Extended Season Fresh Market Blueberry Production

A New Alternative Crop for California

Mark Gaskell, Ph.D.
Farm Advisor
UC Cooperative Extension
San Luis Obispo and Santa Barbara Counties

Early or late-season fresh market blueberries are a promising new crop alternative for California growers. Trials underway in San Luis Obispo and Ventura counties since 1995 are revealing the potential to harvest blueberries beginning in March and extending into July in some coastal growing areas. It is also possible to harvest in the period between September and December if the plants are pruned appropriately. Trials are on-going to determine the optimum pruning time for late season production.

I have discussed the potential for fresh market blueberry (and other small fruit) production in my Blueberry Field Day 1998 Report and previous Central Coast Highlights newsletters (Feb. 2000; Oct. 1996; Mar 1996). One of the most important aspects of growing these crops in this area is related to the potential for off-season fruit harvest. It is possible to manage the crop(s) using a combination of varieties and pruning practices to extend the harvests.

The low-chill, Southern highbush group of blueberries are the varieties that offer the most promise for extended season production on the central California coast. Some of these varieties require little or no chilling to break dormancy and stay green year around if temperatures are mild. Flowering and fruiting is a function of pruning and other cultural practices and temperature during the fruiting period. Even though the plants flower and fruit throughout the late fall and winter months, often there is not adequate heat to ripen the fruit normally. However, I have observed blueberry fruiting and ripening into the late fall (November) and depending on the area, early spring production is also possible. Additional special cultural practices related to soil management are also important for successful blueberry production.

Some initial data is now available illustrating the production potential for several southern highbush blueberry varieties. This trial was established initially because of uncertainty over which of this group of low-chill blueberry varieties offers the greatest potential for production in mild coastal growing areas. I am also interested in the production cycles of these varieties and how different varieties might fit into a production program in different growing areas.

These plants were established in coastal San Luis Obispo County in mid 1997 from 18 month-old plants. Flowers and fruit were stripped from the plants until the 1999 season when a light harvest was taken. The data summarized below is from March through June, 2000.

Production Data

The production data for six Southern highbush type blueberry varieties is summarized in Figure 1, Figure 2, and Figure 3. The varieties harvested thus far, include Sharpblue, Georgia Gem, Marimba, Misty, Gulf Coast, and Cape Fear. Sharpblue is a widely grown, early-season variety and Sharpblue started producing earliest in this trial. The surprise however, is that Sharpblue maintained a production edge over the other varieties throughout the harvest season (Fig. 1 and Fig. 2). The Sharpblue produced highest per plant marketable yields (Fig. 1) and highest number of marketable fruit per plant (Fig. 2) over most of the harvest season. Mean fruit size was highest with Sharpblue early in the season but fell off mid-way through the season (Fig. 3).

Other varieties such as Marimba, Georgia Gem, and Gulf Coast also have shown good overall plant vigor and were productive in this initial harvest. Gulf Coast has been reported to have problems on picking because the fruit does not break free from the stem easily and the stem may stay with the fruit. This was true in this trial and may increase harvest costs for some market situations. And this clearly, trait may limit the suitability of Gulf Coast in commercial fields. Misty can be quite variable in overall plant vigor and this is reflected in MistyÕs relatively low yields in this trial. Reports from the University of Florida indicate that Misty has a tendency to over-produce flowers and fruit on young plants and vegetative development is restricted if plants are not pruned aggressively.

Another marked advantage of mild, coastal growing conditions is the relatively long harvest period which in this trial lasted up to 12-14 weeks. Warmer production areas typically produce berries over a shorter harvest season lasting 3-6 weeks. The total cumulative yield of Sharpblue during the harvest period exceeded 6.5 lb per plant (Table 1) and yields should continue to increase over the next 4-6 harvest seasons. Newer varieties have been bred with reportedly improved fruit quality characteristics over that of Sharpblue. To date we have limited data available showing production potential of different blueberry varieties under coastal California growing conditions. Sharpblue fruit is attractive and flavorful and readily accepted in the marketplace. Sharpblue is widely adapted and vigorous and should be one of the key varieties to be included in new plantings until information is available which clearly shows advantages for the newer varieties.

Cultivation

Successful blueberry cultivation in many parts of California requires special soil and land preparation. Blueberries grow best in an acid soil environment (below pH 5) and many California soils range from pH 6.5 to 7.5. The soil pH should be amended with applications of peat in the initial planting hole and elemental sulfur or other forms of sulfur in the surrounding soil. The amount of sulfur to apply will vary with pH and soil type. The pH change in heavier textured soils is slower than sandy soils and it is important to anticipate the needs of newly established plants when preparing the soil. A rapid reaction results from application of sulfuric acid or urea sulfuric acid materials. Finely ground soil sulfur materials are also effective.

Blueberries have very superficial root systems and are intolerant of drought or poorly drained soils. For best results, establish the planting on raised beds, incorporating finely ground wood waste. The wood waste may be incorporated with fertilizer and sulfur prior to planting. A surface mulch of wood chips should then be applied around the newly established plants to retain moisture and control weeds. Subsequent annual applications of mulch is advisable and additional smaller amounts of sulfur may also be required.

New plantings of blueberries should be kept from producing flowers or fruit for the first three years to allow the plants to develop an adequate plant structure. These trials are only in the fourth year and blueberries remain productive for 15 to 30 years. Much remains to be learned about optimum management of blueberries in these new growing conditions.

Fresh market blueberries are popular and can be a profitable crop during much of the year. One of the most promising aspects of blueberry production in mild coastal areas of California is the prospect of producing fruit for off-season harvest. Traditionally, blueberries for U.S. markets are supplied by offshore production from late September until May. Careful management of cultural practices will enable California growers to expand this promising new crop into new production areas and new market windows.

Evaluation of Southern Highbush Blueberries
for Early Season Production in Two Geographical Areas of California

I collaborated with Manuel Jimenez, farm advisor, UC Cooperative Extension, Tulare County, on a research project in which we evaluated six southern highbush blueberry cultivars in plantings on the Central Coast (CC) and in the San Joaquin Valley (SJV) during 2000.

The CC and SJV sites are at similar latitudes, but the CC site has moderate winter and summer temperatures and the SJV site has colder winter and warmer summer temperatures than the CC site. Four-year old plants of the cultivars Georgia Gem, Marimba, Gulf Coast, Misty, Sharpblue, and Cape Fear were harvested and total fruit weight (TFW) and average fruit weight (AFW) were recorded weekly from each growing area. Production began April 6, 2000, and continued to July 19, 2000, at the CC location. Production began May 6, 2000, and continued until June 13, 2000, at the SJV site. Sharpblue was the earliest producing cultivar at the CC site and one of three cultivars producing on May 6 at SJV. Both Misty and Marimba were early cultivars at both sites. Sharpblue produced highest total yields at both sites, followed by Gulf Coast, Marimba, and Georgia Gem at the CC site. At the SJV site, highest producing cultivars after Sharpblue were Misty and Cape Fear. Sharpblue produced an average of 2357 g per plant at SJV and 3015 g per plant at CC. Misty produced markedly smaller berries than the other cultivars at CC but was third largest, following Marimba and Cape Fear, at SJV.

For more information, contact Mark Gaskell, farm advisor, UC Cooperative Extension, 624 West Foster Rd., Santa Maria, CA 93455; (805) 934-6240; e-mail mlgaskell@ucdavis.edu.