Experiments With Gravel Mulch

Yucca filamentosa ‘Colorguard’ has appeared from under our newly installed gravel mulch.

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Most of the mulches we use are organic and improve the soil as they decay.  Shredded bark or leaves, pine straw, straw, newsprint or brown paper all have their uses.

When we consider inorganic mulches, there are definite benefits along with some obvious deficits.  Inorganic mulch won’t improve soil texture or fertility.  But neither will it harbor fungal disease, come pre-contaminated with weed seeds, provide a nesting site for ants or decay in just a few months.

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New terraces are planted to help control erosion, and mulched with pea gravel (spring 2017).

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I was first drawn to pea gravel mulch as we began to try to control erosion and cultivate the steep slopes of our back garden.    But I was also digging some gravel into the back-fill and planting hole when we installed new shrubs and perennials, to try to thwart the voles who would otherwise devour their tasty root balls.  Finishing the job with a nice mulch of gravel felt appropriate as a further deterrent to rodents.

Pea gravel definitely helps both with erosion control and rodent control.  But it also ‘disappeared’ into the soil on rainy days, after a while, and got covered with leaf litter and other organic matter over time.  I find myself renewing the pea gravel in spots after a while.

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“Soil security”

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Gravel mulch serves to help conserve soil moisture, just like every other sort of mulch.  It shades the soil, shelters root systems, absorbs the shock of falling rain and holds soil in place.

Additionally, gravel reflects sunlight and heat back up into the plants above it, helping to dry the plants more quickly after a rain and thereby deter fungal disease.  Gravel mulch also provides a dry barrier between moist soil and dry plant, preventing crown rot.

Soil doesn’t splash up onto lower leaves and branches, and the gravel perhaps makes it a little harder for invertebrates to travel up and back between soil and delicious plant above.

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Gravel mulch is used most commonly in rock gardens, where many drought tolerant and alpine plants are featured.  Some plants wouldn’t live long with a moist organic mulch, but manage just fine with gravel mulch that protects their crown.  Gravel is coming into vogue again as a fashionable and useful mulch for perennial gardens, too.  I have been reading about perennial and succulent  gardens grown under several inches of pea gravel in various garden magazines.

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Even a thin gravel mulch has helped conserve moisture around these newly planted perennials.

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I also recently enjoyed listening to a presentation by Joseph Tychonievich at the Williamsburg Botanical Garden where he presented his new book, Rock Gardening:  Reimagining a Classic Style.  Joseph inspired me to move ahead with my vision to incorporate more areas of gravel mulch in our sunny perennial beds in the upper garden.

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I use fine gravel as a mulch in potted arrangements, too.

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This area is gently sloping, and erosion isn’t as much of a pressing concern as in the lower gardens.  The entire area was left under several inches of freshly ground hardwood mulch in 2013, as the arborists who cleaned up our fallen trees ground up leaves and branches and simply left it all in place.

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Fresh compost piled on top of existing mulch allows me to plant in this area in 2013, right after the trees came down, without digging into the clay. A light covering of wood chips from the forest floor mulches the planting .

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As that has decomposed, I’ve renewed the mulch with bagged hardwood and Cypress mulch from the local hardware store.  It smells pleasant, and Cypress helps to repel insects.  It has an ecological downside, though as mature trees are cut for mulch.

The soil in much of this area still consists of thick, hard clay, despite my best efforts to dig in compost and improve its texture.  There may be a few inches of good compost on top of the clay, but the clay still holds heavy rainfall and keeps parts of the garden far too wet, especially in winter.

I am beginning to understand that a gravel mulch will promote better growth and vigor in most of the plants we are trying to establish, particularly the Iris and Mediterranean herbs.

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Recently,  I decided to experiment with a much larger gravel mulch in one of the beds that needed some TLC.  I lost several perennials here over winter, and so had quite a bit of bare ground.

On our shopping trip, my partner noticed this beautiful blue green rock quarried somewhere in Virginia.  We decided on the spot to give it a try, and I am very pleased with the results thus far.  Not only is this gravel not going to shift around on a rainy day, but I don’t believe it will sink down into the soil anytime soon, either.

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This three year old Siberian Iris bloomed for the first time this spring, and I hope the new gravel mulch will help it grow more vigorously in future.

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Now, please keep in mind that gravel is the heaviest mulch you can choose, and moving it around and spreading it takes both strength and commitment.  If I had the luxury of ordering up a truckload of it and hiring a crew to spread it for me, that would be a lovely thing.  But I don’t.

Rather, I’m buying it a couple of bags at a time and spreading it by hand.  It is going to take most of the summer to mulch this whole area working with just a few square feet each week.  But I am already seeing the benefit this mulch brings to our plants.

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This is a single bag of gravel spread around our new Monarda.  It will take a few more bags to finish this area….

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I bought three plugs of Yucca filamentosa ‘Color Guard’ about four years ago, as we were first planting this bed.  I wanted them to make a large focal point to anchor the area and planted them in a broad triangle.  Well, let’s just say that I expected them to grow much faster and they have largely gotten lost between larger and floppier perennials.  In fact, one of the three was struggling so much that I dug it up in late winter and planted it into a pot in full sun, hoping to give it a better chance to grow.

Never mind that I kept digging it up every month or so, checking to see if there was any visible growth, and replanting it again with the confirmation of a fresh root or tiny shoot.  That is a sad tale, and I ended up filling the pot with first one plant, and then another, simply to have something to look at besides the empty pot.  I ticked this off as a failed plant and moved on.

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Maybe if I put a fresh gravel mulch in this pot, the Yucca would finally grow?

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But not so fast!  Something of that Yucca was left alive in the original bed.  And finally, a month after I mulched over the area with the new Virginia gravel, look at what has emerged!  Plants really really want to live, and sometimes we just need to improve conditions for them and get out of the way to give them a chance!

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This newly planted Lavender was struggling with our weather extremes, but has improved under the gravel mulch this month.

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Our friends at our local garden center have a running joke that we always buy gravel or compost, if nothing else, and are their best customers for pea gravel. Gravel has made gardening in this difficult site possible.

If you happen to be in the neighborhood, and want to visit with me and bring a little gift, a fresh bag of gravel is always in style.   I’ll be so happy to see you, will show you around the garden and offer you a few divisions of something nice to take away with you.

And I might even let you help spread the gravel while we’re at it!

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Woodland Gnome 2018

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When Your Garden Looks Like Swiss Cheese- Living with Moles and Voles

Moles have large paddle like feet to tunnel through soil. They prefer to eat invertebrates like insects and insect larvae. Image by Michael David Hill, Wikimedia

Moles and voles go wherever they want to go, and eat whatever they want to eat.   They leave raised tunnels in lawns and garden beds.  Both are small mammals, about 4″-6″ long as adults, and both live underground.  Moles prefer to eat insects, earthworms, and larvae that live in the top few inches of soil.  Voles, which look like mice, are herbivores; preferring to eat roots, grass, seeds, and whatever plant material they can drag down into their tunnels.

These destructive critters love freshly dug soil and newly planted plants; a real problem for many gardeners.  When you plant out a bed of transplants voles think you’ve prepared them a luscious buffet.  We’ve had newly purchased plants simply disappear overnight, eaten before they could even root into the surrounding soil.

As many moles or voles as you trap or kill, there seems to be a constant supply of new ones ready to take over the yard, with new ones born regularly between May and October.  There damage tends to be worse after a good rain when the ground is soft.

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A vole hole under a fern in a shaded area is only one of at least four networked holes all connected with tunnels.

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We’ve noticed that mole and vole activity seems to be worse in shaded areas than sunny, and that they go crazy under any area mulched with bark or leaves.  We’ve had whole areas dug up in a single night, and have even found them tunneling under some lawn during the day.  These guys will just destroy new plants and tear up the ground if left unchecked.  Worse, in our yard, we’ve found snakes also use the vole holes and tunnels for their own purposes.

Some people will bait the tunnels with poison, but I choose not to use poisons, especially since we have neighboring outside cats.  Some people leave traps to catch moles and voles.  But then you have to do something with the creatures once trapped.

Eliminating all moles and voles isn’t going to happen in a forested neighborhood with lots of green space, but, there are some things you can do to slow them down.

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Vole hole, through an earlier patch of gravel, and surrounding tunnels in the lawn.

Vole hole, through an earlier patch of gravel, and surrounding tunnels in the lawn.

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First, we destroy the tunnels and holes whenever and wherever we find them.  We stomp the tunnels flat, and fill the entrance holes with pea gravel.  If you find one hole, there will probably be another nearby.  Before I started filling the holes with pea gravel, we put rocks, bottle caps, moth balls, and other treasures into the tunnels to obstruct them.  Moth balls are especially effective at chasing these critters out of a particular tunnel.

Over the years, we have also stumbled across a non-poisonous way to eliminate some of the ‘activity.’  A friend tipped us off to using chewing gum as a bait.  We use sticks of Double Mint or Juicy Fruit gum, still in its wrapper, and torn into three or four portions per stick.  When we find a hole or tunnel, we simply push one of these little baits into the earth before we stomp the tunnel or fill the hole.  This method has proven helpful in reducing the population.

A product called “Milky Spore,” which is a powdered bacterium, can be sprinkled on lawns.  One application will allow this bacteria to grow in your soil, killing off the larvae of the Japanese beetle.  These larvae are a major food source for moles, and many find that using milky spore reduces the tunneling in their lawn.

Milky spore is not poisonous, won’t harm pets or other wildlife, lasts in the soil for years, and is widely available in hardware stores and garden centers.  As a bonus, it will reduce the Japanese beetle population, which may feed on your roses and other perennials in early summer.

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Gravel and Plant Tone ready to be mixed into the bottom of a  planting hole.

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When planting anything new, I mix pea gravel into the “back-fill” under and around the plant.  The gravel can improve drainage in the soil, and will slow voles down as they try to attract the roots of a plant.  I also mulch around newly planted beds with pea gravel to slow down the squirrels who may want to dig them up.

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Use pea gravel in the "back-fill" soil under and around new plantings, and then mulch around the new plant with pea grave. This discourages moles and voles from eating the roots of your new plant, and discourages squirrels from digging around it. Herbs benefit from the reflected heat and sunlight, and the soil is held in place on a slope.

Use pea gravel in the “back-fill” soil under and around new plantings, and then mulch around the new plant with pea grave. This discourages moles and voles from eating the roots of your new plant, and discourages squirrels from digging around it.  Herbs benefit from the reflected heat and sunlight, and the soil is held in place on a slope.

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You might also create a ‘living fence’ of poisonous roots around an area that you need to protect from hungry voles.  You will find that there are many plants with poisonous or irritating compounds in their roots, stems and leaves.  My favorite plants to use this way are Narcissus and Hellebores.  Plant these plants around shrubs whose roots you want to protect, in mixed borders, and as a barrier around areas of lawn.

Narcissus, planted a bulbs in the fall, are an fairly inexpensive investment and multiply over the years.  They grow all winter long and bloom in the spring.  Although their leaves die back in early summer, their roots and bulbs continue to work as a barrier year round.

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Narcissus are beautiful but poisonous. Their bulbs and roots can form a ‘living fence’ to protect other plants form hungry voles.

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Hellebores, an evergreen herbaceous perennial, are available in garden centers from late autumn through the spring.  They bloom from late December through early May, and serve as a ground cover through the summer months.  They have large, fibrous root systems.

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Hellebores bloom through the winter months, but their large root system can protect an area from voles year round.

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Once established, Hellebores produce lots of seedlings, which you can transplant to new areas you want to protect.  Most gardeners cut back the old Helleborus leaves in the spring to make way for new growth.  Consider using old, ragged Hellebores leaves you’ve trimmed back as a mulch around other plants you want to protect.  As the leaves decay, their poisonous compounds enter the soil.

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A new raised bed, bordered by recycled bricks, is filled with topsoil and compost, ready for planting.

A new raised bed, bordered by recycled bricks, is filled with topsoil and compost, ready for planting.

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The best plan to protect your garden from mole and vole damage is to grow in raised beds.  When you build the bed, put a layer of chicken wire or landscaping fabric on the ground; follow with a shallow layer of gravel, then newspaper, cardboard, or brown paper shopping bags.  This suppresses the grown of any grass or weeds up into your new bed.  It will break down quickly, and help retain moisture under the roots as it enriches the soil.   Build the walls of your bed from wood, rock or masonry as tall as you need them, and fill the bed with topsoil and compost.

Laying landscape fabric or chicken wire under a new raised bed will keep the voles from eating the roots of your plants.  You might also use the Hugelkulture method of building a new bed on top of sticks, branches, leaves, or chipped wood.  This woody barrier will also help stop tunneling moles or voles.

You may need to slice through the bed’s lining to plant shrubs or other deeply rooted perennials, but your plants will be protected.  Many plants will grow more vigorously in a raised bed, especially if your soil is compacted or depleted.  It is very easy to plant into the fresh soil.

This is also an easy bed to maintain, and will never need tilling.  Simply add a few inches of compost each spring, and move plants in and out as the season dictates.

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March raised bed

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Plants grown in raised beds and containers grow much better than plants put directly into the soil around our home.  We get larger, lusher plants, with more flowers and fruits; probably because their roots can find plenty of moisture, air and nutrition and aren’t attacked by hungry voles!

The steep grade of our yard makes traditional double digging or tilling not only impractical, but dangerous.  Building up above the present soil makes more sense, gives a better result, and allows us to put down layers of material to stop the moles and voles from digging up to get the roots of our plants.

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Our new butterfly garden in May.

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If you have been frustrated in your efforts to garden or even maintain a lawn by hungry moles and voles, take heart.  There are things you can do to reduce or eliminate the damage they cause, without resorting to poisons.  Once you understand them, you can find ways to reduce their access to the food they seek, and protect both your landscaping investment and your peace of mind.

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Daffodil bulbs planted at a depth of 8″, and about 6″ apart all around the root ball to protect it from voles.

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Woodland Gnome 2013
Updated 2018

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