Hard landscaping was up 27 per cent, outdoor furniture and BBQs 19 per cent, outdoor plants 15 per cent, sundries 12 per cent, houseplants seven per cent and catering 4.6 per cent.
Overall sales for the month were around seven per cent up, and are a similar amount up for the year to date.
GCA chairman Will Armitage said: "The mild and dry September has definitely helped to contribute to the increase in purchases of products to help improve outdoor spaces."
Bents managing director Matthew Bent said: "During the summer, anything garden-related proved successful, from our plants and garden care products to garden furniture and outdoor living. This trend has continued through to September."
He said sales were above budget in garden furniture, accessories and outdoor lifestyle.
Coolings managing director Gary Carvosso said catering was "star performer" with £1m turnover budgeted for in 2014 and growth of 13 per cent year-to-date. He said a coffee loyalty card, employing two bakers and serving afternoon tea had boosted sales.