When to plant blueberries

Acidic soil is the whole game

Blueberries need acidic soil, with a pH of about 4.5 to 5.5. Many Northwest soils west of the Cascades are already close, but soils east of the mountains are often neutral or alkaline. Test before you plant. At the wrong pH, blueberries can't take up iron and other nutrients, and the classic symptom is yellow leaves with green veins.

To lower pH, mix elemental sulfur into the soil. Soil bacteria slowly turn it into acid, which takes months, so ideally add it the season before planting and retest. Avoid aluminum sulfate, which acts faster but can build up to levels that harm the roots. If your soil is alkaline, growing in large containers or raised beds of acidic mix is often easier than fighting it.

Shallow, fussy roots

Blueberry roots are fine, shallow, and have no root hairs. Instead they rely on partnerships with soil fungi to absorb water and nutrients, and those fungi do best in soil rich in organic matter. That's why growers work peat or acidic compost into the planting area and keep 2 to 4 inches of sawdust or bark mulch over the roots. The mulch keeps them cool and moist and slowly adds organic matter.

Shallow roots also dry out fast. Give them about an inch or two of water a week in summer, especially while berries are swelling, ideally through drip irrigation.

Feeding

Blueberries take up nitrogen best as ammonium, so use a fertilizer made for acid-loving plants or ammonium sulfate rather than nitrate fertilizers. Split it into two or three small doses from early to late spring. Too much at once burns the shallow roots. Skip fresh manure, which is salty and tends to raise pH.

Pollination and pruning

Northern highbush blueberries are partly self-fertile, but planting two or more varieties that bloom at the same time gives bigger berries and heavier crops through cross-pollination. They also need a winter chill of roughly 800 to 1,000 hours below 45°F, which Northwest winters easily provide.

Fruit forms on wood that grew the previous summer, and canes are most productive at about three to six years old. Each winter after the plants are established, remove a few of the oldest, grayest canes at the base and thin out weak, twiggy growth. That keeps young, fruitful canes coming.

Pests and diseases

Birds are the biggest loss, so net bushes as berries begin to color. Spotted wing drosophila, a small fruit fly that arrived in the Northwest around 2009, lays eggs in ripening berries, especially later in summer. Picking every few days and refrigerating berries promptly limits the damage. Mummy berry, a fungus that turns berries into shriveled gray mummies, overwinters in fallen fruit; rake up mummies and refresh the mulch in late winter.

Harvest and storage

Blueberries don't get sweeter after picking. Wait several days after they turn fully blue; they keep sweetening on the bush and drop easily into your hand when ripe. Refrigerate them unwashed, and rinse just before eating. They also freeze well spread on a tray before bagging.