Growing Blueberries in Pots: Acidic Mix, Watering, and Winter Care

Why Grow Blueberries in Pots

Blueberries grow well in pots when four things are right: an acidic mix at pH 4.5 to 5.5, a container of 10 to 20 gallons depending on the type, soil that stays evenly moist, and a sheltered place for the winter. The mix matters most. Oregon State University Extension recommends 50 to 80 percent well-aged fine bark, 10 to 40 percent peat moss and 10 percent perlite or pumice.

A pot is often the easier route to that pH. Oregon State states that blueberries require a soil pH of 4.5 to 5.5, which many garden soils do not offer. In a container the gardener chooses every ingredient, so the acidity is right from the first day.

Any type can be grown this way. The same Oregon State guide says that any type of blueberry will grow in a container, and that the larger ones simply need a larger pot.

Choose the Pot Size

Pot size depends on the type of blueberry. Oregon State advises half a wine barrel or a 15 to 20 gallon container for the larger types such as northern highbush, and a 10 gallon or larger container for half-high cultivars.

University of Maryland Extension states the same need in inches: a mature blueberry wants a container at least 24 inches deep and about 24 to 30 inches wide. The Royal Horticultural Society, writing for British gardens, gives smaller figures. It suggests a pot at least 12 inches in diameter for a young plant and 18 to 20 inches for a larger one.

Roots explain the generous width. Blueberries have a shallow root system, generally no more than 1 to 1.5 feet deep according to Oregon State, so a wide container gives the roots more usable room than a narrow, tall one. Whatever the size, the pot needs drainage holes, because Oregon State lists good drainage among the things a blueberry mix must have. Maryland adds that containers standing on a hard surface should be set on bricks so they can drain.

Blueberry Soil Mix Ratio

Three sources give three workable recipes, and they differ mainly in how much bark they use.

Source	Mix by volume
Oregon State University Extension	50 to 80 percent well-aged fine bark, 10 to 40 percent peat moss, 10 percent perlite or pumice
University of Maryland Extension	50-50 potting soil and peat moss
Royal Horticultural Society	Soil-based, peat-free ericaceous compost, sold ready to use

Oregon State sets out what any of these has to achieve: the correct pH for blueberries, high organic matter and good drainage. Any recipe that meets those three tests will do. For blueberries planted in the ground, where the existing soil has to be changed instead of replaced, see the comparison of soil acidifiers for blueberries.

The Maryland recipe is the simplest to assemble because it starts from a bag of ordinary potting soil. If you take that route, the guide to potting mix for containers explains what to look for in the base mix. Ericaceous compost is the British term for a potting mix made for acid-loving plants.

When planting, set the blueberry at the same depth as it sat in its nursery container and water it well.

Varieties for Containers

Half-high cultivars are a natural fit for a 10 gallon pot. Oregon State lists ‘Polaris’, ‘Northland’, ‘Northcountry’, ‘Northsky’, ‘Chippewa’ and ‘Northblue’ in that group. The Royal Horticultural Society names ‘Bluetta’ and ‘Sunshine Blue’ as compact varieties suited to pots.

Plan on two plants. Oregon State notes that although cultivars will set fruit with their own pollen, cross-pollination improves berry size and quantity. Maryland gives the practical version: a second variety in a separate container will encourage cross-pollination as long as the two bloom at the same time.

Patience is part of the choice. Oregon State advises that new plants should not produce fruit in their first season, and Maryland says not to expect a harvest in the first year. Maryland puts the wait for a full crop at about 5 years. Once the bush is established, the guide to pruning blueberry bushes covers the yearly cuts.

Sun, Water and Feeding

Place the container in full sun. Maryland adds that protection from late afternoon sun may be necessary, and Oregon State notes that plants tolerate partial shade with lower yield and fruit quality.

Blueberries are very sensitive to dry conditions, in Maryland’s words, so keep the mix evenly moist. Check a pot by pushing a finger into the mix, and water before it dries out.

The water itself affects pH. The Royal Horticultural Society recommends rainwater over tap water, because tap water is usually alkaline, especially in hard water areas, and regular use raises the pH of the mix. A rain barrel beside the pots is one way to collect it. Where a timer is easier than a watering can, the article on choosing a drip irrigation kit covers the parts.

Feed with a fertilizer made for acid-loving plants. Maryland says to avoid fertilizers containing nitrates or chlorides and to fertilize containers in early spring before the leaves expand. Oregon State explains why: many all-purpose garden fertilizers supply mainly the nitrate form of nitrogen and are not suited to blueberries. The Royal Horticultural Society’s routine for British conditions is a liquid ericaceous feed every two or three weeks from April to August.

Watch the youngest leaves for the sign of a rising pH. Oregon State describes it as yellow leaves with green veins, especially on younger growth. A soil test will show whether the mix has drifted above 5.5.

Winter Care and Repotting

In winter the part of a potted blueberry to protect is the roots. University of Maryland Extension advises keeping containers in a sheltered location, protected from winter winds, from December through March.

The Royal Horticultural Society gives two methods for prolonged freezing weather. Group the pots together or wrap them in burlap, recycled bubble wrap or another insulating material. Or move the pot into an unheated greenhouse, shed or garage until the cold snap has passed. The step-by-step guide to overwintering potted plants covers both methods for other shrubs too.

Repot in late summer to early fall. Maryland gives that window so that the roots have enough time to grow before winter. Use fresh mix at the same ratio, and move up toward the final size: 10 gallons or more for a half-high plant and 15 to 20 gallons for a northern highbush.