Mdj2 Associates director Andy Newman said of the bank holiday weekend, which includes bank holiday Monday on 2 May:
"It looks like May will be the month that now defines the season for many garden centres. The combination of an early Easter, coupled with cool April temperatures have already held back sales, so garden centres will be concerned that temperatures are dropping again this week in the build-up to the all-important Bank Holiday weekend.
"We all know that weather forecasts can change pretty quickly, but with widespread frosts and the threat of wintery showers this week, many gardeners will be cautious about pushing ahead with new planting, especially bedding. Cooler temperatures will also impact barbecue and garden furniture sales. If the Bank Holiday weekend doesn't deliver a strong sales push it will put ever more focus on the rest of May."
Ayletts managing director Adam Wigglesworth said March had been "a solid month" but "April is going to be a disappointment, though it's still all to play for".
Speaking on the Bank Holiday weekend the Met Office said: "It is expected to remain rather cold and unsettled over the weekend, although less cold than this week is likely to be, with a mix of sunshine and showers, often accompanied by brisk winds.
"Some showers likely to be heavy with a risk of hail, and perhaps merging into longer spells of rain at times."