ASPARAGUS

By Henry G. Taber and Vince Lawson

Department of Horticulture

Iowa State University

Updated: June 2008

 

Asparagus is a member of the lily family. Once established, a well cared for asparagus bed should remain productive for 15 to 20 years.

For up-to-date information on varieties and pest managaement obtain FG-600, titled "Midwest Vegetable Production Guide for Commercial Growers", from your local county extension office or from Extension Distribution Center, Printing and Publications Bldg., Iowa State University, Ames, Iowa 50011. You may also access the publication online my using the link on the ISU commercial vegetable homepage

PLANTING

Asparagus requires full sunlight and a well-drained soil though it is adapted to a wide range of soil types -- sandy to silty clay loams. It is usually started from one-year-old roots. Establishing a bed from seed or transplants is possible, but it is much more difficult. A deep sandy loam soil is best. Choose a field not previously planted to asparagus, also avoid fields that have been planted to corn within the last two or three years to reduce severity of the soil borne disease, Fusarium.

Early spring is the best time to plant asparagus crown, from April 15 to May 15. Proper soil preparation is essential. Be sure to apply necessary P and K fertilizer according to soil test the previous fall. For home gardens, thoroughly work well-rotted manure or compost into the top 8 to 10 inches of soil. If this cannot be accomplished in the autumn, manure or a complete fertilizer may be placed in the bottom of the trench when planting. The asparagus roots may be injured is set directly on the fertilizer. For example, apply 100 lbs of 8-32-0 (or similar) in the bottom of the trench at planting, cover with 1" of soil before laying crowns.

The asparagus crown should be planted in a wide trench 6 to 8 inches deep in light, sandy soils and only 5 to 6 inches deep in heavy soils. Spread the roots out in the bottom of the trench with the buds pointing upward. Then cover with 2 inches of soil. Slowly backfill the remainder of the trench as the plants grow through by cultivating. The trench should be completely filled in by midsummer. Research has indicated that shallow planting (les than 5" deep) will produce more, but slightly smaller spears than deeper plantings. Crowns planted too shallow are more susceptible to tillage damage. Also, they will emerge earlier in the spring but will be more vulunerable to freeze injury.

While asparagus is usually started from crowns, it may also be started from seed. Because of the expense of the newer male sterile hybrid varieties, the seed should be started in a greenhouse. The seedlings should be ready for transplatning in 10 to 12 weeks. Irrigation is essential to ensure survival of the new planting.

SPACING

Asparagus crowns should be planted in rows 4 to 5 feet apart, 12 to 18 inches between crowns. The new male sterile hybrids do well in rows 5 feet apart and crowns set 16 inches apart in-row.

Seed should be planted in rows 18 to 24 inches apart, thin to 4 inches between plants when seedlings are 3 inches tall. Transplant roots the following spring.

FERTILIZING

For maximum yield, asparagus should be fertilized early. It manure is available, apply 50 pounds per 100 square feet in late fall or early spring. Apply P and K according to soil test reports the fall before planting. Before planting, apply 50 pounds of N/acre broadcast and disked in. Each year before spears emerge, apply 500 lbs/acre of a 1-1-1 analysis. After last harvest in June, apply 35 to 50 pounds of actual N/acre as a sidedress application. Response to a sidedress N application is questionable on Iowa's heavier soils with an organic matter content >3.0%.

VARIETIES

Mary Washington and Waltham Washington -- old time standards that are no longer recommended.

Hybrid varieties have improved vigor, disease tolerance, and higher yields, and are grown from seeds or crowns.

All-male hybrids. All-male hybrids produce only male plants that do not develop berries or seed. Thus, all the energy that would normally go into seed production in dioecious varieties is available for transfer into the crowns and roots making a larger more vigorous plant. Also, since no seed is produced, the asparagus seedling weed problem is eliminated.

  • Jersey Giant - the first male variety released and one of the best known. Widely adapted, strong consistent yields. Susceptible to Fusarium crown rot but because of vigor will maintain better yields over the years than standard (dioecious) varieties.
  • Jersey Knight - has become one of the most popular. Selected for it's vigor in fusarium infested soil. Widely adapted, probably best tolerance to fusarium and rust, produces a large green spear with pruple bracts, considered to be excellent quality. Good variety for replanting asparagus beds because of disease resistance.
  • Jersey Supreme - new release has been extremely vigorous and productive in trials.

Other hybrids. Atlas, Apollo, and Grande - new hybrids (dioecious, not all-male) released by California Asparagus Seed & Transplants, Inc. that combine traits from UC 157 with the vigor of the Jersey lines. Grande has large spears. Tested in California since late 1980's and have outyielded UC 157 by about 25%. They are not fully tested in the Midwest yet and winter hardiness and disease resistance over time is unknown. Also, they have female plants and the accompanied seed problem.

Purple Passion - has become a home garden novelty. Developed in 1989 by Dr. Brain Benson, California Asparagus Seed and Transplants, Inc. from "Violetto d' Albinga" which is an open pollinated widely diverse cultivar from the western Mediterranean coast of Italy. Purple Passion produces a striking all-purple spear which turns green when cooked. Also reported to be sweeter and more tender than green asparagus. in Iowa trials it has produced fewer, but larger, spears than other cultivars. Well suited for specialty or niche markets.

UC 157 F1 -- a clonal hybrid released in 1975 from the University of California. Good yield potential in Iowa but smaller, thinner spears than the newer hybrids. Also, spears tend to have less purple pigment in the tips than hybrids like Jersey Knight. Winter hardiness and gradual decline in vigor may be a problem in parts of Iowa.

In 1995 a asparagus trial was iniated at several Iowa research stations. A six year replicated trial was carried out at the Muscatine Island Reserach Farm, Fruitland, IA(southeast) and observational plantings were established at Kanawha (north central), Lewis (southwest), and Sutherland (northwest). The Fruitland trial location provided a coarse sandy soil with supplemental irrigation. Conversely, all of the observational plantings were located on fine-testured loam soils and relied on rainfall for moisture. The final summary results are located in the 2003 Fruit/Vegetable Progress Report located on this web site.

Based on yield potential and spear quality we would recommend the all-male hybrids Jersey Supreme and Jersey Giant for new Iowa plantings. Jersey General, Jersey King, and Jersey Knight have also shown good spear quality but lesser yield potential. Grande and Atlas should be considered as alternatives to UC 157 because of their plant vigor and larger spear size, but note that they are dioecious hybrids and the plantings will contain both male and female plants and have the associated volunteer asparagus seedling problem.

PEST MANAGEMENT

For up-to-date information pest managaement control options, as well as weed control, obtain FG-600, titled "Midwest Vegetable Production Guide for Commercial Growers", from your local county extension office or from Extension Distribution Center, Printing and Publications Bldg., Iowa State University, Ames, Iowa 50011. You may also access the publication online my using the link on the ISU commercial vegetable homepage

A poor crop of thin, small spears may be due to several factors. Asparagus prefers a well-drained soil and plants will eventually die out in poorly drained soils. Asparagus should also be fertilized yearly for maximum fern growth that results in large foot reserves in the crown for next year's crop. Harvesting asparagus spears beyond June 15 will reduce the plant's foliar growth and food reserves. As a result, the crop the following spring will be small.

Weed problems

Weeds compete for light, water and nutrients with asparagus and will reduce vigor of the bed if not controlled. Few herbicides are labeled for use on newly planted asparagus. Thus, it is important to plan ahead and use a field with low weed popu;ations, particularly perennial weeds. hand hoeing and mechanical cultivation can be done the first year. poast herbicide can be used for grass control. Gramoxone or Roundup can burn-down weeds before spears emerge.

Current strategies favor no tillage of the asparagus bed once plants have become established. Tillage hurts crowns and roots, brings up new weed seed and can actually make the volunteer asparagus weed problem worse. Before new spears emerge in the spring chop off old ferns to facilitate harvest and apply preemergent herbicide. After last harvest of seasons reapply a preemergent herbicide, if needed. Roundup or 2,4-D can be used to spot treat perennial weeds.

Salt should not be applied to asparagus beds for weed control. Although asparagus will tolerate higher soil salinity than most crops, continued salt use will destroy the soil structure and lead to poor asparagus growth.

Insect problems

There should be little insect and disease damage most growing seasons. The asparagus beetle is the most common insect found in the bed.

Asparagus beetle - There are two types: spotted and common. Each over winter as adults and have 2 to 3 generations per year. The adults lay eggs on the spear tips resulting in an unmarketable appearance. Harvest spears regularly for control. The larvae chews and strips off the green fern leaves.

Cutworms - Feed on the butt of harvested spears, tips, and side of the spears. The feeding damage reults in curved, twisted spear growth.

European Asparagus Aphid - This pest can be serious in the midwest. The aphid does not feed on the spears, but feeds on ferns after harvest and over winters on the fern. Thus, the fern growth becomes dwarf, bonsai like in appearance. The plants are susceptible to winter injury and ultimately to Fusarium infection.

Plant Bugs - They are like aphids with sucking mouth parts. They feed at the tip causing 'tip die-back'.

Leaf miner - The pupae over winter just under the stalk surface. The pupae are contaminated with fungi fusarium resulting in the spread of stem, crown, and root rot.

Diseases

Root rots - There two major types: Fusarium oxysporum and Fusarium moniliforme. The F. oxysporium type is very common and is inherent is all soils. Under stress conditions it can infect the stems, crowns, and roots. The ferns turn yellow in mid-summer, and the crown tissue browns rather than remaining white. The fungi plugs the vascular tissue restricting water flow. The F. moniliforme type is less common, but more serve. It will kill plants outright in a short time. Wet areas of the field are highly susceptible.

To control the root rots avoid plant stress factors such as, low pH, fertility, excessive cutting, and poorly drained soils. Use tolerant varieties and control insects, diseases, and weed growth.

Rust - Prevalent under cool, heavy dew, and/or high rainfall conditions. It has not been a major problem in Iowa, even in the flood year of 1993. UC 157 is more susceptible to rust than the newer New Jersey male hybrids.

Frost - Although not a disease, asparagus is susceptible to frost damage. Low temperatures < 33oF can damage the spears. It may take 5 days for new spears to emerge. Do not extend the harvest season to make up for the loss.

For control of insect and diseases obtain a copy of FG-600, titled "Midwest Vegetable Production for Commercial Growers" from your local county extension office or Ag Publication and Distribution Center, Iowa State University, Ames, IA 50011.

HARVEST

No asparagus should be harvested during the first growing season. Harvest for about 2 weeks early in the second year and until June 15 in each year thereafter.

Harvest 6 to 8 inch spears by cutting or snapping. Use a sharp knife to cut the spears at the soil surface or snap the spears slightly above the ground. Spear diameter should be greater than 3/8 inches. It takes about 3 hours per day to harvest one acre, unless you are using a harvest-aid type of machine.

Asparagus foliage should be allowed to develop after the final harvest. The top growth produces food reserves which are stored in the roots for next spring's crop. Leave the tops standing overwinter to accumulate snow as this provides insulation against extreme cold and sudden changes in soil temperature. Disk under the dead foliage in early spring before new growth begins.

A well cared for planting should produce good yields for 15 to 20 years.

YIELD

Statewide yields have been from 800 to 1,400 lbs/acre. Jersey Giant and UC 157 have yielded 4,000 or more lbs/acre in research trials.

Home gardeners should harvest about 3 to 4 lbs/10 feet of row.

POST HARVEST CARE

Wash with cool water, and cool or store at 32 to 36 F and 95 percent relative humidity, for up to 2 or 3 weeks. The stalks develop tough fibers if stored under warmer temperatures. Bunches vary from 7-10 1/2 inches long and weigh from 1/2 to 2 lbs.

BUDGET

The most current budget information, and suitable for Iowa estimates, is from the University of Kentucky information. Click here (a pdf ) to see the 2005 estimates. They use an aveage wholesale price of $1.49 per lb. Some Iowa average wholesale prices for the month of May were $1.36 in 2006, $1.44 in 2007, and $2.07 in 2008. Also, fertilizer rates and costs would be different for Iowa. For example, lime would probably not be needed. And, KY annual yield values are lower than for Iowa production using the male sterile hybrids. Nonetheless, the spreadsheets illustrate typical operation sequence, machinery, and labor use. You can insert your own values for an estimated budget.

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