The most widely grown blueberries are cultivars of northern high bush blueberries (Vaccinium corymbosum), branching mainly deciduous shrubs reaching up to 1.8m (6ft) in height. Apart from producing fruit they are ornamental, producing bell-like flowers in spring. The foliage has good autumn colour. Half-high blueberries are hybrids between Vaccinium corymbosum and low-bush Vaccinium angustifolium, making more compact plants.
Blueberries need a sheltered site in well-drained, moisture-retentive, acidic soil (pH 4.5-5.5) in sun or part shade. If you can grow azaleas, rhododendrons and camellias in your garden, blueberries should be successful too. Check your soil pH if unsure.
If your soil is only slightly acid, you can try acidifying it to lower the pH to the optimum level for ericaceous plants. However, this would have to be done in advance, ideally the previous summer or autumn.
If you garden on heavy clay or alkaline soils, it is best to grow blueberries in containers. Improve the soil before planting by removing all weeds and incorporating lime-free soil improvers such as composted bark, bracken, leafmould, pine needles or composted sawdust to a fork’s depth. Avoid adding manure or mushroom compost which are too alkaline for blueberries.
Highbush blueberries can reach 1.5-1.8m in height and half-high about 0.5-1.2m. When planting, space highbush cultivars with 1-1.5m (3¼ft-5ft) all round and half-highs with about 1m (3ft) all round. Mulch newly-planted blueberries with pine bark (composted or chipped) or leafmould.
If you do not have an acidic soil or garden on heavy clay, try growing blueberries in containers or raised beds ideally filled with ericaceous soil. If this is not easy to source, RHS members report John Innes Ericaceous potting compost to be a suitable alternative.
When using soil-free media (multipurpose compost), ideally choose a peat-free one, but be aware that peat-free media might require frequent use of chelated iron to avoid chlorosis. Pot-grown blueberries in soil-less growing media often require annual repotting as the compost tires quickly, even if it means changing some of the old compost with fresh and putting the plant back into the same pot. This is because the soil-less potting media loses its structure quite quickly leading to root damage or rot.
Pollination, fruiting & harvesting
Although many blueberries are partly or fully self-pollinating, it is best to grow a minimum of two, cross-pollinated plants tend to produce larger fruit. To achieve this, plant two or preferably three different cultivars to ensure reliable, abundant crops.
Pick fruit when it is completely blue and has a white surface bloom. Fully productive plants around seven years old produce up to 2.25-5kg (5-11lb) of berries.
Watering and feeding
During dry spells water blueberries with rainwater, not with tap water, unless you have no alternative in a drought.
If growing in containers keep the compost moist but not waterlogged and don’t allow the compost to dry out between waterings. Feed container plants every month using a liquid fertilizer formulated for ericaceous (lime-hating) plants, following the manufacturer’s recommendations.
Mulch plants in open ground in spring or autumn with 7-8cm (2½-3in) layer of acidic or neutral organic matter, such as composted sawdust, composted or freshly chipped pine bark, composted pine needles or leafmould. Avoid manure and mushroom compost, as they tend to be quite alkaline.
At Wisley, blueberries, need minimal feeding apart from supplementing annual additions of organic matter with 15g per sq m (½oz per sq yd) of sulphate of ammonia sprinkled round the plants in late winter. If plants are not growing well try an application of fertilizer recommended for ericaceous (lime-hating) plants as directed by the manufacturer. Avoid overfeeding, as blueberries are sensitive to high fertiliser levels. Poor growth may be a result of high pH, excess nutrients (high soluble salts) and fluctuation of soil moisture levels.