Blueberries are a glorious crop for the blue-sky days of midsummer, but not every gardener gets this one right.
You’d think that the native highbush blueberry would be a snap — a large, self-contained shrub without the suckering habit of raspberries (or the thorns). But blueberries make a demand on you that’s out of step with most other edibles in the garden. It requires acidic soil. If you’re like most people, all the growing beds of your garden have been limed at one point or another, because most crops prefer a neutral pH (that is, around 6.5 to 7.0). But blueberries are delighted with a pH of 4.5 to 5.5. You must lower the pH to make certain essential elements available to them, notably iron, zinc and manganese.
How to do it? It makes sense to till acidic materials into the soil before planting blueberries, and to topdress or mulch with them once the bushes are established. Popular additions include peat moss, autumn leaves and leaf mold, regular backyard compost, manure, coffee grounds and pine needles. And all of these, in fact, are worth adding, not only for their acidity but also for their water-holding capacity. But people often complain to me that their blueberries have failed to thrive, despite these efforts. Our farm has quite acidic soil, and even here these materials are not always enough.
In cases such as this, the addition of sulfur solves the problem and makes blueberries grow beautifully. We don’t like to use chemical fertilizers at our place, so we avoid formulations such as ammonium sulfate or aluminum sulfate and go with an elemental sulfur approved for organic growers. The one we’ve used is Tiger Organic 0-0-0-90, made by Arbico Organics, which we found at a local feed store. (Those numbers indicate that it contains no nitrogen, potassium or phosphorus, just 90 percent sulfur.) It’s in pelleted form, and a 50-pound bag covers up to 10,000 square feet. Sandy soils might need one-third less, and clay soil might need up to one-half more. If you’re unsure about how to proceed, consult your local agricultural extension service (www.csrees.usda.gov/extension).
First off, it will help if you already have a living soil, not chemically nourished, so that a healthy population of soil bacteria stands ready to help the product decompose. Second, wait until the temperature is at least 60 degrees; better yet, 70 to 80. And third, water deeply. Nirvana for a blueberry plant is to perch on the edge of a pond or a swampy area — or on a hummock therein. So irrigate the bed until the moisture applied from above meets the ground moisture below, with no dry layer in between.
All this applies as well to the rabbiteye blueberry, native to the American Southeast, as it does to the Northeastern highbush blueberry. Gardeners in the Washington area, poised between North and South, can take their pick.
Damrosch’s latest book is “The Four Season Farm Gardener’s Cookbook.”
Porcelainberry is a highly invasive alien vine that is growing rampantly on trees and bushes, and it’s flowering. Pull it to prevent fruit set next month, and dig out its roots. Don’t confuse this vine with poison ivy, which has three distinct leaflets.
— Adrian Higgins