Herb spirals aren't just another pretty space.
The snail-shaped herb gardens create attractive focal points in gardens, to be sure. But these beauties have brains.
Herb spirals are gaining notice as an ecologically smart herb-garden layout. Advocates of permaculture, a system that stresses living and gardening in harmony with nature, champion spirals for their ability to save water and attract pollinators. They also like that spirals mimic a variety of growing conditions, enabling a gardener to grow an assortment of herbs in a compact area.
At Cleveland's Midtown Urban Farm, an herb spiral rises in a corner of a patch where teenagers learn to grow vegetables. The farm in Cleveland's Hough neighborhood is one of the sites of Cleveland Botanical Garden's Green Corps work-study program, in which urban youths grow crops to sell at farmers markets and to make into their own brand of salsa and vinaigrette.
The herb spiral is edged with a dry-stacked stone wall, which gets taller as it spirals toward the garden's center. Plants including sage, comfrey and creeping thyme thrive along the winding strip of soil that makes up the garden's bed, while a clump of santolina spreads at the apex. Later in the spring, rosemary plants that spent the winter in a greenhouse will be returned to the garden, said Milene Benedict, the site manager.
Because of its smart design, the garden typically requires little watering, Benedict said. But to her, it's more than just a workhorse.
"It think it is very beautiful," she said.
The central concept behind an herb spiral is simple gravity. Water flows downward and in a winding pattern through the bed of soil, so the soil toward the top of the spiral stays drier than soil farther down.
Herbs that require good drainage, then, are planted near the top. Among them are rosemary, lavender, thyme and oregano -- plants native to the dry Mediterranean, said Cynthia Druckenbrod, director of horticulture and conservation at Cleveland Botanical Garden, which displays herb spirals in its gateway and herb gardens.
Midway down the spiral are plants that require a bit more moisture and somewhat richer soil, such as sage, tarragon, basil and cilantro, Druckenbrod said. The lowest portion is home to plants such as parsley, chives and mint, which like abundant water and soil rich in nutrients and organic matter.
Plants are also positioned according to their needs for sunlight, said Vince Kirchner, a master gardener and permaculture specialist from Tiffin, Ohio, who has built a few herb spirals while working to start a business in permaculture design. Plants that need full sun go at the top or on the south side of the spiral. Plants such as cilantro that tend to bolt in the heat (that is, switch rapidly to producing flowers) go on the east side, where they're shaded from the hot afternoon sun.
Various materials can be used to build the spiral's retaining wall, but stone or brick are generally preferred. Those materials absorb heat during the day and release it at night to warm the soil, Kirchner said.
The voids are filled with a mix of soil and other materials. Druckenbrod recommended starting with good soil and adding sand and gravel to the soil near the top and a generous amount of compost to the soil near the bottom. Kirchner, on the other hand, recommended filling the entire spiral with alternating layers of soil, brown organic material such as straw and shredded leaves, and green organic material such as vegetable waste.
Some fill the spaces with straw and then create small pockets for plants and small amounts of soil.
The spiral shape allows for packing a lot of growing space into a small footprint. Kirchner said the design creates 21 to 30 linear feet of growing space in a round space that's just 6 feet across.
The design also lends itself to integration with a water feature. A pond can be added at the base of the spiral for decorative or practical purposes, Kirchner said, such as growing wild rice or holding fish for an aquaculture system.
But not everyone is a fan of herb spirals.
When herb grower Jan Becker created a spiral several years ago at her Becker's Cottage Garden Herb Farm in Springfield Township, Ohio, she found the design made harvesting difficult. She said that when she made the spiral big enough to accommodate larger plants like basil, she discovered those plants blocked her access to other herbs. She also thought the design used more soil than a raised-bed garden and was attractive only when the plants were lush.
An herb spiral might be appropriate for someone who doesn't harvest herbs frequently, Becker said. For an enthusiastic cook, though, she doesn't think it's the best choice.
"In the end, it was not as magical as I had hoped," she said.
Becker's experience raises a caution: "Keep it small," Druckenbrod said. The general recommendation for an herb spiral is 6 feet across and 3 feet tall, so plants remain within easy reach.
A garden design, after all, isn't so smart if it's not usable.HERB SPIRAL TIPS, RESOURCES
• Choose a spot that's sunny most of the day.
• If possible, position the spiral close to the house to make it convenient to harvest herbs for cooking or other purposes.
• Lay the walls of the spiral in the same direction that water travels. From top to bottom, the spiral should turn clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.
• Make the spiral about 3 feet high and 6 feet wide. If you make it bigger, you won't be able to reach all the plants easily, and some of the plants might get too much shade. If you make it smaller, you'll compromise the ability of the stone or brick walls to warm the soil effectively.
• Care for the herbs as you would those in a regular raised bed. Expert Cynthia Druckenbrod recommends lightly fertilizing once a month or so and watering if necessary during dry spells.
A video showing permaculture instructor Dick Pierce overseeing construction of an herb spiral is on YouTube (www.youtube.com; search for "herb garden permaculture").
Permaculture designer Vince Kirchner can be reached through his website, www.greatlakespermaculture.com, or via email at firstname.lastname@example.org.