Trail construction and design for use in native plant gardens
On the trail to a good garden path
Let's quickly step away from some traditional concepts in garden paths - sort of get off the beaten path, if you will.
The tradition of European landscape design is based on well-ordered geometrics: rectangles, circles, triangles. Paths are often the defined space dividing beds, very often lawn but perhaps also made from other paving materials, suitable for a stroll in your Sunday-best shoes and perfect for a nicely-organized botanical display.
If the idea is to include native plants among arrays of botanical specimens, it's a concept that's still going to work quite well, and books abound on nifty ways you can get from one point to another.
But if you're interested in replicating nature, you're probably less inclined to have a path and more interested in a trail. And it is to the concepts of trails we turn for sound ideas on how to navigate through the little wilderness we create for our own pleasure and amusement.
A sketch showing tread width, clearing width, and minimum clearing height for a National Park Service Trail (from the design handbook for the North Country Scenic Trail)
Not surprisingly, government agencies have done a lot of the groundwork for us. When federal, state or local agencies present us with wild places to enjoy, they are obligated to consider the safety and comfort of visitors as well as the safety and comfort of the environment through which they pass. One of the best documented is the North Country National Scenic Trail which traverses a number of states along the Great Lakes.
Why are these standards of value to us? Simply put, by adopting a standard for paths, you create a consistency that pulls your garden design together and focuses your attention on details that can avoid inconveniences.
Typical of National Park Service trails, there are four recreation settings (ROS): urban, rural and roaded natural, semiprimitive and primitive. The first two are likely to be of most interest to gardeners; after all, we stroll. We do not hike.
Primitive ROS in park parlance implies an absolute minimum impact and greater personal risk, and because of that, few hard standards have been established. But remember, trail design standards also protect the environment and because wilderness trails tend to get less regular maintenance, they should be carefully designed.
A cheap but handy tool is a section of four-inch plastic sewer pipe, available at any home center or hardware store. Ours is seven feet long, the standard width of a main path at Pennystone, and marked at 36 inches from either end, the usual width of a service path. It measures, it grades, it tamps, it smooths, and it lightly plows materials being laid for paths. It also helps keep grades smooth over long distances. Laying a level on the top ensures paths stay level from side to side.
Definition of terms:
Tread width - the actual walking surface of the trail, and should be initially constructed or smoothed to standard. In less used areas, the bare tread may eventually evolve into one that requires mowing, but should nonetheless be on a smooth underlying structure.
Clearing width - the area "kept free of brush, limbs, briars, tall grass, weeds and other obstructions that would slap against the hiker or their pack or soak them following a rain or heavy dew." But NPS also recognizes the value of varying the clearing width, widening it at points of interest and narrowing it when aesthetics or control issues arise (for example, to keep a couple of large trees that somewhat crowd the tread or perhaps tightening it up to discourage horses or ATV users. You may not have a herd of mustangs wandering around or ATV enthusiasts revving up at the trailhead - but you probably do have a lawn mower and perhaps a garden tractor).
Clearing height - NPS picks eight to 10 feet to prevent backpack snags, with an eye to winter hikers on heavy snow. Suffice it to say, anything under eight feet becomes a doorway and you and your tools and implements have to go through it safely.
Slope, sustained - Because trail tread must remain stable, steep grades present erosion problems and a less pleasant hike. Calculated in degrees, slope is determined by dividing the vertical distance by the horizontal distance - so, for example, a rise of five feet along 100 feet of path is a 5 percent slope.
Slope, maximum - Sometimes there's no way around a short, steep grade, but there are still reasonable limits for both erosion and comfort.
Cross slope - If a path is cut into the side of the hill, water flowing downhill must be encouraged to cross the path and keep going. But radical departures from level are both uncomfortable and can erode in heavy runoff situations. For what it's worth, a 5 percent cross slope on a 48-inch tread is a drop of 2.4 inches, and yes, your ankles will notice it.
Rest areas and passing places - This is likely not a safety issue in back yard gardens, but consider it from an aesthetic standpoint. By widening the trail clearing in regular intervals at points of interest and providing an inviting place to pause, your design achieves great effect. This spot to linger is a classic and key element in Japanese stroll garden design.
Trail surfaces - Unless you get an enormous number of visitors or are a public garden, hard paving such as asphalt is not a requirement. Stabilized aggregate - the kind of gravel often used in driveways - is a firm surface that when packed with a tamper becomes very sturdy indeed. We've experimented with pea gravel and "crusher run" (one step coarser than sand) and have been astonished at how solid a path can feel under foot. We began with turf but lately have been working with wood chip mulch - the latter being softer but not helpful in areas that stay moist, causing rapid decomposition. While crushed stone is solid, it's also harsher, and we suspect most folks would prefer turf or chips for a softer feel.
| Desired Standard | Urban | Rural/Roaded | Semiprimitive |
|---|---|---|---|
| Tread width | |||
| Hiking segment | 48" | 24" | 18" |
| Accessible segments | 60" | 36" | 28" |
| Clearing width | |||
| (each side of tread) | 24" | 12" | 12" |
| Clearing height (min.) | 10' | 8' | 8' |
| Slope - max. sustained | |||
| Hiking segments | 10% | 10% | 15% |
| Accessible segments | 3% | 8% | 12% |
| Slope (max.) | |||
| Hiking segments | 15% for 100' | 20% for 100' | 30% for 100' |
| Accessible segments | 8% for 30' | 10% for 50' | 10% for 50' |
| Cross slope (max) | 3% | 5% | 8% |
| Passing spot (max. interval) | n/a | 600' | 1200' |
| Rest area interval- max. | 1200' | 1200' | 1/2 mile |
| Surfaces | Asphalt, aggregate, woodchip, sod | Native wood chip, aggregate | Native |
| Accessible surfaces | Asphalt, aggregate | Asphalt, aggregate | Native stabilized aggregate |
If you can't avoid stairways, at least keep the tread-to-rise ratios comfortable for walking. Common materials for risers are rocks, logs, overlapping rocks, plank-style retaining stairways and crib-ladder stairways, but the standards for steps is:
| Rise | Tread |
| 4" | 19" |
| 5" | 15" |
| 6" | 12.5" |
| 7" | 10.75" |
If you've ever hiked in a national park, you've probably walked on a "turnpike," created for areas where stormwater runoff is an issue. The cross section shows trenches a minimum of 10 inches deep on either side of the tread, which is bordered by treated four-inch poles and holds a minimum width of 18 to 24 inches of aggregate. From the National Park Service specification handbook for the North Country Scenic Trail.
One of the more oddly-named forms of trails is a "turnpike." It conjures images of toll booths and high-speed traffic, but it also means a specific style of surface that runs through areas where water and water-logged soil is a problem. It gets its name from early turnpikes, where road builders felled trees that became the edges of the road surface. Held in place by simple spikes, the log poles ran parallel and were filled with a surface material that would offer good drainage - such as stone. On the outside of the logs were trenches to accommodate water runoff. An NPS turnpike is 18 to 24 inches of tread, bordered by two four-inch logs and a trench up to ten inches deep.
Retaining walls to protect trail treads where there are steep dropoffs are built with the biggest stones on the bottom, a minimum of 18 inches thick at the bottom and eight inches at the top. NPS calls for two to three inches of "batter" (or setback) for each inch of wall; the leaning back of the wall balances it against the outward pressure of the soil behind it.
If you have water running across the path, you'll have to consider simple puncheon bridges, culverts or coweeta dips, depending on flow and volume. Never fear, there's standard designs for all - up to and including three-stringer and single-span bridges.
Make a simple compass by attaching a piece of sturdy line to two tent stakes. One goes in the ground at the center point and the other can draw out a smooth curve - in this case, eight-foot radius - or temporarily mark crucial points on the curve.
Curves: Consider the issue of radius
Your path naturally should include curves, which sustain interest in the walk and slowly unveil your collection. But just how sweeping should a curve be? For a hiker on a primitive trail, there's no real minimum. But when you consider vehicles, such as garden tractors - especially towing a cart of any kind - you'll do well to pay attention to standards prepared for trail users that are not on foot. Horse trails must avoid sharp turns on slopes that would represent a safety hazard. Mountain bike users can get by with a four-foot radius curve, but eight feet is preferred. Snowmobile enthusiasts need curves with a hundred foot radius to safely navigate in winter and at high speed.
A good idea is to lay out a garden hose in a clear, flat area with a radius of six to eight feet and drive around it on your implement with whatever attachments you'll use. To make the curve, take two tent stakes, attach a sturdy line of a set length and pound one stake into the ground. Then use the other like a compass to guide the line of the hose into a fairly neat circle. If you can drive with the front tire of the tractor and the tire of the cart outside of the line of hose, you're okay; if you run over the hose, you'll have a problem routinely navigating the garden path.
This may sound ridiculous, but the year we acquired a trailer-mounted leaf shredder that effectively doubled the length of the trailer behind the tractor, we had many problems with low stone walls on tight corners.
The solution is to create runouts, a wide area on the outside of the curve, especially on the down side of slopes. This gives you swing space to safely navigate through the garden plus a visual point of interest when you're on foot.
Keep those tent stakes and that line. You'll use them for marking out curves. To do so, lightly stick one stake in the ground at the edge of a path and step out perpendicular to the line of the path for the center point of the curve. Secure this stake in the ground, then use the outside stake to guide your edge.
Acknowledgement
Our thanks to the National Park Service. See the entire Trail Specification Handbook, mostly in a well-organized pdf format. It covers trail layout, suggests best ways to route a trail, and offers guidelines for all the structures you'd see along an NPS trail from steps to rest facilities.
Remember, park service standards for trails are established to make the outing one of pleasure and interest. Thus, a well-crafted path creates both rhythm and unity in landscape design, following natural or man-made contours and through a series of interesting views. At points of interest, it's not uncommon for a path to widen, perhaps into a mini-clearing that invites the visitor to linger and study the scenery, especially where the path changes direction. Applied to Japanese stroll gardens, the regularity of a standard-width path is modified to widening and narrowing specifically for this effect. But there are standards for minimum and maximum width and the effect it has on the visitor's rate of travel. Applied to parks, there will be little spurs here and there, perhaps going to a secluded campsite or rest facility, a technique that can add adventure and mystery to your own design.
These principles work even in tight quarters. Great stroll gardens are possible in less than 3,000 square feet and usually accomplished with very tight horseshoe path shapes wrapped around higher ground that blocks the view of the opposite side.
Summing up paths, then: plan very carefully and thoroughly. Work on a scale drawing on the kitchen table, then mark it out on the ground itself. If you have gardening equipment that will be on the trail, try it out. Mark the path and walk or drive through it. Study it from all angles of view and if you need to create variances in grade, consider how you'll move the earth to meet your design needs. Spend some time on trails in nearby state and national parks and look at them from a design viewpoint. You'll get great ideas.
