When visitors come up our driveway, one of the first things they see is our herb spiral, which is prominently situated just inside our "Zone 1" environment. They always ask us for details: What is this? and, Why is this bed in the shape of a spiral? It's always fun for me to explain the thinking behind this innovative garden design, and I'm glad to share the concept with you today.
Imagine a long garden row, 12 inches wide and 25 feet long. Now, take that row and coil it around and upward into a spiral. This spiral now has the same 25' row, but only occupies a circular space about 6 feet wide, and perhaps 3 feet tall.
Unlike a flat garden that is essentially a monotonous terrain, the height of the spiral gives you extra options when planting. The higher part of the spiral gets the most sun and has the best drainage, making it ideal for plants, such as oregano or rosemary, that thrive in sunny, well-drained sites. The bottom of the spiral, on the other hand, is the right place for plants that like more moisture, such as comfrey.
The structure itself provides protection for plants. The east side of the structure, for example, will be completely shaded in the afternoon and evening. So, plants that wilt in the hot summer sun can thrive on the eastern side. Plants that love the hot blistering sun can be planted on the west side.
When constructed from brick, stone, or concrete, the spiral acts as a tremendously powerful heat sink during the winter months. Plants that are more cold hardy will have a better chance of surviving the winter if they are grown in the south-facing side of the spiral. The winter sun will warm up the stones all day long, and through the night the radient heat will be released to the benefit of the nearby plants.
Owing to the vertical nature of the spiral, you can grow plants so much closer to each other than you could if the rows were on the same horizontal plane. A basil grown in the upper spiral provides zero competition to its neighbor directly below it. Looking at a spiral from the top down shows a vast mass of plants, but viewing it from the side you can see that they don't even touch each other. This means you can grow perhaps up to twice as many plants in a spiral than you could in a traditional garden with regular rows.
To make our herb spiral, we prepared the area by first completely leveling the site. Then, we dug a 6" trench in the shape of the spiral we wanted to make. Into this trench we ran rebar (reinforcing steel), placed on old bricks. Then, we mixed and poured bagged concrete to create the foundation. With the foundation in place, we then mixed mortar and laid the bricks, row by row, until we had the shape we wanted. Working a couple of hours a day, it took us two weeks to make our herb spiral.
After the bricklaying has been completed, it's time for the fun part: filling it with a growing medium! Considering that this herb spiral is really a very large container, it requires a lot of material to fill. Being a proponent of hugelkultur, I chose to fill the bulk of the bed with old wood that will rot over time and provide a huge amount of organic matter. Once the spiral was filled about 75% with wood, the rest of the bed was then filled with any other organic matter we could find: leaves, grass clippings, shredded wood chips, compost, old manure, good topsoil, etc.
As with all hugelkultur projects, we did find that over time the wood decays and the level of the material drops. We add 4-6 inches of new compost and soil each year to keep the level near the top of the spiral.
Planting the spiral was fun, and we often swap out herbs for new ones. Annuals like basil are grown each year, and we frequently take out herbs we're not wanting anymore and replace them with new ones. In addition to herbs, we also use it to grow vegetables like spinach, lettuce, broccoli and other brassicas, carrots, peppers, eggplants, and so on. Because it's such a beautiful garden, we are proud to have it right next to the house, where it is close to the kitchen whenever we need fresh herbs. This is the final benefit of the herb spiral: Being situated so close to the house means it provides highly convenient fresh herbs and other food for us year round, and maintaining and making use of it is as easy as walking out the door and taking just a few steps out. Every homestead should have an herb spiral (or two!)
July of 2012:
October of 2012:
Early spring, 2013, showing spinach and other annuals:
June of 2014:
Here is a video we took some time ago showing the herb spiral: