Since Maori, the indigenous people of New Zealand, named the country
Aotearoa (land of the long white cloud), the seasons have been of
paramount importance to New Zealanders, many of whom make their living
from the land. New Zealand has mild temperatures, moderately high
rainfall and high sunshine hours throughout most of the country. Its
climate is dominated by two main geographical features, the mountains
and the sea, and each season this creates a playground for adventure.
Spring is grape harvest season and the start of the year’s winemaking.
The many wine regions of New Zealand come alive with wine festivals,
orchard trees in bloom and the last of the skiers on the slopes.
Summer is the Christmas season in New Zealand and the traditional time
for family holidays, relaxing at baches (New Zealand holiday homes)
and playing outdoors.
Autumn explodes in a sea of greens, golds and reds. With settled
weather and cooler days, it’s the perfect time for experiencing New
Zealand’s many walking tracks.
Winter brings snow and winter sports to both the Central North Island
and the South Island, but sub-tropical Northland is still a playground
for sun seekers.
Spring - September, October, November
Summer - December, January, February
Autumn - March, April, May
Winter - June, July, August
Source: http://www.newzealand.com/travel/media/topic-index/four-seasons/four-seasons_home.cfm