A number of vegetables are produced year round in greenhouses. Greenhouse growing is a capital-intensive form of production (with high energy, fertiliser and labour inputs) with high yields. Most growers raise their crops hydroponically in soil-less media, planting into sawdust or pumice-filled bags or into rockwool blocks, and trickling nutrient solutions through the growing medium. In good conditions, greenhouse crops yield 10 to 20 times more each year than a similar outdoor crop.
In 2007, 600 commercial growers raised crops under cover. Their crops included tomatoes, capsicums, chillies, cucumbers, eggplants, lettuces, sprouted beans, witloof, and courgettes. Greenhouse vegetables had a retail value of about NZ$200 million, with exports making up a quarter of these earnings.
Capsicums are grown under cover for the export market, mainly for Japan and Australia. Export of greenhouse-grown capsicums was worth $34 million in 2007. The 11,500 tonne crop was raised by 128 growers in 55 hectares of covered land.
Tomato growers mainly raise their plants in greenhouses and are based in Auckland, Pukekohe, Northland, Waikato, Bay of Plenty, Nelson and Canterbury. In 2007 there were a couple of large tomato-growing enterprises of 20 hectares, but most were 1 to 5 hectares. Some 400 growers produced 42,000 tonnes of tomatoes with a retail value of over $100 million in 2007. Most tomatoes are sold on the domestic market. The small export market was worth $7.7 million in 2007.
Lettuce and salad greens
The salad-greens market expanded in the late 1990s as supermarkets installed refrigerated cabinets into fresh produce sections. By 2006 there were 315 growers of lettuce and mesclun mixes producing year-round supplies from 1,207 hectares of covered crop.