White asparagus is a culinary delicacy that is botanically identical to its common green counterpart, Asparagus officinalis. The striking difference in color is not due to a separate plant variety but is a direct result of specialized cultivation. The pale, tender spears are grown entirely without light, a process known as etiolation, which prevents the natural development of the green pigment, chlorophyll.
Preparing the Ground for Growth
The journey of white asparagus begins with careful site selection, as the perennial plant is expected to produce for 15 to 20 years from a single planting. Growers typically plant one- to two-year-old root structures called crowns, which establish much faster than starting from seed. The longevity of the bed necessitates deep, well-drained, and loose soil, often sandy loam, to allow for the extensive root system to develop freely.
The ideal soil pH is slightly acidic to neutral, between 6.5 and 7.0. Crowns are initially placed in trenches, commonly 5 to 8 inches deep, with the roots spread out. As the first spears grow, the trenches are gradually filled with soil over the course of the first season. This establishes the base for the unique growing method that follows.
Achieving the Signature White Color
The signature white color is achieved through etiolation, the process of growing the plant in the absence of light. Asparagus spears naturally develop chlorophyll when exposed to sunlight, turning them green. Blocking this exposure keeps them pale, as the moment a spear breaks the soil surface and is hit by light, it immediately begins producing the green pigment.
To prevent this, growers use a technique called “hilling” or “mounding,” where tall, compact ridges of soil are built over the rows of crowns in early spring. These soil mounds, or berms, can be 6 to 10 inches high and are carefully maintained. As the spears grow upwards towards the light, they remain buried within the mound, which keeps them blanched and produces the tender, mild flavor associated with white asparagus.
The thickness of the soil mound dictates the length of the white spear. Some commercial operations also use black or white polythene sheeting placed over the mounds. This sheeting helps maintain blanching while affecting the bed temperature to manage growth speed. The complete darkness within the soil ensures the absence of chlorophyll.
The Delicate Process of Harvesting
Harvesting white asparagus is a labor-intensive and precise operation because the spears must be cut before they emerge into the light. The grower monitors the soil surface for small cracks or slight bulges, which indicate a spear is pushing through just below the top of the berm. Timing is everything, as even a brief exposure to sunlight can trigger a color change and reduce the market value.
The worker carefully scrapes the soil away to expose the spear without damaging surrounding developing spears. A specialized long-handled knife is used to cut the spear near the crown, typically 6 to 8 inches below the soil surface. This cutting process requires skill to avoid injuring the delicate underground crown, which is the source of future spears.
After each spear is cut, the surrounding soil is immediately returned to the ridge and smoothed over to maintain the mound’s structure. This action protects the remaining spears from light exposure and ensures the ongoing productivity of the crown. Modern harvesting machines assist by lifting and replacing the polythene covers on larger farms, but the cutting itself often remains a manual task requiring patience and precision.
Maintaining Quality After the Cut
White asparagus is highly perishable and requires immediate attention after harvest to maintain its delicate quality and color. The spears have a high metabolic rate, meaning they continue to age and toughen rapidly once removed from the plant. Prompt cooling is necessary to slow this metabolic activity and prevent the loss of tenderness, which can increase rapidly.
The cooling process often involves hydro-cooling, where harvested spears are immersed in chilled water. This quickly brings their temperature down to the ideal storage range of 32°F to 36°F (0°C to 2°C). Maintaining a high relative humidity, between 95% and 100%, is also necessary to prevent desiccation and wilting. The harvested spears must be kept in the dark throughout handling and storage.
White asparagus is typically stored upright to prevent the spears from bending and is often packaged vertically. This careful post-harvest handling, including rapid cooling and dark storage, preserves the characteristic texture and appearance, contributing to the higher cost and reputation of this seasonal vegetable.