Frosts, based in Buckinghamshire, saw sales down overall by 3% on the same period in 2009, with Saturday up 5%, Sunday 18% down and Monday 4% down.
MD Paul Wright said overall April was up on 2009.
He added: "Everything is to play for in May."
Wright said that while spring bedding had sold well, the move over to summer bedding had been slow because of low night temperatures.
Scotsdales in Cambridgeshire reported similar issues, while South East-based Squires found the bank holiday 25% down, following an April that was 10% up on the year before. Shoots and Millbrook also struggled.
But Webbs in Worcestershire reported it had an "excellent weekend overall" particularly in plants, furniture and landscape materials, with sales up from Thursday to Monday by 16%.
And Dobbies sales and marketing director Phil Douty said: "We experienced a strong bank holiday Monday across all of our 25 stores yesterday - making it clear that the UK has entered into the gardening season with a spring in its step. We're confident that due to the later arrival of spring weather this year, we'll welcome more customers to our stores over the next month than in previous years."