuable tools you can use in your garden, offering a wide range of benefits. It helps protect newly planted perennials and shrubs during cold winters, keeps roots cooler through the heat of summer, retains moisture so you don’t have to water as frequently, and prevents weeds from taking over your beds. Organic options—like bark, shredded wood, and pine straw—also gradually decompose, enriching your soil with important nutrients over time.
However, understanding the right way to mulch your lawn and garden beds is essential, because improper use can do more harm than good. Using the wrong type of mulch or applying it incorrectly can lead to poor drainage, overheated roots, and stressed plants.
To make sure you’re getting it right, we turned to horticultural experts to break down the science behind mulching and highlight the most common mistakes gardeners make. Here’s where things often go wrong—and how to avoid those pitfalls.
Avoid Using Rock Mulch
Unless you're cultivating an extremely hands-off, drought-resistant garden, it's probably not a good idea to rely on rock mulch in your landscape.
“Rock mulches seem to be popular with the low-maintenance crowd, but they aren’t without their liabilities,” says Stacey Hirvela, a horticulturalist with Proven Winners Color Choice Shrubs and Spring Meadow Nursery. “They’re much more expensive and difficult to install, though they do last longer than organic mulches. However, they tend not to stay put as you might think, and they often throw rocks out into your lawn and sidewalks, which is annoying to manage.”
As far as plant health goes, rock mulch offers little benefit for plants. Rock mulches can raise the temperature around plants, and some plants can be sensitive to this, especially hydrangeas and lilacs. It's also a problematic addition when installed over landscape fabric because the combination causes drainage issues, keeping the soil either too wet or too dry. “This combination dramatically reduces gas exchange, causing carbon dioxide to build up in the air spaces in the soil and creating a poor environment for root growth,” says Hirvela.
One caveat: Rock mulches are popular in arid climates because the desert plants that grow there are more adapted to thriving in those conditions. In these circumstances, rock mulches are a good choice because of elevated fire risk, says Hirvela.
Steer Clear of Seeds and Baby Plants
Mulch in your veggie garden must be done with extra care.
“Mulching over transplants is a good practice, but you shouldn’t mulch over newly planted seeds or newly germinated plants,” says Gary Pilarchik, creator behind The Rusted Garden and author of Growing an Edible Landscape. “You don’t want the mulch to smother young plants.”
Pilarchik recommends waiting until newly seeded crops are about two inches tall, then adding mulch by hand, making sure to arrange it carefully around the stems. Use straw, compost, leaves, and shredded hardwoods for the best results in edible beds.
Don’t Use Rubber Mulch
If you think rubber mulch is a good investment because it will last forever, you’d be partially right. It’s never, ever, ever going to break down—or do anything for your soil.
“In the name of all that is horticultural, those rubber mulches should only be used around play spaces, and never in plant beds,” says Hirvela. “They will never decompose, just get mixed into the soil and pollute it with who knows what chemicals, since they’re made of shredded tires and the like.” They also slide around and end up everywhere outside your beds. Just say no!
Don’t “Volcano” Mulch Around Trees
No matter what you see “professional” landscapers doing, please don’t make a giant volcano-shaped pile of mulch around your trees.
“Volcano mulching traps moisture around the tree trunk, leading to rot, disease, and pest problems,” says Kat Aul Cervoni, a landscape designer and founder of Staghorn NYC and The Cultivation by Kat. “The right way to spread mulch is a ‘donut shape,’ and taper it away from the trunk so that it does not touch it.” Ditto for shrubs and perennials.
Say “No” to Cocoa Mulch
Made from the hulls of cocoa beans, this organic mulch does have a nice, light chocolatey scent. However, that’s also what lures pets to take a nibble. It’s also toxic to dogs, so keep cocoa mulch out of your garden if you have curious pets, says Hirvela. According to the ASPCA, ingesting cocoa mulch can cause vomiting, diarrhea, an elevated heart rate, and even seizures in dogs. There are better choices for pet lovers!
Apply in a Light Layer…
Organic mulches such as shredded bark contain a lot of natural waxes that can repel water.
“When mulch is applied in a light layer, say 2 to 3 inches, there are still plenty of open spaces for water to penetrate down to the soil and roots,” says Hirvela. “But a thick layer of mulch breaks down slowly, and you actually want mulch to break down to add valuable organic matter to the soil. Thick layers create low oxygen conditions that take a longer time to decompose.”
If you think your mulch is getting too thick or water seems to be running off it, you may need to remove some of it. However, you can try “stirring” it first, suggests Hirvela. Simply raking it up and breaking up the mulch to expose new portions of it to the air can fluff it and allow water to penetrate the roots again, reinvigorating the decomposition process.
…But Make Sure to Put Down Enough
Don’t try to cheap out! A super-thin layer of mulch isn’t doing its job to suppress weeds or conserve moisture; it’s really just a waste of time if you’ve installed it for those purposes. The ideal depth is somewhere between 2 and 3 inches in most garden beds, but you can lean toward the thicker side (3 inches) in areas where you may not have groundcovers, such as along a row of trees, says Cervoni.
Add It When It’s Cool Out
Sometimes you can’t help it; you have to do garden chores when you can. But when it’s hot and steamy, and you’re putting fresh mulch up against herbaceous plants, you can damage the tender, new growth, especially in spring, says Hirvela. Be cognizant of the risk and keep the new mulch away from soft growth, feathering the mulch out as it nears the plant so it’s not touching the stems, says Hirvela.
Only Choose Natural Colors
Please do us all a favor and put down that bag of bright brick red or pitch black mulch.
“I find anything other than natural mulch looks cartoonish in the landscape,” says Cervoni. “Not to mention the dyes that go into colored mulch leach into the ground.” Stick with mulches that are of a natural color palette instead of odd colors that make your landscape look garish.
