Blueberries are surging in global demand and Central Valley growers are getting in on the action. However, the unique conditions that make the region ideal for growing many crops can pose challenges for blueberry production.
Blueberries have a winter chill requirement. The primary type of blueberry grown in California is southern highbush, which is better adapted to the state’s warmer conditions. But even some southern highbush cultivars used in California require 400 – 550 hours below 45ºF for optimal budbreak and fruit production.
The months-long tule fog in the Central Valley this past winter helped ensure that the full number of chill hours was reached. “The fog acted . . . like an umbrella over the plant,” says Raymond Mireles, Fruit and Almond Advisor for UCCE Fresno and Tulare Counties.
However, fog alone does not guarantee that blueberry bushes will get enough chill — especially as winters continue to get warmer. Moreover, even if the weather is cold, a sunny day can still interfere with chill accumulation.
As Mireles explains, even if the air is cold around a bush on a sunny day, the plants — “just sitting out there in the sun — will start to accumulate heat portions and ultimately counteract . . . the accumulation of chill hours.”
Mireles recommends a few methods to ensure that blueberries get the full chill requirement:
Cover Crops
Laying down a cover crop can stabilize soil temperatures. It’s best to plant these when the bushes are dormant. Good cover crops to use with blueberries include:
· Legumes
· Grasses
· Barley
· Oats
· Mixed blends
It is important to remove these crops before they start seeding. If not, the seeds will sprout and compete with the blueberries for nutrients.
Years with Lower Chill
In the event of a winter with less chill accumulation, there are ways growers can compensate and help with budbreak:
· Use hydrogen cyanamide (such as Dormex) on blueberries when less-than-optimal chill is accumulated. This is best applied 30 – 40 days before bloom.
· Mulch with white plastic, woodchips or sawdust to keep temperatures down and help the bushes retain moisture.
· Apply shade cloth to keep the bushes cool.
· Irrigate consistently.
Kaolin clay can reflect sunlight and reduce surface temperature, but the effect it has on chill accumulation on blueberry is minimal, since chill is driven primarily by ambient air temperatures and will not be significantly affected by clay particles on the bare branches.
Soil Acidity
While the alkaline-rich soils of the Central Valley are excellent for growing, blueberries are another story. They require a more acidic soil (a pH of around 4-5.5 is ideal), so steps must be taken to lower the pH levels for blueberry orchards.
Application of sulfuric acid via irrigation is effective for rapidly reducing pH levels in soil. It is best to begin this process in mid to late March.
In Summary:
· Plant blueberry varieties with an appropriate number of chill hours for your area.
· Deepen the chill by laying down cover crops, but be sure to remove them before they go to seed.
· In the event of warmer weather preventing chill, use hydrogen cyanamide as a growth regulator.
· Apply mulch, shade cloth and regular irrigation to the crop.
· Apply sulfuric acid to rapidly lower pH to the desired level.
While blueberry cultivation in California poses unique challenges, it is proving to be an increasingly profitable crop, making it worth the time and effort.
— By Donald Promnitz, Editor
Leave a Reply