Alton Garden Centre director Andy Bunker said August saw an increase in sales in the plantarea of more than 26 per cent on 2014 and the last four months consecutively were the best ever in 44 years, with sales up a "mouth-watering" 14 per cent cumulatively on the year.
Overall in the whole centre, August was 19 per cent up, with year to date sales eight per cent up.
The Met Office said: "Despite a dry and sunny June and a brief 'heat-wave' at the start of July, summer overall has been cooler than average and cooler than either summer 2013 or 2014. It has also been wetter than average, despite near average sunshine.
"Using provisional figures for the meteorological summer from 1 June to 31 August, Met Office statistics show the UK mean temperature for this summer was 13.9 °C. This is 0.4 °C below the 1981 - 2010 long term average.
"Rainfall overall is slightly higher than average, with the UK having seen 272 mm of rain - which is 13 per cent above the long-term average. However, across southern and eastern England this rain has often come from short, heavy downpours and these have been interspersed with some fine, dry days."
HTA figures show the 2015 calendar year to the end of July is nine per cent up on 2014, with July sales nine per cent up too.
BDO High Street sales tracker reported a 4.3 per cent sales fall in August. BDO blamed exchange rates for more spending abroad, economic uncertainty, threats of interest rate rises and weather.
It said outdoor goods sellers struggled, as did premium lifestyle retailers, but specialist fashon and small ticket gift retailers did well. Home improvement sales were low because of the hoiday season.