An Observation on Chill Hours Accumulated This Year and What to Make of Them

Oct 19, 2016

Since digging for strawberry plants destined for Salinas and Watsonville started at Macdoel just a few days ago, I thought it would be judicious to have a look at how many chill hours we've accumulated so far and what it means for additions to supplemental chill, especially for our day neutral varieties.

I checked with the Lassen Canyon nursery chill accumulator here: http://lassencanyonnursery.com/cumulative-chilling-hours-and-weather-conditions/ .

Looking at the data for Oct 18 of this year and running my calculations via the Utah model (which subtracts chill hours for temperatures realized above 60oF, see previous posts), we have currently accumulated 325 units of chill. Given that last year's chill accumulation was 164 units and by most commentator's opinion a decent accumulation, 325 accumulated chill units this year is very satisfactory.

So what does this mean for adjustments on supplemental chill? Personally, I think growers may want to take the strong field chill in stride, and now look forward to what sort of winter we are going to have. Looking at the NOAA data, we are probably in for a weak “La Niña” system this year, which according to the “Color Outlook Maps” for temperature, we have something like a 40% chance of having slightly warmer than normal temperatures in November, December and January.

http://www.cpc.ncep.noaa.gov/products/predictions/multi_season/13_seasonal_outlooks/color/churchill.php

The question then is what sort of adjustment should or needs to be made to supplemental chill. It's actually not an easy question to answer, given the strong field chill.  Then again the odds of a slightly warmer than normal winter would give me some reason to err on the side of caution and go a tad longer than customary on the supplemental chill .


By Mark Bolda
Author - County Director, Santa Cruz County and Farm Advisor, Strawberries & Caneberries