Head For The Hills: Working With Hillsides

THE DIGGING DILEMMA. Many contractors solve hillside challenges by excavating the hill, but this comes with consequences. Changing the hillside can alter the drainage pattern and jeopardize the health of the foliage on the slopes. Attention to irrigation needs is key.

"I usually put grasses on the high part because they will get the mist and the overspray when I water with rotor heads," explained David Gatti, owner and designer, POPS Landscaping, Marietta, Ga. "I put plants that require a little more water in the middle, and even there I use plants that are more drought-tolerant.

"I put perennials at the lowest part of the hillside, so they will receive the runoff," he added.

Droughts are a major concern in Georgia when working on a hilly property, Gatti pointed out. "We had a drought last year, and all indications are we will have one again," he said. "When your water supply runs off, as it does on hills, this is a major concern."

Another major moisture concern is erosion. Contractors need to minimize land loss by developing a landscape that channels water toward drainage paths.

Bill Trimmer, president, Professional Grounds, Arlington, Va., recommended beginning property inspections with a complete site survey. "You must look at everything, even items that are not on that property," he said.

For instance, a hilltop watershed on an adjoining property is a variable that many contractors tend to neglect because it is not on the property being serviced.

"You may have to install some hardscapes or something that will divert that water elsewhere or channel it under the ground," Trimmer explained. "If you have a hillside with trees that is not extremely steep, but the runoff makes it difficult to get turf to grow on it, that might call for channeling water underground.

"Shade could be prohibiting turf to take hold, so you might have to trim those trees for installation and let them grow back after the turf takes," he continued.

WONDER ABOUT WALLS? Some hillside solutions involve installing materials besides plants. "We have one community where the traffic pattern down the hill caused all kinds of problems with the turf," Trimmer explained. "Our solution was to install a set of steps. That changed the traffic pattern on the hill and allowed the turf to gain a footing.

"You have to really analyze everything that goes on at that site and figure out the best overall solution for the entire property," Trimmer continued.

"And then, you have to stick to your guns," he added. "You are the professional and you should understand much more about what will work."

Appropriate hillside installation materials must be considered in advance.

"It is a thought process that needs to go into the design before you implement it," Gatti agreed. "That is basically the bottom line. Too many landscape contractors don’t think about these issues. They think of being creative, but they don’t think long term.

"When working with hills, I think creatively and I try to also emphasize long-term solutions," Gatti continued. "I always inspect the job and look for potential short- and long-term problems. Sometimes these problems won’t surface for five years, but they will eventually surface."

For Gatti, this is especially critical since POPS offers lifetime warranties on its retaining walls. "We know that if there is a problem, we will be the ones coming back to fix it," he said. "So we do what we can to make sure it is done right the first time."

Not repeating problems is one key to hillside success, Trimmer stressed. "If you go out to a hillside with sod on it that didn’t take, how much sense does it make to put sod on it again?" he asked. "You have to look at why that sod did not take and work with the problem from there.

"That hill might be too steep for sod - the slope might call for a retaining wall instead," he continued. "Or, you might need a catch basin to divert the water somewhere else. You might have to eliminate the groundcover altogether and figure out another plan."

Weighing options in advance produces more successful projects. "When you address the problems from a ‘why?’ standpoint, you get a better handle on what will work, what won’t work, and the differences between the two," Trimmer explained.

Larry Becker, owner, Becker Landscape Contractors, Indianapolis, Ind., cited his "rules" for installation, which are crucial when dealing with variables he experiences such as glacial till, he said.

"Rule No. 1 is to make sure you get all of the water out from behind the hill," he noted. "Rule number two is to understand that not all hills are natural - many were created during site preparation."

Since glacial till is a major issue in Indiana, Becker deals with challenging drainage issues. "We’ll see glacial till, which is an underground stream of water that just keeps on flowing," he explained. "With the development we have seen here over the past few years, glacial till has become more and more apparent."

Becker said that contractors often cut away part of a hill to install a wall, but this can create problems. "If we put footings in that hill and there is glacial till, the ground will always be soft and the footings will not be totally secure, especially when you are changing the complexion of that hill and the resulting hydrophonics," he described.

"That is an issue we have to deal with, and it usually means putting drainage behind that wall to keep the water from eroding the property," he remarked.

The integrity of the wall is another issue to examine. "When we deal with walls, we want an engineer or engineering company to come in and build them, simply because of the risk factor," Becker shared. "If you try to build a wall and the ground is too soft, that wall will eventually give in. Then you have much bigger problems.

"We will walk away from work in certain instances if the customer doesn’t want to pay for the services of a professional engineer," he added. "That is just too important to many of our projects."

RETAINING EROSION. Retaining walls might replace plants as a hillside solution, however, this installation option is not immune to erosion conditions. Here, environmental compliance often comes into play.

"We have had some [hill] projects go pretty wrong in the past, and we have learned from that," admitted Michael Hoffman, owner Hoffman Landscapes, Hartford, Conn. "You are taking a big risk anytime you work with the erosion factor."

Hoffman said that retaining walls are limited in Connecticut because of local government requirements. Anything 6 feet or higher requires a zoning variance, and walls 4 feet or higher require a professional engineer.

"Our major concern is erosion and runoff," Hoffman noted. "When you do a long-seeded slope, you risk the seed being washed away. So if there is a potential for damage from heavy rains, we will stake hay bales down the hillside. We’ll put in a fill fence and back it with hay bales to slow down water.

"Sometimes we have to do several rows to assure there is no damage," he added.

For Hoffman, the local watershed is a critical factor to recognize. "Our area drains into the Long Island Sound," he explained. "We have to make sure that we have a swale built on properties with water gathering at the bottom of a hill to slow the water enough for it to be absorbed into the soil. Any excess water will eventually flow into the Sound.

"And that becomes an issue later when pesticides and fertilizers are applied to the property," he continued. "We need to keep those out of the watershed.

"If there is water at the top of the hill, we want to make darn sure there is enough high ground between that pond and your slope to the river," he said. "If there isn’t, perhaps you need to make that high ground."

Working near water sources can prevent environmental challenges, and contractors should take precautions by applying for necessary permits, Hoffman said.

When working with hillsides, "drainage is king," Becker agreed, stating that nothing else comes first when designing hillside landscapes.

Becker said that there are several drainage systems available to contractors, but they must consider all variables. "We use gravel as a means of drainage," he said. "We use tons of it, which allows the water to drain into the property properly.

"But, you have to cap the gravel with clay so you don’t have a free flowing water problem in retaining walls," he continued.

"You can put gravel in a few times, at the bottom or at the top," he said.

Gatti also uses French drains beneath the turf to hold excess water long enough for it to soak into the soil so it won’t immediately run off the slope. "The yard will be sitting in water, but not necessarily sitting in the water," he explained. "The water has to run off so the yard won’t flood, but I don’t want to let that water run completely off the property because water can be a valuable commodity these days."

"You may have to do some drainage work," noted Trimmer. "But you have to get to the cause of the problem and not just try to patch up a symptom."

Trimmer warned that customers are often reluctant to pay for a proper drainage system, so they install something less expensive and effective. "Too many people think they can solve the problem by patching a lower cost ‘solution’ together," he noted. "But usually that is a short-lived answer.

Often, contractors who excavate a hill, install a retaining wall, and then backfill with the original soil will experience problems. "If you put too much soil in, it will retain water and possibly compromise the integrity of the retaining wall," Becker said.

He recommended replacing soil with gravel. This provides two benefits: the hillside slope will lessen due to the additional material, and the water will drain better, exerting less pressure on the retaining wall.

"Twenty tons of soil will weigh exponentially more wet than 20 tons of gravel simply because of the drainage factor," he said.

"When cutting away hills, you must be careful not to overcut," says Gatti. "You want to bring in some fill, but you don’t want to bring in a lot of backfill, especially if you are using a dry set method. That backfill, when combined with water or moisture will tend to bulge the walls."

Becker has seen more than a half dozen walls fail in the past few years because contractors did not tend to the property's engineering needs. "In some of those instances, the property has seen too much damage for us to solve the problem inexpensively," he said.

Those situations support Trimmer’s advice to trust instincts when recommending a hillside solution. "If you have provided your solution and the customer still thinks it is overbudget, you cannot compromise your work, and risk liability by cutting corners on the integrity of the project," he said.