You build a herb spiral from stacked stone in a rising snail-shell shape of roughly 2 metres wide and 1 metre high at its highest point. You face the opening south, lay drainage at the bottom and work in four moisture zones: dry and warm at the top for Mediterranean herbs like rosemary and thyme, damp and cool at the bottom for parsley, chives and mint. Reckon on roughly 120 to 180 stones, 1 to 1.5 m³ of soil and half a day of work. The best time to build one is early spring (March to April) or autumn.
That is the short version. Below you get the long one, with all the dimensions, quantities, soil mixes and the complete planting plan. After this article you will not need to look anywhere else. I am Fred, and I have built enough of these by now to tell you exactly where it goes wrong and how to get it right the first time.
What exactly is a herb spiral?
A herb spiral is a raised herb bed in the shape of a rising spiral. Because the wall gets higher towards the centre, you create several microclimates at once on a small footprint.
The top is warm, dry and sunny. The bottom is cooler, damper and sometimes half in shade. In between sits a gradual transition.
That lets you grow herbs on less than 3 square metres that normally need completely different conditions. Mediterranean rosemary next to moisture-loving mint, a stone’s throw apart.
The idea comes from permaculture. It is efficient with space, lovely to look at, and it holds heat through the mass of stone. That is exactly why it works so well for herbs.
What dimensions does a good herb spiral have?
Stick to these guide measurements. They are set up so you can work without having to stand on the bed.
| Dimension | Recommendation | Why |
|---|---|---|
| Diameter (width) | 1.8 to 2 metres | Larger than 2 m and you can no longer reach the centre without stepping in |
| Height at highest point | 80 cm to 1 metre | Enough height difference for dry on top and damp below |
| Path width of the spiral | 30 to 40 cm | Room to plant and harvest the herbs |
| Wall height at the bottom | 15 to 25 cm | 1 course of stone is enough at the outer edge |
| Wall height in the middle | 80 to 100 cm | 4 to 6 courses of stone towards the centre |
| Surface area | roughly 3 m² | Room for 15 to 25 herb plants |
Smaller works too, for example 1.2 metre diameter for a small patio. You do lose some of the difference between the zones then. Larger than 2 metres I would advise against, unless you build a path to the centre.
Where do you site the herb spiral and how do you orient it?
Choose a spot with at least 6 hours of sun a day. Herbs want light, especially the Mediterranean kinds at the top.
Face the opening of the spiral south. The spiral then runs from the south side at the bottom, clockwise, up to the centre. That way the south flank catches the most sun and the north side stays cooler and damper at the bottom.
Put it close to the kitchen door. You only pick fresh herbs often if you do not have to walk far for them. That sounds trivial, but it is the single biggest reason herb gardens fail.
Make sure the ground is level and firm. On a slope or loose soil the wall will sink later.
Which stones do you use?
Almost any stackable, weatherproof stone works. You have the choice between dry-stacking or mortaring.
Suitable materials:
- Old bricks (classic, warm, easy to stack)
- Natural stone such as field stones, rubble stone or flagstones (best-looking result, holds heat well)
- Concrete paving slabs or setts (cheap, often free to pick up)
- Broken concrete from an old driveway (sustainable reuse, rough but functional)
Dry-stack or mortar?
Dry-stacking is the easiest and most natural. The gaps between the stones become shelter for insects and sometimes a little fern. This is the classic permaculture method, and it is the one I recommend to most people.
Mortaring makes the wall sturdier and stackable higher, but it is more work and less ecological. Only choose this if you want to build high (above 80 cm) or in a spot where the wall really has to stay crisp.
For dry-stacking: lay the stones leaning slightly inwards, so the wall tilts towards the centre. That keeps it stable.
How much material do you need?
For a standard spiral of 2 metre diameter and 1 metre high. Quantities are guide figures; they vary with stone size.
| Material | Quantity | Note |
|---|---|---|
| Stones/bricks | 120 to 180 pieces | More if you mortar high, fewer with large field stones |
| Rubble/hardcore (drainage) | 0.3 to 0.5 m³ | For the core and the base |
| Coarse sand | 0.2 to 0.3 m³ | Mainly for the dry top zone |
| Garden soil/topsoil | 0.8 to 1 m³ | The biggest volume, fills the whole spiral |
| Compost | 100 to 150 litres | Work into the damp zones |
| Fine gravel (base) | 40 to 60 litres | Optional, for extra drainage at the bottom |
| Pond liner or dish | approx. 0.5 m² | Only if you make a water zone |
In total you move around 1.3 to 1.8 m³ of soil and rubble. That is a full trailer. Have it delivered if you do not have a car with a towbar.
How do you build the herb spiral step by step?
Reckon on half a day to a full day, depending on whether you mortar.
Step 1: Mark out the circle.
Drive a stake into the centre, tie a 1 metre string to it and draw a circle of 2 metre diameter. Mark it with lime or sand.
Step 2: Dig the foundation and lay drainage.
Dig out the whole circle 15 to 20 cm deep. Fill the base with a 10 cm layer of hardcore or rubble. This is your drainage base, crucial so the spiral does not sit like a bathtub after rain. Tamp it down lightly.
Step 3: Build the first course of stone as a spiral shape.
Lay the outer wall as a full circle, but leave an opening on the south side for the entrance of the spiral. From there you let the wall curl inward in a snail-shell shape towards the centre.
Step 4: Build the wall up in height.
At the outer edge the wall stays low (1 course, 15 to 25 cm). Towards the centre you stack higher and higher, up to 80 to 100 cm in the middle. That way the spiral rises gradually.
Step 5: Fill with rubble and soil, from coarse to fine.
Fill the core with rubble first, for drainage and weight. Work outwards and upwards with less and less rubble and more soil. Fill each zone with the right soil mix (see table below). More sand at the top, more compost at the bottom.
Step 6: Finish the top layer.
Finish the top with a planting layer of at least 15 cm of good soil, so the roots have room. At the bottom that layer can be thicker, 25 to 30 cm.
Step 7: Add the water zone (optional).
At the lowest, northern foot, dig a small hollow of 40 by 40 cm and 20 cm deep. Lay pond liner in it or an old plant dish, and fill with water. More on this further down.
Step 8: Let it settle for a week, then plant.
Give the spiral a few days to settle and water it well. Top up with soil where needed. Only then plant.
What is the right soil mix per zone?
This is where most articles are too vague. Each zone wants a different soil. Here are concrete mixing ratios.
| Zone | Position | Soil mix | Moisture |
|---|---|---|---|
| Zone 1 Mediterranean dry | Top, south side | 50% garden soil, 40% coarse sand, 10% gravel | Very dry, fast-draining |
| Zone 2 Mediterranean | Upper flank | 60% garden soil, 30% sand, 10% compost | Dry |
| Zone 3 normal | Middle section | 70% garden soil, 20% compost, 10% sand | Average |
| Zone 4 damp | Bottom, north side | 80% garden soil, 20% compost | Moisture-retaining |
| Water zone | Foot, lowest point | Garden soil + water/pond | Wet |
The logic: at the top you want water to drain away fast, so plenty of sand. At the bottom you want to hold moisture, so compost and organic matter. That way a single spiral mimics four different growing spots.
Which herbs do you plant in which zone?
Now the best part. Every zone has its own residents. Here is the complete layout.
| Zone | Conditions | Herbs |
|---|---|---|
| Zone 1 Mediterranean dry (top) | Full sun, dry, warm | Rosemary, thyme, lavender, oregano, summer savory |
| Zone 2 Mediterranean (upper flank) | Sun, moderately dry | Sage, marjoram, tarragon, hyssop, winter savory |
| Zone 3 normal (middle) | Sun to partial shade, normal moisture | Basil, lemon balm, coriander, chervil, fennel |
| Zone 4 damp (bottom, north) | Partial shade, damp | Parsley, chives, dill, lovage, celery |
| Water zone (foot) | Wet, in or beside the water | Water mint, watercress, mint, self-heal |
A few tips when planting:
Always put mint at the bottom in the water zone or in a separate pot. Otherwise mint runs riot and overruns your whole spiral.
Rosemary and lavender grow big. Give them room at the top and do not plant them too close together.
Perennial herbs (thyme, sage, oregano, chives) you plant permanently. Annuals (basil, coriander, dill) you replace every year. Keep that in mind with the layout: put the annuals where you can easily reach them.
How do you build the water zone or small pond?
The water zone at the bottom is optional but worth it. It keeps the base damp, attracts frogs and insects, and gives water mint and watercress a home.
At the lowest foot, on the north side, dig a hollow of roughly 40 by 40 cm, 20 to 25 cm deep. Lay a piece of pond liner in it with some overlap, or use an old plant dish, mortar tub or zinc bath.
Weigh down the edges with stones so the liner stays put and tucks away neatly. Fill with rainwater.
Put a few stones or branches in it as a climbing-out spot for small creatures. Plant water mint or watercress on the wet edge. Top up with rainwater now and then in dry spells.
Do not want open water? Then the bottom zone can just as easily be an extra-damp soil zone with plenty of compost. That works fine for mint and parsley too.
When do you build a herb spiral?
The best time to build is early spring, March to April. The soil is workable and you can plant straight after the last night frost (mid-May for the frost-sensitive kinds like basil).
Autumn (September to October) is fine for building too. The spiral can then settle over a winter. Perennial herbs like thyme and sage you can plant successfully in autumn; with the annuals you wait until spring.
Building in summer is possible, but then you have to water heavily for the first few weeks to get the fresh planting established. Avoid building in frost, when the soil is unworkable.
What does a herb spiral cost?
That depends entirely on whether you buy material or reuse it. A rough guide.
| Item | Budget (reuse) | Buying new |
|---|---|---|
| Stones | £0 (free via classifieds, demolition) | £50 to £130 |
| Soil and compost | £25 to £50 | £50 to £85 |
| Rubble/drainage | £0 to £15 | £15 to £35 |
| Pond liner | £0 to £10 | £10 to £20 |
| Herb plants (15 to 25) | £25 to £65 | £25 to £65 |
| Total | £50 to £145 | £150 to £330 |
The biggest saving is in free stones. Demolition firms, neighbours removing paving, and online classifieds are full of them. Grow the herbs yourself from seed and you save a good deal more on the plants.
How do you maintain a herb spiral?
Little, and that is the charm. Still, a few regular tasks.
Watering. Especially in the first weeks and in dry summers. Water at the top, and the moisture seeps down with it. The top zone dries out the fastest, so keep an eye on it.
Pruning. Cut back rosemary, thyme, sage and lavender after flowering so they stay compact and do not go woody. Snip annual herbs regularly so they keep producing.
Feeding. In spring, scatter a thin layer of compost over the damp zones. The Mediterranean herbs at the top you specifically do not want to feed; they like poor soil.
Keeping mint in check. Cut back running mint every spring. Otherwise it takes over the whole spiral.
Touching up the wall. After winter, check whether any stones have shifted from frost and settling. Put them back.
Winter. Most herbs are hardy. Cover lavender and rosemary in hard frost with a bit of straw or fleece. Annuals you let die off and replace in spring.
Common mistakes to avoid
Building too big. Above 2 metres you can no longer reach the centre. Stay small enough to reach everywhere.
Skipping drainage. Without a rubble base water sits and your Mediterranean roots rot. The bottom layer of hardcore is not optional.
Putting mint among the other herbs. It smothers everything. Only in the water zone or in a pot.
Using soil that is too rich at the top. Mediterranean herbs want poor, sandy soil. Compost up top makes them floppy and flavourless.
Facing the opening north. Then the south flank misses out on sun. Always face the opening south.
Frequently asked questions
How big should a herb spiral be?
For home use, 1.8 to 2 metre diameter and 80 cm to 1 metre high is ideal. Larger than 2 metres and you cannot reach the centre without stepping in. Smaller (1.2 metres) works on a patio, but then the difference between the zones is less pronounced.
Do you need mortar or can you dry-stack?
Dry-stacking works fine and is the most natural method. The gaps become shelter for insects. Only mortar if you want to build higher than 80 cm or want a crisp, permanent wall. When dry-stacking, let the stones lean slightly inwards for stability.
Which herbs go at the top and which at the bottom?
At the top the dry, sunny Mediterranean herbs: rosemary, thyme, lavender, oregano, sage. At the bottom, on the cooler north side, the moisture-loving herbs: parsley, chives, dill, lovage. Mint and watercress belong in the wet water zone right at the bottom.
How much does it cost to build a herb spiral?
With free or reused stones you can build one for £50 to £145, including soil and plants. Buy everything new and you are at £150 to £330. The biggest saving is free stones via online classifieds or a demolition firm.
When is the best time to build a herb spiral?
Early spring (March to April) is best, so you can plant straight after the last frost. Autumn (September to October) is also fine for building and for planting perennial herbs. Avoid building during frost.
Does a herb spiral need drainage underneath?
Yes. Dig the base out 15 to 20 cm and lay a 10 cm layer of hardcore or rubble. Without this drainage, rainwater sits and the roots of the drought-loving herbs at the top rot.
Can a herb spiral work without a small pond?
Yes. The water zone is optional. Without open water you simply make the bottom zone extra damp with plenty of compost. Mint and parsley do well there too. A small pond does attract frogs and insects and keeps the base wetter.
Want to mark out the spiral precisely with measurements, or combine it with a raised bed, a vegetable planter or a garden border? At fredsdiyplans.com you will find building plans and garden projects with clear dimensions and materials lists, so you get it right the first time. Enjoy your herb spiral.