International horticultural exhibitions and world horticultural exhibitions — defined according to their size and the number of participating countries — started by AIPH have been held in more than 50 countries since 1960.

Chengdu is one of eight cities in China to have hosted the expo, with Kunming, Yunnan province, holding one in 1999, and Beijing in 2019.

"The Beijing expo was the best expo that I'd seen to that point. But when I arrived in Chengdu, I saw that the standard of horticulture has again increased," Edwards said.

"It's already obvious that the expo is simply a part of a bigger project here to green the city, and the expo demonstrates techniques that are going to be utilized throughout the bigger project. So I think it's a very fine example," he added.

Edwards recalled that when he first came to China decades ago, there were only a few plants that would be grown by the industry commercially, and those that were grown were mainly certain species rather than in varieties.

"Now, the quality of the plants on show in Chengdu is the highest I've ever seen," he said.

In addition to plant varieties, the technology used in horticulture has also improved a lot in China in recent years, he noted.

"There were green walls at the 2019 Beijing expo, but I felt that the designers were showing off some new techniques. This year a lot of the gardens have green walls, and I can see they're now being used with confidence," he said.