The Herefordshire grower was founded by chairman Brian Taylor in 1972 and now produces five million plants a year.
New growing beds have increased production of specialist perennials by 60 per cent at its newest Allensmore West site. The plants on the 6.4ha site are sub-irrigated through capillary matting that encourages beneficial microflora and water is recycled through reed ditches.
The main site has a combination of outdoor growing beds, glasshouses and multirollair tunnels with roofs that can be opened automatically.
The business produces 70 per cent of its own plants, with the remainder being made up of Mediterranean and Italian plants.
Allensmore managing director Mark Taylor said the nursery hoped to continue expanding in the future.
"We would like to build the production side and expand our facilities to ensure that we have the space to grow quality plants," he said. "We have to keep raising the bar."
The nursery will be holding an event next month to mark its 40th anniversary.