Growing Asparagus - January 21, 2015
Jeff Schalau, Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County
Asparagus is a perennial vegetable that thrives with moderate care and, following establishment, will produce a spring harvest of fresh succulent spears for years to come. Asparagus prefers an area with full sun and well-drained, sandy loam soil. The asparagus bed should be kept free of perennial weeds such as field bindweed, bermudagrass, or johnsongrass. Choose the location of your asparagus bed wisely as it will likely be in that spot for 15 years or more.
Asparagus plants are dioecious, meaning they produce male and female flowers on separate plants. Some varieties are all-male hybrids that do not produce seed. The most popular varieties are UC157 (male and female plants), Jersey Giant (male only), and Jersey Knight (male only). These three varieties have done well in trials in Utah and produce large, pale green spears and the plants have good disease resistance. The once popular “Washington” varieties are no longer recommended.
Most home vegetable gardeners plant asparagus crowns (established plants with roots attached). Growers grade the crowns as “1-year”, “2-year”, and “3-year” from smallest to largest. In reality, all are one year-old crowns grown from seed or division. Larger crowns have greater vigor and are preferred. Buy crowns or seed from a reputable nursery or seed catalog. The plants get big and rangy (5-6 feet tall), so plant them on the north or east side of your garden to avoid shading other low-growing crops. Plant crowns or seed after the soil has reached 50 degrees F.
Asparagus yields 8 to 10 pounds or more or spears per 100 square feet of bed when well-tended. For most home gardeners, a 20-foot row or 100 square feet of bed is adequate for a family of four. That’s equivalent to 20 planted crowns or 10 pounds of harvested asparagus per season.
When planting seed or crowns, dig a 10-12 inch deep hole and then till and amend the soil in the bottom of the hole. An application of phosphorus fertilizer incorporate into the soil before planting will ensure vigorous root growth. Seeds can be sown and covered with a little soil. If crowns are to be used, they should be spaced 1 foot apart in rows. Each row should be 4 to 5 feet apart. Crowns should have buds facing up and root systems spread out as much as possible. During the first growing season, cover the crowns with loose soil one or two inches at a time as they grow taller. The beds should be filled to the original soil level by early to mid-summer.
Continue adding the soil over time to establish deep crowns. Most references recommend not harvesting any spears during the first year. Instead, allow the plants to grow wildly, fertilize with nitrogen, and keep them well irrigated. This will allow them to photosynthesize at maximum potential and store that energy in the crowns for the following year’s crop. Maintain a 4 to 6 inch deep layer of straw/hay/leaf mulch to suppress weeds and keep the soil friable. Add compost, manure, or nitrogen fertilizer each year following spring harvests. Add that same amount of fertilizer again in July. The idea is to build up energy in the crowns each year.
The following spring, before asparagus emerges, remove the dead tops from the prior year and weed the area. Only harvest a few spears the second year allowing the rest to grow. The third spring, you may start harvesting spears after they reach 7 to 10 inches in length. Harvest spears below ground with a sharp knife. The spear should be green and tender. Spears should be large at the beginning of the spring growth flush. In time, successive spears will become smaller. A simple rule is to never harvest a spear smaller in diameter than a pencil. Allow these pencil-sized plants to grow and store energy for the following year. More information on growing asparagus is also included below.
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Asparagus in the Garden
Utah State University Cooperative Extension
Growing Asparagus in Minnesota Home Gardens
University of Minnesota Extension
Asparagus Information Bulletin
Cornell University Cooperative Extension
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Last Updated: January 13, 2015
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