Outdoor plant sales were around seven per cent up against strong 2011 figures, despite the impending hosepipe ban, with outdoor plant sales up five per cent.
GCA chief executive Phil Slinger said: "Early indicators are that year-on-year we will report a minimum eight per cent uplift in sales for March. The warm weather brought the shoppers out with footfall up four per cent and customer spend up seven per cent on early figures."
March was the warmest since 1997 and sunniest since 1929. Rainfall across England and Wales was 43 per cent of the average.
Adding to the debate on Easter Sunday trading, Slinger said members would like to have the choice on whether or not to open.
"An Olympic amnesty on Sunday trading laws on eight weekends from 22 July is not strongly supported by the majority of members," he added.
"However, if we have a sustained period of inclement weather through the key selling season, members may have to weigh up the cost benefit of trading during the Olympic Games period.
"But on the whole, GCA members want to keep a clear distinction between the lobbying work to ensure a change in Sunday trading laws and the Olympic amnesty," he said.
Alton Garden Centre director Andy Bunker said he was up eight per cent in March. Bedding was slightly down because of drought fears but specimen plant sales were up as people replaced plants lost in winter 2010, he added.