There are 18 soil groups and over 500 documented soil types
New Zealand, with its geologic youth, has dramatic and quite sudden changes in soil type. Even the oldest rocks at 600 million years old are only one fifth of the age of the world's oldest rocks and many of the most productive soils have been formed since the last glaciations period, a mere 10,000 years ago.
The United Nations of Soils
There are 18 soil groups and over 500 documented soil types in New Zealand covering both islands, ranging from raw volcanic and pumice soils, volcanic loams and clays, calcareous soils, recent alluvial soils, organic soils, stony terrace soils, gley soils, brown earths and podzols.
Fine wines are being made from vines with their roots embedded in the friable soils of Kumeu, the sandy loam soils of Gisborne and Hawke's Bay, the older gravel soils of Martinborough and Waipara, the young gravel soils of Hawke's Bay and Marlborough and the youthful sandy loam soils of Marlborough. In Nelson there are the old decomposed gravelly clay loam soils of Moutere, melanic limestone soils of Waipara and the semi-arid soils of Central Otago. And in small parts of Hawke's Bay, Marlborough, Waipara and Central Otago, the dry shallow soils of the lowland hills are home to some of the countries finest wines.
The wines of New Zealand reflect an almost unbelievable diversity of soil.
Vines are grown on a whole range of soils however the vast majority are grown on relatively flat terraces either on or above existing or ancient riverbeds. These terraces are where the soils of low fertility and excellent drainage exist, (two pre-requisites found in soils of leading vineyards the world over). People often find it puzzling, that in many parts of the world the best vineyards are found on elevated slopes, when in New Zealand they are found on the lower terraces. It is because of our geological youth. In other parts of the world erosion, over many millennia, washed the tops off mountains exposing gravelly soils for vines on the upper slopes. Gravelly soils near the rivers were covered with wash, making them no good for great wine. New Zealand has been eroding for such a short time that the hills still have their tops and the terraces still have naked gravels, exposed to the vigneron.
On these terraces the gravels have been deposited by the rivers for more than 10,000 years plus, and depending on the whim of these wandering rivers, there is often significant variation as to the type and amount of sediment the river deposited. At times volcanic, at others fine sediments of clay and silt from the hills, at other times small gravels, at others large boulders, depending on what phase of eruption, flood or glacier the country was in at the time.
And when the rivers retreated it was left to the wind (this is a windy country), to lay down its layers of loess - the type of loess depending on what type of soil the wind picked up - that might have been volcanic, ash or mica or quartz or sandstone. Add to this the very different regime of temperature and rainfall that these different soils have endured: the sub tropics of the north to the arid cold of the south, and you understand that the soils of New Zealand are not easily categorized.