Garden centres in 2012 were two per cent down overall on the previous year, the GCA's Barometer of Trade (BoT) results confirmed.
The best performing categories were catering, Christmas and gifts.
GCA chairman Peter Burks said: "Despite the unpredictable and unseasonable weather playing a large part in making 2012 a very tough year for garden centres, our BoT results show that member garden centres can, and have relied on, non-traditional categories to boost their sales throughout the year.
"They adapted to the challenges of the past year by reducing their dependency on plant sales and focused on other areas of the business.
"Christmas product sales for the year saw a significant leap, up 10.35 per cent on 2011, catering also had a great year, up 8.84 per cent, clothing was up 5.47 per cent, gifts up 4.49 per cent and pets and aquatics up 3.42 per cent.
Burks added: "I’d like to congratulate all our members on their adaptability, flexibility and sheer hard work in 2012. As an industry that is traditionally weather-dependent, last year could have been disastrous.
"It is testament to our members innovative nature that sales were so high in certain areas.
"I’d like to wish everyone all the best for 2013, we all learned a lot of lessons this past year. If the British weather takes an unpredictable course again this year at least we will all be prepared."
The lack of sunshine and unseasonable weather affected outdoor plant sales most noticeably, the category stands at 13.03 per cent down for the year. Furniture and barbecue sales also suffered, standing 9.93 per cent down, seed and bulb sales 8.21 per cent down and hard landscaping 8.56 per cent down.
The BoT reports produced by the GCA allow member garden centres to compare their trading positions with other GCA garden centres.
Raglan Garden Centre owner Martin Davies said: "Christmas rescued last year for us and we ended up fractionally up on 2011. We know that if there is the right things in place people will come out here. They are the weather and a couple of nice offers.
"In early February we offer a special deal to bring them in through a door drop leaflet. It's a genuine buy one get one free on Scotts compost through Future Marketing. We sold 3,000 bags last February so it gets the season going and people interested."
Melanie Sewell, catering manager and director at Fron Goch Garden Centre in Wales, which is a member of the GCA, said: "Our café has shown increased sales of 12.1 per cent during 2012. As our catering offer represents 34 per cent of total turnover, it helped turn 2012 into a pretty good year.
"We did not have a café until 2007 and now café turnover has reached £665,000. No one can afford to neglect this area with high gross profit margin and profitability.
"During 2012 we concentrated on driving sales through buy one get one free vouchers for breakfast and offers on hot lunches and introducing afternoon teas, in addition to improving profitability through controlling food and labour costs."