Sales of houseplants were up 1.92 per cent while sales of outdoor plants were down -17.47 per cen. Clothing sales were up 9.95 per cent and catering was up 8.90 per cent.
Overall year to date figures are 2.19 per cent up.
Iain Wylie, GCA chief executive, said: "April was a very cold and wet month so it’s no surprise that sales in traditional categories were down. The frost seemed to linger a lot longer this year, which would have put a lot of people off gardening.
"Another factor for poor sales was that Easter was very early this year, in March, compared to 2015, when it was in April.
"Despite sales in traditional categories being down, there was some positivity in clothing and catering. Food hall and farm shops sales were also up 3.70 per cet compared to the same month last year."
Seed and bulb sales were down -9.28 per cent, garden sundries were down -16.21 per cent and furniture and barbecues sales were down -23.50 per cent.
Steven Palmer, financial director at Squires Garden Centres, which has centres across Surrey, Berkshire and Sussex, said: "Direct comparisons are distorted due to Easter falling in April in 2015 but not in 2016. The unseasonably poor weather in the south meant reduced demand for traditional seasonal gardening products, including furniture.
"However, demand for gifts remains robust and bird care products benefitted from the poor weather."
Sales in pets and aquatics departments were up 1.45 per cent. Gift sales were down -1.14 per cent and hard landscaping down -12.68 per cent.
Mark Winchester, managing director at Blackbrooks Garden Centre in East Sussex, said: "April was unseasonably cold and while our gifts, clothing and catering were up, our horticultural products were down. The only real winner was our houseplant department, but this could have been in part due to a redesign incorporating a walk through department on the way to the checkouts, resulting in a 100 per cent uplift in sales."