The roof of the classrooms of the Amenity College of Horticulture, located within the National Botanic Gardens, Glasnevin, Dublin, is best viewed from the top of the number 19 bus.

College director Dr Paul Cusack smiles as he imparts this gem of wisdom. The roof is covered with a carpet of sedums, which flower in summer. Designed by architect Ciaran O'Connor, who is also responsible for the new library and herbarium, the tiny college rejoices in wood and glass.

Cusack's spacious office is in a separate building - the old herbarium. The walls are hung with photos of the garden's herbaceous border and pond, the first sunset of the millennium at Killiney Hill (taken by Cusack himself), as well as a framed print of the garden's strawberry tree, painted by Deborah Lambkin.

The subject of another of Cusack's own photographs - profuse pink, white and red valerian, beside steps going down to the sea - will be familiar to most southside DART travellers. Cusack also uses this as a screensaver.

There's a stack of classical CDs on his desk and a large artificial dragonfly perches on his filing cabinet. A beautiful, peaceful place to work, situated within one of the most beautiful settings in Ireland.

Cusack is mindful of his good fortune. "I didn't do well at school. I hated every day. I just scraped through the Leaving Cert with a minimum of everything. I had the impression that I wasn't capable of proceeding. But I got a place in UCD's agricultural science programme.

"I worked very hard at university. I liked the subjects." In fact, he liked it so much, he took six years to gain his degree. After two years in college, all students spent one year on work experience. Cusack spent two.

"I was enjoying it. I spent a year at Albert College and then a year with the famed Barney Johnson, who had a garden centre in Cabinteely. He was a fantastic man with a terrific knowledge of plants." Back to UCD, in 1969, he completed third and fourth year of the course. "I was very interested in entomology. An opportunity came up in the agricultural zoology department, to look at the occurrence of pests in stored products, mainly grain cereals. It involved doing a survey of grain storage facilities from mills, to farm stores to bread vans and bakeries." Prior to beginning the project, he went to London for some training, and spent time on London docks investigating the holds of ships bringing dried fruit and grain from exotic-sounding places. "That was really exciting."

Back in Ireland, working on flour mites and their predators was also fascinating, he says. "And I got a PhD as well," he says, almost wonderingly. "The Botanical Gardens is a fantastic place for insects; the dragonflies at the pond are amazing. It's so easy to encourage insects. I have a mobile home in Wexford and I have plants and lots of buddleia. It's incredible on a summer's day. You can just sit and watch them for hours as they land and lift off."

Cusack joined the staff at the college on December 4th, 1973, at 25 minutes to three. He apologises wryly for the exactness but says he can't help remembering the precise times and dates of events. "When I finished my PhD, I wanted to do something broader than entomological research, so, like most ag grads, I applied for a job in the Department of Ag. I could have ended up doing anything but I was lucky to get a job here. I couldn't see myself sitting in an office going through files and schemes."

The Botanics were founded in 1795 when the Royal Dublin Society took possession of land at Glasnevin. This followed a petition for funds by Dr Walter Wade, the society's first professor of botany, to the Irish Parliament. The gardens were handed into State control in 1877, and become the responsibility of the Department of Agriculture before being transferred to the OPW (the forerunner of Duchas) in 1992. This latter date was very important for the gardens, says Cusack, as it marked the beginning of a major programme of restoration and expansion.

Teagasc (then ACOT) had already separated from the Department of Agriculture in 1980. The college now offers between 50 and 60 first-year places on its flagship course, a national diploma in horticulture, which is run jointly with Blanchardstown IT.

Cusack says he is pleased the course is now in the CAO, as it attracting more school-leavers, although it maintains a substantial quota of matures. This first year comprises 30 school leavers and 20 matures. The job scene for graduates is very good at present, he says. There will also be the possibility of proceeding to a degree (an applied degree, stresses Cusack) in the future. Horticultural students attending the college have the opportunity to work with a unique collection of plants.

Cusack liaises closely with the director of the gardens, Dr Donal Synnot. As we walk around the nursery area of the gardens (which is off limits to the public), Cusack introduces a student who is boring holes in cork, which will be used as a medium for other plants.

In the new library and herbarium (strictly research facilities), completed four years ago, he is clearly proud that students are afforded the opportunity to use world-class facilities. "In the past, students used to scramble between different building looking for books, etc," he says.

Now, they can browse hundreds of botanical journals, at their leisure, as well as consulting books dating from 1532 onwards. Or they can just gaze out through the wall of windows, and enjoy the vista of the gardens in its late autumn foliage.

Downstairs, the herbarium contains a collection of dried and pressed plants, with each specimen serving as a voucher, a record of one plant growing in Ireland or abroad. A volume containing about 600 plants collected in the famous Dutch botanic garden at Leiden in 1661 is among the oldest anywhere.

Nearby, the palm house, dating from 1884, is next in the list for renovation. Emptied of plants, it has a forlorn, rusted charm, which Cusack has captured in a series of photographs.

Part of Cusack's job involves going to careers' fairs and schools to promote the national diploma in horticulture. His own appreciation and enjoyment of the Botanic Gardens, with its varied plant and insect life, its historic glasshouses and new buildings, must, surely, inspire, would-be horticulturists with a desire to train there.