The garden centres were judged to have the best festive displays in the country by the organisation and will receive their awards at its golden jubilee conference in January.
GCA chief executive Iain Wylie said: "We announced the regional winners of our Christmas display competition at the end of November and were very impressed with the standard of entries this year. Following this, the area winners were all judged for a second time and these two national winners were selected at the end of last week as the duo with the most dazzling displays.
"I’d like to heartily congratulate Barton Grange in Lancashire, who won in the Destination Garden Centre category, and Castle Gardens in Dorset who scooped the top prize in the Garden Centre section of the awards."
The garden centres were judged on the innovation, inspiration and excitement created from the way their Christmas products are displayed. The range of products available, accessibility, how easy it is for customers to find and select products and ‘wow factor’ were also taken into consideration in an assessment of the overall commercial proposition.
Andy Campbell, GCA inspector and judge of the national Christmas displays competition, said: "I last carried out the national judging of the Christmas competition several years ago and since then the creativity and commerciality of the regional finalists has just got stronger and stronger.
"I have just visited 15 garden centres over eight days and I am hugely impressed by the professionalism of their Christmas merchandising and displays. It is clear to me that garden centres lead the way in this field."
The runners up in the Destination Garden Centre category were Bents in Cheshire and Whitehall, Lacock in Wiltshire. In the Garden Centre category, the runners up were Burleydam Garden Centre in Cheshire and Pennells Lincoln.