Garden centre group Wyevale saw £5 million knocked off sales as the Golden Jubilee celebrations and the World Cup distracted people from gardening.
The group said the shortfall - calculated in the two weeks surrounding the delayed bank holiday weekend in June - was compared with sales during the May bank holiday last year.
The disappointing performance came on top of cold, wet weather in May and the early part of June which hit sales of plants, furniture and barbecues.
Like-for-like sales slumped 21.6 per cent in May, although this was skewed by the loss of the spring bank holiday weekend.
Wyevale, which is the UK's biggest garden centre group with 123 stores, calculated the combination of events cost it between £1 million and £1.25 million in profits during May and June.
But a bumper March and April meant for the 26 weeks to the end of June, like-for-like sales rose 1.7 per cent in total.
Operating profit before tax was expected to be up 17.2 per cent at £16.5 million.
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