How to grow blueberries

A blueberry is an ericaceous plant — the family that contains rhododendrons, azaleas and heathers — and like its relatives it needs distinctly acid soil, pH 4.5 to 5.5. That is more acid than almost any vegetable wants, and well below ordinary garden soil.

Above about pH 6 the plant cannot take up iron, and the symptom is unmistakable once you know it: new leaves turn yellow while their veins stay green, then redden and scorch at the edges. The bush does not die quickly. It sits, makes a little growth, fruits poorly, and declines over years — which is why the problem so often goes unrecognised.

Test before you plant, not after. A cheap soil test is the single most useful thing you can do for this crop, and it is the only crop on this site where we would say that.

If your soil is not acid, do not fight it in open ground. Amending a bed downward by a full point of pH is a losing battle against the surrounding soil and the water you irrigate with. Grow in containers or a dedicated raised bed filled with ericaceous compost instead, where you control the whole volume.

The maritime Northwest is unusually well placed here: much of the region's soil is naturally on the acid side, which is a substantial part of why Oregon and Washington grow so many blueberries commercially.

Water matters too. Hard tap water is alkaline and will raise the pH of a container over a season. Rainwater is free, soft, and exactly what this plant evolved in.

Blueberry roots are fine, shallow and — unusually — have no root hairs, relying instead on a fungal partnership to take up nutrients. Three practical consequences follow, and they explain most of the crop's care.

They dry out fast. A blueberry needs steady moisture through the growing season and suffers quickly in drought, particularly while fruit is sizing.

They cannot be dug around. Never hoe or fork near a blueberry — you will destroy the feeding roots, which are in the top few inches. Weed by hand or, better, by mulching so thoroughly that nothing germinates.

And they want an organic, open rooting medium. Mulch with pine bark, pine needles, sawdust or leaf mould, two to four inches deep, topped up annually. That mulch is not optional decoration; it is doing the job the plant's roots cannot do alone.

Plant in autumn or early spring, at the depth the plant was already growing, and tease the roots out if it is pot-bound — blueberries left in a spiral rarely establish.

Feed only with an ericaceous or acidifying fertiliser. Ordinary balanced feeds and anything containing lime will push the pH the wrong way, and bone meal is a particularly common mistake.

Blueberries fruit best on wood that is two to four years old. Older wood keeps living and keeps producing less, so the object of pruning is a bush that is continually renewing itself rather than one that is merely tidy.

For the first two or three years, prune almost nothing — just remove damaged or crossing shoots, and strip off the flowers in the first year so the plant establishes rather than fruits. It costs you one small crop and repays it for twenty years.

From about year four, in late winter, take out one to three of the oldest stems each year, cutting right down to the base. Old wood is recognisable: thicker, greyer, flakier, and carrying twiggy unproductive side shoots. Removing it prompts strong new stems from the crown.

Also take out anything dead, anything crossing through the centre, and any thin twiggy growth at the tips that will make only tiny berries.

The aim is roughly six to eight strong stems of mixed ages on a mature bush, open enough that light and air reach the middle. Beyond that, blueberries need less intervention than almost any other fruit.

Most blueberry varieties will set some fruit alone, but nearly all set a heavier crop of larger berries when a second variety flowers alongside them. Two bushes of different varieties is the single cheapest yield improvement available, and choosing ones that overlap in flowering season is the only subtlety.

Picking is the pleasant part and has one rule people routinely get wrong: a blueberry that has turned blue is not necessarily ripe. Give it several more days after colouring, until it drops into your hand at the lightest touch. A berry you have to tug is a berry that will taste sharp.

They ripen in clusters over several weeks, so pick every few days rather than stripping the bush.

Birds will take every berry, and unlike with strawberries they will do it in a morning. Netting on a frame is the only reliable answer — held clear of the bush, secured at ground level, and taken down after harvest so nothing gets caught in it.

Blueberries freeze better than any other fruit here: spread them on a tray, freeze loose, then bag them. They keep their shape and go straight from the freezer into baking.

There is a book on our shelf called Success with Small Fruits, published in 1881 by a commercial grower who covers strawberries, raspberries, blackberries, currants and gooseberries in exhaustive detail. It does not cover blueberries. Neither does Fearing Burr's 1863 catalogue of American vegetables, and neither does our 1912 planting table.

The reason is simple: there was no such thing as a cultivated blueberry. People gathered wild ones — and repeatedly failed to bring them into gardens, because nobody understood that the plant required acid soil and a fungal root partnership.

That changed in the 1910s at Whitesbog, New Jersey. Frederick Coville, a USDA botanist, worked out the soil chemistry; Elizabeth Coleman White, whose family farmed cranberries there, paid local pickers to find outstanding wild bushes in the Pine Barrens and bring them in. Between them they selected and crossed the first named highbush varieties, and every blueberry in every supermarket descends from that work.

The watercolour below is from that lineage. Brooks, painted for the USDA in 1940 by J. Marion Shull, from a specimen at Whitesbog itself — the place the crop was made.

It is the youngest domesticated fruit most people grow, and it is worth knowing that when a guide tells you blueberries are fussy. They are not fussy. They are wild, and only just.