In an interview with Horticulture Week due to be published online this Friday, Spicer said he would like to think conifers are on their way up "for a couple of reasons".
First, because of "a load of new varieties coming up that are colourful and useful," said Spicer.
Contrasting high popularity of conifers in the USA, Holland, Germany and Poland with the UK, he blamed "spruce monocultures" in Scotland for "putting everyone off" as well as the "double whammy of leylandii cypress all over the suburbs."
"So people were against conifers but hey have no idea about the new stuff - I hope they get through and get more popular," said Spicer.
Meanwhile he said he hopes the encyclopedia will create some interest. "We've printed 5,000 and are looking at worldwide sales, particularly in the USA," added Spicer.
Spicer named his top conifers as follows: Taxus baccata 'Standishii', Chamaecyparis obtusa 'Nana Gracilis', Picea glauca 'JW Daisy's White', Picea pungens 'Globosa' and Chamaecyparis lawsoniana 'Minima Aurea'.