Plant of the month for May – blueberries


You know blueberries are good for you. They are full of antioxidants and other healthy phytonutrients. Do you also know that you can grow them in Hawaii? Probably not. Though the plants need special conditions to thrive and produce well, growing your own blueberries is possible in Kona.

The only blueberries to consider growing here are hybrids in the southern highbush group, known botanically as Vaccinium corymbosum. Several subtropical southern highbush cultivars have been developed in Florida and California with low-chill requirements that can thrive and produce without the lengthy winter chill that temperate climates provide.

Blueberry plants are attractive in addition to producing delicious and nutritious fruit. Their small green leaves and shrublike growth habit make them excellent choices for hedges or edging plants, depending on the variety. Some of the low-chill varieties can reach 6 feet tall and will spread to nearly 4 feet around. In addition to their attractive shape, the plants also produce small white or pink flowers in the spring followed by the colorful blue berries.

In 2007, the University of Hawaii partnered with the USDA in a study to assess the potential for blueberry production in Hawaii. The southern highbush blueberry cultivars tested were Biloxi, emerald, jewel, misty, sapphire and sharpblue. Though they all grew and produced, pest problems arose that eliminated the potential for commercial blueberry production in Hawaii. Backyard and small farm production, however, remains possible in the islands.

The testing helped define several requirements for growing blueberries here. Most members of the Eriaceae family of plants, including blueberries, are native to temperate climates and grow best in acid soil that drains well. Other family members include cranberries, huckleberries, azalea, rhododendron, several heaths and heathers as well as our native ohelo. All of these plants grow best in soil with an acid level between pH 4 and 5. This can be challenging at lower elevations in Hawaii where soils are more alkaline. Most members of the family also require a winter chill in order to produce flowers and fruit. Though new low-chill blueberry varieties are being developed, they will all do best when grown at elevations above 1,000 feet where nighttime temperatures drop below 60 degrees.

The UH study identified several problems growers might encounter. At first, the biggest problem appeared to be birds. It seems nearly every species of bird in Hawaii likes blueberries as much as we do. The test site installed netting tents to completely cover the bushes and protect the fruit. Several years into the study, a nasty pathogen arrived. The rust fungus, Naohidemyces vaccinii, caused damage to the leaves, limiting their ability to photosynthesize and reducing the plants’ productivity. Only a few fungicides are available in Hawaii to manage blueberry rust, and they have limited effectiveness and sometimes caused phytotoxicity issues.

In addition to needing acid soil, blueberry plants require full sun and about an inch of water per week. Care should be taken in watering, however, as overwatering can cause root rot. The plants will do best if fertilized regularly with a fertilizer for acid-loving plants. Gardens in West Hawaii do not necessarily have acid soil or plants that require this level of acidity or the same amount of water as blueberries. Wise growers will plant their bushes in large containers where the soil and water can be designed and controlled to meet the needs of their blueberry plants. Blueberries have a shallow root system and can adapt easily to being grown in containers.

Creating an acid soil that drains well will go a long way toward helping your blueberries thrive. Mulching blueberries heavily can help acidify the soil while holding moisture in the root zone. Remove the flowers from your plants during their first year, to encourage vegetative growth. When fully developed shrubs, they will produce more berries and the fruit will be larger.

Small plantings may not immediately attract birds, but you may want to plan ways to protect your bushes once they start to fruit. If you have a few plants, creating a frame and covering it with bird netting to the ground can keep the birds away.

Though it is difficult to control rust fungus, avoid monocropping or crowding your blueberries to help prevent an infestation. In very cool, wet, rainy areas, plant your blueberries under cover as a precaution against the fungus. Check any plants you buy for symptoms; do not buy plants if you see symptoms of disease. Read more about blueberry rust at ctahr.hawaii.edu/oc/freepubs/pdf/PD-51.pdf.

Pruning to maintain vigorous main stems and stimulate new shoot growth will help with blueberry production. It can also open up the plant to air flow that can help prevent diseases. Judicious pruning can prevent overbearing which can stress the plant. For large, flavorful fruit, maintain a balance between berry production and new shoot growth.

For increased blueberry production, plant several varieties to encourage cross pollination. Of the many low-chill cultivars, sunshine blue, star and emerald are readily available in Kona. Several local nurseries have these varieties in stock or can get them for you.

Sunshine blue is a semidwarf variety that determines at about 4 feet. It is a compact plant that yields large crops following a flush of showy pink flowers. With a chill requirement of only 150 hours and a tolerance for less acid soils, it is more tolerant of lower elevations than other varieties. It is also self-pollinating.

Star is characterized by its short, heavy harvest with as few as two pickings when young and only a slightly longer harvest season when mature. This variety seems somewhat resistant to rust, as well.

Emerald grows quickly and produces large fruit over a long harvest period. It can grow to 6 feet tall and just as wide. It needs nearly 250 chill hours and will produce best where nighttime temperatures drop to 55 degrees or below.

All blueberries are easily propagated from cuttings. Full instructions and videos are available online.

Recently, some cultivars have been patented and should not be propagated for large-scale production. Check on this when you buy your plants.

If you love the taste of blueberries, nothing is better than enjoying them right off the bush.

Though they are somewhat tricky to grow here, the joy of harvesting your own fresh berries may outweigh the challenges of growing your own in Kona.

Diana Duff is an organic farmer, plant adviser and consultant.