The Palm House at Kew has nothing on this

Diarmuid Gavin visits the National Botanic Gardens in Dublin
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In Ireland, the mecca for anyone with even a vague interest in horticulture is the National Botanic Gardens at Glasnevin in Dublin.

Founded in 1795, it is packed with treasures gathered from around the globe. As a centre for learning, it has few equals, and I was given my first introduction to the garden world there. It took me no time at all to learn the difference between a spade and a shovel, and even know how to use them. Half our time was spent in the lecture hall learning the science, and the other half saw us on "section work" - spending six weeks in various parts of the gardens.

As young students, each move was monumental in scale. In summer, everyone wanted to be posted to the fruit garden - just as the strawberries and grapes were ripe. In winter, everyone wanted to end up in the glasshouses, where you could water banana trees in a T-shirt and shorts while the ground outside was heavy with snow. In summer,these hot and steamy constructions were hell.

One of the houses was the curvilinear range dating from 1843 and designed and built by Richard Turner. One of Turner's other main projects was the great Palm House at Kew, which was designed and made at his foundry in Dublin before being shipped to London.

By the beginning of the Eighties, both buildings were in need of serious work. At Kew, they decided to replace the structure with an aluminium replica. This left Dublin with one of the finest and last remaining cast- iron buildings in Europe, and its fate was set when Prime Minister Charles Haughey handed control of the gardens over to the Office of Public Works, a body which does a similar job to the National Trust in the UK.

Architect Ciaran O'Connor was put in charge of restoring the range, and he and his team set about examining the options. Rather than a replica, they decided to move into new areas of technology to undertake the task. What they have achieved is nothing short of astonishing.

A lot of iron had rusted, and the building was dismantled piece by piece. It was X-rayed and the rusty bits were cut out. A trip to London led to the discovery of the iron from Kew languishing in a scrapyard. This was bought and taken to Dublin.

Cast-iron had never before been welded, so a way to do this was developed. Special paints were created, 12 coats in all, and these were baked into the lengths of metal.

With that, the Turner Conservatory rose again. The transformation was miraculous. With the addition of computer-controlled heating, ventilation and humidifying systems, it was now a state of the art structure, while still remaining every bit a wonderful historical record. During a visit to Dublin, the conservatory is a must-see.

The National Botanic Gardens of Ireland are a mile north of central Dublin, close to Glasnevin cemetery. Open 9am-4.30pm daily. Entry free. Part of the conservatory, and an exhibition on the restoration, are open 11.30am-12.30pm, and 2-3pm.