Fruit and Nut
History
The cultivated blueberry, sometimes called the highbush blueberry, is closely related to the wild European bilberry or blaeberry found in many of our upland areas. While the wild bilberry is a small plant with varying amounts of tiny intensely flavoured berries, the highbush blueberry grows on tall plants and produces heavy crops of blackcurrant sized (or often larger) berries.
The cultivated blueberry hasd been bred from selected plants of the wild highbush blueberry Vaccinium corymbosum of eastern North America. Some modern cultivars also have some Vaccinium angustifolium (N.American low bush blueberry) in their ancestry. V.corymbosum x angustifolium hybrids produce smaller more compact bushes of 0.7-1.4 metres, while pure V. corymbosum cultivars are more typically 1.6-2.2 metres . All cultivars are relatively long lived, and in good conditions will live for up to half a century.
The native peoples of North America have used the blueberry for thousands of years. They did not cultivate the plant but managed the healths where it grew wild by burning the vegetation every few years to kill off invasive plants and encourage new growth. The European immigrants to the New World soon discovered blueberries and saw them as a valuable wild food. By the late eighteenth century settlers were staking claims on blueberry picking grounds and by the early to mid-nineteenth century blueberries were being collected on a commercial scale. They were used to feed troops during the American Civil War.
The requirement of blueberries for acid ground was not understood for a long time, and as a result, early attempts at cultivation were not successful. Elizabeth White, the daughter of a successful cranberry grower, and Frederick Coville, a botansit working for the US Department of Agriculture, are credited with the pioneering of blueberry cultivation in the early years of the twentieth century. Working both together and seperately, they collected good specimens from the wild and instigated a large scale propagation programme involving thousands of plants.. The outcome was a number of distinct cultivars. One of these, Rubel (1912) is still in cultivation today. Other early cultivars still commonly planted include Jersey (1928) Coville (1936) and Dixy (1936).
In 1941 the cultivar Bluecrop, a [Jersey x Pioneer] x [Stanley x June] cross, was introduced. Its drought tolerance and ability to produce big crops year after year soon gave it a dominant position in commercial blueberry plantations, which persists to this day. However in recent years other cultivars have become popular. These incude Bluejay, Duke, Nelson, Spartan, Sunrise and Toro.
Cultivation
Blueberries require good drainage yet an adequate supply of water during the growing season, especially during fruit production. They do best in a dry acid soil of pH 4.5-5.0, though will tolerate higher pH if mulched with acidfying material such as peat, pine needles or pine bark. Peaty soils that are prone to waterlogging may be improved with the addition of copious amounts of sand, combined with deep drainage. Conversely, the water retention capability of excessively sandy soils may be enhanced by adding generous amounts of organic material derived from leaves, bark or pine needles.
Many growers make the mistake of planting blueberries in land formerly used for vegetables or other soft fruit such as currants or gooseberries. If these previous crops did well then this land is almost certain to be insufficiently acid for blueberries. Most vegetables do best in a neutral or slightly acid soil (pH 6.0-7.0) while currants prefer a pH of 5.5-6.0.
A better indicator would be heather, which prefers a pH of 4.5-5.5. Like blueberries, many heathers only succeed in well-drained ground.
Another mistake sometimes made by intending growers is to plant blueberries straight into cleared bog (peat). Although the pH might be right for blueberries, pure peat suffers from very poor drainage and in these conditions blueberries will certainly fail. However, former bog has the potential to be developed into very high quality blueberry land providing the issue of drainage is fully addressed. Sometimes, peatlands may be excessively acidic. The presence of wild cranberry (Vaccimium oxycoccus) or crowberry (Empetrium nigrum) may be indicative of very low pH.
When grown on a commercial scale, highbush blueberries are spaced at 0.9-1.5 m, with rows 2.4-3.0 m apart. Typical density is 2500 plants per hectare. Closer spacing will increase early yields, but set-up costs are higher. In some cases, closer planting may add to disease risk. Also, if the distance between rows is reduced below 2 m, it becomes difficult to get between the plants. On the other hand, high planting densities offers greater protection to wind and may be the best option on more exposed sites. Yields on mature bushes are in excess of 4 kg per annum, and sometimes as high as 8 kg.
Highbush x lowbush blueberry crosses (V.corymbosum x angustifolium) are spaced at 0.6-0.9 m, with rows usually at 1.8-2.4 m apart. The distance between rows could be reduced to as little as 1.5m, but access becomes more difficult.Yields are 1.5-3 kg per annum. The highbush x lowbush cultivars are more tolerant of difficult soils and wind exposure.
Blueberries are also very suited to pot culture, which can solve the problem of unsuitable soils. Bushes grown in pots should be gradually potted up into larger pots over about a ten year period, with the ultimate pot size being 70-110 litres. For mature pot-grown plants, yields of 0.5-2kg per annum are typical.
One of the best features of blueberries is that good yields are possible even in exceptionally poor summers. They just love summer rain. Once picked they have a fairly good shelf life - certainly far longer than most other soft fruit.
When establishing a blueberry plot, it is advisable to grow on small plants for one or two years in pots or in a lining-out bed. Like most varieties of fruit, bluberries do not tolerate weeds. Beds should always be kept weed free. Heavy mulches of wood chip, bark or pine needles (up to 100mm in mature beds) will be beneficial.
Cropping
Early varieties will begin cropping late July and continue for the month of August. Mid season varieties will crop from early August until mid September while late varieties will continue producing fruit until early October.
Nutrition
Blueberries compare quite well to most other fruit in terms of nutrition. 100g of blueberries contain the following:
Carbohydrates 15 percent
Protein <1 percent
Water 84 percent
Fats <0.5 percent
Calories 57
100g of fresh blueberries also contain 10mg Vitamin C, 20 µg Vitamin K, small amounts of vitamins A, B and E, and most minerals, notably manganese.
Further reading
Blueberries, Cranberries and Other Vacciniums, by Jennifer Trehane of Trehane Nurseries, Dorset, England (Royal Horticultural Society 2004)
The Highbush Blueberry and its Management, by Robert Gough (Food Products Press 1991). Excellent text that also covers highbush x lowbush crosses.