"Don't be fooled by the crowds milling around the rose beds." That's gardener Akemi Sugii's perplexing heads-up for anyone planning a visit to next week's open days of the Ark Hills rooftop garden she manages in Tokyo's upmarket Akasaka district.

That's because, Sugii says, the high point of her handiwork is not to be found in the showy ranks of red, white, yellow and pink roses, but in a far more subdued section of the garden dedicated to plants native to Japan and East Asia.

Sugii is one of many horticulturists and environmental activists in Japan calling for increased use of native plants in gardens and landscape projects.