- Cardboard without ink or tape: enough to sheet mulch an 8x8 area.
- Long stake, wooden markers, and string to measure circle and lay-out spiral
- Stones or bricks for your walls
- Organic matter such as worm castings, straw, and/or leaf litter
- Top soil: approximately 9 cubic feet
- Compost: 4.5 cubic feet
- Suggested plants: Rosemary, Lavender, Sage, Chives, Mint, Thyme, Basil, Cilantro, Parsley
- Tools: shovels, wheelbarrows, trowels
A key concept behind an herb spiral is gravity. Water flows down and travels in a winding pattern through the soil, so the soil at the top of the spiral stays drier than soil farther down. Herbs that require sun and good drainage, such as rosemary, lavender, and thyme are planted near the top. Midway down the spiral are plants that require a bit more moisture such as sage, basil and cilantro. The lowest section is best for parsley, chives and mint, which need ample water and will tolerate light shade from upper levels.
- To start, select a location in a sunny, accessible area. Clear the ground of grass and weeds. You may wish to suppress weeds by a covering the ground with alternating layers of cardboard and compost. The layers of cardboard sheet mulch and organic matter exclude light, killing grass and weeds; then allow decomposing organisms to gradually “compost” this dead plant material and improve the soil with organic matter.
- Next, drive the stake into a central point of the ground where you wish to position your herb spiral. To determine the perimeter, stretch out the string attached to the center stake to mark out your circle, drawing a line in the soil with the other stake or marking points of the circle with wooden markers. The diameter averages between 2 ½ – 3 ¼ feet from the center.
- Use stone slabs, bricks or large rocks to construct the walls. Stones and brick absorb heat during the day; then release it at night to warm the soil. Build the stone wall by layering stones/bricks on the outer edge. Once you have your basic shape laid out around the circumference, add a second tier of stone/bricks. Note the outside ‘wall’ of your spiral is lowest (e.g. 2 bricks high or perhaps 1-2 rocks depending on size – enough to retain your soil). Continue to stack upwards to create a spiral shape, allowing about 1 ½ feet width to plant into. As the wall gets higher, you can fill in with gravel or sand for drainage; this will also stop a collapse as it gets higher. Remember to leave enough space for compost and topsoil.
- Fill the interior of the spiral with soil & compost. To save money on top soil, add organic material first then dress with top soil. Good sources of organic matter that will build soil fertility include your own compost, worm castings from your worm farm, and for lower layers, materials like leaf litter.
- Finally, it’s time to plant the spiral! Herbs that require sun and good drainage are planted near the top. We suggest thyme, lavender, and rosemary. In the middle, plant herbs that require moister soil conditions, such as sage, basil, and cilantro. Then at the bottom of the spiral, plant thirsty herbs like mint, parsley and chives. Shade tolerant plants should go on the north side, those that like more sun can go on the south side.
Don't forget to consider your planting zone and follow planting instructions given by your nursery to ensure proper spacing and growing conditions for each plant. After planting the herbs, top dress each plant with a bit of extra compost. Water the plants well. You have done it! Enjoy fresh herbs in your cooking while knowing you have created a happy habitat for pollinators!