Growing Asparagus - February 21, 2007
Jeff Schalau, Associate Agent, Agriculture & Natural Resources, Arizona Cooperative Extension, Yavapai County
Asparagus is a perennial vegetable that thrives with little care and can produce an early spring harvest of fresh succulent spears. Asparagus prefers well-drained, sandy loam soil and comes back each year from underground storage roots and rhizomes. For some, asparagus is an acquired taste. However, if you like asparagus, it is an interesting crop that is usually expensive when purchased at the market.
Most backyard gardeners plant asparagus crowns. The nursery industry grades 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. Larger crowns have greater vigor and are preferred. Buy crowns or seed from a reputable nursery or seed catalog. Asparagus requires a garden area with full sun where it will grow for many years. 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 after the soil has reached 50 degrees F.
When planting seed or crowns, dig a 10-12 inch hole and then till and amend the soil in the bottom of the hole. A liberal dose of phosphorus fertilizer should be added to the soil before planting. Phosphorus will help 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. Cover the crowns with loose soil up to the original soil level at the bottom of the hole.
Once plants are one foot tall, backfill them with 6 inches of soil. Continue adding the soil over time to establish deep crowns. Do not harvest during the first year. Instead, allow the plants to grow wildly and keep them well watered. This will allow them to photosynthesize at maximum potential and store that energy in the crowns for the following year’s crop.
The following spring before asparagus emerges, remove the brushy, dead tops, weed the area, and fertilize with 1.2 pounds of 5-10-10 fertilizer per 100 square feet of bed. Only harvest a few spears the second year allowing the rest to grow. Sidedress that same amount of fertilizer again in July. The idea is to build up energy in the crowns each year.
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. A simple rule is to never harvest a spear smaller than a pencil. Allow the remaining plants to grow and store energy for the following year.
Asparagus plants are dioecious, meaning they produce male and female flowers on separate plants. The seedlings produced by these plants can sometimes become a weed problem. Some varieties are all-male hybrids that do not produce seed. The most common varieties are UC157, Mary Washington, and Martha Washington, Jersey Giant, Jersey Knight, and Jersey King. UC157 is probably the best variety for our climate. For more information on growing asparagus, see the Texas A & M Cooperative Extension publication at: http://aggie-horticulture.tamu.edu/extension/easygardening/asparagus/asparagus.html.
What about the age-old question about why eating asparagus can result in odd smelling urine (rotten cabbage, ammonia, etc). Biochemists have isolated sulfur-containing compounds including, but not limited to methyl mercaptan. These odd smelling compounds are likely to be caused by the breakdown of asparagusic acid: a compound unique to asparagus.
The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at firstname.lastname@example.org and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/.
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