Kew plants 100 to 200 trees a year, he said, mostly grown from wild-collected seeds. "We have gone from field-grown to Air Pots, which gives them a good fibrous root system. We want to get them out young and early."
He added: "Each tree I plant has to tick a number of boxes - scientific, educational, conservation, aesthetic and so on. The Indian horse chestnut Aesculus indica is a hard-working tree - the variety 'Sydney Pierce' is particularly floriferous -and it's resistant to Cameraria. We may be able to give that resistance to A. hippocastaneum [the common horse chestnut] by micro-injection - we have some evidence this works."
On the oak processionary moth (Thaumetopoea processionea), now an established noxious pest in the area, he said: "We spray 450 oak trees in the garden each year as a prophylactic measure in early May. It's not good for my staff to spray when the caterpillars' hairs are being shed."
- For full conference report, see next week's Horticulture Week magazine.