Supermarkets have rationed 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.
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.
Concerned healthy eaters have been sharing pictures of bare supermarket shelves with the hashtags #lettucecrisis and #courgettecrisis, while complaining that prices have nearly tripled in recent weeks.
Retail analyst Rob Gregory posted a photo on Twitter of empty boxes in a Tesco and a sign that read: “Due to continued weather problems in Spain, there is a shortage on Iceberg and other varied lettuce products.
“To protect the availability for all customers, we are limiting bulk purchases to three per person.”
He tweeted: “My local Tesco also affected by the lettuce and salad rationing. Not much there to ration though!”
Sarah Morton, from Manchester, tweeted a photo of a Morrisons shelf label stating customers could only buy a maximum of two each.
She wrote: “Why? I don’t get it @Morrisons #arewerunningout.. #lettuce & #HOWMUCH££”
Joey O’Hagan tweeted: “Just seen iceberg lettuce for £1.40 in Sainsbury’s. A few months back it was 40p.”
Spain normally supplies half the vegetables on the European market during the winter months.
Supermarkets have been forced to look as far afield as the US west coast - more than 5,300 miles from Britain - to meet demand.
Coos Hessing, of Hessing Super Fresh, said the situation for lettuce was “particularly severe”.
“There have simply been too many cold days, and what’s most bizarre about this situation is that it has hit all of south-eastern Europe.
“We had seen this before, but you’d need to go back to 15 years ago,” the buyer told industry site Fresh Plaza.
Consumers may see lettuces around two-thirds smaller than usual on sale, while buyers have been looking to the USA and Egypt in order to keep supplies from drying up, Mr Hessing said.
Fepex, Spain’s largest growers’ association, said the extreme conditions amounted to a “force majeure” and the availability of outdoor-grown vegetables will depend on conditions improving in the coming weeks.
“It is a situation Fepex envisages remaining until at least early April for leafy vegetables grown in the open air, like lettuces, endives and spinach, and their availability will depend on weather in February and March.”
A Tesco spokesman said they were “experiencing some availability issues” due to the bad weather in Spain
“[We] are working with our suppliers to resolve them as quickly as possible,” he said.
A Morrisons spokesman told the Daily Mail: “As a result of the fact that the Spanish harvest has been very difficult this year, we have just about enough coming in to supply our customers.
“We want to stop local tradespeople and restaurateurs coming in and buying lots of stock.”