Account manager Marc de Bruin said: "It's a little bit more expensive but planting on the green roofs is an investment."
Oakover Nurseries flew the flag for the UK, being the only British grower exhibiting at the event. Managing director Brian Fraser said: "We took over plants that are unusual to Holland and we've sold the whole stand to a Dutch man."
The Quercus bimundorum 'Crimson Spire' submitted by C Verhelst won a gold medal. Judges said: "Contrary to the known European fastigiated oaks, it has an excellent red autumn colour." The variety is highly resistant to powdery mildew.
Andre van Nijnatten en Zn's Ilex crenata 'Allgold' won silver. Judges said: "Handsome plant with relatively small leaves and a fresh appearance." It is resistant to scorching in summer.
Silver-winning Rudbeckia 'Dublin' was introduced by Handelskekerij Exceptio. It boasts large, deep, golden yellow semi-double flowers. Judges said: "The combination of a relatively compact habit and handsome flowers is an innovation."
Bronze-winning Abelia 'Lynn' (Pinky Bells) was a joint entry by Valkplant and Leon Van Lint. Judges said: "The young shoots turn bronze in autumn and go well with the pink flowers."
Thuja plicata 'Kager's Beauty' submitted by Peter Leenders also won bronze. Judges said it was a "nice conifer with an informal habit" and a "strong plant that grows well."
A group of delegates from Morocco attended to explore the possibility of establishing a trade link with the Dutch tree nursery sector. A spokesperson for the group said they had a number of interesting business discussions.