Herb spirals

While herb spirals have been springing up in gardens in recent years, most of the ones available in garden centres bear little relation to the original idea and function as simple planters.

The technique of cultivating herbs in a spiral mound made of stones was developed by the Australian permaculture designer Bill Mollison. The idea is ingenious in its simplicity – different site conditions for a wide range of culinary herbs are created in a small space and the stones act as a heat store for heat-loving herbs. But apart from the fact that herb spirals often appear out of place in gardens, most of them are just too small. For a herb spiral to work as intended, it needs to be at least five, or better eight metres in diameter. Only then can there be proper separation between where the individual herbs are growing: the Mediterranean herbs grow at the top in the less nutrient-rich soil, herbs that need more nutrients grow further down, and herbs that like moisture and lots of nutrients grow at the bottom. Small herb spirals have to be treated like containers, with the soil replaced every few years. It is not possible to create different growing conditions in smaller herb spirals. And that causes another problem: for healthy growth, many annual herbs – but also chives and parsley – need to be transplanted every two years if not every year. Most herb spirals do not allow this kind of crop rotation. This can also be the case in larger herb spirals, where it was possible to create the different growing areas by bringing in different soils. You often also see herb spirals that are beautifully built, but then simply filled with the earth from the garden. A rosemary plant growing in a herb spiral in clay-rich soil – taken from the garden – will not survive the winter despite the heat-giving stones surrounding it. That's why I recommend either laying out herb spirals of the correct size or if this is not possible – as in most smaller gardens – laying out a Mediterranean herb mound or raised herb bed.

Raised Mediterranean herb bed
Much easier to construct are Mediterranean herb mounds or small, 20–40 cm high raised herb beds, which are perfect for all Mediterranean herbs (up to max. 40 cm high). These herb beds, which are usually round or curved rather than square, can be designed in any conceivable shape using tuff stones or bricks. The bed is then filled with soil intended for roof gardens or containers, and then magnesium lime, stone powder and silica sand are added to create the perfect raised bed for Mediterranean herbs. But every herb has its perfect location in the garden. Many herbs need nutrient-richer soil and grow best in a vegetable patch, while others don't need any complicated preparation of the soil and will also thrive beautifully in herb beds laid out directly on the topsoil.

Mediterranean herb mound
Gardeners who dream about lush lavender beds or fragrant thyme paths can create simple herb mounds – in every conceivable shape and size – using soil intended for roof gardens and pavers. A Mediterranean herb mound is much easier to construct than a herb spiral. The most important ingredient is the right soil: it must be one intended for roof gardens. But you can also mix it yourself: 80-90% brick rubble or lava and 10-20% mature compost. The stones ensure a mild microclimate, while the backfilled mounds protect the plant roots against waterlogging, even in winter. The plant soil must be porous, so no clay! Rose-scented thyme lines the paths, and the different varieties of lavender perfume the air with their fragrances. Round-headed leeks, rosemary and eremurus are a good fit here.

Andrea Heistinger
VIKING gardening expert

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