Supermarkets have limited the number of lettuces each customer can purchase in stores and iceberg, sweet gem and romaine varieties have been taken off sale completely by some online.
An extreme mix of drought followed by flooding and freezing conditions has severely affected growers in southern Spain, while poor conditions have also hit farmers in Italy, Greece and Turkey.
Dieter Lloyd, spokesman for the Leafy Salads Growers’ Association, said: “I think people are getting very surprised by the notion of rationing.
“But generally people don’t buy three heads of iceberg, or six packs of baby gem.
“The reason they are doing it (rationing) is because grocers, wholesalers, restaurants and hospitality outlets were going to the retailers and buying trays of produce.
“The retailers are trying to curb that because they want the produce to be available for customers rather than the hospitality industry or the wholesale market or greengrocers.”
Experts have warned that if the weather does not improve in the coming weeks the problem may continue until April, with customers hit by price rises.
The lettuce shortage follows similar reductions in the supply of courgettes, while salad peppers, broccoli and cabbage supplies are also under pressure.
Gardening guru Alan Titchmarsh welcomed the lettuce shortage as a reminder to consumers about the origins of their food.
Titchmarsh, originally from Ilkley, said: “As long as it’s there, people take it for granted.
“But we are dependent on climate and weather and growing skill and sometimes the weather throws things at you that you can’t legislate for.
“It reminds people not to take food and food producers for granted.
“And, to be absolutely honest with you, every now and again it’s good that sometimes thing like this happens because it just reminds people what skill it takes.”
Titchmarsh, 67, who is presenting a new show on Channel 5 exploring National Trust properties behind the scenes, said: “They don’t grow themselves, fruit and veg. They have to be grown.
“And if it gives people more respect and sympathy towards growers, I’m all for that.”
The lettuce shortage follows similar reductions in the supply of courgettes, while peppers, broccoli and cabbage supplies are also under pressure.
A spokesman for Asda said it was doing everything it could to support its growers and bring them back to full supply as soon as possible.
A Morrisons spokesman said: “Our availability of broccoli and iceberg lettuce is good. However, other businesses are experiencing shortages and we have seen some bulk buying in our stores.
“We have therefore had a cap on sales of broccoli and iceberg lettuce to ensure we maintain good supplies for our regular customers. As you can imagine, most customers don’t buy more than three broccoli at a time.”
Prime Minister Theresa May’s spokesman said the Department for Environment, Food and Rural Affairs (Defra) was “monitoring the situation”.