The supermarket chain, which has around 350 branches and 167 garden sales "pods", has an 8.2 per cent share of the grocery market in horticulture. For outdoor plants this rises to 18 per cent, according to analyst IRI. Waitrose's total grocery market share is 5.2 per cent.
Allensmore commercial director Jane Davies said: "Reserves are equal if not more than 2015. We're more than happy with the reserves we have got off them."
A Waitrose representative said: "Horticulture is one of the strongest areas of our business and is seeing some of the most significant growth figures (sales are up 13.2 per cent year to date). Our customer insight shows that after cooking, gardening is our customers' favourite hobby - and we have plans to build on current success by growing our offer again next year."
Allensmore recently announced a deal with Blooms of Bressingham for 4.5-litre perennials and will launch a two-litre range in February 2016 as a trial for a year.
The Herefordshire-based grower will build 0.4ha of glass in 2016 after building 0.8ha in 2015. Allensmore's new outdoor production nursery takes the total production area from 8ha to 24ha, to make it a "top-three production nursery in the UK". The focus is on "big plants in colour".