Episode 16

Project: Herb Spiral

A herb spiral is an ingenious way of growing a wide range of herbs in a small space. A design like this increases the planting area and creates growing niches for a wide array of culinary and medicinal herbs.

The size of the spiral will be dictated by the size of your available area. Typically a 1.5 to 2m spiral diameter that rises to 1 to 1.5m will give you ample growing room for all the basic herbs and many exotics too. The spiral at Greenacre was designed to fit into Toby’s back garden between the vegetable beds, and is around 1.6 in diameter by about 800cm high.
Choose an open sunny location for a herb spiral as most herbs need sun to develop the oils and concentrate the taste which will give your cooking such a depth of flavour.

Materials used may be anything that retains soil; sleepers, stone, brick, cement blocks or even stacked bottles. We are using a sand stone that fits in nicely with the overall look of the garden. To save cost, you might want to use a less expensive material, such as breeze blocks, to support the internal structure where they will not be seen.

Before starting your spiral you may want to lay some material to suppress the growth of weeds which may come up from the ground. Landscape fabric, cardboard or even old carpet, will keep the weeds down, and still allow for good drainage. If you are building on grass, remove it first; you want a solid footing for the walls. Once the grass decomposes, the walls will shift, and weaken the structure.

First mark out the circle with a bamboo stake and some string. Sand works well as a marker on soil, marker paint works well on grass. Level the soil with a rake and then tread it to firm it up.

When you are satisfied that the ground is level and solid, mark out your spiral. This will be your guide as you begin. Lay the first level of stone, making sure it is as solid as possible. Back fill with soil, and tread it in to keep the walls in place. Lay the second level of stone slightly back from the first, so the wall leans in toward the centre as you work up. Continue to backfill with soil, compacting it with each layer. It is this compaction that gives the walls their strength. If you wish, you can plant some herbs vertically into the walls as you go. Thymes and other creeping herbs are ideal for this; alpine strawberries are another option.

Should you want to use mortar to hold the stone in place, do not back fill with soil as you work up, but add your soil at the end, once the mortar is dry.

Depending on what soil you use, you may want to customize it to suite the needs of what you are going to be growing in your spiral. Most herbs will grow well in good quality topsoil, especially as the spiral is essentially a raised bed with excellent drainage. Horticultural grit or sharp sand will add extra drainage if you are concerned about your Mediterranean herbs surviving our British summers.

Once your spiral has reached its finished height, take a moment to admire your handy-work, before you begin phase 2, the planting.

Your spiral will be roughly divided into a sunny and a shady side, the top of the spiral having the most free-draining soil. Plant sun lovers like rosemary and sage on the top, and thyme, oregano and other Mediterranean herbs along the south-west facing, sunny side. Basils too will love this sunny warm location. The north-east side will be best for parsley, sorrel and chives; those that are happier in a cooler, more moist location. Mints and lemon balm are best kept in pots which you can sink at soil level as the roots of both these herbs can spread rapidly and become invasive.

Toby mulched the herb spiral at Greenacre with a stone mulch. This has a number of advantages, primarily to keep the soil from splashing onto the leaves and keeping them fresh for the harvest. It will also suppress weeds and help the soil to warm more quickly in the spring.

Remember to keep harvesting herbs, even if you are not using them all. You want to encourage fresh new growth, and keep them from flowering and surplus herbs can either be dried or sometimes frozen for use during the winters. At the start of the following year, replace herbs that are tired or those that have suffered over the winter. Cut hard back woody herbs like rosemary and remember to sow some basil for the window sill that you can plant out in early summer to keep the spiral looking fresh and to maximise its production of herbs.