Blueberries

Site selection and preparation:

Blueberry plants require superior soil growing media with good drainage and internal aeration as well as good water holding capacity. Ideally, the soil should be sandy loam in texture with an organic percentage of 3% or more. Preferably sites where agricultural lime was not previously worked in which would have artificially raised the ph level and might be too high to economically lower the ph level to around 4.5 (KCl ph). Elemental sulphur can be used to lower the soil ph, but it takes time for the soil bacteria to break down and adjust the ph which can take 6 -12 months depending on the climate and soil conditions. Composted and untreated pine bark can be worked into the soil to lower the ph level and to add organic matter. Sphagnum peat moss can also be incorporated as this is a great natural product that will lower the soil ph level, helps with aeration and water retention.

Blueberry bushes prefer full sun but they can tolerate partial shade.

Blueberry roots are very shallow and require aeration. The roots are fine, fibrous and do not have root hairs and therefore do not compete well against weeds which must be eliminated before planting. Weed control should begin the year before planting with means of herbicides and/or cultivation. Avoid sites that are waterlogged, have poor drainage or have a permeable layer close to the surface. Raised beds, 15cm-30cm high can be used if the soil is marginally drained or if the water table is lower than 60cm.

Blueberry plants can also be container grown in pots or bags. We recommend using at least a 23L pot/grow-bag as the plants do get fairly large. A basic potting medium is a mixture of pine bark mulch or acid compost mixed in with about 20-30% Canadian peat moss. The plant can then be directly planted into this mixture. A bit (about 15%) of sandy soil can also be used if it has been tested to ensure that the ph level is less than 6.0.

For optimum control, growth and yields, we recommend using the best suitable growing medium for the specific production system and climate. Throughout the years we have tested various different growing mediums, pots and grow bags on a few thousand of our mother plants, so please feel free to consult us on various options as we can also advise and supply these items.

If planted directly into the ground, a hole with the size of 40cm x 40cm x 40cm can be made where the mixture, mentioned above, can be placed into. When transplanting the plant, make sure to plant it at the same depth to ensure that the crown is not covered or the roots exposed. If peat moss is used in the planting medium, make sure to first wet it well, otherwise it will act as a wick and draw the moisture from the plant roots.

Planting Blueberries

As mentioned in the site selection section, blueberry plants can easily be planted in containers, but a fairly large size would be needed in order for the plant to thrive and produce a good crop. If planted directly into the ground, a hole of 40cm x 40cm x 40cm can be made where the planting medium can be placed into. When transplanting the plant, make sure to plant it at the same depth to ensure that the crown is not covered or the roots exposed. Even adding a little bit of peat moss (about 5dm to 10dm) to the planting area close to the small plant, would greatly benefit its growth. Avoid placing too rich fertilizers such as manure or chemical fertilizers in the planting hole as they may burn the roots.

It is highly advisable to have the soil tested so that the required amendments can be made prior to planting, especially for the rectifications of the ratios between calcium, magnesium and potassium.

Spacing

Blueberry plants can be planted as close as 60cm apart which will form a thick hedge after a couple of years, but in general, most fields are planted using a plant spacing of 0.75m to 1.2m between plants with spacing between rows of 1.8m to 2.8m which would result in a plant density of 3000 to 6200 plants per hectare when planting directly into the soil. The distances between the rows will depend on which equipment will be used for cultivation, harvesting and pruning. With smaller-scale operations, hand harvesting is normally used where the row spacing’s are narrower. Most blueberry farmers plant about 5500 plants per Ha, but some who use 25L to 28L pots or grow-bags plant up to 7000 plants per Ha for optimum production using a spacing of 0.75cm x 1.9m to 2.2m (between the rows).

Mulching

A thick layer (10-15cm) of organic materials such as pine bark mulch, acid compost or sawdust can be used as a mulch as protection from extreme heat and cold temperatures. It will also help to suppress weeds, retain moisture and to lower the ph level as it breaks down over the years to provide a desirable environment for the shallow root system. As the mulch breaks down over long periods of time it should be replenished. Do not use bark or sawdust from redwood or cedar trees.

Plastic mulch, also known as Agri weave is a synthetic woven mulch that permits the air and water to the soil but prevents sunlight penetration which helps prevent weeds from germinating as well as to keep the root zone cooler saving costs on labour, herbicides, water and fertilizers.

Irrigation

The amount of water needed per plant or plantation would depend on the soil type, rainfall and climate conditions. Compared to other fruit crops blueberries do not need much water but care must be taken to keep the moisture consistent, but not overwatered. Younger, newly established plants require the most care to make sure that their roots do not dry out or get waterlogged. During the summer months, when the plant is growing and fruiting, 20mm to 30mm of water is needed per week. We found that in most climates, a water budget of at least 3L/plant per day is required. Irrigation is usually applied with drip irrigation, but micro-sprinklers and overhead irrigation can also be successfully used. Irrigation during late summer and early fall will stimulate fruit bud formation which would increase the yield of the following harvest.

For commercial berry operations, proper planning is required for optimum growth, quality and yields. Berries For Africa can advise on various qualified and reputable irrigation planners, suppliers and installers.

Fertilising your Blueberries

Blueberries are very sensitive to over fertilization and readily soluble fertilizers can cause plant injury and death if applied incorrectly. With these plants a “spoon feeding” approach must be taken where small amounts, more often provided, is best. Traditionally blueberries do not require as much fertilizer as other crops, but a well balanced fertilization program is necessary for optimum plant growth and crop production.

Start to fertilize in early spring and stop during mid-summer to avoid too much new shoot growth during late summer and early fall which may lead to winter injury on the tender new shoots especially if planted in the very cold areas in the country where heavy frost occurs.

Blueberry plants are salt and nitrate sensitive. Nitrates and chlorides should be avoided in fertilizer blends for blueberry plants. It is recommended to use fertilizers that provide nitrogen in the form of ammonia such as, Ammonium Sulphate (21%N), Mono Ammonium Phosphate (MAP) or Urea. Ammonium Sulphate generally works well as the plant would use the nitrogen in the ammonium form and would also react with the soil to assist in lowering the ph level during long periods of time. Only use 5g (1 teaspoon) Ammonium Sulphate every 3-4 weeks on small, one year old plants and water in well. Spread the fertilizer along the top of the roots and avoid fertilizing on the crown (stem) of the plant. If the soil ph is below 5.0, Urea nitrogen is preferred as it will not lower the soil ph over time. Potassium Sulphate or Mono-potassium Phosphate (MKP) are suitable sources or potassium. Alternatively, a very slow-release, coated fertilizer such as Osmocote Pro 8-9, Haifa Multicote 9 or Talborne Organics 3:1:5 can be used to provide a wide range of nutrients. Application rates of 15g for smaller plants and 50g on larger plants are common practice, but make sure that the specific label instructions are followed. Blood meal, cottonseed meal and soya meal are very good sources of organic fertilizers. Avoid using manures as they are normally too alkaline when decomposed, contains salts and rich in nitrate-nitrogen which can damage the plants.

For commercial operations we recommend to have the soil and water tested before adding any nutrients into the soil or water.

Pruning your Blueberries

No hard pruning is needed during the first 4 years of the plant, but the fine twiggy, low growing vegetative shoots that grow sideways and do not bear fruit, should be pruned out. Remove any dead wood leaving any bright coloured lateral branches. On older plants, some of the older branches must be pruned during winter or after harvest to promote new growth and assist with air circulation and light penetration. Leave 8-12 healthy, upright canes which are younger than 6 years old as they will produce the best quality fruit. New suckers will grow from the crown each year. To avoid crowding and to keep your bushes young, keep the two healthiest and strongest looking suckers and prune off others if there are more than two. Pruning is normally done after harvest with the Southern High Bush and during winter with the Northern High Bush and Rabbiteye varieties.

Pests and birds

In South Africa we are fortunate that not many natural pests and diseases are found on the blueberry plants and fruit. Blueberries are resilient to many of the common problems associated with other soft fruits.

Other than than minor pressures from insects such as bollworms, aphids, thrips, weevils, beetles, grasshoppers, locust and a few bird species, pests and diseases are not a serious problem. An integrated pest management programme can be incorporated for crop protection and there are many registered chemical and organic pesticides available in SA.  Birds can be a localized issue and bird netting can be used if desired if a great percentage of the fruit is eaten.
Bird deterrents such as bird tape or electronic systems such as the “Bird Guard” have been reported to work well in some areas especially where there are other natural birds of prey present in the area.