Managing a blueberry orchard
Planting
Prepare the site by spreading about 1t/ha of superphosphate copper zinc mix and cultivate in. Rip tree rows before planting. Good quality compost at 10 litres per hole can be applied and worked into the planting hole of young trees, especially trees which are to be grown organically.
The best time to plant is in the cooler months, especially April, May and September. Rows running north to south are preferred as they can take maximum advantage of the sun. Space rows 3–4m apart with 1.2–1.4m between plants for Rabbiteye varieties and 0.8–1.0m apart for Southern Highbush varieties.
Mulching around the young trees with coarse compost is beneficial to protect the blueberry's fine shallow root system, especially on sandy soils. Maintain this for at least the first two years after planting.
Fertilisers
Apply complete NPK fertiliser blends (containing 12–15% nitrogen, 2–5% phosphorus, 14–17% potassium, magnesium, calcium, sulphur and trace elements) at 60 grams per application per plant for young plants in early spring, and another in early summer. Increase the rates as plants grow.
Feed mature plants 150g each of the complete fertiliser in early spring, followed by a side dressing of 130g of ammonium sulphate and 100g of potassium sulphate at intervals of five or six weeks until the middle of summer.
Distribute the fertiliser evenly around the base of the plant, avoiding the stem and leaves and water in to avoid burning the plant. Ammonium sulphate and potassium sulphate can be applied through the irrigation system.
Use of fertigation through drip irrigation system is also an effective way to fertilise plants. Contact consultants on setting up such a system.
Examine leaves for deficiency symptoms during the spring–summer growth phase and conduct an annual leaf nutrient test for correct nutrient levels. Collect the first fully mature leaf (about five or six leaves from the tip) for analysis in January. Adequate levels of nitrogen and potassium in the leaves are 1.5–2.0% and 0.8–1.5% respectively.
Sodium and chloride levels higher than 0.2% and 0.5% respectively indicate toxic levels in the soil and/or water supplies.
Nitrogen is the most important nutrient, but do not over-fertilise, as this encourages vegetative growth and suppresses flowering and fruit set. Nitrogen deficiency is seen as yellow leaves and small fruit.
Potassium deficiency is less common and shows as a tip-burn on the leaves.
Magnesium deficiency can be seen as yellow areas between the green veins. If this appears, apply magnesium sulphate at 50–100kg/ha.
Boron deficiency is sometimes a problem and presents as yellow leaves, dieback and a deformity at the tip of the fruit. Borax at 18kg/ha can be applied to the soil to correct boron deficiency.
Zinc deficiency is seen as leaf distortion and blotchy yellowing. Zinc sulphate at 18kg/ha can be applied to the soil to correct this deficiency.
Irrigation
Blueberries have a shallow fibrous root system. While rainfall in winter should be sufficient, they will need supplementary irrigation during the warmer months using either trickle or micro-jet irrigation sprinklers. Minimise overhead wetting from sprinklers as this can cause ripe fruit to split.
Eastern Australian work suggests that high quality water with less than 300mg/L (0.46mS/cm) of total soluble salts is needed.
The demand for water is heaviest from September to early February during fruit set and fruit growth. Another critical period is from February to April for initiation of flowers for the following crop.
Maintain watering in the final two to three weeks of fruit growth to maximise berry size. Increase watering during heat waves, but avoid over-watering causing waterlogged conditions that can lead to root rot.
The amount of water needed varies with location but should replace about 100% of evaporation. Using tensiometers can assist in irrigation scheduling, resulting in more efficient water application and confining water to the top 30cm of soil mound, avoiding over-watering and leaching of fertilisers out of the root zone.
Tensiometers should be monitored before irrigation and then the next day to see if target tensions are reached. In loamy soils apply irrigation once tension reaches 20-30cbar.
Pruning
Little pruning is needed until cropping commences. Prune then to maintain vigorous wood growth to promote fruit production.
Fruit is borne on the previous year's growth. Remove flowers in the second spring to ensure good shoot growth. Prune plants during winter when they are dormant. Remove spindly older growth from young plants and encourage young, healthy shoots to form a vase-shaped bush.
Pests
Blueberries may need netting to reduce damage from birds, especially silver eyes. Light brown apple moth and looper caterpillars can damage the fruit and foliage, and may need to be controlled with registered sprays.
Grey mould (Botrytis spp.) can develop on ripe fruit during cool humid periods and can be controlled with registered fungicides.
Pollination
Most blueberry varieties are self-pollinating. However, cross-pollination with compatible varieties helps ensure good fruit set and berry size.
Blueberry flowers are pollinated by honey bees. Beehives at the rate of two hives per hectare will improve pollination.
Yields
A mature bush can produce 2–4 kilograms per plant per year. New South Wales reports indicate that yields from three year-old plants are up to 2.5t/ha. Mature plantings after five to seven years can yield between 7.5 and 12.5t/ha per year.