How to Make an Herb Spiral

If you've grown herbs, you know they offer some impressive benefits but present challenges, too. 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, most gardeners try again in a different flowerbed or in patio pots where they can keep a wary eye out. If you've ever wanted to maintain your herbs together, give them a better opportunity to look their best and provide them with the special care they need, think about incorporating them into an herb spiral.

What's an Herb Spiral?

The structure of an herb spiral produces artificial microclimates that result when small but significant environmental variations occur as the spiral changes direction and elevation. 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. 

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 a large number of herbs because specimens are planted up as well as out, which 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 Making an Herb Spiral

An herb spiral is a hardscape feature, the same as a fish pond or stone planting box. With proper planning, you can install one in a weekend and use any of a variety of materials you may have on hand, including rocks, stones, pavers, cinder block, bricks or even recycled bottles, depending on your budget and the look you want to achieve. An elaborate spiral can even incorporate a water feature, like its own mini pond.  Once assembled, it is 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. 

An herb spiral is eye-catching and dramatic when viewed from a second-story window or deck, and its structure offers the gardener an opportunity to cultivate different environmental zones, modifying the soil to suit specific plant specimens.  All can work together in the microcosm of the spiral garden. This same circular, elevated structure will help keep plants from sprawling and balance the problem of placing dense small plants in close proximity with 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 optimum watering efficiency. Just place moisture-loving plants at the bottom of the spiral and leave Mediterranean or other drought-tolerant varieties toward the top. When you water, moisture remains in a contained area. You water less, and the different zones, dry on top and moist down below, offer plants what they need.

How to Build an Herb Spiral

Layout

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 far as your outstretched arm or your reach to the center from any spot around the spiral's circumference. 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 6 to 6.5 feet in diameter. A gradual rise to the center should also give a 6-foot spiral a maximum elevation of about 39 inches.

Materials 

I've said there are lots of potential choices here, and there really are. From reinforced brick and concrete to loose stones, you can spend an entire season pondering the merits of different hardscape decisions. Rather than focus on aesthetics, let's look at some practical considerations. 

Brick and stone are both popular, and either will require about 2 cubic yards of material. Rebar-reinforced brick will potentially last for decades, but it will be more expensive than other options 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, and large stones can hog a surprising amount of potential planting space.

Both brick and stone hold in the heat. This could be important in cold or borderline climates, where a jump of a few degrees can mean the difference between keeping your favorite herbs within reach and having to source them at the market during the fall. Hardscape materials 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. 

What else is out there? Although less popular, prefabricated synthetic and recycled materials are an option, 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, like soil, amendments as needed, organic material like grass clippings, leaves, and 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. Structure and spacing.

Practical Suggestions

There are lots of interesting ways to construct herb spirals, but many share characteristics in common. Let's walk through some basic steps you can use as a jumping-off point:

Choose a plant-friendly spot large enough for the spiral and a walkway around it.  Ensure it gets at least 6 hours of sunlight a day.

Clear the area of weeds and debris.

Cover the spot with a weed deterrent like garden fabric, newspaper, gravel or cardboard.

Install a stake at the center of the spot you've prepared, with a mark at the 39-inch point. Place another stake three feet or so from the center where you want the beginning of the spiral, the lowest point, to be.

Draw a preliminary spiral using the stakes as a guide. If you have trouble working out the shape, you can employ a loosely wound garden hose as a guiding tool and use chalk, stones, paint or twine to mark the spiral once you're satisfied with the layout.  Here are a few things to keep in mind:

The reinforcing material you choose will have an impact on the available planting area the spiral contains.  The ideal width of the soil-filled depression you're creating should be 12 to 15 inches front to back. You can get away with less if the herbs you'll be keeping are relatively small. 

In a six-foot spiral, you'll be able to create three coils around, two large and one smaller at the apex.

The orientation of the spiral can be important. It's traditional to place the ground level opening, the beginning of the spiral, facing north. Bottom-tier plants will receive the most moisture, and moisture-loving options like mints, sweet woodruff, lemon balm and watercress thrive when grown in mild, north-facing locations. 

This simple but effective strategy isn't always the best choice, though. For example, herb spirals can also include decorative elements like a pond or statuary. If you do add a special feature, you may want your spiral positioned to show it to advantage. Just be sure to pay attention to the different zones you're creating. A southern exposure will be sunnier, hotter and dryer, so build with that in mind.

This is also the time to recognize and plan for the special needs of any extras you have in mind, like access to running water and the availability of electrical service.

This is heavy work, so position the stone pile nearby and enlist the aid of some helpers if you can.

Herb spiral Installation Considerations

Begin by putting down a layer of stone or 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're leaving enough space for the plants, and step back to check that your curves look clean and the overall shape is pleasing.

Start building additional layers, moving along the spiral to gradually increase the elevation. 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 a little over 3 feet tall (39") at the center point. Use the mark you made on the center stake as a guide. 

Add 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 an 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 (Laurus nobilis) 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

Small spirals - 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.

You can mix and match your favorite herbs with 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. 

Special Note: I originally published this article in the now-defunct Maximum Yield Magazine.