This month’s RHS London Flower Show has migrated east, from the shelter of the Horticultural Halls in Westminster to the wide, open spaces of the three-acre gardens at Inner Temple. In fact, it is a return to the show’s roots, as these gardens were the venue for what was then called the Great Spring Show for 14 years, until 1911, when it transferred to the ground of the Royal Chelsea Hospital to become the celebrated Chelsea Flower Show.

The last time the show was held at Inner Temple the plants were exhibited in two long marquees, visitors arrived by carriage and top hats and parasols were much in evidence. Today there is just one marquee with several smaller pavilions and trade stands dotted around the grounds, and the exuberant planting in the 230ft long borders — tapestries of brightly coloured dahlias, rudbeckias, heleniums, cosmos and asters on the upper terrace of the — gardens sets the season firmly as end of summer.

A report on the show in Amateur Gardening in June 1908 talks of “a brilliant display of flowering and foliage plants as well as fruit trees and vegetables”. It continues: “It hardly seems credible that such results could have been achieved in a spring which has undoubtedly been one of the most unfavourable within recollection.”

This year’s band of exhibitors have had to contend with similarly appalling weather, and it is remarkable that they have managed to present a wide range of late summer/early autumn blooms — from eucomis, gaura and clerodendrons to crocosmias, asters and Japanese anemones — in such excellent condition.

Several of the exhibitors have made historic links. Pennard Plants’ display includes heritage potatoes such as Salad Blue (whose skin is the colour of an aubergine) and Arran Victory (which has a pale-purple skin) and wonderful accoutrements such as a swan-necked onion hoe, a cucumber straightener (a transparent glass tube in which the fruit was grown) and a grape storage bottle (a flat-sided bottle filled with water and charcoal with a curved neck into which the stems of the grapes were inserted to keep them fresh).

Ascott Park, a former home of the Rothschilds and now in the hands of the National Trust, displays myrtles, scented geraniums and a conference pear tree as reminders of the medals won by Leopold Rothschild when he exhibited at the show from 1897-1904.

Rothschild was one of several of the gentry who exhibited alongside the professional growers. Even the RHS president of the time, Sir Trevor Lawrence, managed to slip some of his own orchids into the first Inner Temple show, and one of the 200 or so historic clematis varieties exhibited by the Guernsey grower Raymond Evison includes the red-flowered Clematis texensis “Sir Trevor Lawrence”, raised in 1890 that was named after the president.

This is one of the few 100-year-old varieties in Evison’s national collection that is still available to gardeners today. According to Evison, who grows a quarter of the world’s young clematis plants, we modern gardeners require our clematis to be both generously floriferous and long lasting, while most of the ones raised in this country in the 19th and early 20th centuries have fewer flowers and bloom for several weeks rather than months.

An exception, which takes centre stage in Evison’s display, is C. “Jackmanii” which is smothered in large, velvety-purple blooms. It was bred by the Woking nursery Jackmans 150 years ago and flowers from early July until September.

“This was a tremendous breakthrough,” Evison says. “It was the second hybrid to be bred in Europe and it is still hugely popular today. It is such a great plant for growing with roses.”

Although they may not give such long performances, many of these older varieties have a special charm and delicacy such as the rarely seen C. “John Gould Veitch”, which has pale-lilac double blooms. This was named after a member of the famous family nursery which collected in the Far East and the Antipodes and sent back the not-so-delicate New Zealand flax (Phormium tenax) as well as several striking palms. The next time this fascinating collection of clematis will be on view to the public is May 2009, in Guernsey.

The RHS Inner Temple Show today 10am-6.30pm, Saturday 10am-5pm (plant sell-off at 4.30pm); rhs.org.uk/flowershows