Morrisons, Aldi and Tesco have adjusted some of their specifications as the hot, dry weather impacts fruit and vegetable crops.
Fruit and vegetable crops across the UK have been affected by the heatwave, with carrot growers warning of a shortage and onion growers facing reduced numbers and smaller vegetables.
In response, Morrisons, Aldi and Tesco supermarkets have been reviewing the specifications they require growers to meet.
A Morrisons spokesperson said: "Our customers say reducing food waste and supporting farmers is really important to them.
"We speak to our farmers all of the time about how crops are ripening. If their crop is not ripening as expected – due to extreme weather – we have the option either of relaxing specifications to help them out or including it in our Wonky range.
"Recently we have relaxed our specifications for salads - including lettuce, cucumbers, celery, herbs and peppers.
"Unless the standard product is on promotion, Wonky will always be cheaper to encourage customers to buy it."
Aldi was assessing each product individually according to market conditions and availability. It was in close contact with growers and had adjusted some specifications to support growers while maintaining quality.
A Tesco spokesperson said: “During the current spell of warm weather, we have been working with our British growers to ensure we take as much of the crop as possible.
“Some fruit and vegetables might be smaller or blemished due to the growing conditions we’re experiencing, but they still provide the great quality and taste our customers expect.”
The supermarket said the cool wet spring and dry summer had impacted yields for Cornish early potato growers, made worse by instances of scab. In response they had allowed larger than normal levels of dry scab into packs.
For strawberries, they have reviewed the specifications on the minimum average level of sugar and ensured the smaller sized strawberries produced this year have been available to customers.
Apricot growers had also seen reduced yields so it had reviewed size and appearance specifications.
And Iceberg lettuce had been maturing and bolting before reaching the normal size and weight but the supermarket had been working to accept lower weights in order to take as much crop from growers as possible.