Mulch Myths!

Mulch is a subject that gardeners, green professionals, and non-plant-geek homeowners all have an opinion on. These opinions vary as much as there are different types of mulch, but along with the many choices available today come many misconceptions and myths about mulching.

First, let’s define…Mulching is a verb; it’s what you do with “Mulch,” a noun. You can “mulch” with any material; compost, pine needles, wood chips, gravel, clam shells, wine corks, etc., by spreading it around on the ground, around trees, in flower or veggie beds. Mulching is basically covering bare ground so it’s not exposed.

A “perfect” mulch provides at least four benefits:

1. Enriches the soil below as it breaks down.
2. Conserves moisture.
3. Help suppresses weeds.
4. Looks good.

I’ve listed these in order of importance to a healthy garden and ecosystem. Other benefits include erosion control and protecting against soil temperature fluctuations.

Myth #1: You should only mulch in spring.

There is NO right or wrong time to mulch. Many prefer to mulch in early spring because it can be easier before all the dormant plants emerge. Others prefer autumn if they are using shredded leaves or compost, especially in veggie gardens, so it can be incorporated into the soil before spring planting.

Myth #2 Dyed mulches are “BETTER” than other mulches!

This myth stems from the fact that mulching, the verb, is not the most appealing job for homeowners who don’t want to spend any more time outdoors than they have to, let alone shovel mulch. God love ‘em, they just want it to look good and be done with it…forever. The idea of mulching every year is as dreaded as tax season or that annual visit to the dentist. They like the way it looks when fresh, but when it ‘fades’ it’s viewed as a negative trait. “Freshening up” the mulch just to improve the faded color is a must for these people. Those who can afford to hire someone to mulch for them want to make every dollar stretch. So what’s a mulch-dreading, budget-minded homeowner to do?

Enter mulch manufacturers who market the dyed mulches to these homeowners with promises like, “It never fades!” “Mulch less often!” “Save money!”

Pros

-“Fade-Resistant” does not mean “Fade-Proof.” Dyed mulches will fade, just not as fast as natural mulches.

-Conserves moisture.

-Helps suppress weeds.

-Looks good…to some people. If you are going to use it, please stick to natural colors like brown or black.

Cons: Does not enrich soil!

-These mulches can be full of chemicals that leach out into the soil, harming the beneficial bacteria, insects, and earthworms that we NEED to keep our soil and gardens healthy. The detrimental effects of these chemicals can weaken, even kill, plants, especially young plants. Spread this mulch with your bare hands, and you’ll see how easy the color comes off. Now picture those chemicals on your kid’s shoes or bare feet, your pet’s feet, on your edibles…

-It’s not just the dyes that are the problem; it’s the wood used to make the mulch, mainly what is called C & D (construction and demolition) waste, often contaminated with pesticides called Chromated Arsenicals (CCA), which, according to the US EPA, could have chromium, copper, and arsenic in them. Use of CCA ended in 2003, but C&D waste may include repurposed wood that could have come from before then. (Also marketed as “Environmentally Friendly” since they are reusing the materials…AKA making money off of their trash!)

The Mulch & Soil Council (MSC) has a voluntary MSC Certification Logo certifying that mulch or soil is free of CCA-treated wood, but you have to look for it on a label.

Myth #3 Rubber mulch is better than other mulches!

Here we have the same backstory as with dyed mulches, but with one “improvement” the mulch manufacturers zoned in on. Whereas dyed mulch, being wood (I use that term loosely), will eventually break down, rubber mulch will not. And it comes in even more fabulous colors! Another marketing favorite for rubber mulch is the claim that they are saving the planet by reusing tires.

Pros

-More fade-resistant than dyed wood mulch.

-Conserves moisture.

-Helps suppress weeds.

-Looks good.

Cons

-Does not enrich soil.

-Chemicals used in rubber mulches are actually more toxic than dyed mulches. Recycled tires can leach heavy metals, zinc, and volatile organic compounds (VOCs) into the soil. Again, this hinders plant growth and eventually ends up in the groundwater.

It’s become a favorite for playgrounds where it can provide some “bounce” if a child falls and provides fun, colorful designs where it’s usually bonded together vs loose. However, you might want to rethink letting your kids run around barefoot on the rubberized playgrounds or in loose rubber mulch.

-HIGHLY FLAMMABLE. Need I say more? Difficult to extinguish and emits a toxic smoke.

-The extreme heat retention can actually bake and kill plants if the toxic chemicals don’t do it first.

-Lightweight rubber mulch that isn’t bonded can wash out in heavy rains.

Myth #4 Gravel is the best mulch-it lasts FOREVER!

This one’s gonna hurt…I have seen people break their backs shoveling decorative gravel into their beds, under the mistaken impression they have won the mulch game. THEY WILL NEVER HAVE TO MULCH AGAIN! And it looks so good, pristine even…for about a year.

Then reality sets in. Reality in the form of detritus that settles into every little nook and cranny between the individual gravel pieces. Then the weed seeds settle into the same crevices where they are protected until they germinate. You think pulling weeds out of a wood mulched planting bed is bad, try pulling weeds out of a gravel bed. This is where yet another environmental strike happens-using herbicides to kill all those weeds in the gravel to spare your fingers and back. And guess what…sure it killed them all, but now you have to remove all the brown dead ‘bodies’…and they are saturated with herbicide. (Please wear gloves.)

IF you have gravel bed dreams for your Japanese style garden, remember that gravel beds like pictured above have staff to keep them clean and raked routinely daily or at the minimum, weekly.

Pros-Lasts forever!

-Conserves moisture.

-Looks good, for a while.

Cons

–Does not enrich soil.

-Gravel, if installed correctly, will have a barrier between the gravel and soil, be it porous landscape fabric or even old-school plastic. (not recommended) This helps keep the gravel ‘clean’ since, over time, soil will work its way up and dirty it. The problem is if this is a bed with plants, water is now limited, no organic matter is working its way into the soil, and any soil organisms are being starved, so move out.

-Heat issues in full sun situations. Glare, especially off white rock, can intensify this. Gravel and rock absorb heat during the day and release it at night, which increases a plant’s water needs, which they are not getting enough of in the first place, if a barrier is used. If a barrier wasn’t used and the gravel was laid on bare soil…that’s a whole different maintenance issue. Either way, you end up with hard-to-maintain beds and an even harder situation to remedy. Removing gravel is much harder than adding it.

-Planting in existing gravel is a nightmare and requires making openings in your barrier. Many landscapers will, and should, charge more labor to plant in gravel. Using gravel for pathways is a time-honored tradition, using gravel around plants is usually only a good idea in rock gardens where no landscape fabric is used, and the plants are geared toward the harsh conditions.

-Maintenance issues. You might be saving time by not mulching every year, but the only way to keep gravel beds from becoming overrun with weeds is by being vigilant year-round. Using a blower to keep leaves and debris from settling in can help, as will removing any weeds before they go to seed.

Myth #5: Any wood will do for mulch. Cheaper is better!

As mentioned above, cheap wood is used to make cheap mulch. That means C & D wood-which brings us back to Myth #1.

Pros

-Less expensive.

-Conserves moisture.

-Helps suppress weeds.

-Looks good.

Cons

–Besides the same chemical leaching that can happen with unknown wood sources, like with dyed wood mulch, studies have shown that this type of mulch can use up more nitrogen from the soil, trying to break down, robbing it from the very plants you are trying to nurture.

-Beware the marketing scam saying it’s 100% “Natural” and check for the MSC Certification Logo certifying that mulch or soil is free of CCA-treated wood. 100% just means it’s not dyed or made from tires, etc. If the wood chips are pale or light colored (think new 2×4” colored), it’s not very good for plants, especially perennials. A general rule of thumb is that the darker and finer the mulch, the better it is for plants.

–If cost is a concern, how does FREE sound? Depending on where you live, many parks or municipalities offer free mulch and wood chips for residents. No, they don’t deliver, but you can’t beat the price, AND it’s all natural. The mulch is ground to a nice consistency and, being dark brown, looks great. Wood chips, the chipped remains from tree work, are coarser than mulch. Some tree companies will actually deliver a load to you for free. Wood chips work well for pathways, chicken coops, or other utility areas where bare soil turns to mud, but use finer, richer natural mulches for planting beds.

-Using leaves in the fall is another free source of mulch. Instead of raking those leaves and sending them off with your yard waste, spread them onto the lawn, mow over them, and use the clippings in your planting beds. Or make “Leaf mold” by composting the leaves for 1-3 years. Leaf mold is one of the best mulches for plants.  (See myth #9)

Myth #6: Always use landscape fabric (AKA “Weed barrier”) under the mulch to prevent weeds.

Probably the biggest marketing scam in horticulture history. The majority of weeds come from ABOVE ground, not underground. Those dandelion seeds in your neighbor’s yard ride over on the wind, not underground runners. Those tiny honeysuckle seedlings were deposited by birds “taking care of business” in a tree’s branches or along a fence. Do NOT use any barrier between soil and wood mulches. This totally defeats the #1 benefit of mulch: enriching your soil.

The only time I recommend landscape fabric is for use under gravel walkways and similar applications. There are different grades available, but make sure it’s porous so water drains through; do not use solid plastic, even under walkways.

Landscape fabric, even when installed correctly, eventually finds a way to peek up on corners, etc. Over time, it’s easily torn and prone to breaking down, especially when exposed to the sun. If you are using it under gravel, you’ll have to add gravel now and then and hope you can match it.

-If used on an incline, I have seen wood-based mulches float away in heavy rain as the fabric turns into a landscape “Slip-n-Slide”. Only use it under gravel, and even then, avoid inclines or the gravel will wash out!

Myth #7 Mulching against my foundation will give me termites!

The chances of a termite, or any other creature, surviving the chipping process used in creating wood-based mulches are slim to none, and even if one did survive, its survival is doomed since it’s separated from its colony. Termites prefer the cellulose found in solid wood. Organic, wood-based mulches aren’t going to provide termites with enough of a source for heavy feeding. What attracts termites is the moist environment and the cover that mulch can provide. Termites and other creepy-crawlies live in soil, whether you mulch or not. If you still have concerns, leave a 4-6” space between your foundation and the mulch.  

Using rubber mulch to avoid termites will still provide the moist environment they prefer, even if they can’t eat it.

Termites do have preferences when it comes to wood, though. Cypress sapwood, loblolly pine, and slash pine are favored, while Cypress heartwood has actually been rated as termite-resistant.

Myth #8 Mulching with coco shells will kill my dog.

Coco shell mulch is a byproduct of chocolate production and contains dangerous levels of methylxanthines. It also contains theobromine and caffeine, which can cause severe symptoms like vomiting, diarrhea, tremors, seizures, and, in rare cases, death. So, this myth is true, not just for dogs, but for cats too. Its chocolate scent is attractive, making it a high-risk garden product.

Myth #9 Pine needles are acidic.

Sorry, but even though pine needles themselves are acidic (pH=3.2–3.8), they do not lower soil pH when used as mulch. Once it breaks down, the pH levels off in the neutral range around 6-6.5. Pine needles do, however, make a great mulch that hits all four priority points, and if you have pine trees, you get free delivery right in your yard.

Pros

-Hits all four priority points.

-Super lightweight.

-Can be free if pine trees are nearby.

Cons

-The color might not appeal to everyone-Orangish when fresh, but greys over time.

-Breaks down faster than regular hardwood mulches.

Myth #10 You can’t mulch with compost.

As mentioned above, you can mulch with just about anything. That doesn’t mean you should, but in the case of compost and leaf mold, it not only checks all four priority points but also adds an extra boost in the form of organic fertilizer. The almost-black color of compost makes it a favorite among some gardeners, as the dark color really makes flower and foliage colors stand out. You can even make it yourself, for free, but this takes time.

Pros-

-Hits all the priority points, plus extra fertilizing properties.

-Dark color sets off plants beautifully.

-Available in bulk, bags, or made in your own backyard.

Cons-

-Breaks down faster than hardwood mulches. Some gardeners like to mulch with a mix that’s half hardwood mulch and half compost to make it last longer.

-Will fade to some degree, but still retains a dark grey/brown color.

Myth #11: You should remove the old wood-based mulch before you put down new wood-based mulch.

I have no idea how this one got started. Removing “old” wood mulch interrupts the natural breakdown process you want from mulch so it will enrich your soil. The only time you should remove old mulch is if you are hopefully replacing an undesirable mulch, like mentioned above. OR, removing mulch around trees that is piled too high, AKA “Volcano Mulching.” A mulch layer should run between 2-4” tops and not run up against a plant’s base. (Think donut, not volcano!) If adding new mulch will put you over 4”, either don’t mulch, or apply a very thin layer to “freshen” things up. Lightly raking existing mulch can make it look even and fresh without applying new mulch.

Myth #12 GROSS! Fungus in my mulch is BAD!

It’s common under certain conditions to occasionally see fungus in natural mulches-even in new bags of mulch. What you are really seeing, though, are fungus fruiting bodies. These can be in the form of mushrooms, white stringy bodies, or other odd-shaped and colored organisms and usually appear when we’ve have ample moisture.  Fungus is what Mother Nature uses to break things down, like a clean-up crew coming in and breaking down tables after a party. You don’t normally see fungus until it “flowers” in a sense and sends out spores from the conks and mushrooms you do see. When you see these fruiting bodies, be happy that your mulch is being broken down as Mother Nature intended. If you are worried about a pet or child eating them, just rake the area.

Myth #13 You HAVE to mulch if you have any sort of planting beds.

The main idea behind mulching is not to have bare soil. Bare soil will soon be overrun with weeds, is prone to erosion, and dries out extremely fast. This hastens nutrients and organic matter loss, things we need in the soil to make our plants happy. Not to mention, bare soil doesn’t look pretty.

Mulch is the “Icing on the cake” that makes a landscape or garden look finished and well-cared for… this is why you see freshly mulched landscapes at homes for sale or in gardens on tour.

An alternative to mulching is just having more plants to cover any bare soil. These can be ground covers, usually one type of very low-growing spreading plant like Liriope, or even evergreens like prostrate junipers.

So, what’s the takeaway here? If you or your landscape company are going to mulch, do it when it’s good for you, and use all-natural, dye-free mulches that hit all four priority points to eliminate all the concerns and confusion. The results benefit your plants, the environment, and you!

-Comments or questions? Email Garden-Lou at gardenloustl@gmail.com

Words and photos by Jo Batzer

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