The first Saturday morning of October, early: the Public Gardens. It is all so lovely and fresh; I feel full of hope, in the moment. I have an appointment to meet the botanist Giovanni Bonier. He arrives with his bulldog, Bimbo, who is very interested in the cats. They arch their backs and spit at him, run up trees and glare – in particular, a large black one. In contrast, Bimbo seems an amiable bulldog who only wants to play.

It is the perfect morning to be strolling along these well-remembered paths striped with the now lengthening shadows. The sun has begun to relax its grip on the earth, the light is softer; there is a subtle change of colour on the mountains and on the sea. I love every season in Sicily, but perhaps autumn best.

I am to have a guided tour of the flowers. As Giovanni explains, they come from all over the world, the names as sumptuous as the plants themselves.

There is Capparis spinosa, part of the caper family, whose small buds are picked as a relish. Then Cuphea from the Greek ‘kyphos’, which means ‘curved’, alluding to the curved fruit capsule; it has sprays of orange-red tubular flowers.

Every plant has its history. Here is the Bird of Paradise, the strelitzia, named after Charlotte of Mecklenburg-Strelitz, wife of George III. Its name is apt, the three-sepalled, two-petalled blooms curiously resembling an exotic bird’s head. There is the Jacaranda, its name originating from the Brazilian/Indians. This variety, Mimosifolia, has numerous leaflets and small purple blue flowers with a white throat.

The nuts of the mandorla (or almond) tree are used widely in Sicily for all kinds of confectionery. This variety is the Prunus dulcis (Asia minor), easy to spot with its very dark bark and pink flowers.

Brugmansia sanguinea lives up to its name, with its bright-red ‘Angel’s Trumpets’. Originally, these flowers were used by the American Indians as a hallucinogen; it takes its title from another ‘name’ in natural history: Justine Brugmans, who lived from 1763 to 1819.

Salvia leucantha is a white version of the more familiar fiery red Sage. The stamens of its flowers work on a rocket mechanism: the visiting bee has pollen pressed onto its head as it pushes against a sterile projection from the anther. The word ‘salvia’ means to heal or save. Used herbally, it is medically approved in Germany. Extracts taken internally have been recommended for anxiety, insomnia and digestive problems. It is sometimes used externally for insect bites and infections of the throat, mouth and skin.

London apothecary John Parkinson (1567–1650) gave his name to Parkinsonia. The more popular name is the Jerusalem Thorn – a spiny shrub with little sprays of yellow, pea-like flowers, dotted with orange. It comes from Central America.

We pause by a huge cedar tree, magnificent with its blue-green, needle-like leaves, but, as Giovanni explains, it is overshadowing other plants and drawing all the strength from the soil. Lofty though it is, he feels it ought to come down.

I ask him what it is like to be young and educated and living in Sicily. As a botanist he gives me an analogy in plant life: the roots of a kind of fatalistic thinking are planted so deep that it is impossible, in his opinion, to change it: ‘They cannot see the big picture, cannot get together. Each has his own point of view and won’t compromise.’

The garden is a mishmash of different periods. There are trees that Florence Trevelyan almost certainly brought from the East and many rare plants and flowers, which should stay exactly where they are. But there are others planted without any forethought and these should be severely pruned or taken out. He points out plants in the wrong places, such as the sun-loving hibiscus positioned among those plants that enjoy the shade.

The pavilions, designed by Florence Trevelyan, were christened ‘the beehives’. They were made of a variety of materials, from stonework facing in varying cuts and dimensions at the base to alternating brickwork and the lava-stone detail of the turrets to rustic logs on the little balconies and jetties. Now they are being allowed to fall into ruins. There is also the ‘Alice in Wonderland’ behaviour of those who tend the parterre, which is a mixture of stones and bricks. Giovanni explains wryly that the gardeners spend hours sweeping it with old-fashioned bristle brooms. A machine exists, but it is not used.

We come to the cactus garden, where I say that I think it’s not in keeping with the rest of the garden. Giovanni agrees with me.

‘It has always taken outsiders to get things done here,’ he explains. ‘We’ve been colonised by so many different invaders, but, although the people have been enriched by their civilisations, they have never gone on to develop these ideas. [Di Lampedusa’s classic] The Leopard says it all. In spite of that, I wouldn’t live anywhere else. The climate is perfect. And I am not an employee of the council but a consultant so not as answerable, even if sometimes one feels unappreciated. When I first started to work in the gardens I catalogued all the flowers. But do you see any labels?’

‘There are two kinds of people,’ he adds. ‘You give some money, they eat the lot; you give it to others, of course they eat some of it but they do something with the rest.’

And so we continue, I to smile with delight, he to list all these flowers: the datura white, yellow cream and rose striped, purple Salvia, bright-yellow tagetes, the roses and hibiscus. Giovanni is a mine of information. There is the fascinating Dragon tree with its small, fragrant flowers. The resin from its stems is the source of ‘dragon’s blood’ used in varnishes and photo engraving. Good that it is here – in the wild this elegant tree is endangered due to overexploitation.

We gaze up into the odd whorled branches of the Araucaria (the Monkey Puzzle tree); its leaves are whorled too. The fruiting cones take several years to develop and, as they mature, they break up. And here is a ginger tree, Zingiber, sounding straight from Edward Lear. The rhizomes of this species are used for the many kinds of ginger we find in the shops: fresh, green or root, crystallised, dried. Another variety, Alpinia, has three large, lobal lower lips.

But what is the name of ‘my’ beautiful weeping shrub, which I’ve stopped to admire since May? Russelia, Giovanni tells me, named after Dr Alexander Russell – sometimes ‘coral plant’, ‘fire cracker’ or ‘fountain plant’. It has pendant stems, simple leaves and two-lipped, five-lobal flowers that go on and on.

We part by the new statue given to the town hall by sculptor Piero Guidi in the previous year: two travellers cast in antique bronze sit on the bench by the entrance gates. Her head leans on his shoulder; she has a small case.

The only strange thing about them is that both sprout a full set of wings.