Herbs can be headstrong and unpredictable. The mojito mint you reserve for special occasions can make a bid for more space by overrunning your favorite perennials, and the precious and pricy saffron bulbs you planted last season might easily give up the good fight if your soil doesn’t drain quickly enough. After a bad experience, though, most gardeners try again—only in a different flowerbed or in patio pots where they can keep a wary eye on them. Another option to maintain the herbs together, giving them a better opportunity to look their best and gardeners an opportunity to provide them with the special care they need, is to incorporate them into an herb spiral.
What’s an Herb Spiral?
If you’ve seen a snail shell or chambered nautilus, you have a general idea of the shape an herb spiral will take. In this case, as the curve winds from the outside toward the center, the reinforcing walls become gradually taller, topping out at the center point of the spiral. Gaps between the walls are backfilled with soil and planted out with herbs. The structure of an herb spiral produces artificial microclimates, which result from the small, yet significant environmental variations that occur as the spiral changes direction and elevation.
Consider this type of bed the herb lover’s version of vertical gardening, and a permaculturist’s dream of a generous, efficient, yet flexible growing space. It can house plenty of herbs because specimens are planted up as well as out. Also, its shape makes it possible to locate a spiral garden close to a kitchen door for convenience or in a postage stamp-sized urban garden.
The Advantages of an Herb Spiral
Herb spirals offer the gardener an opportunity to cultivate different environmental zones, modifying the soil to suit specific plant specimens. Everything can work together in the microcosms of the spiral garden. This same circular, elevated structure will also help keep plants from sprawling, and balance the problem of placing dense small plants close to taller, spindly ones.
There’s more good news. If you live in an area where water rationing or drought conditions are a problem, an herb spiral offers a structure naturally designed for optimal watering efficiency. When you water, moisture remains within the spiral, filtering down from the top to the bottom. Just place moisture loving plants at the bottom of the spiral, and leave Mediterranean and other drought-tolerant varieties toward the top. So, not only do you water less, but the different zones—dry on top and moist down below—offer plants exactly what they need.
Last, but not least, herb spirals look good. They are a hardscape features, same as fishponds or stone planting boxes. With proper planning, you can install one in a weekend using any of a variety of materials you may have on hand, including rocks, stones, pavers, cinderblock, bricks, or even recycled bottles. An elaborate spiral can even incorporate a water feature, like its own mini pond. It all depends on your budget and the look you want to achieve. Once assembled, however, all spirals make a natural focal point that will help balance the corners and straight lines that tend to make a backyard landscape look more rigidly cultivated than pastoral. They’re also particularly eye-catching and dramatic when viewed from a second-story window or deck.
How to Build an Herb Spiral
Layout and Location
Before you start thinking about turning your whole backyard into a huge herb spiral, there are some scale issues to consider. All those herbs you’ll have growing around in circles need to be maintained and harvested. To do that effectively, you’ll have to be able to reach into the center of the spiral. That limits the overall size to about twice as wide as your outstretched arm. You can make a spiral smaller or larger than that, but a smaller spiral won’t produce as many useful microclimate zones, and a larger one will be harder to keep up. The most practical size is about six to 6.5 feet in diameter. A gradual rise to the center should give a six-foot spiral a maximum elevation of about 39 inches.
You’ll also need to choose a plant-friendly spot for your herb spiral. Make sure it gets at least six hours of sunlight a day, and it’s large enough for both the spiral and a walkway around it. Also, plan for the special needs of any extra features you have in mind, like access to running water and the availability of electricity.
As I said before, there are lots of potential choices here. From reinforced brick and concrete to loose stones, you can spend an entire season pondering the merits of different hardscape decisions. So, rather that focusing on aesthetics here, let’s look at some practical considerations.
Brick and stone are both popular, and you’ll require about two cubic yards of either material for a spiral. Rebar-reinforced brick will potentially last for decades, but at a higher cost than other options, especially if you choose to have it professionally installed. Using a rustic material like stone produces a sturdy spiral, but it can be a challenge to dry stack as the height of the reinforcing wall increases. Also, large stones can hog a surprising amount of potential planting space. Both brick and stone hold in the heat, which could be important in cold or borderline climates where a jump of a few degrees can mean the difference between keeping your favorite herbs in handy reach and having to source them at the market during the fall. Hardscape materials like these can be heavy, too. If this is a DIY job, don’t discount the effort involved in toting heavy loads from your driveway to the far reaches of your property. If you’re going to use it, position the stone pile nearby and enlist the aid of some helpers if you can.
Although less popular, prefabricated synthetic and recycled materials are options, as are wood, bamboo, metal pipe, and creative solutions like wire mesh frames filled with small stones.
After you decide on a structural foundation for the spiral, start assembling the stuff you’re familiar with: soil; amendments as needed; organic material like grass clippings, leaves, straw; and bark or another mulch product. For a six-foot spiral, you’ll need between 12 and 14 cubic feet of soil and organic matter.
There are lots of interesting ways to construct herb spirals, but let’s walk through some basic steps you can use as a jumping-off point. First, clear your planting area of weeds and debris, and cover the spot with a weed deterrent like garden fabric, newspaper, gravel, or cardboard. Next, install a stake at the center of the spot you’ve prepared and make a mark at the 39-inch point. Then, place another stake three feet or so from the center. This is where the beginning—that is, the lowest point—of the spiral will be.
Now, draw a preliminary spiral using the stakes as a guide. In a six-foot spiral, aim to create three coils: two large and one smaller at the apex. Also, each soil-filled “level” you’re creating should be 12- to 15-inches wide. You can get away with less, however, if the herbs you plan to plant are relatively small. Also, keep in mind that the reinforcing material you choose will have an impact on the available planting area the spiral contains. If you have trouble working out the shape, you can employ a loosely wound garden hose as a guiding tool. Then, use chalk, stones, paint, or twine to mark the spiral once you’re satisfied with the layout.
The orientation of the spiral can also be important. It’s traditional to place the ground level opening—the beginning of the spiral—facing north. This benefits moisture-loving plants like the mints, sweet woodruff, lemon balm, and watercress, which thrive when grown in mild, north-facing locations. This simple, but effective strategy isn’t always the best choice, though. For example, you may want your spiral positioned to show off a decorative element like a pond or statue that you plan to incorporate. No matter the orientation, though, just be sure to pay attention to the different zones you’re creating, and remember that a southern exposure will be sunnier, hotter, and drier.
Now that you have everything laid out, begin by putting down a layer of stone or other structural material in the shape of the spiral you’ve drawn on your chosen spot. Once it’s in place, measure to make sure you’ve left enough space for the plants and step back to check that your curves look clean and the overall shape is pleasing.
Next, start building additional layers, moving along the spiral to increase the elevation gradually. If you are dry stacking stones, intersperse smaller rocks, gravel, and organic material to fill cracks and create even and steady layers. Remember, the finished spiral should be 39-inches tall at the center point. Use the mark you made on the center stake as a guide.
Then, begin adding prepared soil to the trench, slowly filling it as the walls of the spiral grow. Slope the soil surface so it’s somewhat higher in back where it rests against the stone support wall.
Once the installation is complete, water the soil and let the spiral settle for six weeks or more. This is also a good time to include some accessories that will help you manage and monitor your spiral in the coming months and years. To this end, installing a soaker hose assembly is a good option, as is adding a rain gauge or investing in a monitoring system with multiple sensors that will help you understand and control the different microclimates within your new vertical bed.
Plants for Your Herb Spiral
After letting the herb spiral settle, it’s time to add some culinary, medicinal, fragrant, and fun herbs. Stick with smaller plants and shrubs, avoiding trees like bay that will outgrow the space and could present big headaches come transplant time. Here are a few popular options that will take advantage of the different zones in your spiral’s design:
Dry and sunny (top) - oregano, sage, rosemary, tarragon, saffron crocus, lemongrass, lavender
Good light, drains well (mid, south-facing) - basil, dill, marjoram, cilantro, thyme, calendula (pot marigold)
Moist with partial light (low to mid-level) - chives, parsley, chamomile
Moist and shady (low, north-facing) - mints, lemon balm, catnip
If you have a small spiral, or ended up with one that has some narrower planting areas, dwarf versions of popular herbs like sage, rosemary, and basil are available.
While spiral growing is fantastic for herbs, it’s also a great way to raise your favorite flowers and other plants, including some of the smaller vegetables. Just make sure you can distinguish the herbs you plan on using for culinary and medicinal applications from strictly ornamental plants that may be toxic.