New blueberry rootstock appears to offer advantages

Nearly 20 years ago, research began in earnest to address the then-unthinkable prospect of commercially growing blueberries in the San Joaquin Valley. In just a few years, it was found to be a success, although often a costly endeavor.

New research in just the past two years could breathe new life into those endeavors and a plot of blueberries that still stands at the Kearney Agricultural Research and Extension Center in Parlier.

M. Isabel Hernandez, a doctoral candidate in plant sciences at the University of California, Davis, said grafting of blueberries could hold a key to competitiveness of both small and large California blueberry farms.

Hernandez spoke at a Small Farms Grafting Training Day at Kearney about the likely advantages of grafting blueberries onto a rootstock that grows wild, mostly on the East Coast: the Sparkleberry.

The Sparkleberry is not a commercial variety and is not available from nurseries, she said. But it has some decided advantages over the blueberry as a rootstock.

For one, it can tolerate soils with a higher pH level. That means there may be no need to inject acid into the soil, a step that Hernandez said is considered less than environmentally friendly and one that makes it very difficult to grow organic blueberries, particularly in the San Joaquin Valley, where soil pH is often at 6 or 7, whereas blueberries do best in soils that are 4.5 or 5.5 pH.

And acidification can be costly.

A second advantage of the Sparkleberry rootstock is that it sends roots deeper into the soil, as deep as one meter or so. By comparison, blueberry roots usually go no deeper than 30 centimeters.

"That is advantageous in a drought," Hernandez said. "It's good for water uptake."

Another advantage to the Sparkleberry is that it commonly has a single trunk, compared to blueberry plants that have multiple trunks.

"That's good for mechanical harvesting," Hernandez said.

And the harvesting season can be extended with use of the Sparkleberry rootstock, because it continues growth after harvest of the blueberries. Hernandez said that it would be necessary to manage fertilizer applications differently with the rootstock.

Because Sparkleberry plants are not available at nurseries, Hernandez said the best way to start them is to propagate plants from suckers of growing plants. She said growing from seeds is not advisable.

She said vegetative blueberry buds should be collected when dormant, and kept moist and in a refrigerator until March. She advises grafting four buds into the rootstock and keeping plants indoors for three months to protect against high heat and humidity.

"We experienced high mortality during a heat wave," Hernandez said.

She recommends wearing protective polyethylene gloves with the brand name "No Cry" when grafting, because tools are quite sharp and injuries can occur.

She said she prefers "whip and tongue" grafting and the use of parafilm and rubber bands to keep new buds in place. Buds should be taken from branches that are about the width of a pencil.

Research into grafting onto the Sparkleberry was conducted at Kearney and at UC Davis. The project was funded by a grant for $137,058 from the California Department of Food and Agriculture.

One of the pioneers in blueberry research at Kearney was Tulare County UC small farms advisor Manuel Jimenez, who retired in 2013. The UC Small Farm Program helped lead the way in introducing blueberry production to California farmers. Most early blueberry acreage planted in California was on smaller farms.

Jimenez and others with UC initiated blueberry observation trials at Kearney in 1997.

The results of those trials indicated that southern highbrush blueberry cultivars were well adapted to the valley. Several key, early season cultivars were identified as likely suited to the region. The highbrush blueberry cultivars require fewer chill hours to produce fruit.

The workshop at which Hernandez spoke was attended by many small farmers, many of them Asian. Michael Yang, UC Hmong agricultural assistant in Fresno County, translated talks from English to Hmong.

(Dennis Pollock is a reporter in Fresno. He may be contacted at agcompollock@yahoo.com.)