Establishment and production in New Zealand

Blueberries are easy to grow in well prepared sites, require little care and are naturally resistant to many pests and diseases. There are a large number of varieties to choose from, giving growers the opportunity to harvest fruit from November to April. In New Zealand blueberries are mainly grown for fresh and processed export markets.

“Blueberries were number one in antioxidant activity when compared with 40 other fruit and vegetables.” - Tuffs University, Boston, USA.

Recent popularity of this berry due to health linkages has driven consumption to new levels. Market demand over the past few years has consistently exceeded supply.

Check soil suitability before planting

Soil requirements

Blueberries have very specific soil requirements. They have a shallow fibrous root system and will only thrive on moist, free draining acid soils with a high proportion of organic matter.

Well drained peat soils are ideal, but mineral soils such as sandy or silt loams are also suitable, provided peat moss or mulch is added during planting and on a regular basis afterwards. Heavy clay soils which crack in summer and become waterlogged in winter are generally not suitable for blueberries unless heavily amended with organic matter and sand.

Blueberries do best with a 20-30 cm mulch of bark, acid compost, sawdust or grass clippings over the roots to conserve moisture, prevent weeds and over time increase the soil organic matter.

Crop establishment

All perennial weeds must be eliminated before planting. This is vital for successful plant establishment. Blueberries are poor competitors in the first five years, and the use of residual herbicides on young plants is not generally recommended.

Ten year old "bluecrop" plant

Before planting a soil test should be completed. Soil pH is most critical, and should lie between 4.0 - 5.2. Suggested MAF soil test levels for the macro-elements are P, 15-25; K, 6-10: Mg, 10-12; and Ca<8. Soils with high calcium will require a lengthy spell prior to planting. Deep ploughing will help to deplete concentrations of Ca to a level that is suitable for healthy plant growth. Soil pH can be reduced with the addition of sulphur. Sulphur comes in various forms and will affect the soil and macro-elements in different ways. We advise all growers unsure of the form to use to employ the services of a qualified soil consultant.

Fertilisers

Blueberries are low fertility plants, requiring only light applications of nitrogen, phosphate, and potash in the first three or four years. Fertiliser application rates should be guided by plant performance and the need to replace nutrients removed by the crop.

Ammonium sulphate and diammonium phosphate are the best forms of nitrogen because the plants require an acid soil. However, these need to be applied carefully to avoid damaging roots.

Potassium sulphate is preferred to muriate of potash (KCl) to prevent possible plant injury from chloride.

Slow-release complete nutrient fertilisers, such as Osmocote‚ Plantosan‚ or Osmoform‚ 19:2.2:11 can be used at the beginning of the growing season as an easy alternative to mixing individual compounds, but are more expensive. We recommend slow release fertilisers to new growers unfamiliar with the blueberry.

Irrigation of young plants is essential

Irrigation

In selecting a site it is essential that adequate water is available for irrigation during the growing season. Irrigation is vital for the full development of berries which swell rapidly in the last two weeks of ripening. Lack of water results in undersized, dark berries and a poor crop. Water is most economically applied by trickle irrigation. A trickle line on both sides of the plant may be needed to ensure uniform wetting of the root zone, but avoid over-watering. Young plants in particular are sensitive to drought stress and water-logging. On deep peat soils blueberries can be grown without irrigation, but plant losses and low yields are common.

A good organic mulch (see section on Soil requirements) will assist in reducing water stress.

Bird protection

Birds can cause serious damage to fruit, and on small plantations netting is advised. Even on larger properties, where netting the entire crop is often regarded as not practical, the crop losses are becoming severe to the point that many growers are now netting minimally, eg, draping nets over individual rows, similar to that used by grape growers. Over the past five years certain bird species have developed a taste for the dormant fruiting buds during winter leading to extremely severe crop losses.

Pests and diseases

Blueberry plants are naturally resistant to many common pests and diseases. Phytophthora root rot is the most serious disease and can be a major problem on waterlogged soils. Leaf-rollers, blackvine weevil, scale, and root chewing pests such as grass grub larvae may also occur and need to be controlled.

Pruning

Young plants may require a light pruning at planting to help develop an optimum shape and overcome transplant shock. After this the only pruning recommended is to remove the fruit buds in the first two years to maximise the vegetative plant growth. Fruit is borne on last season’s wood, and vigorous wood bears the largest fruit. Pruning consists of removal of dead or diseased wood, weak growth, and old twiggy branches after fruiting. After four-five years some of the oldest branches may need cutting back to encourage vigorous new growth. Most growers aim to prune about 25-33 percent of the fruiting canopy annually, resulting in most of the plant being turned over every three-four years.

Varieties

Blueberries are classified into three major commercial types; the Highbush blueberry, Vaccinium corymbosum, is the most common, the Rabbiteye blueberry, V. ashei and Lowbush blueberry, V, angustifolium and V. myrtilloides. They differ mainly by way of their stature, deciduous or evergreen habit, winter chilling requirement and fruiting season; thus it is important for growers to select species that are suited to their particular climate.

Cluster of "nui" berries

In New Zealand most blueberry production is based on Northern Highbush and Rabbiteye varieties. Northern Highbush require a moderate to high (at least 700 hours) amount of winter chilling, while Rabbiteye varieties require a moderate amount of chilling (400-500 hours). Recently, low chill (200-400 hours) Southern highbush varieties from Florida and North Carolina have been imported and are now available for commercial testing. These varieties, and also the Rabbiteye blueberries, can be grown in warmer climates. Some of the variety releases from the HortResearch Ruakura breeding programme are also moderate to lower chill requiring.

Rabbiteye production in New Zealand has expanded in recent years, largely because of the ability of this species to crop late in the season (February-early April). Rabbiteye blueberries can be grown in most localities, but require temperatures of 20-25ºC in late summer to fully ripen the berries.

Yield

Fruiting of young plants is discouraged for the first two years to allow plants to grow freely and reach desired shape and cane density for cropping. Rabbiteye varieties can be cropped in their second or third season, a year ahead of highbush which are slower to establish. A healthy highbush should produce between 500-1000gms of berries in its third growing season. This should increase by 50-100 percent each year to reach typical yields of 3-4kg/plant by year five. At maturity a well managed plant can yield around 8-10kg of berries.

A well-managed small block

Plant spacing

Planting patterns differ for highbush and rabbiteye, largely reflecting pollination requirement, plant growth habit and vigour.

About 80 percent of the flowers need to be pollinated successfully to produce economic crops. Rabbiteyes should be spaced up to 2m apart within rows as they are more vigorous and a planting design that favours cross pollination is required. Usually this means that instead of planting solid blocks of rabbiteyes rows of pollinating varieties need to be interspersed in a pattern that maximises pollination yet is manageable from a harvest perspective. Most highbush are self-fruitful and can successfully be planted in large blocks but these also benefit from cross pollination by producing larger and earlier berries. Distances between rows are normally 2.6-3.5m apart depending on variety and equipment to be used. Final plant density should be between 2500 - 3500 plants per hectare.

Economics

For economic analysis consult your horticultural adviser.

Plant availability

Most plants that are currently available from blueberry nurseries* have been propagated from softwood cuttings and are sold either as rooted cuttings in 5cm tubes or as a grade suitable for planting out in a well managed field. Tubed plants should be grown on for a minimum of one year in pots or in a field nursery before planting out. After 1-2 seasons growth plants are usually robust enough to be set into the field. Planting normally takes place in autumn or early spring when roots are actively growing.

More Information

• www.blueberriesnz.co.nz
• www.hortnz.co.nz
• Bramble Production - Perry C Crondall, PhD