Stats NZ’s update to 2025, released on 2 October 2026, tracks frost days, growing degree days and growing-season length at 30 climate sites across Aotearoa New Zealand. Over 1972–2025, growing degree days very likely increased at 28 of the 30 sites, with no site showing a very likely decrease. Among the 27 sites where frost was recorded, frost days very likely declined at 17 and very likely increased at two. These are long-run local trend classifications, not one nationwide measurement or a description of every year.

A frost day is one on which the recorded daily minimum air temperature falls below zero degrees Celsius. In the latest ten-year state period, 2016–2025, Tara Hills in Canterbury averaged 106 frost days a year, the most among the 30 sites. Auckland, Wellington, Whangārei and Whangaparāoa in Auckland recorded no frost days in that period. This comparison describes averages over the most recent decade, not the long-run trend calculation, and it does not imply that every farm or garden nearby experienced identical conditions.

Growing degree days summarise heat accumulation available for plant and insect development. The indicator adds the part of each day’s average temperature above a 10°C base threshold; a day below that threshold contributes zero. Stats NZ uses this base because it is associated with good pasture growth, particularly clover, and is relevant to dairy, beef and sheep farming. For 2016–2025, Whangaparāoa had the highest average annual total, 2,420 degree days, while Lake Tekapo had the lowest, 674. These values are not crop yields, pasture volumes or measures of water availability.

Growing-season length is calculated separately. Its start is the first day of the first five-day period when growing degree days remain consistently above zero; its end is the first day of the first five-day period in the following calendar year when they remain consistently at zero. From 1972 to 2025, the season very likely lengthened at 24 of the 30 sites, with no very likely decrease. A longer season does not automatically mean more farm output. Stats NZ notes that additional warmth may not translate into growth where other conditions, such as adequate moisture and nutrients, are missing. More warmth can also increase water and heat stress and extend pollen and pest seasons.

The statistics use station temperature records from Earth Sciences New Zealand’s National Climate Database. The 30 sites were chosen to represent local conditions around places where many people live, rather than every part of each region. Some records were extended with data from earlier stations nearby. Where daily observations were missing, data from the Virtual Climate Station Network were used to fill gaps. These choices help produce a longer consistent series, but do not make the 30 locations representative of every farm microclimate.

“Very likely” is a statistical category for confidence in a trend; it does not state the trend’s size or guarantee that it will continue. Year-to-year weather variability affects short-term readings, and Stats NZ says growing degree days respond to climate variability such as El Niño as well as longer-term climate change. The indicator does not identify the cause of any single frost event, forecast a particular crop’s yield, or prescribe planting dates for an individual farm. For farmers, the figures are background evidence to combine with local soil moisture, crop variety, elevation, in-season forecasts and field observations.