Botanical Society Conservatory at Kirstenbosch
History and Design

by Ernst van Jaarsveld

The successful fundraising scheme to build a conservatory at Kirstenbosch was initiated in 1995 by the Botanical Society and Brian Huntley, Director of the National Botanical Institute. Donors included Anglo American and private individuals (over R3 million was donated by Kay Bergh, Leslie Hill, Mary Mullins and Ian Roddihough so the four corner units of the conservatory have been named in their honour).

Building operations were completed in January 1996 at a cost of R5.5 million. It is the only conservatory of its size designed to house arid-adapted flora. Most of the world's conservatories exhibit tropical and subtropical flora.

The design

The Botanical Society Conservatory with its triple-pitched roof was designed to blend in with the backdrop and climate of Table Mountain. The conservatory is situated on the warm north face of Boschheuwel, the hill adjoining the eastern part of Table Mountain. The house was partly dug into the red granitic soil and occupies an area of 40×40 m² (1 600 m²). The roof varies from 7-14 m in height, and the building has a central main room 23.4×23.4 m² with four small corner units of 80 m² each.

Before the building started the chief consultant architect had several meetings with the Kirstenbosch horticulturists who explained what was wanted. We warned him not to base the house on European glasshouses as our climatic conditions are so markedly different. Local conservatories designed on European principles tend to overheat during summer months and costly cooling apparatus has to be installed. We showed him the existing open-frame houses and asked him for something with opening sides for the warmer months. He came up with a design where three of the four sides of the building are permanently open, and air drainage directly above the upper cement frame is also available. This design has already proved ideal, as even during the hottest day there is some airflow. Should the temperature rise above 28ºC, roof windows open automatically and when the temperature reaches 34ºC, fans drain the hot air from the roof. (The natural air drainage is so successful that during the summer the fans did not come on at all, and I predict that it will never be necessary!)

The main house

The house was designed around a large baobab tree with beds laid out in a spiral around it. The central `amphitheatre' that houses the baobab is built of local quartzitic sandstone. The paths, made of a concrete-laterite mix, are without steps, making it easier for the disabled to see plants from close up.

In 1994 the plan of the house was handed to me and I was asked to formulate a planting design. Taking into consideration plant culture, education and a natural design, I decided on a holistic approach, using the existing beds to represent the major arid and semiarid ecological regions of South Africa. I not only grouped them ecologically, but also orientated the plantings in the conservatory according to their natural distribution. Thus the northern parts of the house represent the northern parts of South Africa, and so on. Regions represented include the succulent Karoo (Namaqualand, Richtersveld, Knersvlakte and Little Karoo), Nama Karoo and Namib Desert (Karoo, Bushmanland, Tanqua Karoo and parts of Namibia) and the dry bushveld regions (KwaZuluNatal, Mpumalanga and Northern Province).

On a visit to Israel in 1994 I was impressed by a geological park in Tel Aviv and decided to use not only the natural rocks from each region but also the soil in a shallow top dressing, so the budget made allowance for collection of rocks from arid parts of South Africa. A basic soil mixture consisting of 2 parts clay-loam, 1 part compost and 1 part sand was used under the dressing.

The first rocks were collected on a trip to the Knersvlakte and the last from Langvlei Quarry, Worcester. All in all we made 15 journeys between March and December collecting rock and plants. The formal stone walls and concrete paths were constructed by George Kayster and his team under the watchful eye of Philip le Roux, Kirstenbosch's Estate Manager. The style of the walls is the same as the rest of the walls at Kirstenbosch. Made of local quartzitic sandstone dressed by the team, this craft is a longstanding Kirstenbosch tradition.

The plant landscaping of the main house and lower corner units took nine months. In choosing plants, I had to bear in mind not only ones which are well represented in each of the arid regions but also those which would provide maximum educational value (plants with ethnic value or ones with interesting histories).

Tour the Conservatory

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