Blueberry

Light and exposure

The blueberry likes light and sun to sweeten its fruit well, while tolerating light shade during the hottest hours. In a temperate climate, a position with sun in the morning and at midday, with a little shade in the afternoon, gives excellent results without stressing the plant. Under a harsher sun, in a hot or Mediterranean climate, afternoon shade becomes plainly necessary.

Avoid spots too exposed to wind, which dry out the foliage and the soil. As it grows very well in a pot, you can place it where it makes the best of the sun, moving it with the season if need be. A sheltered, bright corner against a pale wall suits it perfectly.

Watering

This is where everything is decided, and it is the most important point to understand: water the blueberry with rainwater, never with tap water as soon as that water is hard. Chalky water raises the pH of the substrate, blocks the uptake of iron and causes chlorosis, that yellowing of the leaves between the veins that weakens the plant. Set up a rainwater butt, it is almost a must to succeed.

For the rest, the blueberry has fine, shallow roots that dislike both drought and standing water. Keep the substrate cool and moist at all times, above all in a pot where it dries fast, and above all during fruit formation. An acidic mulch on the surface reduces watering and keeps the moisture in.

Soil and repotting

The blueberry demands an acidic soil, with a pH of 4 to 5.5, rich in organic matter, light and cool. On the neutral or chalky soils that are the commonest case, the simplest and most reliable solution is growing in a pot or tub filled with ericaceous compost, or with a mix of ericaceous compost and acidic potting soil.

In open ground, only plant it if your soil is already acidic, otherwise dig a wide pit of at least sixty centimetres that you fill with ericaceous compost, cutting it off from the surrounding chalky soil. Then maintain the acidity each year with a suitable mulch. A soil that is too chalky condemns the plant to languish, whatever your good will.

Temperature and humidity

On the cold side, no worry: the shrubby blueberry is very hardy and takes frosts of minus 20 degrees and beyond without damage, which places it in USDA zones 4 to 7, a few varieties holding down to zone 3. It even needs a good spell of winter cold, in the order of 800 to 1000 hours below 7 degrees for the northern highbush varieties, to flower properly the following spring: under too mild a winter the flowering stays thin and ragged.

Flowering, in spring, remains the delicate moment, because a late frost can damage the flowers. In open ground, it spends the winter outside without protection. In a pot, the roots are more exposed to frost: during a very harsh winter, group the tubs against a wall or wrap them with a fleece or leaves to protect the root ball.

Pruning and upkeep

In the first years, the blueberry asks for almost nothing: let it fill out and just remove the dead or broken wood. A young plant above all needs to build its framework.

From the fourth or fifth year, prune in winter, during dormancy. The blueberry fruits on two to three year old wood, then the old branches exhaust themselves. Each winter remove the oldest and darkest branches at the base, the spindly wood and the shoots that cross in the centre, to open up the bush and encourage vigorous new growth. You thus take out a fifth to a quarter of the old branches per year.

Pests and diseases

The blueberry is little prone to disease when its needs are met. The main trouble you will meet is not a disease but a deficiency: iron chlorosis, due to too high a pH or to watering with chalky water. The leaves yellow between the veins, which stay green. The answer is always the same, reacidify the substrate and go back to rainwater.

In damp conditions, still watch for grey mould (botrytis) on the fruit and a few leaf spots in mild overcast weather: open up the bush by pruning and do not wet the foliage needlessly. The real predator is the birds, blackbirds first, which spot the ripe berries before you do.

Propagation

The blueberry propagates from cuttings, but it is a slightly slower and more delicate exercise than for other fruit shrubs, which explains its medium difficulty rating. In summer, take cuttings of semi ripe wood, or in winter cuttings of hardwood, and plant them in a very acidic mix, based on ericaceous compost and sand, kept constantly moist with rainwater.

Rooting can take several months and the success rate stays modest without well managed conditions. For most gardeners, buying young plants in containers remains the simplest and surest route, all the more so since you need several varieties in the garden anyway.

Month-by-month care calendar

Green Hub tips

• Rule number one as soon as your tap water is hard: water only with rainwater. Chalky water raises the pH and blocks the plant, which yellows and declines.
• Leaves that yellow between veins that stay green signal chlorosis: your substrate is no longer acidic enough, react quickly with mulch and rainwater.
• Plant at least two different varieties side by side. Cross pollination gives a more abundant harvest and clearly bigger berries.
• In neutral or chalky soil, forget classic open ground: a large tub of ericaceous compost makes you master of the pH and simplifies everything.
• Set up the bird net before the first ripe berries. Once a blackbird has spotted your blueberries, it will leave you none.