Asparagus is a perennial crop. The plant produces two distinct structures: the tender, edible spears that emerge in spring, and the tall, feathery ferns that develop later in the season. Pruning involves both harvesting the desirable spears and removing the old, dead foliage to prepare the plant for winter. Understanding this annual cycle is necessary for maintaining the vigor of the underground storage structures, known as the crowns.
When to Start Harvesting Spears
Harvesting in an established asparagus bed, typically in its third year or later, begins in early spring when the soil warms and the first spears emerge. Spears are ready for harvest when they are six to ten inches tall and have tight, compact tips. During the peak season, a daily harvest may be necessary because spears grow rapidly in warm weather.
The harvest period should last approximately six to eight weeks, though the exact timing depends on the plant’s vigor. Stop cutting when the new spears become noticeably thin, often less than the diameter of a pencil. Allowing the remaining spears to grow into ferns allows the plant to build up energy reserves for the following year. Spears can be harvested either by snapping them off by hand at or near the soil level, or by using a sharp knife to cut them just below the soil surface.
Post-Harvest Fern Management
Once the harvest window closes, the remaining spears grow into tall, bushy, fern-like foliage. This growth acts as the plant’s food factory for the rest of the growing season. The green ferns perform photosynthesis, generating carbohydrates and sugars that are stored in the root crowns. This carbohydrate storage is directly responsible for the number and girth of the spears produced the following spring. Removing healthy, green foliage prematurely severely limits the energy reserves the crown can accumulate. Therefore, no cutting or pruning should occur during the summer and early fall while the ferns are actively growing.
Cutting Back for Winter Dormancy
The second main pruning activity occurs once the growing season is over and the plant prepares for winter dormancy. The correct timing for this cutback depends on the condition of the foliage, not a specific calendar date. Gardeners should wait until the ferns have completely yellowed or browned and died back naturally.
This natural dieback usually occurs following a hard frost in late fall or early winter. Waiting for this stage ensures that all stored energy has been fully transferred from the foliage back into the underground crowns. The dead material should be cut back close to the ground, leaving a stubble of one to two inches above the soil line. Remove and dispose of this debris from the garden bed. This practice helps eliminate pests, such as the asparagus beetle, which often overwinter their eggs on the old fern stalks.
Pruning New Asparagus Beds
The establishment phase for a new asparagus bed requires patience, as the focus is entirely on strengthening the crown. In the first year after planting, no spears should be harvested; all emerging shoots must be allowed to develop into ferns. This restriction allows the young root system to establish itself and build a solid energy foundation.
During the second year of growth, a light, introductory harvest is permitted, lasting only two to three weeks. After this short period, cutting must stop so the remaining spears can grow into ferns for the rest of the season. In both the first and second years, the ferns are left to grow all summer and are only cut back once they die naturally in the fall, following the method used for established beds.