Why a herb spiral earns its space

A herb spiral packs an entire herb garden into about a square metre of ground while doing something clever with the way water and warmth behave. The spiral wall, stacked higher at the centre and coiled outwards, slopes in every direction at once. That gives you a hot, dry, sun-drenched crown for the Mediterranean herbs that sulk in damp British soil, and a cooler, shadier, damper foot for the leafy sorts that bolt or toughen in full sun. The stone holds heat through the day and releases it at night, which is a real kindness in a cool, wet summer.

It is also a handsome thing to have near the kitchen door, no more than a few steps from the chopping board. You will pick far more herbs when they are within reach than from a distant vegetable bed.

Sit it right before you shift a single stone

Position matters more than the build. Aim for a spot that gets at least six hours of sun a day, ideally south or south-west facing and sheltered from cold winds by a fence or wall. A little reflected warmth from paving or brick is a bonus.

• Mark a circle about 1.2m across with a cane and a length of string, keeping the radius even.
• Choose level ground. On a slope, a spiral wobbles and the top dries out faster than you can water it.
• Avoid the drips of overhanging trees, and keep well clear of tree roots.
• Keep it close to the house. Herbs that are out of sight are herbs that go to seed apologetically.

Building the spiral, layer by layer

You need stone, brick or broken paving for the wall, rubble for drainage, and a good quantity of soil. Work from a fixed centre point and coil outwards, so the wall reads as one continuous ribbon.

• Set the first course wide, about 35cm at the base, bedding stones with their broadest face down.
• Tilt each stone very slightly inward. That small lean stops the wall spilling into your lap and helps hold water in the soil.
• Build up the centre to about 60cm, with the spiral finishing nearly at ground level at the outer end.
• Fill as you go, rather than building the whole wall and then hauling soil up. Rubble at the bottom for drainage, then your growing mix on top.

Leave planting pockets roughly 15cm wide between stones, and keep the gaps small enough that soil does not wash out in a downpour.

The soil mix and the sunny top

Mediterranean herbs want lean, gritty, free-draining ground — rich soil makes soft, floppy plants with weak flavour. A rough mix is three parts topsoil, one part garden compost and two parts grit or horticultural sand. If you garden on clay, be generous with the grit.

Plant the crown and the upper south-facing side with rosemary, thyme, common and golden oregano, sage, marjoram and winter savory. Creeping thymes are lovely tumbling over the top stones. Space them properly; they will fill the gaps within a season.

The middle and the damp foot

The lower, inner curves stay cooler and hold more moisture. This is where chives, parsley, coriander, chervil and salad burnet belong — and where mint can finally be allowed out. Plant mint in a pot sunk into the soil, its rim just above the surface, or it will run through the whole spiral within a season. A pot of mint at the base is also convenient for a last-minute jug of summer cup or a handful of mint tea.

Basil goes in the warmest pocket through summer only. It sulks below about 10°C, so treat it as a guest rather than a resident.

Keeping it going through the year

Water the spiral by pouring at the top and letting it trickle down, which is the whole point of the design: the top dries first, the foot stays damp. In a dry July, a good soak twice a week beats a daily sprinkle.

• Top-dress with a thin layer of compost each spring. Do not feed more than that.
• Cut thyme, oregano and sage back after flowering to keep them bushy and stop them going woody.
• Trim chives hard after each flush of flowers and they will keep producing tender leaves.
• Watch for slugs around mint and parsley, and check rosemary for vine weevil if it is growing in a pot.

Rosemary is the one to fuss over. It hates cold, wet roots, so in a heavy-soil garden plant it at the very top and work a handful of extra grit around its collar. Thyme and sage will shrug off most of what a British winter throws at them, and you can keep picking through the colder months.

Within a season, the spiral will look as though it has always been there — and you will wonder how you ever cooked without it.