In recent years, the Royal Horticultural Society’s trials at their garden at Wisley, south of London, have added a new element – visitors get to vote for their favorites.

This year visitors to Wisley voted on buddlejas, butterfly bushes, and two brand new American varieties came out well ahead of over 100 other varieties.

‘Miss Ruby’ received more than twice as many votes as the second placed variety, ‘Lo and Behold Blue Chip’, which itself was a good step ahead of the third placed ‘Raspberry Wine’. This and ‘Blue Horizon were, again, noticeably ahead of all the rest.

Now, there’s something more special about these two buddleias other than the fact that they’re both American. Unlike almost all the other entries in the trial these two are not forms of the old – and sometimes invasive – favorite Buddleja davidii. They are complex hybrids involving other species and both were raised by Dr Dennis Werner, until recently in charge of the JC Ralston Arboretum at the University of North Carolina.

‘Miss Ruby’ is upright in growth and relatively compact as buddlejas go, reaching 4-5ft/1.2-1.5mm, with noticeably silver foliage and vivid pink flowers. And it’s surprisingly hardy, down to zone 5. ‘Miss Ruby’ is a hybrid between ‘White Ball’ and ‘Attraction’, neither of which are widely grown, and so has in its background B. davidii, B. fallowiana and B. globosa.

The horribly named ‘Lo and Behold Blue Chip’ is startlingly dwarf – not really like a buddleja at all. The plants I’ve had on trial this summer did not reach more than 18in/45cm in height and were wider than they were high. The short spikes of blue flowers would, I’m sure, have been produced more prolifically had I been able to find a site for it in full sun. ‘Blue Chip’ is a hybrid involving B. davidii var. nanhoensis ‘Nanho Purple’, B. globosa and B. lindleyana.

There’s one more thing bout these two new buddlejas. they produce hardly any seed. ‘Lo and Behold Blue Chip’ does not produce fertile pollen and is reluctant to produce seed even when pollinated by a different buddleja - so that’s a big plus. ‘Miss Ruby’, while not actually sterile, also produces very little seed.

This is all great news for anyone worried about the fact that Buddleja davidii is invasive in some areas.

In North America, both these new buddlejas will be available from a number of sources in 2009. I’ll bring you details of their availability in Britain as soon as I get some news.