Gardening Articles: Edibles :: Vegetables
by Christopher O. Bird
For several years in the 1980s, my wife and I lived just north of Germany's Black Forest, where one culinary highlight in late spring and early summer is white asparagus. More tender, milder, and nuttier in flavor than green asparagus, it quickly became our favorite vegetable, though we'd never particularly liked the green type. In general, white asparagus is preferred over the green type in Europe, though some Americans find it less sweet. White seemed to be the only kind of asparagus grown in southwest Germany, and today, it's the only kind I grow in southwest Virginia.
Actually, white asparagus is not genetically different from the green kind. It's simply any asparagus grown in the dark, or blanched. The traditional way to blanch asparagus is to mound mulch or sand around the spears as they emerge. But that technique is a lot of trouble, because it must be done daily, and it makes the spears grubby. All that's really required to blanch them is to keep them under an opaque cover.
A Simple Blanching Method
I grow my asparagus in a 4-foot-square raised bed, framed by 2 x 12's of lumber. I use pressure-treated lumber, but if you're leery of pressure-treated wood in the garden, consider applying a wood preservative to untreated wood or using rot-resistant cedar. The resulting structure looks like a sandbox. During each spring harvest, I cover the entire bed so the spears are in complete darkness, except during the few minutes required to cut spears every couple of days.
I use a simple method to keep the plants in the dark: I cover the raised bed with another box that's basically a second 4-foot-square frame with a top made of 1/2-inch plywood. The asparagus shoots grow inside this box. I simply set the top on the raised bed, without hinges or other attachments.
Untreated pine is fine for this, because it's lighter and cheaper and doesn't rot during its brief period of annual use. (The top stays in the basement the rest of the year.) However, the top is fairly heavy (about 75 pounds) and awkward to maneuver. Many gardeners would need help. I wanted the cover to withstand the strong spring winds here in the Appalachian foothills. An alternative in other regions might be to use 1 x 12's, then weigh down the top with bricks if necessary.
Even if I were growing green asparagus, I would still use a deep raised bed filled with rich soil to ensure vigorous plants and harvests. In fact, I use the same kind of bed for my strawberries and all my annual vegetables.
How to Build a Covered Raised Bed
Here are some tips for constructing sturdy raised beds out of 2 x 12's. First, use treated, preserved, or rot-resistant lumber as described above. Untreated wood rots in a few years, and replacing it around a bed like this is awkward. To avoid gaps and soil leakage, make sure your cuts are straight and square. Use three 4-inch deck nails (the ribbed kind used in deck construction) per joint. Smaller or nondeck nails don't hold as tightly.
If you like, you can trim the top edges of the bed with 2 x 4's. Attach them wide-side-up to the edges of the raised bed frame. The molding makes it easier to set on the top cover.