Asparagus is a perennial vegetable often harvested as one of the first crops in spring. The question of whether it grows underground is nuanced: the plant’s permanent structure is below the soil, but the edible portion is a shoot that grows rapidly above the surface.
The Underground Structure of Asparagus
The permanent, below-ground body of the asparagus plant is called the “crown,” which functions as the plant’s energy storage and growth center. This crown consists of a dense, fleshy mass of roots and an underground stem called a rhizome. The fleshy roots are packed with carbohydrates that the plant uses to fuel the initial rapid emergence of spears in the spring.
The crown allows asparagus to remain productive for 15 to 30 years in the same location. The rhizome portion of the crown grows horizontally and vertically, producing new buds annually from which the spears originate. These buds remain dormant until soil temperatures rise consistently above 50 degrees Fahrenheit, signaling the start of the growing season.
How the Edible Spear Emerges
The edible asparagus spear is technically a young stem shoot that sprouts from the buds on the underground crown. This shoot grows vertically, pushing upward through the soil layer to reach the sunlight. Once the spear breaks the soil surface, it begins to photosynthesize, giving it the characteristic green color. If a spear is prevented from exposure to light (by mounding soil over it), it remains white, which is the method used for white asparagus. The spear is only tender and edible in this tightly packed, unbranched stage before the tip begins to unfurl into feathery foliage, a process called “ferning out.”
Harvesting and the Life Cycle
Spears are typically harvested when they are between six and ten inches tall and still have tight tips. Growers cut the spears using a knife at or just below the soil line, or they snap them off by hand near the base. The harvest season is limited, usually lasting six to eight weeks in the spring, as the spears must be allowed to mature into ferns eventually. The fern-like foliage is the mature stage of the stem, and its role is to capture solar energy through photosynthesis. This energy is transported back down to the crown, where it is stored as carbohydrates for the following year’s spear production.