Blueberry
Blueberry
Blueberry
Blueberry
Blueberry plants: suitable soil matters more than winter cold
Blueberries grown for their large fruit belong mainly to the genus Vaccinium and descend primarily from North American species. They should not be confused with the European bilberry, Vaccinium myrtillus, a low woodland plant whose smaller fruit has deeply coloured flesh and different cultivation requirements.
Northern highbush blueberries and several compact hybrids are sufficiently winter hardy for most cool temperate regions of Europe and can ripen their fruit reliably where they receive enough light.
The principal cause of failure is usually not winter cold. It is unsuitable soil, an excessively high pH, hard irrigation water, poor drainage or the drying out of the plant’s shallow and delicate root system.
A blueberry planted in unsuitable ground may remain alive for several years while becoming yellow, producing little new growth and carrying almost no fruit.
Preparing a broad and permanently suitable root zone is therefore much more effective than placing one bag of ericaceous compost into a small planting hole surrounded by calcareous soil.
The principal types of cultivated blueberry
Northern highbush blueberries
Northern highbush cultivars, derived mainly from Vaccinium corymbosum, form upright shrubs generally reaching approximately 1.5 to 2 metres.
This group contains most of the large-fruited varieties grown in cool temperate regions.
Cultivars differ in ripening season, vigour, fruit size, firmness, flavour, crop regularity and winter hardiness.
Northern highbush blueberries are usually the most suitable choice for gardens across northern, western and central Europe where the soil can be maintained at the required acidity.
Half-high and compact blueberries
Half-high blueberries were developed by crossing taller highbush plants with low-growing and exceptionally hardy species, particularly Vaccinium angustifolium.
They often remain between approximately 50 centimetres and 1.2 metres in height.
Their compact habit makes them easier to grow in large containers, cover with netting and harvest.
The fruit may be smaller than that of the largest highbush cultivars, but some selections possess an intense flavour closer to that of wild blueberries.
Lowbush blueberries
Low forms derived from Vaccinium angustifolium spread gradually through underground rhizomes and can form a fruiting ground cover.
They generally produce small but highly aromatic berries.
They are well suited to naturalistic acidic gardens, but harvesting is slower than from an upright cultivar carrying large berries at a convenient height.
Southern highbush blueberries
Southern highbush cultivars were developed for climates with milder winters and longer growing seasons.
They generally require fewer winter chilling hours and may begin growing or flowering too early in colder continental or northern regions.
Some cultivars lack sufficient winter hardiness, while others survive the winter but flower during damaging spring frosts.
Rabbiteye blueberries
Rabbiteye blueberries, derived mainly from Vaccinium virgatum, are vigorous plants adapted to long and relatively warm summers.
They frequently ripen too late for cool European regions and are more dependent on cross-pollination than northern highbush blueberries.
A cultivar capable of surviving the winter is not necessarily able to complete fruit maturity reliably before autumn.
Can one blueberry plant produce fruit?
Most northern highbush cultivars are self-fertile and an isolated plant can set fruit using its own pollen.
Self-fertility does not mean that a second cultivar is unnecessary.
Cross-pollination between two compatible cultivars flowering at the same time often increases the number of seeds within each berry, resulting in larger fruit, earlier maturity and a more abundant crop.
For reliable production, planting at least two compatible cultivars of the same general blueberry type is therefore recommended.
Rabbiteye cultivars are much more dependent on cross-pollination and should be planted with another rabbiteye whose flowering period overlaps.
A highbush cultivar should not automatically be assumed to be a suitable pollinator for a rabbiteye.
Blueberry flowers are visited by bumblebees, honeybees and other insects. Bumblebees are especially effective because they can vibrate the bell-shaped flowers and release pollen through a process known as buzz pollination.
Cold, windy or persistently wet weather during flowering can reduce pollinator activity and result in small berries, irregular maturity or poor fruit set even when two compatible cultivars are present.
Useful characteristics when choosing a blueberry cultivar
Ripening season
Combining early, mid-season and late cultivars extends the blueberry harvest and prevents the entire crop from becoming ripe at the same time.
In cool, elevated or maritime locations, extremely late cultivars may ripen slowly as autumn temperatures and light levels decline.
An earlier cultivar that develops full sweetness reliably is often more useful than a very late variety offering a longer theoretical harvest but poor final fruit quality.
Flavour
Blueberries may be very sweet, sharp, strongly aromatic or relatively mild.
Some cultivars develop their best flavour only several days after the whole berry has turned blue.
For eating directly from the plant, flavour should take priority over fruit size alone.
Exceptionally large berries are attractive and quick to pick, but they are not always the most aromatic.
Berry size
Large berries are convenient for fresh eating and reduce the time required to harvest a given weight of fruit.
Fruit size is influenced by cultivar, pollination, water availability, pruning and crop load.
A naturally large-fruited cultivar can still produce small berries when flowers are poorly pollinated or the shrub carries too many fruiting branches.
Firmness
Firm berries tolerate handling, refrigeration and freezing more successfully.
Softer fruit may provide a particularly pleasant texture when eaten immediately but normally requires faster harvesting and cooling.
Firmness should not be confused with immaturity. A berry picked too early may be firm because it has not yet developed its full sugar and aroma.
Shrub habit
A compact cultivar is easier to grow in a container and protect with netting.
Vigorous upright cultivars require more space but may carry large crops where the root zone remains acidic, moist and sufficiently aerated.
An excessively open cultivar can bend beneath the crop, while a very dense cultivar may require more renewal pruning to maintain light within the centre.
Concentrated or extended maturity
Some cultivars ripen a large proportion of their crop over a relatively short period, making them convenient for processing and freezing.
Others mature progressively and are more suitable for regular picking and fresh consumption over several weeks.
Blueberries require genuinely acidic soil
Blueberries grow best in soil with an approximate pH between 4.2 and 5.5.
Within this range, their roots can absorb iron, manganese and other essential nutrients effectively.
In neutral or calcareous soil, some of these nutrients become progressively unavailable even when the soil contains them in sufficient quantities.
Young leaves then become yellow while their veins remain greener, producing the characteristic appearance of iron chlorosis.
Applying iron may temporarily improve the colour of the foliage, but it does not provide a durable solution where the pH remains too high.
Before planting several blueberries in open ground, measure the soil pH rather than relying on the appearance of the soil or on the plants already present nearby.
Where the soil is only slightly above the desired pH and contains little lime, gradual acidification with elemental sulphur may be possible when carried out sufficiently long before planting.
In strongly calcareous, heavily buffered or alkaline clay soil, a large container or an isolated raised bed filled with suitable acidic substrate is generally more reliable.
A narrow hole of ericaceous compost surrounded by calcareous ground is not a permanent solution. The roots soon reach the surrounding soil and irrigation water gradually alters the pH of the original planting pocket.
The soil must remain moist but highly aerated
Blueberries possess a fine and dense root system concentrated mainly within the upper layers of soil.
These roots require both regular moisture and a large amount of oxygen.
The growing medium must therefore retain water without remaining permanently saturated.
Compacted soil or a planting hollow that remains waterlogged encourages root suffocation and diseases associated with Phytophthora.
Fibrous organic matter helps maintain a structure that holds moisture while preserving air spaces.
Composted pine bark, suitable acidic leaf mould and peat-free ericaceous substrates can be used according to the method of cultivation.
Avoid wood ash, lime, marl, strongly alkaline compost and fresh manure.
A fertile amendment can still be harmful when it increases pH or creates an excessive concentration of mineral salts around the fine roots.
Irrigation water can gradually raise the pH
Blueberries tolerate neither prolonged drought nor large fluctuations in soil moisture, especially during flowering, fruit swelling and the formation of flower buds for the following season.
Their shallow roots require more regular observation than those of a deeply rooted fruit tree.
Rainwater is preferable where mains water is hard and contains high levels of bicarbonates.
Repeated watering with calcareous water can gradually raise the pH of the substrate, particularly in containers and small isolated beds.
Water deeply enough to moisten the whole root zone without maintaining the soil in a permanently waterlogged condition.
A substantial organic mulch reduces evaporation, limits sudden changes in moisture and protects the shallow roots from high soil temperatures.
Composted pine bark, pine needles and non-calcareous wood chips can be used as mulch.
Apply mulch to soil that is already moist and keep it slightly away from the base of the branches.
Planting blueberries in open ground
Planting directly into the garden is recommended only where the soil is naturally acidic or where a sufficiently broad root zone has been prepared and can remain acidic over the long term.
A dormant young plant can be installed from autumn to early spring whenever the ground is neither frozen nor saturated.
Where a container-grown blueberry is already in leaf or flower, wait until the main risk of late frost has passed.
The young tissues of a plant that has begun growing under protection are less frost-resistant than the dormant wood of an established shrub.
Prepare a wide area rather than a narrow planting hole.
Remove couch grass, bindweed and other perennial weeds carefully and loosen the soil only when it has drained sufficiently to retain a good crumb structure.
The roots must be able to develop horizontally through a relatively uniform, acidic and aerated medium.
Position the root ball approximately at its original depth and avoid compressing the substrate excessively.
Water thoroughly after planting and apply an organic mulch.
Keep the root zone free from grass and perennial weeds and provide water throughout the first growing season whenever rainfall is insufficient.
Dense lawn competes directly with the shallow blueberry roots and should not be allowed to grow against the base of the shrub.
Growing blueberry plants in containers
Container cultivation is often the most reliable option where the garden soil is calcareous.
Use a broad container with numerous drainage holes and enough volume to maintain stable moisture and temperature around the roots.
Fill it with an acidic and aerated substrate capable of retaining water without becoming compacted.
Small pots dry rapidly and their pH changes more quickly. For long-term cultivation, increase the container size progressively as the root system expands.
Water with rainwater wherever possible and do not leave the container standing permanently in a full saucer.
The substrate should remain moist, but the roots must continue to receive air.
A container-grown blueberry depends entirely on the gardener for water and nutrients.
Apply a fertiliser formulated for acid-loving plants at a low dose and replace part of the surface substrate periodically without damaging the shallow roots.
A container provides less insulation from severe cold than open ground.
Even hardy compact cultivars benefit from protection against prolonged freezing of the root ball and exposure to drying winter winds.
Fertilise carefully without damaging the roots
Blueberries require moderate rather than heavy feeding.
Their fine roots are sensitive to high concentrations of soluble salts and excessive fertiliser.
Use a product intended for acid-loving plants and divide low applications between the early stages of growth.
Avoid late nitrogen feeding, which prolongs shoot growth and prevents the young wood from maturing properly before winter.
A yellow blueberry plant does not necessarily require more fertiliser.
Where young leaves become yellow between greener veins, examine the pH and irrigation water before adding further nutrients.
An excessive dose of fertiliser cannot correct nutrient unavailability caused by an unsuitable pH and may damage the roots further.
Which wood carries the blueberry crop?
Flower buds form mainly close to the ends of shoots produced during the previous growing season.
They are normally larger and more rounded than the smaller, more pointed leaf buds.
Young and vigorous branches carry good-quality fruit, while very old stems gradually produce numerous fine twigs, smaller clusters and reduced berry size.
Pruning should therefore preserve sufficient healthy growth from the previous season while progressively renewing the oldest stems from the base.
Uniformly shortening every branch tip removes a large proportion of the flower buds that have already formed.
How should a blueberry plant be pruned?
Prune very lightly during the first years.
Remove only broken, weak, trailing or badly positioned branches and shoots growing into the congested centre.
On a small plant with limited growth, removing the flowers during the first season can encourage rooting and the production of stronger new stems.
From approximately the fourth or fifth year, begin removing some of the oldest stems gradually.
Old branches can be recognised by their greyer bark, dense fine branching and reduced production of strong new shoots.
Maintain an open shrub containing stems of different ages.
Remove very fine twigs, crossing branches and low growth that will touch the ground beneath the weight of the berries.
Do not trim a blueberry like a hedge and do not shorten every branch to the same height.
This removes many flower buds, encourages dense regrowth and gradually reduces fruit size and quality.
How can a fully ripe blueberry be recognised?
A blueberry is not always fully ripe as soon as the whole surface appears blue.
It may continue increasing in size and sugar concentration for several days after completing its colour change.
A ripe berry is blue close to the stalk, slightly soft, aromatic and detaches with almost no resistance.
A red or green area around the point of attachment generally indicates incomplete maturity.
The berries within one cluster do not all ripen simultaneously.
Several selective picking rounds allow each fruit to be harvested at its best stage while the remaining berries continue developing.
Harvest during dry weather, place the fruit in shallow containers and cool it promptly.
Do not wash blueberries until shortly before eating or processing them, as washing removes part of their natural bloom and reduces storage life.
Important blueberry problems
Chlorosis
Young yellow leaves with veins that remain green frequently indicate an excessively high pH and reduced availability of iron.
Check the soil, container substrate and irrigation water before applying repeated iron products or additional fertiliser.
Root suffocation and root rot
A blueberry declining in wet ground may be suffering from oxygen deprivation or a root disease associated with Phytophthora.
Growth stops, branches become yellow and the affected roots turn brown.
Suitable drainage and correct siting are the principal preventative measures.
Cankers and stem dieback
Several fungi can cause stem lesions, dieback and the death of individual branches.
Remove dead or infected wood back to healthy tissue and prevent the shrub from becoming excessively dense and humid.
Anthracnose and grey mould
Anthracnose and grey mould can affect flowers and ripening berries, especially during prolonged humid weather.
Harvest regularly, remove damaged fruit and maintain sufficient airflow through the shrub.
Spotted-wing drosophila
Spotted-wing drosophila, Drosophila suzukii, can lay eggs in ripening blueberries, particularly in late cultivars.
Pick frequently, cool the fruit quickly and remove overripe, damaged and fallen berries from the growing area.
Birds
Birds may remove a large proportion of the crop before it reaches full eating maturity.
A fruit cage or properly tensioned net provides the most reliable protection.
A loose net placed directly over the branches can trap birds and still allow them to reach berries close to the surface.
Which blueberry plant should you choose?
For planting in open ground across cool parts of Europe, choose northern highbush or hardy half-high cultivars and compare their ripening season, flavour, vigour and fruit size.
For a small garden or permanent container, choose a compact or half-high cultivar that is easier to repot, prune and protect from birds.
For an extended harvest, combine early, mid-season and suitably late cultivars whose flowering periods overlap.
This combination usually improves cross-pollination and berry size as well as extending the picking period.
For the strongest wild-blueberry-type flavour, consider compact or lowbush-derived cultivars rather than selecting exclusively according to maximum fruit size.
For freezing and handling, prioritise firm berries and a relatively concentrated maturity period.
In calcareous ground, do not rely on a cultivar advertised as slightly more tolerant of higher pH.
No conventional blueberry cultivar behaves as a genuinely lime-loving plant. A large container or correctly isolated acidic raised bed remains the more reliable solution.
The best cultivar cannot compensate for an unsuitable root environment. Before comparing berry size and flavour, make sure that an acidic, moist and well-drained growing medium can be maintained permanently.
Frequently asked questions about blueberry plants
Are two blueberry plants required for fruit?
A self-fertile northern highbush cultivar can produce alone, but a second cultivar flowering at the same time normally improves yield, berry size and crop regularity. Rabbiteye blueberries are more clearly dependent on cross-pollination.
What is the difference between a blueberry and a bilberry?
The European bilberry, Vaccinium myrtillus, is a small woodland plant whose fruit has deeply coloured flesh. Cultivated North American blueberries form larger shrubs and normally produce larger berries with pale flesh.
Can blueberries be planted in calcareous soil?
Not reliably in ordinary open ground without substantial preparation. Lime maintains an excessively high pH and eventually causes chlorosis. A large container or isolated acidic bed is generally more dependable.
Is one bag of ericaceous compost in the planting hole sufficient?
No in calcareous ground. The small acidic pocket is gradually influenced by the surrounding soil and irrigation water. Prepare a broad, permanently acidic zone or grow the plant in a container.
What pH is suitable for blueberries?
An approximate pH between 4.2 and 5.5 is normally suitable. Conditions outside this range increasingly restrict the availability of iron and other nutrients.
Which water should be used for blueberries?
Rainwater is preferable, particularly where mains water is hard. Repeated watering with water rich in bicarbonates can gradually raise the substrate pH.
Why are the leaves turning yellow?
Where young leaves become yellow while their veins remain greener, the pH is often too high and iron has become unavailable. Waterlogging, root disease and other stresses can also cause yellowing.
Do blueberries tolerate wet soil?
They require regular moisture but their roots also need abundant oxygen. Permanently saturated soil causes root suffocation and encourages root rot.
Can blueberry plants be grown in containers?
Yes, and this is often the most reliable solution in calcareous gardens. Use a large container, acidic and aerated substrate, rainwater and a mulch that limits drying.
Can ordinary multipurpose compost be used?
It is not normally suitable on its own because its pH may be too high and its structure may deteriorate over time. Use a substrate specifically formulated for acid-loving plants.
When should blueberry plants be pruned?
Prune during dormancy, mainly once the shrub is several years old. Remove old, weak, trailing and congested branches progressively without shortening all of the flower-bearing tips.
Why does my blueberry flower but produce little fruit?
Possible causes include poor pollination, frost damage, cold flowering weather, excessively high pH, drought, root problems or a plant that is still too young.
Is a blueberry ripe as soon as it turns blue?
Not always. The berry may continue increasing in size and sweetness for several days. Harvest when it is blue close to the stalk, slightly soft and detaches readily.
Why are the berries small?
Frequent causes include insufficient pollination, drought, excessive crop load, ageing fruiting wood or a cultivar that naturally produces smaller berries.
Why does my blueberry grow poorly despite receiving fertiliser?
The pH may be too high, the roots may be waterlogged or the fertiliser concentration may be excessive. Additional feeding cannot compensate for an unsuitable root environment.
Can blueberries grow in partial shade?
They can grow in light partial shade, but flowering, fruit size, sugar concentration and crop regularity are generally better in a sunny position.
How long can blueberries be stored?
Storage life depends on cultivar, maturity and handling. Firm, dry and promptly cooled berries may keep for several days or longer under refrigeration, while fully ripe soft fruit should be eaten or frozen quickly.
Should blueberries be washed before storage?
No. Store the fruit dry and wash it shortly before use. Washing removes part of the natural surface bloom and encourages deterioration.