Alton Garden Centre director Andy Bunker said this week has seen good sales because of the "Chelsea buzz" but after three days with temperatures in the high 20s his one concern is that the bank holiday weekend will be too hot for people to buy plants.
He said: "The FA cup final and hot weather: in our location, they're down the beach. Barbecues and garden furniture do well but plants not so well. If it's a bit cooler, then great."
Bunker said he would be happy to be 10% up after April and May, which he said accounted for more than a third of annual plant sales. He expected at the end of the month to be 10-15% up minimum on planteria sales.
Buckingham Nurseries' Chris Day said the garden centre had had its best spring for seven years and he was encouraged by prospects for the bank holiday.
Day said this week had been "encouraging" after 10 days of damp and unseasonal weather caused a dip in sales.
He said the turnaround in weather had led to a "resurgence" in sales, and he expected a "very planty weekend with a bit of outdoor living out there". He added that firepits were selling well.
Cook's Garden Centre owner Paul Cook said after breaking records in 2016 and a good March and early April 2017, sales turned "lack lustre", then poor
He said the Stourport centre, which also sells at many RHS shows, is running "slightly behind" last year, and the season needs a few weeks of good sunny weather in June to make it a real success.
B&Q said seasonal sales were up 17.5% after the first quarter this week, despite overall sales being down.
The Met Office has issued a warm weather warning for Kent and forecast warmer than usual weather for June.
Warm air from southern Europe will push UK temperatures into the high 20°Cs in the south by Thursday and the mid 20°Cs further north from mid-week onwards.
"By Saturday we could see temperatures topping 30°Cs in one or two places. As well as warm days in many areas, night-time temperatures could also be above average giving us some warm, muggy nights potentially making it difficult to sleep.
Deputy Chief Meteorologist Chris Tubbs said "Over the preceding [bank holiday] weekend it will probably become cloudier and less hot from the west with some outbreaks of rain, which could be heavy and thundery at times. Eastern and south-eastern parts will more likely than not stay dry, sunny and locally hot through Saturday too and possibly beyond."
Not-for-profit water efficiency organisation Waterwise recommended this week that gardeners should use more mulch and bark to reduce evaporation by up to 75%. Despite recent rains allaying fears of hosepipe bans, it reminded gardners they could collect up to 80,000 litres a year from the roof into water butts. Garden sprinklers, which can use 1,000 litres of water an hour, should only be used in the morning and evening, or lawns can be left to go brown, it said.