James Whitcombe
Why a Herb Spiral Works So Well on a Patio
A herb spiral takes up roughly a square metre of ground and still manages to give you a dozen different growing conditions. That is the trick of it. Instead of a flat bed where every plant gets the same soil and the same amount of sun, you build a coiled mound of bricks or stone that rises to about 60cm at the centre, with a path spiralling down to the base. The top is free-draining and baked by the sun. The bottom is cool, sheltered and stays damp. Everything in between offers something different.
For a small UK garden, that range matters. Thyme and rosemary sulk in wet compost but thrive on a hot, gritty summit. Parsley and chervil prefer the cooler, moister base. Basil, which so often disappoints outdoors in Britain, does far better on a sheltered sunny ledge halfway up than it ever does in an open border. You get a kitchen garden that suits each plant rather than forcing them all to compromise.
Choosing Your Spot and Gathering Materials
Find the sunniest, most sheltered corner you have — ideally six hours of direct light in summer, with a wall or fence to cut the wind. On a patio, place it on a solid, level surface rather than on gravel or decking that might shift under the weight once the spiral is filled and soaked.
For building materials, almost anything solid and stackable will do:
- Bricks — easy to lay in a curve and cheap if you can find reclaimed ones. Avoid anything that crumbles.
- Stone or slate — heavier and slower to place, but it holds warmth and looks settled from day one.
- Concrete block — the budget option; hide the raw edges with a little soil and low-growing herbs.
You will also need rubble, broken pots or coarse gravel for the core, plus a planting mix of roughly two parts multipurpose compost, one part topsoil and one part horticultural grit or sharp sand. That grit is not optional — drainage is the whole point of the design.
Building It, Layer by Layer
Mark out a circle about a metre across. Lay your first course of bricks around the outside, but leave a gap of around 25cm as the entrance to the spiral path. From there, keep laying inward in a gentle coil, each course stepping slightly back and slightly upwards, so the walls lean in and hold each other up.
Don't rush the height. Aim for three or four courses at the outer edge and build up to around 60cm at the centre, where the spiral closes. Fill the hollow middle with your rubble as you go — this is what lifts the mound and stops it turning into a bog. Once the walls are up, work your planting mix down between them, firming it lightly and leaving a shallow channel along the path so water can run down rather than straight off.
Let it settle for a week or so, watering it well, before you plant anything. If the levels drop, top them up.
What to Plant Where
Think of the spiral as a series of tiny gardens stacked together, and match the plant to the conditions.
- Summit (hottest, driest, sharpest drainage): thyme, rosemary, oregano, sage and winter savory. Add a handful of grit around the crowns.
- Upper and middle slopes: basil on the south-facing side, coriander, chives, dill and flat-leaf parsley. Basil does best here — warm roots, but not bone dry.
- Lower slopes and shading north side: chervil, salad burnet, sorrel and land cress.
- Base (coolest, wettest): mint, lemon balm and watercress. Always sink mint in its own pot before planting, or it will race around the whole spiral within a season.
Space plants generously. A spiral packed to bursting will shade itself, and you will lose the microclimates you built it for.
Keeping It Thriving Through the Year
Water little and often in summer, aiming at the soil rather than the leaves, and preferably in the morning. The top of the spiral will dry out within a day during a hot spell, so push a finger in before reaching for the can — the base may still be sodden while the summit is parched.
Feed with a diluted liquid seaweed or comfrey every fortnight from late spring to late summer, but go easy on the Mediterranean herbs, which prefer lean conditions. In autumn, cut back the soft growth, tidy the spent annuals and mulch around thyme and rosemary with grit to keep winter wet off their crowns. Check that the base of the spiral still drains freely before the rains set in. Basil, coriander and chervil are best replaced each year; mint will die back and return on its own.
Small Tweaks and Common Mistakes
- Building it too flat. If the centre is only 20cm high, you have made a salad bowl, not a spiral. The height is what creates the dry top.
- Skimping on grit. Heavy, sticky compost kills thyme faster than frost does.
- Forgetting the path gap. Without an entrance, rainwater has nowhere to go and the whole structure floods from the top.
- Letting mint loose. A sunken pot is the only reliable answer.
- Planting everything at once. Start with half a dozen herbs, see what thrives in your particular corner, and fill the gaps next spring.
Built well, a herb spiral will give you years of cut-and-come-again pickings from a patch no bigger than a doormat — and it looks rather good while it does it.
