- Parent Category: Gardening Fact Sheets
- Category: Gardening Fact sheets 2012
- Created on Sunday, 27 May 2012 16:16
- Last Updated on Thursday, 12 July 2012 21:45
- Written by Howard
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Blueberry Care and Cultivation
Blueberries (Vaccinium corymbosum) require a very acid soil, (pH 4.5-5.5), which is well drained but moisture retentive. Where this cannot be provided they are best grown in 30-38cm (12-15in) diameter containers of ericaceous compost. Choose a sheltered site in full sun or part shade.
Bushes for containers can be planted at any time in good growing weather, but in the ground, plant after leaf fall (November to March). Prepare soil by digging in composted bark or sawdust. Then trim off tips of branches and remove any flower buds so the plant will establish strong roots in its first year. Space bushes 1.5m (5ft) apart, although compact cultivars can be planted closer. Mulch newly-planted blueberries with composted or chipped pine bark, or leafmould if available.
For container growing, buy a bush in a 2-litre pot and check the rootball in spring every couple of years (lift plant from its pot) to see if it needs repotting. A 50-litre pot may finally be needed.
Blueberries should be watered little and often using rainwater. Do not allow to dry out even if this means resorting to tap water in dry spells. Mulch open-grown plants with bark mulch or pine needles to conserve moisture.
After pruning, apply an acidic mulch of composted bark (or leafmould where available) and a dressing of fertiliser. Use 50g per sq m (1.5oz per sq yd) of Growmore, plus 15g per sq m (0.5oz per sq yd) sulphate of ammonia. Pelleted poultry manure is a suitable organic alternative (applied at 150g per sq m) but, as it is usually alkaline, also apply flowers of sulphur at the rate of 15g per sq m. Alternatively, apply a dressing of sulphate of ammonia, sulphate of potash and bonemeal, or apply a potash-rich or ericaceous liquid feed fortnightly during the growing season.
The largest fruit is borne on the thicker, more vigorous shoots produced the previous spring or early summer. Strong stems that appear in late summer may also bear fruit at the tips. Pruning is carried out in late February/early March when the fruit buds are visible.
Young plants need little pruning in the first three years. Aim to produce an open centred bush, by removing horizontally growing or overly long shoots, weak stems, as well as dead or diseased wood. Prune to an upright shoot or healthy bud where possible.
On mature plants remove older stems lacking in vigour. Remove thin, twiggy stems as well as any damaged or diseased shoots, crossing or horizontal shoots a or stems close to the ground b. Cut back some branches to the base c and others to strong upright shoots. Stems that fruited the previous year should be pruned to a low, strong-growing upward-facing bud or shoot. By the end of pruning an established bush, you should have cut out roughly 15 percent of the old growth.
Blueberries have two flushes of growth. In spring they bear flowers on the tips of the previous-season’s growth. These flowers become the first crop of berries. New sideshoots develop just below these berries. Later, (usually in July), strong new shoots grow from the base of the plant, and produce flower and fruit buds at their tips. This second, later crop of berries is usually plumper than the first.
Blueberries benefit from cross-pollination by other varieties, which results in better fruit set. Keep plants in a sheltered spot to encourage visits from pollinating insects.
Pick fruit in stages as it ripens, protecting from birds if necessary. Ripe fruit should part easily from the cluster and will be deep mauve with a grey bloom. Each bush can provide 2-5kg (4.5-11lb) of fruit.
Early highbush blueberries (ripening from July)
‘Bluetta’ Compact, moderately vigorous and slightly spreading; very hardy.
‘Duke’ AGM Sturdy, upright habit; 1.5m (5ft) high; yellow/orange autumn colour; mild flavour and good keeping qualities; very hardy; heavy cropping – branches may need support if heavily laden; blooms late although fruits early, so a good choice for areas with late frosts.
‘Spartan’ AGM Upright habit, particularly fussy about well-drained soil with plenty of organic matter; orange autumn colour and rich, tangy flavour; very hardy.
‘Patriot’ Open habit, fairly vigorous, large berries with excellent flavour; some tolerance of wetter soils; fairly hardy; fruit does not keep as well as some others; fruits in two main flushes; resistant to root rots; early to mid season.
‘Toro’ Stocky, compact, slow growing; attractive pinkish flowers and brilliant red autumn colour; bronzy young growth; large, full-flavoured berries in hanging clusters; tends to ripen quickly and have a concentrated period of harvest.
‘Hardyblue’ Upright, vigorous, high yielding; large bush; some tolerance of heavier soils; very hardy; yellow/orange autumn colour; red stems all winter; sweet flavour.
‘Bluecrop’ Vigorous, very open and erect habit; high yielding; good flavour but berries can be tart if picked too early (when still reddish); red autumn colour; very common cultivar grown worldwide.
‘Legacy’ Vigorous, upright and then spreading; better for mild southern areas; may be evergreen in warmer climates; bright orange autumn colour; high yielding; one of the best flavoured.
‘Chandler’ The largest fruits of all the cultivars; better in areas with mild winters, but doesn’t mind a long winter; vigorous, upright but well branched habit; 1.5m (5ft) high; mid-late season harvest.
‘Nelson’ Very hardy; vigorous, upright habit; large berries with good flavour; mid-late season.
‘Brigitta’ Upright, vigorous habit; 1.5m (5ft) high; easy to grow in all climates; large firm berries that keep exceptionally well for up to eight weeks in the fridge; no ability to be self-fertile.
‘Elliot’ The latest of all; best grown with other late season blueberries to ensure cross-pollination occurs; vigorous, upright habit; high yields of small to medium fruits.
‘NorthCountry’ Small fruits with authentic wild American blueberry taste; up to 40cm (16in) high and 1m (3ft) spread; some tolerance of less acid soils; tendency to sucker; excellent autumn colour.
‘Northsky’ Extremely hardy but also grows well in warmer climates; 30-40cm (12-16in) high and 60-90cm (2-3ft) spread; dense foliage and brilliant red autumn colour; profuse white blossom and small berries with a wild blueberry flavour; fairly reliably self fertile.
‘Northblue’ Larger fruits than many of the other half-highs; very hardy; 60-90cm (2-3ft) high; can over-crop, and blossom thinning may be necessary in the earlier years to prevent the bush producing fruit at the expense of formative growth.
‘Chippewa’ Fruit of a size and flavour more akin to the highbush varieties than to the wild American lowbush blueberry; up to 1m (3ft) high with a compact, spreading habit.
‘Misty’ Suitable for warm areas with hot summers and mild winters; usually evergreen; bright but glaucous foliage; shocking pink flowers; medium to large berries with excellent flavour.
‘Sunshine Blue’ Only for mild areas; may be evergreen; compact, up to 1m (3ft) in height; more tolerant of less acidic soils; brilliant pink flowers fading to white; heavy crops of tangy, medium sized berries over a long period; quite self fertile.
Lowbush blueberries (Vaccinium angustifolium and Vaccinium myrtilloides) are low-growing wild North American blueberries. They are very hardy, with a suckering habit, and have smaller fruits with a distinctive ‘wild’ blueberry taste.
Bilberries (Vaccinium myrtillus and Vaccinium caespitosum) are native to upland moors of the UK and Europe. Low-growing suckering shrubs, they are lower yielding than the cultivated blueberries, but their fruits have a distinctive, intense flavour.
Southern highbush blueberries are hybrids bred for areas with high summer temperatures and little winter chill. They are suitable for gardens in the southern half of the UK, and for sunny, dry south-facing positions, perhaps in a sheltered courtyard. Many are evergreen. They are more drought-tolerant than other blueberries, and also more reliably self-fertile.
Cranberries (Vaccinium macrocarpon) have a trailing or groundcover habit, and are evergreen, with autumn colour and dainty flowers. They have a suckering habit and thrive in boggy peat or sand soils with a high water table. But they can make good container and hanging basket plants, when watering is attended to assiduously.
Lingonberries (Vaccinium vitis-idaea) are speciality crops in Scandinavia and the USA. They are more drought-tolerant than cranberries, similarly suckering, and have a similar but slightly less astringent taste.
Cranberries and lingonberries ripen later than blueberries, being a mid and late autumn crop, rather than a late summer and early autumn crop.
In warm climates, cranberries may not develop their characteristic red colour. However, the taste is usually unaffected, and ‘white’ cranberries are a commercially exploited crop in warmer parts of the USA.
Blueberries, cranberries, bilberries and lingonberries all come under the Latin genus of Vaccinium.
North American highbush blueberries (cultivars of Vaccinium corymbosum) are mainly deciduous shrubs 1-2m (3-6 ft) in height. Grown mainly for their fruits, they also have ornamental value, with autumn colour, red winter stems, and small, pretty bell-like flowers in spring. Some cultivars are evergreen in mild areas.
Half-high blueberries are hybrids between Vaccinium corymbosum and Vaccinium angustifolium. They are good patio and container plants, reaching only 45cm-1m (18-38in) in height.
An open, sunny, frost-free, sheltered position is best. Partial sun may do if full sun cannot be provided.
An acid soil is essential (pH 4.5-5.5). Acid sand and peat soils are the natural habitat of wild Vaccinium species. Soils that support rhododendrons, heathers and camellias without effort are usually suitable for blueberries and related fruits.
Rich clays or loams are less suitable, and a chalky or alkaline soil is definitely unsuitable. Neutral soils can be suitably acidified with acidic mulches and fertilisers. On alkaline or heavy clay soils, it is best to grow blueberries in tubs of John Innes Ericaceous compost.
Blueberries and cranberries will not grow in waterlogged soil. Good drainage is essential.
Prepare the ground by digging in composted sawdust, composted pine bark. If none of these are available, you can use peat. Plant bushes after leaf fall (November - March). Tip back the branches and remove any flower buds before planting, so that the plant can concentrate on establishing its roots in the first year of growth. Addition of manure to the planting hole is not advisable. Mulch newly planted blueberries with composted sawdust, sand, leaf mould, chipped pine bark, or peat (if no alternative is available).
A 1.5m (5ft) spacing between plants is suitable for most blueberries, although some of the most compact cultivars can be planted at 1m (3ft) spacings. Container-grown plants usually establish better in the garden than bare-root plants. For pot growing, start with a plant in a 2-litre pot, and check the rootball every two years to see if it needs re-potting into the next size up of container. A 50-litre pot may be needed eventually.
Water blueberries with rainwater rather than with mains water. In dry spells, it may be necessary to supplement with mains water. Feeding with an ericaceous fertiliser, and mulching with acidic organic matter is necessary to counteract the alkalinity of mains water.
It is important to water little and often. Blueberries, and in particular cranberries, must not be allowed to dry out. Water the soil under the branches, and apply at the rate of 50-litres per sq m (11 gallons per sq yd), adjusted according to the area taken up by the bushes.
Feed after pruning with 50g per sq m of Growmore (or another balanced fertiliser having equal proportions of nitrogen, phosphorous and potassium), plus 15g per sq m of sulphate of ammonia.
Pelleted poultry manure is a suitable organic alternative (apply at 150g per sq m), but as it is usually alkaline, it should be applied with flowers of sulphur (at 15g per sq m) to counteract this alkalinity.
Mature bushes benefit from an additional 50g per sq m of sulphate of ammonia in June, if cropping is heavy or growth is weak. Alternatively, a liquid ericaceous plant fertiliser can be given fortnightly during the growing season.
Mulching with acidic organic matter in spring and autumn helps to keep the pH low, as well as to conserve moisture and keep down weeds. Suitable materials include composted sawdust, composted or freshly chipped pine bark, peat, leafmould and pine needle leaf mould. Avoid manure, mushroom compost, ordinary John Innes compost and wood ash, as these all contain lime and are alkaline in pH. Cranberries respond particularly well to mulching with sharp sand.
Blueberries fruit best on wood that is one to three years old, although older branches will also produce a little fruit. New plants therefore need no pruning for the first three years after planting. Subsequently, bushes are pruned to encourage vigour and to maintain an open centred shape.
Blueberries have two flushes of growth. In the spring they bear flowers on the tips of the previous season’s growth. These flowers become the first crop of berries. New sideshoots usually develop just below these first berries. Later in the season (usually July), strong new shoots grow up from the base of the plant, and develop flower and fruit buds at their tips. This second, later crop of buds and berries are usually plumper than the first, producing larger fruits. Production of this second crop of renewal growth and fruit is a sign that the blueberry plant is in good health.
Pruning is best carried out in February or early March, when the fruit buds are visible, but may be done at any time during the winter. Remove any crossing or horizontal shoots, any weak or twiggy stems and branches, any diseased or damaged growth, and any stems that are dragging on the ground. Remember to remove the twiggy growth at the ends of the branches that fruited last season, effectively tipping them back to a strong, upward-facing bud or branch. Then cut out one in six of the oldest stems from the base of the plant, removing the woodiest, thickest and most unproductive examples. From one sixth to one quarter of the total growth can be removed from the bush each year.
Hard pruning is recommended, as it tends to result in larger, earlier fruits, and to encourage earlier and more vigorous renewal growth.
After pruning, mulch the bushes with suitable acidic mulch from the list of choices above.
In Scotland and colder parts of Northern England, the second flush of renewal growth produced in the summer may fail to ripen. Dieback can occur, with hollow wood below the dead tips. In this case, the affected shoots should be cut back to sound wood, 15cm (6in) from the base.
Blueberries, cranberries and related berries flower in spring, usually from March to May.
Even blueberries that are partially self-fertile benefit from cross-pollination by other cultivars. Three cultivars are recommended for optimal pollination and yield.
Different cultivars flower at slightly different times, but sufficient overlap usually occurs for pollinations to be successful. Some very late season blueberries may not cross-pollinate an early flowering cultivar.
In very cold areas, the earliest flowers can be at risk of frost damage. A double layer of horticultural fleece thrown over the plant will usually provide sufficient extra protection if frost is forecast. Some of the early-fruiting cultivars actually flower quite late but then ripen quickly, so cultivar selection is important in frost-prone areas.
Blueberries should be picked in stages, as they ripen, from late summer to early autumn. Fruit in the same cluster may ripen at different times, and four or five pickings may be necessary over the course of the harvest. Each plant generally provides 2-5kg (4.5-11lb) of fruit.
Cranberries and lingonberries ripen later than blueberries, being a mid- and late autumn crop, rather than a late summer and early autumn crop.
Blueberries are picked by rolling the berries between the forefinger and thumb to remove them from their stalks. They should come off easily, and feel soft to the touch. Fruit generally turns blue and then develops a white surface bloom over a period of a few days. It is only then that they are ready for picking.
Blueberries have excellent keeping qualities, keeping fresh in the fridge for at least a week.
Birds are the main pests, and bushes will need the protection of a fruit cage, or nylon netting stretched over a wooden frame.
Weeds can be kept at bay with regular hoeing or by application of a contact weedkiller such as Weedol.
Botrytis (grey mould) can be a problem in damp and poorly ventilated sites. We recommend increasing plant spacing, pruning for openness, and improving ventilation.
Phytphothora fungi can affect the roots of Vaccinium plants grown in insufficiently drained soils.
Blueberries are usually trouble free in the UK. Vine weevil can be a serious pest of containerised plants, and winter and tortrix moth larvae can occasionally decimate leaves and young fruits.
Blueberries can be propagated from cuttings. Evergreen species tend to grow better from semi-ripe cuttings (taken in late June - early July). Deciduous species grow well either from semi-ripe or from softwood cuttings (taken in late spring). Select shoots that are 10-15cm (4-6in) long, and tear them off the main stem with a ‘heel’ of older wood attached at the base. Remove the lower leaves, and dip the base and heel in a hormone rooting powder or liquid. Insert the cuttings into a mix of 25% soil-free ericaceous compost, and 75% sharp sand. Place in a heated propagator with a bottom heat of 20°C, in a partially shaded position. Rooting should take about four weeks.