Why a herb spiral earns its place

A herb spiral crams half a dozen different growing conditions into about a square metre of ground. The south side bakes in sun, the apex drains almost instantly, the base stays damper, and the north face gives a sliver of shade. Rosemary, parsley, mint and chives all want different things from soil and water, and a spiral gives each of them its own patch within arm's reach of the kitchen door.

It also adds height to a small garden without the weight of a raised bed, and the walled sides create warm, sheltered pockets that suit both herbs and the pollinators that visit their flowers.

Pick the sunniest corner you have

Aim for at least six hours of direct sunlight, ideally against a south- or west-facing wall. Brick and stone radiate warmth back into the planting after the sun has moved on, which suits Mediterranean herbs beautifully. Shelter from strong wind matters too, particularly for rosemary, which can be scorched and snapped by a cold easterly.

• Size: a base circle of 1 to 1.5 metres is plenty for a household. Any larger and you will be stretching over the top to reach the far side.
• Height: stop at around 60 to 90 centimetres at the apex. Taller spirals look impressive but dry out too fast and topple more easily.
• Position: close to a path or back door, level or gently sloping ground, and clear of overhanging trees that drip and shade.

Building the spiral: stones, slope and soil

Mark out your circle with sand or a length of string, then build from the outside inwards. Reclaimed brick, sandstone, broken paving or whatever your local reclamation yard has going spare all work well. Use dry-stone construction with no mortar: the gaps give you planting pockets for thymes and campions, and they let excess water drain away.

Build the wall as you fill, rather than stacking the whole thing first. Soil supports the stones and stops them shifting. Work in courses roughly 15 to 20 centimetres wide at the base and tapering as the spiral rises towards the centre, checking stability with a firm push as you go. Never perch a stone so it overhangs the one below.

For the growing medium, mix roughly two parts topsoil, one part well-rotted compost and one part horticultural grit. Make the lower spiral richer and heavier, and the upper spiral grittier still, until the top is close to equal parts soil and grit. Leave a shallow dip at the base of the spiral as a natural sump, where moisture collects and thirsty herbs can settle.

Planting up: from thirsty mint to drought-loving rosemary

Plant in spring so roots establish before winter, and water everything in well. Then follow the drainage gradient.

• Top of the spiral: rosemary, thyme, oregano, winter savory and sage. Sharp drainage, full sun, and a gravel mulch to keep foliage dry and slugs off.
• Middle slopes: parsley, chives, chervil, coriander and summer basil. These want moisture that drains but never dries out completely.
• Base and sump: mint, chives and wild strawberries. Sink mint in a pot with the rim a couple of centimetres above soil level, or it will run through the whole spiral within a season.
• Shaded north face: parsley, chervil and salad burnet, which appreciate a break from the fiercest midday sun.

Give each plant room to breathe. Crowded herbs sulk, mildew and bolt, so four to six plants per zone is usually enough in a spiral this size.

Ferns and cottage-style planting around the edges

Ferns are not spiral material, since they want shade, damp and leaf mould rather than sun and grit. But they earn their place in the same corner, tucked at the shaded base or against a north-facing wall nearby. Hart's tongue fern copes with drier shade, while male fern, lady fern and soft shield fern prefer moisture. Water them through their first summer, mulch with leaf mould each autumn, cut tired fronds back in late winter before the new croziers unfurl, and divide congested clumps in spring.

Around the outside of the spiral, let things loosen up in proper cottage style. Chive flowers left to open feed the bees, and calendula, nasturtium, violas, feverfew and borage will seed themselves into the gravel and gaps if you let them. Lavender and catmint along the sunny edge, alpine thymes and campion pressed into the wall crevices, and informal drifts rather than neat rows. Bare soil is the enemy of this look, so keep it covered with self-seeders and grit.

Keeping it going through the year

Water the base more often than the top. Once established, rosemary and thyme need almost nothing, but mint and parsley will thank you for a slow soak in dry spells. Pinch out herbs regularly to keep them bushy, cut chives back to about five centimetres after flowering, and replace woody rosemary and sage every three or four years while you have cuttings coming on.

In autumn, tidy spent foliage, top up the grit mulch and resist heaping compost over Mediterranean herbs. Winter wet kills far more thyme and lavender in the UK than frost ever does, so raise the crowns with a handful of grit before the rain sets in. Come spring, the spiral will be the busiest, most useful square metre in the garden.