Blueberry Prescription

Talk about an easy fruit! Backyard blueberries have few -- often no -- insect or disease problems. The bushes are easy to prune. No need to harvest crawling on your knees (as with strawberries) or fighting thorns (as with brambles). And no need to replant (ever), because a blueberry bush will live 50, maybe 100 or more, years.

Best of all is the flavor; fully ripened blueberries have sweetness and aroma that store-bought blueberries cannot match. Backyard blueberries can hang on the bushes for a few days after they first turn blue, and this allows time for their flavor to really soar.

Okay, blueberries are easy, but success with this fruit still requires attention to three details: variety, soil, and birds.

In contrast to most fruits that you find in the market, the blueberry is a native shrub, growing wild along the East coast, in parts of the Upper Midwest, and in the Pacific Northwest. The blueberry is also a market upstart, with breeding and the first commercial plantings initiated only in the early part of the twentieth century. To their credit breeders have created varieties adapted beyond their native ranges, so that nowadays you can grow blueberries just about anywhere in the United States and many parts of Canada.

Kinds of Blueberries

Blueberries are partially self-fertile, which means they bear some fruit without cross-pollination. But when at least two different varieties grow near each other, yield is higher and fruits are larger. Planting more than one variety can also stretch out the harvest season for several weeks. Before narrowing your choices to specific varieties, choose which type or types of blueberries are best suited to your climate.

Lowbush. The most cold-hardy blueberries are lowbush types (Vaccinium angustifolium, USDA Hardiness Zones 3 through 6), growing no more than about 8 to 18 inches high. Snowfall covering these low shrubs protects them from winter cold. Plants spread by underground runners to form a solid mat of plants which -- with their dainty, bell-like flowers in spring, and fiery red leaf color in fall -- make an attractive ground cover.

Native Americans enjoyed lowbush blueberries long before European settlers arrived. Although a few named varieties exist, nurseries mostly sell unnamed seedlings. Many commercial plantings consist of wild plants encouraged to grow in much the same way as the Native Americans grew them. Lowbush blueberry fruits typically are about 1/4 inch in diameter, very sweet, and covered with a powdery blue bloom.

Highbush. Most fresh-market blueberries are the highbush type (V. corymbosum), so named for the 6-foot-high plants on which they are borne. Northern and southern subtypes of highbush blueberries are available. Some popular northern varieties include 'Bluecrop', 'Blue Ray', and 'Earliblue', adapted for zones 4 through 7. Southern highbush types do best in zones 7 through 10 and include varieties such as 'Gulf Coast', 'Misty', 'O'Neal', and 'Reveille'. 'Sharpblue' can grow in zones 7 through 11. Compared to lowbush berries, the fruits are large: 1/2 to 1 inch in diameter.

Rabbiteye. These blueberries (V. ashei) are native to the Southeast and so are heat-tolerant (zones 7, 8, and 9). The bushes grow 10 or more feet tall, and the 1/2- to 1-inch fruits have a thick skin that helps them hang well on the bush, even in the heat, to develop full flavor. For good cross-pollination, plant two or more varieties with bloom seasons that coincide; 'Beckyblue' and 'Bonitablue', or 'Powderblue' and 'Tifblue', for example.

Half-high. In recent years, some of the best qualities of both highbush and lowbush blueberries have been combined into what are known as half-high blueberries. These varieties have size and flavor qualities that are between those of their parents, and generally do not spread by runners. Half-high varieties such as 'Chippewa', 'Northblue', and 'Northland' are hardy into zone 3.

Soil Requirements

Blueberries are finicky about soil; it must be moist yet well aerated, very rich in humus, and very acidic (pH 4.0 to 5.0). Wild blueberries often inhabit boggy areas, but the plants are actually perched on hummocks; likewise, give your backyard blueberries well-drained soil. The shallow roots of blueberry plants compete poorly with weeds or lawn, so make sure the ground beneath each bush is also free of weeds and grass.

Before you plant, test the soil's acidity. If the pH of your soil is not sufficiently low (acidic enough to suit blueberry bushes), apply sulfur, available at garden centers. A very alkaline soil, with pH above 7.5, needs drastic treatment. Once you've used sulfur to adjust pH initially, provide long-lasting acidity as well as humus by mixing a generous bucketful of peat moss into the soil at each planting hole.

Finally, right after planting, blanket the ground with 3 inches of organic mulch, and water thoroughly. The mulch keeps the soil moist, and as the lower layers decompose, they enrich the soil with humus. Sawdust (not from treated wood) is ideal, but any organic material is satisfactory. Regular watering is critical during the first growing season.

Beating the Birds to the Berries

The third part of the prescription for blueberry success is dealing with birds. The same delightful garden visitors we attract with feeders and birdbaths will strip bushes of a large portion -- sometimes all -- of a blueberry harvest. Gardeners have come up with all sorts of ways to thwart birds: balloons painted with large eyes, strips of foil-covered Mylar, pie pans dangling above the bushes, fake owls and snakes, black cotton thread woven among the branches. These devices all work for a while, and they work best on flocking birds, like crows. However, many birds that enjoy blueberries, including robins, jays, and orioles, are not flocking birds.

Birdproof netting is an effective way to fend off birds. Don't just drape a net over the bushes, though. Harvest will be a hassle, and birds can still fly underneath the net.

The ideal protection is a walk-in birdproof cage. Support posts can be permanent or temporary, but put the net up only during harvest season, so the net lasts longer, and the rest of the year the birds can flit about and hunt for insects.

A blueberry cage need not be an eyesore. It might resemble a Victorian folly or a rustic arbor. For my cage, I pound 8-foot lengths of metal conduit into the ground, connect their tops with PVC pipe, and drape on the net. Any netting with 1-inch (or smaller) mesh works. When harvest is over, I pull out the conduit, take apart the PVC pipes, roll up the net, and put it all away until the following year.

Maintaining the Plants

Prune in winter. A highbush blueberry stem remains most productive for four to six years, depending on climate. When stems reach 1 to 1-1/4 inch in diameter, they become less productive. So first, cut away, near ground level, the oldest stems. Also shorten young, weak stems, and remove older twiggy growth. Remove some stems in the center of the bush if they crowd, and shorten or remove stems that droop to the ground. Some highbush varieties, such as 'Cabot' and 'Pioneer', produce excessive fruit buds on each shoot, so shorten the fruiting stems until only three to five of the fruit buds remain.

Prune rabbiteye blueberries slightly less than you would highbush blueberries. Cut away just enough to keep the bush from growing too tall and its center from becoming too shaded, by lopping old, large stems to the ground.

The best fruits of lowbush blueberries are borne on the youngest stems, especially those growing directly from the ground. Stimulate new stem growth with severe pruning by cutting the plants to the ground every second or third winter. Plants won't bear the season following pruning, so if you want fruit every year, divide the planting into halves, or thirds, and prune alternating sections each year.

Yearly Soil Upkeep

Annual attention to the soil keeps blueberries healthy and productive. Monitor soil acidity, and if it rises too much--or if you notice young leaves yellowing between their veins--sprinkle sulfur on the ground out to the drip line. Also, replenish mulch, and remove weeds that compete for nutrients.

Fertilize in late winter if growth was poor the previous season. Avoid fertilizers like sodium nitrate (a component of many organic fertilizer products) that make the soil more alkaline. Soybean meal or cottonseed meal, at 2 pounds per 100 square feet, is ideal. If you use concentrated fertilizer, apply the equivalent nutrient content in two applications--one application in early spring and one in late spring. In general, I recommend you avoid concentrated fertilizers, because blueberry roots burn easily.

Harvest Tips

The way to tell berries that have just turned blue from those that have been on the bush for a few days is to tickle the clusters: Only fully ripe berries will drop into your hands.

Making Soil for Blueberries

If your soil is alkaline, as in many areas of the West, it isn't feasible to acidify it sufficiently for blueberries but you can still grow them by making soil. Excavate a hole 2 to 3 feet deep and 6 feet wide. Fill it with a mix of equal parts of peat moss and sand. Because both peat moss and sand are nutrient-poor, fertilize annually with fertilizer and soybean or cottonseed meal to supply mostly nitrogen, and maintain a mulch of any organic material over the surface. If you irrigate, and your water is also alkaline, acidify it with 2 teaspoons of vinegar per gallon of water.

Photography by National Gardening Association

Article published on June 23, 2008.

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