Keith Kridler Mt. Pleasant, Texas
Below is a link to our nearby agricultural research center chilling hours page. New Zealand should have similar research centers that have been tracking weather for many years.
http://etweather.tamu.edu/chill.htm
Interesting thing for our part of Texas is that back in the 1970’s they recommended peaches with only 650 to 800 chilling hours. In the 80’s they went to 700<850 hours. The last few years as you can see from the charts we are actually having longer colder winters and peach farmers are now planting a mix of varieties that will bud from 800<1000 hours of chilling. Peach trees in East Texas have a lifespan of less than 20 years so they routinely replace 5% of the trees annually and guess what the temperatures will be for the next 10 years or so when a variety will peak in production.
Notice for Texas we seldom get but a hand full of hours in October were the air temperature is below 45*F.
At the top of this page is also a chart that tracks the amount of rainfall per month for the last 15 years or so for this area. This is also a trigger for daffodils to sprout as they need some ground moisture for the roots to start forming.
Then you also have to consider quantity of clear sunny days as even on cold days the sun can warm up the soil to the depth where daffodil bulbs are planted. Mulch or height of grass covering the daffodil bulbs from year to year as compared to bare dirt will also greatly affect soil temperatures. We seldom get a snow cover but in some areas this is a big factor in soil temperatures.
Many countries and states are also tracking the egg laying and hatching of frog eggs due to water temperatures or the various species of insects hatching out of shallow water. VERY similar results as compared to what daffodils need to sprout and grow.
Normally for my area when blooms of Ice Follies are beginning to die down there are enough insects out and about that our native cavity nesting birds will already have eggs in our nestboxes. This is going to be a VERY early spring by up to three weeks bloom time but our ultimate chilling hours will be basically the same as last year or at the most one week less of temperatures <45*F. Sorry I did not convert all these to C* but it would be a good science project to over lay some of the basic rainfall and temperature factors with someone who has taken photos of the same daffodil plantings at their peak bloom times over the years. Again various bird groups track the “first egg” of the season for various species but these are often affected by various factors also that are hard to figure. KK