"Perfect gardening weather" led to some shortages, but "we managed to keep stock on the shelves and we're learning what customers want", she said.
Grow your own, herbaceous and box topiary are top sellers. She forecast that gardening will grow as fast as the rest of the business in 2015 and locations such as inner-London stores for Waitrose's outside box store gardening format, which the supermarket likes because it adds "seasonal change" to stores, are being considered for 2015.
Speaking at the fourth annual NFU/Waitrose "UK Horticulture" exhibit at the RHS Chelsea Flower Show, Coupe added: "Waitrose has a largely British proposition although there are challenges sourcing UK topiary."
On Waitrose cut flowers, she said 40 per cent are British and, in high season, 60 per cent are from the UK, particularly peonies, stocks, sweet peas and sweet williams. Winter pot plants from Hills add to the UK offer.
Supplier Butters said with buying patterns there has been a shift towards higher-value "instant garden" products, with its portfolio of items ranging from £2 retail to £100 and its fastest-growing part of garden plants is the £8-£20 range.
Butters added: "British flowers are the biggest area of focus in Butters Flowers business and represent 50 per cent of all flowers we source. Lincolnshire is the single biggest area of production but we also source large volumes from Cornwall, Suffolk, Norfolk and Hampshire."
British growers Featured at Chelsea
Designed by Penny Riley, the NFU/Waitrose exhibit showcased seasonal plants, flowers, fruit and vegetables from across the country and won a silver gilt.
The many suppliers included Berry Gardens (strawberries and raspberries), Allensmore (begonia, campanula, coleus, dahlia, heliotrope, heuchera, salvia), Hill Brothers (begonia, calla lilies, hydrangea, orchids) LF Geater, Matthew Naylor, Real Flower Co, Sue Lamb and Univeg (aliums, peonies, lilies).