RHS Journals
The Garden
February 2007
Peaks and troughs
How do you make a rock garden in a country with few natural rock outcrops? Rather than import stone, Wiert Nieuman at the Botanic Gardens of Utrecht in the Netherlands pressed broken paving, sewage pipes and pig troughs into service, as Jon Ardle found.
Images: Tim Sandall
A country without mountains, lying barely above sea level and criss-crossed by drains and canals that channel away its high rainfall may seem a strange place to grow alpine plants, but the University of Utrecht Botanic Gardens does just that. And to the highest of standards. The secret, as ever with alpines, is to provide good drainage so that excess moisture drains quickly away.
Alpine gardeners in the UK are spoiled for choice when it comes to finding rocks for the garden from a plethora of quarries, but the Netherlands has few natural outcrops of useable stone (only in the south of the country).
The bones of Utrecht’s original rock garden, the largest in the Netherlands, were in fact imported from Belgium in the 1960s and 1970s. From the late 1980s however, gardener Wiert Nieuman began experimenting with recycled, more environmentally-friendly materials. Sourced locally, these save the considerable ‘quarry miles’ cost of transporting stone into the country.
Pipes and tiles
In 1988, Wiert acquired some glazed terracotta sewage pipes, which were sawn in half using a diamond saw and chopped into lengths to make unusual troughs. Their ends were sealed with broken tiles, bases drilled with holes and filled with free-draining compost. Made of similar material but with a flatter profile were several pig troughs. Both types were glazed, so inert, and suitable for acid- and alkaline-loving plants. They were planted up with sempervivums, sedums, dianthus and saxifrages and made pleasing additions to the garden.
The pipes and troughs were joined three years later by a large raised bed, 10m (30ft) long, constructed of salvaged dark grey roof tiles stacked into strata. With both the top and sides planted up, the bed looks surprisingly natural.
Sophisticatedly spherical
What Wiert calls his ‘eycatchers’ and the current centrepiece of the rock garden are three spheres between 1.5-2m (5-6.5ft) tall. Constructed in 1995-96, these are made entirely of broken paving stones some 5cm (2in) thick. A pipe runs through the centre of each, with a sprinkler head for watering at the apex. They were built in circular layers, each approximately 2cm (0.75in) wider than the one below up to their equator, from where the layers contract by the same amount in each subsequent course, forming the sphere.
Some of the slabs were cut to fit each layer, their broken edges always facing out for the most natural look. Holes and gaps at the edges - the future planting crevices - were packed with sandy soil from the garden as each layer was completed, but planting only took place once each sphere was completed, with lime-loving species hugging the curved surfaces and thriving in the high pH provided by the concrete paving.
Easy alpines such as Armeria (thrift) and Sempervivum did well on the spheres, so more difficult or choosy plants were subsequently tried. Aspect has proved important: on the shadier north-facing sides plants such as Haberlea rhodopensis and Asplenium ferns thrive, while Daphne arbuscula, Primula marginata, Draba and many saxifrages enjoy the sunnier parts. Dionysia aretioides prefers the more sheltered lower parts of the spheres, where it flowers spectacularly.
More raised beds were constructed from the year 2000, and Wiert strips down and replants the troughs with fresh compost and plants every three or four years to keep them looking their best.
The gardeners at Utrecht Botanics call their creations ‘recycled rock gardening’. The spectacular displays bring plants nearer to eye level to be appreciated better, and show natural stones are not a prerequisite for a good rock garden.
Jon Ardle is Features Editor for The Garden
Reclaim and recycle
All sorts of waste materials can be used to provide the conditions alpine plants enjoy.
Find out more
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