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Chilling Requirements in California Strawberries
Cold conditioning, or chill requirement, is an essential part of growing and producing strawberries in California. The chilling requirement is defined as being the cumulative period, usually measured in number of hours below a certain temperature, which is needed to produce the internal changes in the strawberry plant that result in the normal sequence of growth following winter dormancy. In strawberries, hours accumulated of temperatures between 28 and 45 degrees Fahrenheit are considered to be effective and are counted as towards chill requirement.
Chill requirement in strawberry is made up of two essential parts. One part is what the plant accumulates in the field before being harvested, and the other is accumulation of chill after harvest and the plant is in storage. There is a difference between the two. In-field chill takes place when the plant is still in the soil, out in the open and still has all its leaves. Supplemental chill takes place after harvest of the plant and occurs in a constant near freezing temperature, in the dark and the plant has none to very few leaves left.
Since the grower has little control over the accumulation of chill in the field, he or she should focus on the management of supplemental chill. Generally, growers should know that a high degree of supplemental chill in strawberry results in more vigor, meaning more vegetative growth, and less fruiting. A lack of supplemental chill will result in a plant which is less vigorous and with more tendency to fruit.
The catch is that growers need to strive to strike a balance between vigor and vegetative growth and fruiting. Too little vigor will result in a plant of reduced fitness which does not have a capacity to bear a great number of fruit, whereas a plant with large amounts of vegetative growth will have its fruiting ability compromised, since it is dedicating too many resources in the production of leaves, crowns and runners.
Additionally, accumulation of chill in the strawberry transplant makes it stronger and better able to survive the stress of harvest and subsequent transplant. Harvest of transplants means their leaves are cut off, they are ripped from the ground, tumbled in a drum and exposed to drying out in the open air. So, while in theory it is possible to grow good productive plants from transplants that are short of the recommended chill requirement, in practice, namely a commercial operation, plants lacking in supplemental chill requirement will not do well and some will probably not survive transplanting.
For University of California strawberry varieties, it is imperative that growers follow storage chill recommendations. These recommendations are based on years of research and should not be taken lightly.
Below are listed the storage chill recommendations for several popular UC varieties.
|
Variety
|
Type
|
Supplemental chilling
|
|
Albion
|
Day neutral
|
10-18 days
|
|
Aromas
|
Day neutral
|
10-21 days
|
|
Camarosa
|
Short day
|
0-7 days
|
|
Chandler
|
Short day
|
< 7 days
|
|
Diamante
|
Day neutral
|
10-21 days
|
|
San Andreas
|
Day neutral
|
10-18 days
|
|
Portola
|
Day neutral
|
10-18 days
|
From UC publication 3351 “Integrated Pest Management in Strawberries”
Finally, growers should know that to a small extent, plant vigor stemming from an excess or lack of supplemental chill requirement can be controlled by early season flower management. Removing flowers early in the season, such as in January on the Central Coast, allows the plant to continue to develop vegetatively, and would make up for a small deficiency in chill. Removing flowers later or not removing them at all slows the plant vegetative growth and would put the brakes on, so to speak, on a plant with an excess of chill requirement.
Comments:
2.
Mahmoud- Please contact me directly by my email. Look it up on the ucanr website for Mark Bolda. I can get you the information directly in this manner.
Mark
3.
Hi my name is Aldo Juarez and i work at Growers Transplanting, Inc in Salinas, Ca. This year we are going to experiment with greenhouse grown strawberries. We are new to this commodity especially in greenhouse grown transplants. Our plan is to transplant in late August or early September to hit the November Market and on. How wouold chilling hours work with us and what would be the best way to achieve those chilling hours in central California since thats our warmest time of the year.
4.
Hi Aldo,
If you are going to transplant in August, that means you will have access to frigo plants (plants which have been frozen in the cooler since January). These plants should be extraordinarily vigorous and I would expect that you would not have difficulty getting fruit by November. I would make the suggestion that you experiment with a mix of varieties, and definitely try a mix of short day plants and day neutrals. The day neutrals might not be the first to produce, but may be producing for longer than the short days. Please let me know if you need more information, I think the area of greenhouse production of strawberries in this area is pretty interesting.
5.
hi pleas more information of gaviota and camarosa Chilling Requirements( hours) in hydroponics culture in greenhouse and can you guide me in hydroponics Nutrition formula for strawberry .
6.
Hello Mark,
Interesting stuff...I live in Panama. Although this is rain forest summers are very dry with little rain and water gets scarce. The soil is also poor requiring expensive amendments to grow most plants.
A little while ago I set up an aeroponic system meant to grow green crops (lettuces) tomatoes, beans etc. I quickly found out that I had to chill my water tanks to get good results with the greens. We are getting amazing results so far and I have been trying to gather info on growing strawberries aeroponically.
My question to you is do you think that proper chilling could be achieved by chilling the roots i.e. using chilled water to spray the roots or do you think the whole plant needs be chilled?
Your thoughts would be much appreciated.
Thanks
Eric
7.
Eric, my first thought would be the whole plant needs to be chilled, since that is how it goes dormant. The roots would not be enough - then again I've never done that before and couldn't tell you for sure.
8.
Hello my name is Bernardo Sánchez and I live in Malaga, Spain.
Sorry for my inglis.
How many days need artificial chilling in box with plastic bag for the plug plant strawberry have 0 hours natural chilling. Albión, Portola and San Andreas.
Thanks.
Bernardo.
Thans
9.
Hello my mane is Bernardo and I live in malaga, spain.
Is posible the total acumulated of chilling hours in plug plant strawberry with artificial chilling in box with bag plastic before planting neutral day strawberry.
Thanks.
Bernardo.
10.
Can a home gardener grow Albions for several years from the same plants, or should they be dug up and refrigerated for 10-18 days in the winter? The location is Orange County, Ca.
11.
Hi Linda,
I would not recommend growing Albions for several years running and digging them in the winter. Remember that you are accumulating problems in the plants over time, as well as the plant losing vigor as it ages. Best to replace the plants with new ones - you may want to check with your nursery though to see what kind of cold conditioning they got prior to being sold.
Posted by Mahmoud Daib on March 10, 2011 at 3:14 AM