White asparagus offers a unique flavor and tender texture that distinguishes it from its green counterpart. Celebrated in Europe, this prized vegetable is the same plant as green asparagus, but its pale color results from a specific cultivation technique.
Understanding White Asparagus
The distinct white color of white asparagus arises from etiolation, a process that deprives growing spears of sunlight. Without light, the plant cannot produce chlorophyll, the pigment responsible for green color. This lack of chlorophyll development changes its appearance, taste, and texture.
White asparagus has a milder, sweeter flavor with less bitterness than green asparagus, and its texture is more tender and delicate. While green asparagus can have a “grassy” taste, the white variety offers a subtle, sometimes nutty, aroma.
Preparing Your Garden Site
Preparing the ideal growing location is important for white asparagus, a perennial crop productive for 15 to 20 years or more. Asparagus thrives in full sun, requiring at least 6 to 8 hours of direct sunlight daily. A well-drained site is important, as asparagus does not tolerate standing water.
The soil should be deep, loose, and rich in organic matter to accommodate its extensive root system, which can reach 5 to 6 feet in diameter and 10 to 15 feet deep. Before planting, amend the soil with ample well-rotted compost or aged manure to enhance fertility and drainage. Asparagus prefers a slightly acidic to neutral soil pH, ideally between 6.5 and 7.0, so a soil test before preparation can help determine if amendments are needed.
Planting Asparagus Crowns
Asparagus is planted using one-year-old dormant roots, known as crowns, in early spring, a few weeks before the last frost. Before planting, soak the crowns in water for one to two hours to rehydrate them. Prepare a trench approximately 6 to 12 inches deep and 12 to 18 inches wide, with shallower depths for heavy clay soils and deeper for sandy soils.
Within this trench, create small mounds about 4 inches high at the bottom. Place the asparagus crowns on top of these mounds, spreading their roots evenly with the growing buds facing upward. Space crowns 12 to 18 inches apart within the trench; if planting multiple rows, ensure rows are at least 3 to 4 feet apart for plant spread. Initially, cover the crowns with only 2 to 3 inches of soil and water thoroughly to settle the soil around the roots.
Achieving White Spears (Blanching)
The distinctive white color of asparagus spears is achieved through blanching, a process that prevents sunlight from reaching the emerging shoots. As the asparagus spears begin to emerge from the soil in early spring, when they are just a few inches tall, they must be completely covered.
One common method involves mounding loose soil, straw, or compost directly over the emerging spears. The mound should be substantial enough to completely block out all light, often reaching 8 to 12 inches high. Alternatively, specialized blanching covers, such as dark buckets, drainpipes, or black plastic sheeting, can be placed over individual plants or rows. The goal is to maintain complete darkness around the growing spears.
Consistency in covering is crucial; any exposure to sunlight will cause the spears to begin greening. The covering material also helps to keep the soil loose, allowing the tender spears to push through easily without becoming tough. Monitoring the mounds frequently, perhaps every day or two, helps ensure spears are harvested before they break the surface and are exposed to light.
Ongoing Care and Maintenance
After planting and blanching, ongoing care maintains a healthy and productive white asparagus bed. Consistent soil moisture is important, especially during dry periods, as asparagus needs at least one inch of water per week. Deep watering is preferable to frequent shallow watering.
Annual fertilization contributes to vigorous growth; a balanced fertilizer or well-rotted compost can be applied after harvest. Weed control is important, as asparagus has shallow roots easily damaged by aggressive weeding. Mulching with organic materials like straw or wood chips helps suppress weeds and conserve soil moisture. Allowing the fern-like foliage to grow throughout the summer after harvesting helps the plant photosynthesize and store energy in its crowns for the following year’s crop.
Harvesting and Long-Term Yield
White asparagus requires a waiting period of two to three years after planting crowns before the first harvest. This allows plants to establish a robust root system for long-term productivity. When spears are ready, reaching 6 to 10 inches in height and about pencil thickness, harvest them by cutting just below the soil line. This method ensures spears remain white and tender.
The harvesting season lasts about 6 to 8 weeks in established beds, from mid-April through June. Spears can emerge quickly, sometimes within a day, so daily checks are useful. After harvest, let remaining spears grow into tall, ferny stems; these ferns are important for photosynthesis, replenishing energy reserves in the crowns for the next season. In late fall, once ferns have yellowed or turned brown, cut them back to the ground. Applying a layer of winter mulch helps protect crowns and contributes to continued productivity for many years.