Shrub · Ericaceae
Blueberry
Vaccinium corymbosum
Hold the soil acidic with a second bush nearby, and the canes hang heavy with dusky blue fruit each summer.
Full sun
Every 3–7 days
USDA 4–7
5–12 ft · 1.5–3.7 m
Overview
The highbush blueberry is a many-stemmed, woody shrub of the heath family, kin to the rhododendrons and azaleas, with upright canes that age from green to a ridged grey-brown. It grows wild in the damp, acidic ground of eastern North America, and that origin shapes the plant from root to tip. Set in the acidic, peaty soil it evolved in, a single bush thickens into a dense crown of canes that fruits for decades.
What stands out underground is as telling as the canes above. The plant feeds through a shallow mat of fine, threadlike roots that want a low pH between 4.5 and 5.5 and quickly suffer in either dry or waterlogged soil. Once those roots take hold, the woody frame turns hard and resilient, with bark that carries it through winters as cold as -22°F (-30°C).
In spring the canes hang with small, urn-shaped white to pale-pink blossoms that nod in clusters along last year's wood. Set two or more varieties that bloom together and the flowers give way to far more fruit, swelling larger, ripening earlier, and weighing the branches more heavily. The clusters thicken as the bush matures, reaching full, fruit-laden form around its third growing season.
Care
The short version: full sun, acidic soil at pH 4.5 to 5.5, steady moisture over the shallow web of fine roots, and a second cultivar nearby so the blossoms set a heavy crop.
Light
The bush fruits best in full sun, ideally six or more hours a day, with the berries coloring deepest where the light reaches the canes. A little partial shade is tolerated, but the yield thins and the fruit ripens more slowly and tastes less sweet.
Water
Keep the root zone evenly moist at all times, giving about 1 to 2 inches of water a week. The shallow, threadlike roots sit close to the surface, so they dry out fast and recover poorly from drought, above all while the green berries are swelling.
Soil
Soil is what the whole plant turns on. Blueberries need acidic soil at pH 4.5 to 5.5, moist but free draining and dark with organic matter. Work peat moss or pine bark into the ground before planting, since the fine roots simply will not take hold in ordinary garden soil.
Temperature
Northern highbush is hard-wooded and cold hardy, its bark holding through winters down to about -22°F (-30°C) and summers up to 95°F (35°C). The cold months are needed in their own right, since the canes require a stretch of winter chill before the flower buds will open.
Humidity
Average outdoor humidity, around 40% to 70%, suits the bush, so the air around the leaves needs no attention. Moisture at the roots and air moving through the canes do far more for the plant than humidity ever will.
Feeding
Feed from spring into early summer once new shoots push, using an acid-forming fertilizer built on ammonium nitrogen, such as an azalea or rhododendron blend. Keep nitrate fertilizers and lime away, since both lift the pH the wrong way for these roots.
Pruning
Prune in late winter while the canes are bare and dormant. On a mature bush, cut out the oldest, greyest canes once they pass six years and thin any weak, crossing, or dead wood, leaving 6 to 10 strong canes to carry the fruiting laterals.
Repotting
A container blueberry needs fresh acidic mix every 2 to 3 years, repotted or top-dressed. Roots circling the inside of the pot, water running straight through, and growth that stalls with less fruit all show the plant has filled its container.
Size & spacing
A highbush blueberry builds a crown of canes 5 to 12 feet (1.5 to 3.7 m) tall and 4 to 6 feet (120 to 180 cm) wide. Give each bush room to spread so light and air can reach right into the heart of the canes.
When to plant
Blueberries move through a temperate year in clear stages. New bushes go into worked soil in early spring, or in fall where winters stay mild, when the canes are bare. The urn-shaped blossoms open in mid to late spring, and the green berries blush and darken to ripe blue through summer, picked from June into August.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: early spring once soil is workable (or fall in mild zones)
- Harvest: blooms mid to late spring; harvest summer (June to August), with full crops by the third growing season
Hardiness
USDA hardiness zones: 4–7
Temperature: down to -34°C
Troubleshooting
Most blueberry trouble shows up plainly on the plant: in the color of the leaves, or in branches that flowered yet carry little fruit. Either soil that is not acidic enough or a single bush with no pollen partner lies behind it. Match what you see on the canes and foliage below, then correct the cause rather than the symptom.
Leaf blades paling between bright green veins
When the leaf tissue turns pale yellow while a fine net of veins stays green, the bush is showing iron chlorosis. It almost always means the soil pH has risen too high for the roots to pull iron and manganese, and the youngest leaves at the tips of the shoots fade first. Test the soil, acidify it with elemental sulfur at the recommended rate, and switch to an ammonium nitrogen feed.
Fix:
- Acidify soil with elemental sulfur per soil-test recommendations
- Mulch with acidic pine bark or peat
- Switch to an acid-forming ammonium nitrogen fertilizer
Canes full of bloom but bearing few berries
Branches dense with urn-shaped flowers that then hold almost no fruit usually point to poor cross-pollination from a single cultivar standing alone. The blossoms need pollen from a different plant to set. Add a second highbush variety that blooms at the same time, and protect the bees by holding off on sprays while the flowers are open.
Fix:
- Plant two or more different highbush cultivars that bloom together
- Encourage bees and avoid spraying insecticides during bloom
Toxicity
For homes with pets or children, the plant is safe from its roots to its fruit. The ripe, dusty-blue berries are a healthy treat, and the smooth leaves and woody stems hold nothing toxic. The only thing to watch is how much is eaten, since a large amount of any fruit can upset a small stomach.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Blueberries are safe for cats, and a ripe berry or two makes a fine treat. Most cats sniff at the round fruit and walk away, so there is nothing to worry about.
Dogs None
Dogs can eat the ripe, soft berries with no trouble, and many love them. Keep the portion small, since a big bowl of any fruit can loosen the stomach.
Horses Safe
The berries and the smooth green leaves are safe for horses to nibble. Offer them as an occasional snack rather than a regular part of the feed.
Rabbits Safe
Rabbits can have a berry or two as a treat. The fruit is sugary and soft, so offer only a little and lean on hay and greens for the bulk of the diet.
Livestock Safe
Cattle, goats, and sheep can browse the leafy canes without harm, since the plant holds nothing toxic. A heavy load of ripe fruit is still best kept modest.
Birds Safe
Birds are drawn to the dusty-blue ripe berries and will strip a bush of them if allowed. The fruit does them no harm at all, which is exactly why gardeners net their plants.
People Safe
Blueberries are a healthy snack eaten fresh, baked, or frozen, their flesh sweet and pale inside the blue skin. Every part you would eat is safe for children and adults alike.
No special handling precautions are required around pets.
Varieties
Hundreds of blueberry cultivars exist, told apart mostly by when their berries color up. A mix of early, mid, and late types stretches the run of ripe fruit and gives the bushes the cross-pollination they need.
Bluecrop
Bluecrop is a widely grown midseason northern highbush whose canes carry heavy clusters of large, firm berries and shrug off hard winters.
Duke
Duke ripens early with firm, even berries of uniform size, yet blooms late enough to dodge most spring frosts.
Elliott
Elliott bears late, hanging firm, tart berries on the canes into the end of summer.
Companions
Blueberries pair well with other acid-loving shrubs that share their soil, and badly with anything that wants the dry, limey ground they can't tolerate.
Plant near
Rhododendron: Shares the same acidic, moist, well-drained soil requirements so culture is identical.
Azalea: Acid-loving ericaceous shrub with matching pH and moisture needs.
Keep apart
Lavender: Prefers alkaline, dry soil that is incompatible with the low pH and steady moisture blueberries need.
How to propagate
A new blueberry can be coaxed straight from the canes of the one you have. Either root a cut length of stem, or bend a low, supple cane to the ground and let it strike roots where it touches the soil.
Stem cuttingsModerate
Softwood cuttings in late spring to early summer; hardwood cuttings taken from dormant wood in late winter · 6 to 12 weeks to root, with transplanting the following season
Cut stems are the main way growers raise more blueberries. Take soft, green-tipped softwood in late spring to early summer or firm, leafless hardwood from dormant canes in late winter, then sink them into a moist, acidic peat and perlite mix under high humidity. White roots form in 6 to 12 weeks, and the rooted stems move on the following season.
LayeringEasy
Spring · One growing season to root before separating
Layering is the simplest route of all. In spring, bend a low, whippy cane down until a length of it lies against the soil, then bury that section while it stays joined to the parent bush. Roots grow from the buried stem over one growing season, and the rooted cane is then cut free as a new plant.
Myths
A single blueberry bush will fruit just as well on its own.
A lone bush does set some fruit, since highbush types are self-fertile, but the canes never carry what a planting of two or more will. Pollen moving between different cultivars lifts the yield, swells each berry rounder, and brings the clusters on earlier.
Burying coffee grounds will quickly acidify soil for blueberries.
Coffee grounds barely move the pH around the roots, and the little they do takes a long time. Reliable acidifying comes from elemental sulfur applied to a soil test, not from kitchen scraps.