Asparagus is a long-lived perennial vegetable that can provide decades of spring harvests once established. Because this crop occupies the same spot for many years, the initial choice of planting time and location is important for long-term success. Illinois’s significant north-to-south length means gardeners must consider their specific microclimate. This article focuses on the precise timing and method for successfully planting asparagus crowns.
Optimal Planting Window in Illinois
The best window for planting asparagus crowns in Illinois is determined by the condition of the soil, not a fixed calendar date. Gardeners should plant as soon as the soil is workable in the spring, meaning it is no longer frozen or excessively waterlogged. This period generally begins in mid-to-late March in Southern Illinois and extends through early May in the northern parts of the state, with Central Illinois falling between those dates.
Planting in this spring window allows the crowns to establish their extensive root system before the stress of summer heat arrives. The ideal soil temperature for planting is around \(45^\circ\text{F}\) to \(50^\circ\text{F}\), which is cool enough to keep the dormant crowns from sprouting too quickly. Planting one-year-old crowns, rather than seeds, is recommended as it shortens the waiting period for the first harvest by at least a year. The goal is to get the roots into the ground and ready to grow.
Preparing the Planting Site
Asparagus plants will remain in the same location for 15 to 20 years, making advanced site preparation a high priority. The bed must be situated in a spot that receives full sun, defined as six to eight hours of direct sunlight daily. Well-drained soil is necessary, as asparagus crowns will quickly rot in saturated conditions. Raised beds should be considered if the site has heavy clay or poor drainage.
Before planting, the soil needs deep preparation, involving loosening it to a depth of 12 to 15 inches to accommodate the developing root system. Amend the soil with aged compost or manure to improve structure and fertility. Asparagus thrives in a neutral to slightly acidic environment, ideally with a soil pH between 6.5 and 7.2. A soil test should be performed to determine if lime is needed to adjust acidity. Gardeners should select all-male hybrid varieties, such as ‘Jersey Knight’ or ‘Millennium,’ because they dedicate their energy solely to spear production, resulting in higher yields.
Step-by-Step Planting Method
Planting the asparagus crowns begins with digging a trench 12 to 18 inches wide and 6 inches deep. Within this trench, create a low mound or ridge of soil down the center to support the crowns. This ridge allows the fleshy roots to be spread out uniformly and downward.
The crowns should be positioned 9 to 18 inches apart along the ridge, ensuring the buds face upward. After positioning the crowns, cover them initially with only about 2 inches of soil, avoiding compaction. The remainder of the trench will be filled gradually over the course of the first growing season. This incremental backfilling prevents young spears from having to push through a deep layer of soil all at once.
First-Year Establishment and Harvest Timeline
After the crowns are planted, careful management is required to ensure the plant stores enough energy for future harvests. During the first year, the focus is on establishment, which means maintaining consistent soil moisture and aggressive weed control. Weeds directly compete with the crowns for water and nutrients, so they must be removed regularly. Cultivation should be shallow to avoid damaging the roots.
As the spears grow, continue to add soil incrementally to the trench until it is level with the surrounding garden bed. The spears must be allowed to grow into tall, fern-like foliage, which is responsible for photosynthesizing and storing energy in the root system for the next season. No spears should be harvested in the first year. A light harvest, lasting only one to two weeks, may be taken in the second spring if the ferns were vigorous. The asparagus patch will reach full production potential, allowing for a standard six-to-eight-week harvest period, starting in the third year after planting.