Supermarkets are preparing to fly in emergency salad from the US after heavy rains and flooding in Spain hit supplies.

About 80% of fresh produce – including leafy salads as well as celery and broccoli – sold in the UK at this time of year comes from the Murcia region in southern Spain.

Suppliers spoken to by the Guardian said yields in the region had dropped to as low as 30% of those expected at this time of year on some crops, such as little gem lettuces, as farmers’ fields were inundated last weekend. Celery yields have dropped to 40% of normal levels while some citrus crops, including satsumas and clementines, have also been affected.

“There has been a deluge of flooding in that part of Spain and they have got blocked roads, flooded dispatch facilities and mobile rigs for picking as well as crops that have been washed away,” said Anthony Gardiner of G’s, a major supplier to the supermarkets with operations in the UK and Spain.

He said the past week had been “incredibly challenging” and that supply difficulties could last for weeks.

This week farmers have struggled to access fields and organise deliveries amid heavy flooding that had left roads and some workers’ homes deluged. But the loss of newly planted seedlings means there is likely to be further shortages into January and February, just as Brits seek out salad for their new year health kick.

One wholesaler said some supermarkets were planning to fly in stock from the US and at least one supermarket confirmed it would do so.

“These have been among the worst downpours we have seen since these farms were established in the 1980s,” a spokeswoman for the British Leafy Salads Association told trade journal the Grocer. “The rainfall has been so intense that the ground is saturated and there is nowhere for the excess water to go.”

Andy Weir at Reynolds, which supplies national restaurant chains including Pizza Express and Carluccio’s, said: “We have managed to maintain availability as we buy from contracted growers and they have pulled out all the stops. There is a massive shortage in the market and if you don’t have a contract of supply you will struggle.”

He said difficulty in organising new planting to replace lost seedlings was likely to mean salad supply problems would emerge again in February and March when those crops should be harvested.

Some supermarkets including Sainsbury’s and Aldi had signs up warning shoppers they were experiencing salad shortages ahead of Christmas.

A spokesperson for Sainsbury’s said: “There has been limited supply of our iceberg and gem lettuce due to weather conditions in Spain but deliveries to stores are now taking place. We are doing all we can to ensure customers can buy the lettuce of their choice for Christmas and Boxing Day.”

Aldi said it was experiencing shortages in some areas, but Tesco and Morrisons said they had no serious shortages.