The humble tomato - a staple of many homes - is due to soar in price because of natural disasters wiping out crops across the Tasman.

Horticulture NZ is blaming floods and storms in Queensland for a looming shortage, with one retailer tipping prices to rise by as much as 30 per cent. Capsicum prices could also soar.

Fruit and vegetable prices have already risen 21.4 per cent in the year to May.

Peter Silcock, chief executive of Horticulture NZ, said: "There's usually quite a bit of product imported into New Zealand. At the moment these imports are not occurring because of shortages in Australia."

At this time of year Australian tomatoes usually make up 20 to 30 per cent of the fruit on shelves in New Zealand.

Poor weather has also affected the crops of New Zealand greenhouse growers - who have been growing less in recent years because of a reliance on Australian imports.

Since June 2006, Statistics NZ showed that the highest price for tomatoes was $9.32 a kg in August 2007. Capsicums were $13.67 a kg in August 2009. In May, prices stood at $10.60 a kg for capsicums and $6.30 a kg for tomatoes.

According to Grey Lynn produce retailer Earl Rigden, shoppers can expect to pay $15 to $20 a kg for red and green capsicums, with tomatoes rising to $10 a kg, or possibly more.

Vine-ripened tomatoes will cost about $15 a kg.