Furniture and barbecue sales were up 12.10 per cent.
Hard landscaping was up 8.74 per cent.
Clothing sales rose 13.96 per cent.
Seed and bulb sales were down -16.50 per cent.
Outdoor plants were up 2.55 per cent.
Houseplant sales were up 1.48 per cent and garden sundries were up 6.48 per cent.
Pets and aquatics sales were up 4.07 per cent, food hall and farm shop sales up 1.92 per cent and catering 4.55 per cent. Gift sales were down -3.26 per cent.
The regions that saw the biggest increase in sales during the month compared to the same month last year was South Thames at 6.77 per cent up and Wales and West at 6.37 per cent up. The Midlands area saw the biggest YTD change of 18.84 per cent.
HTA figures show August sales were five per cent up.
GCA chief executive Iain Wylie said: "We did enjoy some good weather this summer and from the results of sales in furniture and barbecues it looked like the Great British public spent a lot of this time in their gardens, which is great to see."
Squires Garden Centres finance director Steven Palmer said: "August was a good trading month for our garden centres with strong sales in plants and lifestyle categories. Our Café Bars continue to trade strongly reflecting the increasing UK trend for eating out."
Creative Gardens director Philip Gass said: "August was a decent month trading for us, weather was mixed but nonetheless sales across the board were up around three per cent at each of our centres compared to the same month last year.
"Some of the noticeable improvements on August 2015 was the bird care department, which was up more than 200 per cent, helped by a club customer promotion. Plants were up 8.7 per cent and gardening general was up 15.7 per cent. Coffee shops and gift shops struggled a bit in August, partly as a result of less customer club promotion in the café. Our transaction count was down slightly but average sales increased by 8.1 per cent."
Mike Burks, managing director of The Gardens Group, said: "It’s been a good summer with all parts of the business working well. Summer is a growth time at the moment albeit on a much smaller scale than the key seasons."