Boulders and rocks make low-maintenance focal points for lively yards, even in a Wisconsin winter

This summer, I got gifts for my garden.

They included a variety of plants. I even got a small tree.

But the best gifts were the large boulders for a new garden bed, and the dozens of small, smooth rocks to be used to identify my plants.

Why do I love them so?

They add nterest to my garden beds, will never have to be replaced, and they need no maintenance.

Boulders are popular,  and they  stand the test of time, said Samantha Carlson, a landscape architect at Bret Achtenhagen Seasonal Services, a landscaping firm in Mukwonago.

“What’s so great about them is that Wisconsin has all kinds of natural resources, and boulders are one of them. … There are local quarries right in our backyard. You can pull stones from Lannon, Chilton or Fond du Lac. By adding boulders to a garden, you are celebrating the state’s natural history and you give your gardens a unique look.” she said.

Perennials and annuals accent the area where Judy  Schmidt added boulders to enhance a ditch and reduce erosion at her Franklin home.
Perennials and annuals accent the area where Judy Schmidt added boulders to enhance a ditch and reduce erosion at her Franklin home.

They can be used in any style of garden, and they instantly become a focal point, she said.

“Mostly boulders add a rustic kind of element in a garden, but I have also seen them in formal beds. … They even add some winter architectural interest. The plants all go away in our Wisconsin climate, but a nice boulder collects snow and adds structure in winter,” she added.

While boulders, which are typically any stone greater than 10 inches in diameter, can be used in different styles of garden beds, not all applications are decorative, said Rob Holly, a landscape architect and director of design, build, sales at LandWorks Inc., a landscaping Services firm in Sussex.

“Sometimes it’s a way to tie architecture into a landscape, for example using the same kind of stone that’s in the house in the landscape,” but they can also be used for “traffic control” — for example, to prevent people from cutting corners across a property, he said.

Holly said he tends to think of them in more informal settings, but there are ways to use them in formal gardens. An example would be a single boulder in the center of a boxwood hedge, or boulders in all four corners of a boxwood hedge.

When selecting boulders, look first at your home architecture and your gardens, Carlson said.

“You are always responding to the existing site conditions. You want it all to have a cohesive look,” she said. An example would be a boulder that complements a home's stone veneer.

A single boulder accents a small garden bed. Echinacea, hostas and annuals surround it.
A single boulder accents a small garden bed. Echinacea, hostas and annuals surround it.

Unique boulders add character

Next look for boulders that are unique in some way.

Carlson  hand-picks boulders for projects.

“I call them specimen boulders. ...  They might have a really cool fractured face or some other special characteristic.”

Holly also likes to use boulders with unique characteristics, and he makes sure those characteristics aren’t lost when he installs them.

“When we find these things, we try to highlight them or honor them. You try to put that area to the front to make it more unique. Or you can make it something you have to discover,” he said.

An example would be a boulder set in a circular bed so its unique characteristic can be seen only when you walk around it, he said.

“Something I really enjoy is how much of the history of the stone you can see in the boulder. Sometimes you can see drill marks that were made when they quarried out the boulders. Or maybe there’s a shape that could hold water — a place where water rippled across the boulder,” he added.

Different shapes for different spots

Boulders' varied shapes also   lend different looks to a landscape.

Carlson said she often uses the larger flat stones, called limestone outcroppings, in garden beds, retaining walls, and for steps.

In garden beds or around patios, she often selects pieces about 24 inches high so they can be used as seating.

“That offers the homeowner a place to sit while gardening, or sitting in the patio or around the fire pit or the campfire. I love putting them into a living space.”

She added that she recently worked on a project in East Troy on Lake Beulah where the homeowners used large pieces of outcropping and pieces of reclaimed timber to make two long benches they could sit on when relaxing near their patio and fire pit.

Winnebago Outcropping stone from Chilton is used for decor and seating at a home in East Troy.
Winnebago Outcropping stone from Chilton is used for decor and seating at a home in East Troy.

Boulders with flat tops and bottoms and lots of angles give a crisp modern look to a home's architecture, Holly said. Some of these pieces can be “locked together” and are often used in sloped areas or freestanding walls.

“Instead of trying to stack rounded boulders together, these have points and planes that fit together nicely so they won’t slide past each other if used in a sloping area,” he said.

When it comes to size, a rounded boulder about 24 inches across would be good for a small garden bed, Carlson said. But for a large bed, “you could use three or four that are as big as a piece of equipment could handle. Here, it’s the bigger the better,” she said.

Getting the right number of boulders

How many boulders you add can depend on your home and landscape, but also personal preference.

Less is usually better, Carlson said.

“You don’t want to do too much. The really large ones make an impact, for sure. You can add a single boulder, you can group three together, or add a grouping of three and then set one off to the side.”

There are no hard and fast rules about how many boulders to add, Holly said.

“I usually go by what looks good. Two on one side and one on the other side can be a good look. If you put two together, typically the larger one is in back to create a backdrop. But sometimes you may have multiple viewing areas. For example, you may be looking at it with the house behind it, but you can also see it from a window in the house.

“The odd numbers tend to be a little more natural looking and would lend themselves to sites where gardens are more informal. Formal gardens tend to be more symmetrical, so then you might use an even number of boulders.”

Where to put the big rocks

But, no matter what style of garden boulders are added to, the design can often take time to perfect.

“A lot of times it’s done by feeling,” said Holly. “You might set them out and arrange them, and then you stand back and see if you should add one more. Or if it doesn’t look right, you might take one away. As a contractor, we bring out some extras to play around with and we can take back what we don’t need.”

Although this is easy for professionals to do with the right equipment, it’s not easy for homeowners. A 24-inch boulder can weigh 700 to 900 pounds, Holly said.

With multiple boulders, colors, shapes and sizes should be mixed, Carlson said.

“You want to create visual interest. You want them each a little bit different so the eye bounces from one to the next. Rhythm in the landscape is good as it comes back to mimicking nature,” she said.

But on occasion, she admitted, she will set a boulder into a garden in a way typically not found in nature — standing on one end, for instance.

While there is an art to selecting the right boulders for a property, there is also an art to placing them in a landscape.

“You should set them below the grade so they look like they’ve been in that spot for years,” said Carlson. “If you don’t, it feels like they’re not connected to the earth. You want them to look grounded in the landscape. … You want to mimic nature.”

She suggests digging an indentation 2 to 4 inches deep for the boulder.

Holly likes to bury up to a third of the boulder.

“My personal preference is to dig them in. …The key is not to have the waist of the boulder visible. … The biggest part around should be at ground level or below the grade of the earth” to give the impression that it could be bigger and that it was there naturally.

At a home in Delafield, gunmetal boulders from north central Wisconsin “shoulder in” custom lawn terrace steps and transition the adjacent grade.
At a home in Delafield, gunmetal boulders from north central Wisconsin “shoulder in” custom lawn terrace steps and transition the adjacent grade.

The art of installing boulders

In addition to accenting garden beds, boulders are used to create different styles of walls, water features and rock gardens.

“Sometimes we do what we call a soft wall. It’s a slope with boulders in it, but they aren’t tightly stacked and there are plants in between. That gives it a looser and more informal look.”

For that look, boulders are first set in place and then the area is backfilled with soil or gravel, he said. In walls where soil is added, plants are set in between which helps keep the soil in place.

“We also see them used in water features where the boulders will give a reason for the water to change direction when it goes around the boulder,” he said.

A blue-gray angular granite boulder was used to create a low-maintenance water feature. A hole was cored through the center of the stone. A basin and pump are hidden below the decorative slate. at a home in Waterford.
A blue-gray angular granite boulder was used to create a low-maintenance water feature. A hole was cored through the center of the stone. A basin and pump are hidden below the decorative slate. at a home in Waterford.

Carlson said she uses boulders in water features, too. A popular installation she does is a “bubbling boulder.”

“We drill all the way through the boulder, and then it becomes a very simple pond-less water feature without a lot of maintenance. We find a lot of times people want to introduce elements of water into their landscapes but they don’t want the upkeep of a pond. There is a plastic basin under the stone, and a simple pump that recycles the water. We can even up-light them with landscape lighting.”

After boulders are added, plants can be set in place.

Varieties that grow low to the ground are best, so they don’t compete with the boulders, Carlson said. Low-growing ground covers, short annuals, and even short ornamental grasses like Prairie Drop seed are good choices.

What do boulders cost? Holly said the price can vary greatly.

They can go from about $100 a ton for common types, to $1,000 or beyond per ton for unique boulders. Trucking to the site and the installation would be an additional cost.

Perennials were planted on the sloped areas by a ditch at the Franklin home of  Judy Schmidt, as shown  Sept. 23.
Perennials were planted on the sloped areas by a ditch at the Franklin home of Judy Schmidt, as shown Sept. 23.

Making the most of a ditch

Judy Schmidt added a few boulders to garden beds around the front of her Franklin property, but added tons of them to a long, wide drainage ditch that stretches across her backyard.

She said she added them in the late '90s because the yard around the ditch sloped down, making it difficult and dangerous to mow.

But she also wanted to make the space beautiful.

“I wanted to put rocks on the banks to abate erosion, but I also wanted to make that drainage ditch look interesting. I wanted to make it look more like a creek,” she said.

She first had 30 tons of boulders added by Stone Oak Landscapes. The boulders were set into the sloping area that already had fist-sized rocks in it.

“The staff at Stone Oak worked hard to place the stones on the slope to make it look as through they were always there,” she said.

Once the boulders were in, she added plants, but after a while chipmunks made tunnels around and behind the boulders, water got behind them, and some of them slid down to the bottom of the ditch.

To remedy the problem, she had Terra-Firma Landscape reposition the fallen boulders then add Lannon stone to stabilize the area about 10 years ago.

“I had to remove the plants I put in and then replant everything,” she said.

Today her gardens are a striking space where garden clubs tour each summer and people stop to look when they drive by.

Because the area is shady, she planted hostas around some of the boulders. She also added plants that would hold in the soil like Grow-Low Sumac and Purpleleaf Wintercreeper.

Schmidt, a Master Gardener volunteer and a member of the Daylily Society and the Bonsai Society, said adding boulders to a landscape could start with the boulder or with the space.

“If you find a cool-looking rock that you like so much you want it in your yard, then you have to find the right space for it. You can also have an empty area that you feel needs something to finish it off.

“Either way you have to have an idea as to how you want to incorporate it into the landscape because it’s going to be focal point,” she said.

A grape-colored heuchera and a hosta were planted around this boulder in  Judy  Schmidt's garden, as seen Sept. 23.
A grape-colored heuchera and a hosta were planted around this boulder in Judy Schmidt's garden, as seen Sept. 23.

Stones have a place in the yard, too

Smaller boulders, or even stones, can also be added throughout a yard, as you would add garden art, Schmidt said.

Holly said he sees some gardeners using small, smooth stones to mark plants.

 “They are being used by people who are passionate about their gardens or their plants,” he said.

Liz Feagles of Madison is one of those gardeners. Early this year she bought a 75-pound bag of small smooth stones to mark the plants in her yard.

She said she saw this method of marking plants used at a garden tour last year in Milwaukee.

She used a special marker to write the names of plants on the stones, then sprayed the stones with a spray sealer.

“People who walk by on the sideway comment about them. They say it’s nice to know what’s planted, and I feel the same way. As soon as I put a plant in the dirt, I forget its name."

Small stones and special markers are used to identify plants in Madison gardener Liz Feagles' yard.
Small stones and special markers are used to identify plants in Madison gardener Liz Feagles' yard.

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This article originally appeared on Milwaukee Journal Sentinel: Boulders and rocks make low-maintenance focal points for lively yards