We should all stand (or sit, open-mouthed) in awe at the great difference between a cold blueberry and a warm blueberry. Think of blueberry pie. We owe much to the person, probably a native North American in what we now call Maine, who first cooked the fruit.
An uncooked blueberry is waxy blue outside with a green-gray pallor inside. Cold, it's a tart, prim, buttoned-up Puritan of a fruit. A cooked blueberry has turned red-purple; the berry has gone from Puritan to odalisque. A cooked peach is juicier and sweeter than a raw peach, but it's still peach-colored. Apples quickly turn to sauce. The blueberry's sweet purple transformation, by comparison, is near-miraculous.
The explosion of flavor and color has to do with a substance called anthocyanin, the pigment (Greek: anthos = flower, kyanos = blue) found in flowers and plants, particularly in the skin of blueberries, eggplants, and cherries. As Harold McGee, author of On Food and Cooking: The Science and Lore of the Kitchen, explained it, heat breaks down the berry skin's cell walls, releasing the pigments into the pulp and turning it reddish-purple. The same breakdown that liberates the pigments from the skin also unlocks the sugars from their little cellular chambers. The quality that chefs appreciate—that the blueberry retains its nice shape—is the result of a high skin-to-pulp ratio. Apples quickly turn to applesauce because the ratio of skin to pulp is lower.
Blueberries are relatively easy to grow in a home garden. You need sun, you have to get the soil right, and you have to keep the birds away from the fruit. As with any plant, it's best to re-create something akin to the conditions in which it evolved. For most blueberry bushes, that's the sunny hills at the edges of our Northeastern forests, where the soil is acid.
Soil ranges from acid to neutral to alkaline. Acid soils are commonly found where rainfall is heavy and a lot of leaves and bark and, let's face it, dead animals fall on the ground. Two forces come into play: Rain leaches alkaline minerals out of the soil, and the decaying plant and animal stuff releases humic acid. Most plants grow fine in mildly acid soil. But blueberries and rhododendrons, mountain laurels and heathers, all relatives in the ericacaeae family, must have the acidity to thrive. The soil need not be fertile, however. In Maine and the Maritime Provinces of Canada, blueberries are the weedy pioneers in burned-over fields. In the Midwest, they grow best in the sandier lakeside parts of Michigan.
The West begins, writer Joan Didion observed, where the annual rainfall drops below 20 inches a year. The West also begins where that low rainfall leads to alkaline soil. Blueberries are unhappy in the dry West because the alkalinity in the soil reduces the availability of certain elements, principally iron, that they need. (Though they can grow in the rainy Pacific Northwest.)
If you do a soil test and find that your garden soil isn't acid enough for blueberries (a pH of between four and five is ideal), you can add sulfur. I recommend the chelated form—small, lentil-like pellets—because it's less messy and cheaper than the powder. Work it gently into the surface of the soil. You can also use any good fertilizer marketed for azaleas and rhododendrons.
Add the fertilizer very gently, because you don't want to disturb blueberry roots. They're fine and sit near the surface, and they need constant moisture, coolness, and a lot of organic matter. A quick way to raise your odds of success is to mix a bucketful of peat moss into the soil in the planting hole. After planting, add four inches of mulch, ideally pine needles or pine bark. Plant the bushes in spring in cold regions, autumn in mild.
Like almost every kind of fruit-producing plant, blueberries don't tolerate clay soil. It has varying levels of acidity; more important, it doesn't drain well. You'll note from the labels that early blueberries in the market come from the sandy, fast-draining pine barrens of New Jersey.
Why go to the trouble of growing them? "Anyone who doesn't grow blueberries is a fool," declares Lee Reich, author of Uncommon Fruits for Every Garden, who has grown 30 blueberry plants for 20 years, watering them only the first three years and never using pesticides. (By the way, people generally think gardeners are gentle, patient types who are placidly in touch with the seasonal cycles. In fact, the majority of pros are entertainingly cranky, opinionated, and antisocial.) In addition to blueberries' good taste (even uncooked), they're pretty (fall leaf color of red and orange) and they've gotten expensive. They've increasingly been marketed as low in fat and high in antioxidants, which are supposed to protect us from free radicals. (Antioxidants and free radicals being terms tossed about by health-food-store staff that are fully understood by about six people in the world.) Probable though not yet scientifically proven, the case for the blueberry as a life-extender and -enhancer has significantly raised demand for them in Europe and Asia, particularly Japan. (How long till we see a salmon-blueberry sushi?) This is good news for our trade imbalance: 90 percent of the world's crop is produced in North America, a quarter of that in Maine.
The kind of blueberry bush that turns northeastern hillsides red and orange in fall is the low-bush blueberry. Its fruit is more expensive, because the smaller bushes (less than two feet tall) grow smaller berries that are hand-picked. Wild stands of low-bush blueberries are managed commercially, a rarity among food crops. The high-bush grows up to six feet and can be harvested mechanically (a machine shakes the bushes and puts the ripe berries that fall onto a conveyor belt). This plant produces the plump, large berries you see in grocery stores. There's also a blueberry called rabbiteye that grows in the south; it can produce flowers without a freeze.
Blueberries are a good crop for small farmers not only because their price is high but also because they have a longer shelf life than many other berries. (Raspberries turn moldy capriciously.) Blueberry skins have tannins, related to those blue anthocyanins, with antimicrobial qualities that inhibit rot.
The most touching blueberry fact: In the early 1860s, the town of Bethel, Maine (then pop. 2,523), sent its young men off to the Union Army with dried blueberries in their packs. Though they played no starring role in the Ken Burns documentary, blueberries were made into juice for Civil War soldiers as a scurvy preventive.
I, too, a gardener and erstwhile pro, can be cranky and opinionated. Two instructions: Should you find yourself driving through Maine this summer and see a sign for a church supper or volunteer fire department breakfast, take advantage of a chance at a sublime pie or pancake. And should you make a blueberry pie or crumble at home (blueberries freeze well, so you can do this any time of year), add only lemon zest and cinnamon and use half the sugar called for in the recipe.