Environ. Horticulture, Pears, Cherries, and Viticulture
University of California
Environ. Horticulture, Pears, Cherries, and Viticulture

Delving Deeper into the Concept of Supplemental Chill

Supplemental chill, also known as cold conditioning, takes place after harvest of the transplants, which have gone dormant because of their exposure to the decreasing daylength and lower temperatures of the nursery fields of Northern California where they are grown. Postharvest supplemental chill occurs in a constant near freezing temperature, in the dark and when the transplant has no to very few leaves left on it.

What supplemental chill is actually doing is breaking (reversing) plant dormancy, which sets into motion a series of metabolic events in the plant resulting in a promotion of vegetative growth and inhibition of new inflorescence formation. Petioles grow longer, leaf blades get bigger and more runners are formed as dormancy is broken through supplemental chill. All of this is consistent with the industry understanding that a longer period of supplemental chill results in more plant vigor, again meaning more vegetative growth and less fruiting. The challenge for the berry grower is to strike a balance between the vigor of vegetative growth and the fruiting which is greatly desired.

Growers already know this, but berry cultivars vary greatly in their sensitivity to the dormancy breaking supplemental chill. Generally speaking, short day strawberry varieties need very little – something on the order of one to three days - to break dormancy and in fact most become tremendously vegetative when chilled in excess over the recommended few days.  In contrast, day neutral varieties need substantially more days of chill, most often in the range of one to two weeks, to develop the normal balance of vigor and fruiting following planting.  Since longer periods of chill are associated with greater vegetative vigor, organic growers tend to chill their plants longer before planting, in the range of 30% longer, so as to enable the plant to handle less hospitable soil environments.

Posted on Friday, November 17, 2017 at 2:59 PM


Thanks for this interesting post Mark. I always learn something good here. The last comment about organic growers using longer supplemental chilling got me thinking. At the USDA-ARS organic research program, we only plant strawberries every 4 years with lots of cover crops during the off years to try to build and maintain soil health or quality and make the soil hospitable to the strawberries. Thus far this has worked really well for us. I wonder if there are any simple and reliable measurements of the soil to help growers know in advance if their soil is one where the longer supplemental chilling is needed. I also wonder if longer suppl. chilling is needed on sandy than clay soils. Thanks for any thoughts on this.

Posted by Eric Brennan on November 18, 2017 at 5:48 AM

Hi Eric, this is actually a really good question. Generally speaking, local organic growers have tended towards lengthening their chill times to pump up plant vigor for a soil which is not as easy to grow in, but as you point out there are soils which, while not fumigated, are managed in a way (rotation, soil amendments, low pathogen and weed load), present a pretty darn good growing environment already.  
I'd say it's an open question, but easily tested. On a decently managed organic soil, I'd look to test three chill lengths, and depending on the variety, might want to look at one week, two weeks and three weeks of chill and test the plant response through measurements of vigor and production.  
If you are game we should look into it.

Posted by Mark Bolda on January 3, 2018 at 2:37 PM

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