Viticulture is the science of growing grapes. In New Zealand, grapes are mainly grown for wine production. Some are also grown as table grapes.
For much of the 20th century, grape growing was confined to the warm northern half of the North Island. Although 19th-century settlers had managed to grow wine grapes in a number of regions, and an early viticultural expert identified suitable areas in the southern North Island and South Island, few grapes were grown south of Hawke’s Bay until the 1970s.
The government ran a viticultural research station at Te Kauwhata, in the Waikato, from 1901 until the 1980s.
As recently as the 1960s, government viticulturalists advised that the South Island was unsuitable for growing wine grapes. In the 1970s and 1980s, some people chose to ignore this advice. They planted the right grape varieties for their sites, and went on to produce award-winning wines.
Grape plants are woody climbing vines belonging to the genus Vitis. Their stems can reach 35 metres in length, but in cultivation are pruned back to 1–3 metres. They produce clinging tendrils that allow the growing stems to attach themselves to upright supports.
Each of the thousands of varieties of grape has a distinctive leaf, which is hand-sized, circular or oval, and usually lobed. The flowers are tiny, green and arranged in bunches. They are self-fertilising and wind-pollinated. The fruit is a spherical, pulpy berry containing two to three seeds, and is yellow-green, blue-black or reddish-purple when ripe.
Grapevines are deciduous. As the weather cools and the days shorten in autumn (March–May), their green leaves turn yellow and crimson, then drop off. The leafless stems, known as canes, then enter a period of dormancy over winter, which is the time for pruning.
When spring (September–November) arrives and average temperatures reach 10°C, buds swell then burst, and leafy shoots appear on the canes, followed by flower clusters. Shoots grow rapidly during summer, and fruit develops and starts to ripen. Fruit is harvested from late February for early-ripening varieties, through to mid-May for late-ripening grapes.
In the 2000s New Zealanders grew cultivars of Vitis vinifera, the European or wine grape, as did 19th-century settlers. But between 1900 and 1970, a North American grape, Vitis labrusca, and hybrids of American and European grapes dominated New Zealand’s vineyards. Chosen because they were resistant to phylloxera – the root aphid that infected some young vines in the late 1800s – they cropped well, but generally produced inferior wines.
Of more than 8,000 known grape cultivars, only about 50 are grown in New Zealand. In the 1970s and early 1980s, Müller-Thurgau and cabernet sauvignon were the leading varieties. This had changed by 2007, when sauvignon blanc was the most common type planted (10,491 hectares), followed by pinot noir (4,441 hectares), chardonnay (3,918 hectares), merlot (1,447 hectares) and pinot gris (1,146 hectares).
For decades Albany Surprise was the most widely grown table grape in New Zealand. Originating from Isabella, an American variety, it was selected and propagated by George Pannill at Albany, Auckland, around 1900. It is a prolific producer of large black berries with a sweet taste and tough skin.
The root-ruining phylloxera aphid was found in some Auckland vineyards in 1895. Growers were advised to destroy all vines harbouring the pest, and replant with grafted European varieties grown on phylloxera-resistant American rootstocks – a practice that had saved the vineyards of Europe.
For over a century many New Zealand growers followed different pathways, growing American or hybrid grapes if phylloxera was present in their region, or ungrafted European grapes in phylloxera-free districts. For a time these strategies paid off, and New Zealanders drank fortified wines made from the hybrid varieties such as Baco and Seibel.
Slowly but surely, phylloxera spread throughout New Zealand – as predicted by early 20th-century government viticulturist Romeo Bragato. By 2007 it was present in all wine-growing regions, and many growers had pulled up their ungrafted European vines and replanted with grafted stock. New Zealand grape growers continued to investigate which rootstocks best suited their sites, and best matched the grape varieties and wine styles they wanted to produce. Most of the rootstocks used in New Zealand are derived from three American species – Vitis riparia, V. berlandieri and V. rupestris, or their hybrid combinations.
Table grapes are grown in greenhouses in northern New Zealand for export. Around 20 tonnes are air-freighted to Japan each year, where they are mostly sold as gifts. The most common varieties are Muscat of Italia (a green grape) and Black Beauty.
Table grapes sold in New Zealand are imported from Chile, Australia or California.
Grapes have been grown successfully from New Zealand’s subtropical north (latitude 37°S) to the southern climes of Central Otago (latitude 45°S), where winters are harsh and summers hot. For wine production, grapevines need a cool period in winter, when the plants are dormant, and a warm period in summer and early autumn to ripen their fruit.
In most of New Zealand, spring and autumn frosts are always a possibility. Early autumn frosts can damage the grape crop just as it is ready for harvest, and late spring frosts can wipe out young shoots and flowers. In cool summers, grapes may not ripen properly, or fail to develop the sugar and flavour levels winemakers need.
Grape growers can limit frost damage by heating the air near their vines with diesel heaters, or spraying water over the plants. Helicopters or wind machines are used to mix warm upper air layers with the cool air at ground level. In spring and autumn, growers monitor the temperature each afternoon and request a helicopter to stand by if it looks as if a frost might develop.
Since 1970, grape producers have increasingly moved from warm, wet northern and western locations (around Auckland and the Waikato) to eastern and southern areas with hot, dry summers and autumns (Hawke’s Bay, Marlborough, Canterbury and Otago). The warm, humid summers of the western North Island encourage the growth of moulds that infect leaves and rot fruits.
Most eastern and southern vineyards require irrigation in summer.
Grapevines for quality wine production generally do best on freely draining, low-fertility soils. However, New Zealand vineyards are planted on many soil types – ranging from Northland’s heavy, water-retaining clay loams to the dry, stony silts of the Wairau Valley in Marlborough. In New Zealand, vines are grown on flat and gently sloping land at low altitudes – mostly with young soils of moderate to high fertility. This can lead to vigorous canopy growth at the expense of fruit production.
Good wine starts in the vineyard. It is the grape grower’s job to deliver a quality crop to the winemaker. The grower must match a grape variety to its site and manage its growth through the seasons.
Through trial and error, and bitter experience, New Zealand growers have learnt they need to plant healthy vines of a suitable variety for their site. Most now plant certified virus-free vines, grafted onto phylloxera-resistant rootstocks.
For years New Zealand growers could not be assured of the identity of grape varieties purchased from nurseries. Varieties look very similar, especially in the dormant stage, when cuttings are sold. Major suppliers now guarantee the identity of their material by DNA analysis or by having it checked by an internationally recognised expert (an ampelographer).
Growing vines need some form of support to hold them above the ground and to maximise sunlight on their leaves. In New Zealand, they are trained onto a wire trellis system attached to posts in the ground. There are various ways of arranging shoots and leaves, but most New Zealand growers use the vertical shoot positioning method. Trellis rows are usually oriented north–south so each side of the canopy gets similar amounts of sunshine.
The density of planting varies between vineyards. Rows may be spaced 1.5 to 2.5 metres apart, with plants 0.9 to 2 metres apart.
If grapes are not pruned each year, they develop many unproductive shoots and soon become a tangled mess of leaves and stems. At least 90% of the previous season’s growth is removed each winter. Vines are either spur pruned – where one or two branches are permanently trained along a trellis wire and the side branches are cut back to two or three buds – or cane pruned, where one or two new branches are selected each winter and trained along the wires, and the rest are removed.
The Silver Secateurs contest to find New Zealand’s best grape pruners is run each year alongside the Romeo Bragato viticultural conference. Competitors prune and tie four sauvignon blanc grapevines, and are judged on the quality and speed of their work.
As grapes ripen, their sugar levels increase and acid levels decrease. The fruit is ready for harvest when its sugar levels are 20–24%. The grower assesses ripeness by testing the juice on an instrument called a refractometer, checking if the seeds have turned brown, or seeing if a berry can be easily pulled from its cluster.
The largest vineyards mechanically harvest their grapes, with one machine doing the work of dozens of hand pickers. Small vineyards producing boutique table wines still hand pick their crop.
The main insect pest of grapes is phylloxera (Daktulosphaira vitifoliae), a tiny aphid that sucks sap from vine roots. Within a few years of infection, the vine declines in vigour, losing leaves and producing small crops. There are no economic ways to rid a region of phylloxera once it has arrived. It spreads from vineyard to vineyard on soil carried by the wind, people or machinery, or through contaminated plants. Although most vineyards are planted on phylloxera-resistant rootstocks, in 2007 a quarter of plantings in the Wairarapa and nearly 40% in Central Otago were of ungrafted vines, which are not resistant to the pest.
After phylloxera, mealybugs are the main insect problem in New Zealand’s vineyards. They too are sap-suckers, and decrease the vigour of vines. They also transmit leafroll viruses from vine to vine. Most growers use insecticide sprays to control mealybugs.
Starlings, blackbirds and silvereyes can ruin an entire grape crop over the two-month period from when the berries swell until harvest. Growers protect their crop with fine netting or use guns to frighten birds.
Rabbits can debark young vines, so growers enclose their stems in plastic sleeves.
The Falcons for Grapes project is an attempt to boost the numbers of the rare New Zealand falcon in the Marlborough region, while reducing damage to grapes from other birds. Fledgling falcons are hand-raised in artificial nests and fed daily. They fly around the vineyards, scaring away small birds and rodents, and catching some as supplementary food.
Powdery mildew first devastated Northland vineyards in the 1870s and has been a problem in New Zealand ever since. Unlike most fungal diseases, it flourishes in dry weather. It affects all green parts of a vine and begins as powdery blotches on the upper surface of leaves. Fungicides are sprayed to restrict its spread.
Downy mildew is another mould that affects all green parts of the vine. It appears in moist conditions and requires fungal sprays for its control.
Botrytis is a grey mould that is prevalent in warm, damp conditions, and rots bunches of grapes. Growers reduce the risk of botrytis by plucking leaves around the berries, allowing air to circulate. Very occasionally a condition known as noble rot develops in botrytis-infected grapes. The berries shrivel, then dry out and do not rot. They produce a sweet, full-flavoured wine.
A large number of viruses infect vines and can significantly affect crop yield and quality. They arrived in the country with infected propagating material before New Zealand was able to test for their presence. Much virus-infected grape stock was unwittingly distributed through the country by the government viticultural research station at Te Kauwhata.
Grape leafroll viruses are of the most concern. There are at least nine different associated viruses. One of them (GLRaV-3) is widespread in North Island vineyards and by 2004 was becoming common in Marlborough. The virus was transmitted to vines and rootstocks during grafting. In the vineyard it is spread by mealybugs. There is no treatment for infected vines – they must be removed.
Jackson, David. The wine drinker’s guide to the vineyard. Palmerston North: Dunmore, 2004.
Jackson, David, and Danny Schuster. The production of grapes & wine in cool climates. Rev. ed. Lincoln: Lincoln University Press, 1997.
Scott, Dick. Pioneers of New Zealand wine. Auckland: Reed/Southern Cross, 2002.