Dramatic beds begin with great service...paths
Here's a little exercise (literally) to get you started thinking about paths in the practical sense.
Fill a half-gallon milk bottle with water, cap it securely and kneel down on a convenient patch of floor. Reach out as far as you comfortably can and put the bottle in front of you. Now, without leaning so far that you have to brace yourself, grasp the bottle and lift it straight up, then slowly put it straight down. What you've just done is some serious weeding, pulling one of those big nasty invasives out of the ground.
The distance from your knee to the milk bottle is a proper width of a flower bed. In my case, that's about 30 inches, or two and a half feet. If you can get at the bed from both sides, you can just about double the width of the bed -- say, five feet.
Anything wider and you're going to need a service path. I know: a lot of gardeners take a long step into a bed and put their foot down between a pair of plants, bend over and do gardening chores while balanced kind of like someone frozen in a tai chi pose. This works for the rare occasion, but when it's the order of the day, the grueling chore of garden maintenance quickly degenerates into misery. And then it gets put off. And then the garden quite literally goes to seed.
Instead, create a service path, which effectively makes the bed about ten feet wide if you have access to it from both sides, or five feet if it's a border, plus the width of the path itself. The impact can be stunning, because beds can become quite wide and permit the establishment of great masses of plants.
Just as the name implies, a service path is the discreet access into the heart of garden beds to perform maintenance and not intended for visitor traffic. An excellent service path will be hidden from view from the perspective of the main path through the garden, usually by a line of plantings that gives the illusion that there's no path in there at all. Some clever gardeners cut the path below the normal grade of the bed surface, particularly when foreground bedding plants aren't very tall.
But sometimes a service path can make a dramatic statement. I recently visited an herb garden where the beds were laid out in large circles with a stone paver path coming in from the outside edge to a mini cul-de-sac in the center. With five feet of planting space on either side of the center, the bed was about 14 feet in diameter and truly elegant in simple formality.
Other service paths are simple branches off a main path to give access to a spot just out of easy reach. These are the ones that don't have to be more than a foot wide, since it represents just a few steps into the bed to work on difficult-to-reach spots, such as a distant corner.
A service path of mulch discreetly slips through tall background plantings to divide a very large bed into two manageable parts.
When it comes to paths, take a hint from the brilliant civil engineers who built railroads: the earth may rise and fall, but the track is on the shallowest possible grade, hopefully zero. Railroads take sometimes long winding routes to accomplish this efficiency, go through cuts and fills and have minimums on radius of curves for speed and safety. If you apply the metaphor to your own bed, you'll surprise yourself by creating all kinds of drama. And isn't that what a great garden bed is all about?
All sorts of materials can be used for service paths. Perhaps the easiest and most discreet is mulch material, with fine gravels and sand coming next. Pavers of some sort - usually flat stone that's comfortable to traverse on foot - are at the top of the work chain because they need to be set carefully to avoid stumbles, stubbed toes, and loss of balance. But all demand a certain amount of excavation to be level side to side and rise and fall at only minimal grade. If you have access to inexpensive or free mulch, dig down six inches or more (use the soil to build up the beds on either side), spread and tamp or roll the material as tight as possible. A thick weed barrier is useful, especially when you periodically have to dig it up because it's become compost. If you choose sand or fine gravel, four inches should suffice, but, again, tamp it. Pavers usually go down over several inches of composite gravel topped by at least two inches of sand.
A service path is also real handy for water lines, like hoses, but should be laid out with care. When hoses go around curves and get yanked for that extra few inches on the business end, they can do a lot of damage. Sometimes it's simply better to tuck a hose into the edge of a path at the start of the season and retrieve it when winter nears, leaving it in place for the sort of use that makes gardening a pleasure rather than a chore.
If you plan to install somewhat permanent water lines, be sure that they are sufficiently below grade to avoid being punctured by garden tools and lay evenly on well-tamped material to permit draining in the winter. It's a good idea to keep them along the edge of the path for emergency access.
And since we're going to the effort of laying out a useful path for maintenance, let's consider moving safely and comfortably through the space. A wheelbarrow is a couple of feet wide, but because it rolls on a single tire it has good maneuverability in a tight space. A two-wheeled cart needs more turning radius. A person on foot can pass through in a very narrow space. But if you plan to work by hand, practice with a couple of buckets of water to get a feel of moving around with the sort of bulk you'll be carrying when full of weeds, new plants, tools, fertilizers and the like.
Sometimes a service path is so nice that it becomes a favorite shortcut, especially when Aruncus dioicus is madly in bloom
Both a wheelbarrow and good safety practice for carrying stuff in and out of the bed demand a smooth, trustworthy path where you can maintain good balance and not damage the plants you've worked so hard to show off. It doesn't have to be obvious (although it can be); taller plants grow up and arch gracefully enough to block the service path from view, but give way when the gardener slithers through.
I'm ignoring garden tractors, which need at least a four-foot path just to drive through; under those circumstances, you no longer have a service path, but a regular thoroughfare.
When starting to organize a bed design that will require a service path of some sort, it's a good idea to rehearse a bit. Setting up a proposed route on the actual site is best, but you can get a space sense in just a patch of lawn. Mark out your proposed path with a series of three-foot tall garden stakes (the kind you might use for supporting plants in parallel lines to create a bit of a maze. Now go through it with a wheelbarrow or cart or just yourself with a couple of loaded pails of water. If you even touch any of the stakes, it's too narrow. Modify your plan. You'll appreciate it on a hot summer day when the work is nasty and the load is heavy.
Pushing a loaded wheelbarrow or cart up hill in a garden can be a problem too, so if you have grades on the property, build a test load and get a sense of the effort you're going to have when hauling equipment and supplies to the future home of that splendid azalea or stand of rudbeckia. If you need steps to get up the hill, you're certainly not going to have much fun with a wheelbarrow full of mulch.
Once you've got a service path planned, it's a simple matter of extending 24 to 30 inches to either side for the bed itself; where it gets wider, consider small offshoots of the path to step into remote corners.
And finally, you get to couple beds together along regular walking paths - beginning the foundation design of a really swell garden.
