Note: Dr. Howard Ellison, Rutgers University, NJ, developed the "super male" genotypes used in "all-male" hybrid production, and is the originator of the all-male asparagus cultivars currently being used. Seed production of these hybrids is based on vegetative propogation (usually by tissue culture) of the parents.

Seed of all-male varieties produces only male plants. These all-male hybrid plants are higher yielding and more tolerant to diseases such as fusarium wilt and asparagus rust. They have greater longevity than female plants or mixed plantings. They do not produce seed, eliminating the problem of volunteer asparagus which becomes a "weed" problem. Seed of conventional varieties such as Mary Washington produces both male and female plants.

Most of the asparagus production in the Pacific Northwest is for processing, but production for the fresh market is also important.

White asparagus can be produced from any variety by the exclusion of light. In Asia and Europe where white asparagus is much more common than in the United States, this is done by mounding soil over the row to a much greater depth than needed for green asparagus. Spears are cut while still under the surface when they push the soil upward or when a wet spot is noted on the surface of the soil just before the spear breaks through. A long knife is then used to cut the spear. Spears must be handled in the absence of light to keep them white. This system is very expensive.

Some white asparagus has been produced under black plastic tunnels. These are low covers supported by wire hoops. One side of the tunnel is buried by soil, the other held down by steel rods, wood or some other weights. Tunnels are opened periodically for harvest and then closed again. Varieties that are tolerant to high temperatures, such as the California hybrids, might be best adapted to this system.

VARIETIES

Standard varieties: Mary Washington (tips remain tight and slow to fern), UC 500W.
For trial: Jersey Queen (a giant female selection of Mary Washington).

All-male varieties: Jersey Giant, Jersey Knight. Although seed of all-male hybrids may cost 40 to 50 times as much as standard varieties, research from Washington State University indicates that, for certain varieties, the extra establishment cost may be compensated for in the first year of full production by the increased yield. Other all male hybrids for trial: Greenwich, Jersey Gem, Jersey General, Jersey Jewell, Jersey King, Jersey Prince, Jersey Titan.

Note: A variety performance planting established at the Malheur Experiment Station in 1994 indicates that (based on 4.5 weeks of harvest in 1997) Del Monte 361 has the highest US#1 grade yield of "mammoth" and "total" sizes and among the highest in the "large" grade, followed by Jersey Giant, Mary Washington, UC 157, and Jersey Knight, in decreasing order. Cumulative yields for 1996 and 1997 were similar. The proportion of U.S. No. 2 yield was low for all varieties (10% or less) and differences among varieties in U.S. No. 2 yield were not significant. For a complete report of this study, contact Dr. Clint Shock, Malheur Experiment Station, 595 Onion Ave., Ontario, OR 97914. Clinton.Shock@orst.edu.

Synthetic varieties (crowns intermediate in cost), plants may be a mixture of males and females: Synthetic 4-56 (mostly male hybrid plants but can run 30-40% females).

Standard hybrids (plants are 50:50 males and females): Jersey Centennial, UC 157. Also the Dutch hybrids Limbras 22 and 26; German hybrid Lucullus. (Dutch and German hybrids have been reported to have tips that fern quickly and do not hold as well at high temperatures, and are sensitive to rust).
California hybrids for trial: Apollo, Atlas, Grande. California hybrids, developed for warm conditions, produce spears which do not open or "fern" as quickly as do other varieties under warm temperatures. However, these varieties do not survive as well under cold winters, so they should be tested for several years before adoption for significant acreage.
Also for trial (F2's): Idalee F2.

Novelty purple asparagus: Viola (a tetraploid also known as Purple Passion). Purple asparagus turns green when cooked as the purple pigment is destroyed by heat.

An excellent discussion of asparagus varieties is found in Ohio State University Bulletin 826, Asparagus Production (Varieties Section).

COMPANIES PROVIDING CROWNS, TRANSPLANTS, OR SEED

Seed, crowns, or tranplants available from:

California Asparagus Seed & Transplants Inc., 2815 Anza Ave., Davis, CA 95616
Davey-Joan's, PO Box 173, Rt. 13, Williamstown, NY 13493
Daisy Farms, 91098 60th Street, Decatur, MI 40945.
Horticultural Products & Supplies., 1307 W. Morehead St., Charlotte, NC 28208
Jersey Asparagus Farms, Inc., 105 Porchtown Rd., Pittsgrove, NJ 08318
Nourse Farms Inc., P.O.B. 485 RFD; South Deerfield, MA

Seed only:

Pan American Seed Co., P.O.B. 438, W. Chicago, IL
Sunseeds Genetics Inc., 2320 Technology Pkwy, PO Box 1438, Hollister CA 95023
Nunhems Seeds b.v.; Haelen, Holland; The Netherlands
Zenner Bros. Seed Co. Inc., 2455 SE 11th, Portland, OR 97214

ADAPTABILITY

Stand losses from gopher damage and excessive winter rainfall which results in long periods of soil saturation, and risk from certain diseases have inhibited production in the Willamette Valley. Commercial plantings are restricted mainly to the drier areas east of the Cascades. Plantings west of the Cascades should be limited primarily to the Rogue River Valley.

SOIL AND SITE SELECTION

Asparagus should not be planted in any field in which asparagus had been planted in the past. If it is necessary to do so, the soil should be fumigated to reduce the incidence of Fusarium wilt and several root rots.

Asparagus can be grown on many types of soil, but good drainage is imperative. The best types of soil for permanent plantings tend to be those which are deep, loose and light. Sandy loams are ideal. Asparagus roots may reach a depth of 10 feet and the soil should allow full development of the storage roots.

Soils ranging from slightly acid to slightly alkaline (pH. 6.0-7.5) are best. Asparagus will tolerate soils too acidic or too alkaline for many other crops, but yields on such soils may be depressed.

In selecting sites, consider risk from soil insects. Check for wireworms if old pastures or alfalfa fields are to be used. See "Insect Control" section below for appropriate controls if necessary.

SEEDLING AND CROWN PRODUCTION

Asparagus seeds number approximately 19,200 per pound. Approximately one pound of seed is needed to produce enough crowns (11,000-15,000) for one acre of irrigated production.

Asparagus crown nurseries are planted using about 8-10 lb/acre. For a transplant nursery, plant l to l.5 inches deep and 1-2 inches apart in rows 2 feet apart. Seed should be planted in late spring in well-prepared fertile soil which is around 75 F. Crowns are grown through the summer and dug the following spring for transplant to commercial fields.

DIGGING CROWNS

In the spring, cut and remove the old tops and dig crowns leaving 8-12 inches of storage root. Crowns should be dug just before buds have started to grow.

CROWN PLANTING AND TRANSPLANTING

Asparagus fields are generally established from the first of March to the end of April in the lower Columbia Basin.

Growers should purchase well-graded l-year old crowns from reliable sources or nurserymen, or grow their own crowns from seed if irrigation is available.

New research indicates that fields can also be established from much younger transplants which are grown in greenhouses and may be only 8-10 weeks old. For such plants perfect seed bed preparation, transplanting and irrigation practices must be exercised.

Plant only into fertile well-drained loams, sandy loams and muck soils which are free of perennial weeds.

Use only the largest and best crowns. Under dry land farming conditions, 5,500 crowns per acre are required. Plant in furrows 4-5 feet apart 6-8 inches deep, with crowns 2 feet apart.

On irrigated land, ll,000-15,000 crowns per acre or more are required. Plant in furrows 4-5 feet apart, 8-10 inches deep and with crowns 6-9 inches apart. Stagger plants in the bottom of the furrows. Depth of planting is an important factor in spear diameter. Since the number of spears per acre, per season, is similar from year-to-year, spear diameter is an important factor in yield.

Spread out roots with buds up, and cover with not more than l.5 inches of soil and irrigate with 1-2 inches of water. Fill in furrow gradually by cultivating as plants grow.

DIRECT SEEDING

Direct seeding of asparagus is not recommended but may be used where irrigation and proper planting and tillage equipment is available. Seed in well-drained, well-prepared sandy, sandy loam or muck soils that are free of perennial weeds and grasses. Seed at a rate of 2 to 3 lb seed/acre, 1/2 to 1 inch deep, into open furrows 6-8 inches deep. As seedlings begin to grow, begin to refill the furrows gradually and carefully so as not to bury young seedlings.

FERTILIZER, East of Cascades

Fertilizer applications should always be based on current soil test information. The following recommendations are general guidelines for eastern Oregon. These recommendations are quoted, where applicable, from the Washington State University Fertilizer Guide FG-12:

Asparagus is somewhat unique in its fertility requirements. Although the nutrient removal is very low in harvested spears, the storage capacity for these nutrients in the roots, crown, and ferns is surprisingly high. This would imply that the requirement for nutrients may be very high during establishment and very low after the first two or three seasons.

The following data, adopted from various sources, illustrate the point:

                                       ------pounds per acre------

                                           N        P2O5      K2O
Removal in 4 tons of harvested spears      37        12        27
Stored in roots, crown, and ferns       200-300   100-150   300-400

NEW PLANTINGS:

NITROGEN

This table gives N fertilizer rates for different crop residue situations:

If previous cropping was:                   Apply this amount of N

                                                    (lbs/acre)
     New land                                           280
     Corn or small grain, residue removed               220
     Corn or small grain, straw plowed under            260
     Potatoes or sugar beets                            200
     Beans or peas                                      200
     Alfalfa (no top growth)                            180
     Alfalfa, considerable top growth plowed under      140
     Vetch or other legume green manure                 140

Nitrogen liquid fertilizer formulations having herbicidal effects:

AN-20, ammonium thiosulfate, and mixtures of these two materials as well as monocarbamide dihydrogensulfate (monourea sulfuric acid) can be used successfully in a number of crops to provide nitrogen and sulfur. The amount of nitrogen per gallon of material, the rate at which it is applied, and the phytotoxicity of the material determines how these materials can be used.

All of these materials, when applied at the proper time and manner have the added benefit of ancillary control of many small (less than 3 inches) broadleaf weeds such as groundsel, pineapple weed, shepherdspurse, mallow, pigweed, hairy nightshade chickweed and many others. Poor, or no control is obtained on lambsquarters, purslane, henbit, black nightshade, knotweed, sow thistle, malva goosefoot and grasses.

In asparagus, these materials must be applied before the asparagus spear protrudes through the soil surface. Spears may be seriously injured if contacted by any of the materials.

AN-20 fertilizer formulation (Do not allow contact with spears or fern):

This is a manufactured 20-0-0 formulation (containing 20% N) that may be applied at 50 to 70 gallons of product per acre as a foliar spray. This formulation weighs 10.55 lb/gal and contains 2.11 lb N/gal of product and would provide approximately 100 to 140 lb N/acre (but some N is lost through volatilization). Do not irrigate for 48 hours after application, but then irrigate sufficiently to move the fertilizer into the root zone.

Note: Mixtures of AN-20 and ammonium thiosulfate (usually 1:1) can be made which will reduce the amount of nitrogen applied, provide some sulfur (if AN-20 only would have been applied, and reducing the sulfur if only ammonium thiosulfate were to be used), and be as effective as either material alone. Application rates are still held at 50 to 70 gallons of the mixture per acre.

Note: This formulation is different from a solution that could be prepared by dissolving ammonium nitrate in water. Such a solution would not have the same concentration or herbicidal effect.

Ammonium thiosulfate (Do not allow contact with spears or fern):

This is a manufactured 12-0-0-26 formulation (containing 12% N and 26% sulfur) and weighs 9.33 lb/gal. It may be applied at 50 to 70 gallons of product per acre as a foliar spray. This solution contains 1.12 lb N and 2.4 lb S per gallon of product and would provide approximately 55 to 75 lb N/acre (some N may be lost through volatilization). At the application gallonage mentioned, about 150 to 168 lb S are also applied. Do not irrigate for 48 hours after application, but then irrigate sufficiently to move the fertilizer into the root zone.

Note: Mixtures of AN-20 and ammonium thiosulfate (usually 1:1) can be made which will reduce the amount of nitrogen applied, provide some sulfur (if AN-20 only would have been applied, and reducing the sulfur if only ammonium thiosulfate were to be used), and be as effective as either material alone. Application rates are still held at 50 to 70 gallons of the mixture per acre.

Monocarbamide dihydrogensulfate (monourea sulfuric acid) 15-0-0-16 (N- phuric)(Do not allow contact with spears or fern:

This product may be applied at 10 to 30 gallons of product per acre. It weighs 12.65 lb/gal and contains 1.9 lb N and 2.0 lb S per gallon of product. It is most generally used at about 15 to 20 gallons per acre providing approximately 28 to 38 lb N and S per acre (but some N is lost through volatilization). Apply in sufficient water to get good coverage (approximately 1:1 dilution). Do not irrigate for 48 hours after application, but irrigate then to move the fertilizer into the root zone.

CAUTION: This solution is corrosive, and can injure skin and damage spray equipment. Use proper safety precautions and suitable spray equipment (stainless steel).

When any of these treatments are used, subsequent nitrogen sidedressings should be reduced by a portion of the amount of N applied in the treatment.

PHOSPHORUS (P)

Phosphorus deficiency is rare in asparagus. Crop removal of P by asparagus is very small:

If your soil test*                      Apply this amount (lb/acre)
reads approximately:                      (adjust rate depending on
                                           your actual test value):

ppm phosphorus (P)                                   P2O5
           2                                         300
           4                                         200
           6                                         160
           8                                         100
      10 or more                                       0

                           POTASSIUM (K)

If your soil test*                       Apply this amount (lb/acre)
reads approximately:                      (adjust rate depending on
                                           your actual test value):

ppm potassium  (K)                                   K2O
           30                                        240
           60                                        190
           90                                        140
          120                                        100
     more than 120                                     0

Phosphorus and potassium fertilizers should be injected about 6 inches deep between rows in fall or early spring.

SULFUR (S)

Sulfur may occasionally be deficient because of low S content in the water or soil. If S is known to be deficient, apply fertilizer at a rate which will supply 60 lb S per acre.

ZINC (Zn)

Zinc deficiency in asparagus has been demonstrated, but the problem is rare. Where the soil test for Zn is below 0.8 ppm or on new land where leveling has exposed limy subsoil, apply Zn fertilizer before planting at a rate which will supply 20 lb Zn per acre.

BORON (B)

Boron deficiency is uncommon east of the Cascades. When soil test for boron is below 0.5 ppm, apply fertilizer at a rate which will supply 4 lb B per acre.

SALINITY

Although asparagus is tolerant to soil salinity, a salinity level of 4 to 6 mmhos/cm may indicate a salinity problem and further tests should be made. A salinity level above 6 may indicate a serious salinity problem.

ESTABLISHED FIELDS:

For the first three years, 100 lb N/acre should be broadcast and incorporated in late fall or early spring or injected at the end of the cutting season. Incorporate all plant residues shallow enough to avoid crown damage. After three years, apply 40 to 80 lb N/acre annually. For all other nutrients, use the section on "New Plantings."

GENERAL COMMENTS:

Other elements: Other than N, P, K, Zn, and S, research has not shown a need for additional fertilizer materials for asparagus. Even when the soil test shows low boron values, boron fertilizers have not given yield responses. The practice of applying mixes of various elements "for insurance" is not recommended.

Important: Fertilizers are of little value where other factors are limiting. For high yields, follow good management practices regarding irrigation, pest control, etc.

FERTILIZER, West of Cascades

As noted above under Adaptability, asparagus production is not recommended west of the Cascades. For those who choose to establish plantings in the Willamette Valley or western Washington, the following recommendations adapted from Michigan State University may be more applicable than the fertilizer rates quoted above for east of the Cascades.

Asparagus (crown production): Adjust the pH to 6.8 before planting, because asparagus does not grow well on soils below pH 6.0. Before seeding, disc in 50 lb N/acre and the amounts of phosphate and potash potash determined by soil test. When asparagus plants are about 6 inches high, sidedress with 50 lb N/acre.

Asparagus (new planting): The year before planting, test the soil and apply lime to attain a pH of 6.8. In the spring broadcast 50 lb N/acre and the recommended amounts of phosphate and potash and plow 12 inches deep. It is important to get adequate phosphorus below the crowns before planting. Apply 30 lb phosphate/acre in the furrow at the time of setting crowns. After the fern is 6 inches high, sidedress with 50 lb N/acre.

Asparagus (established plantings): Annual N applications should be split between pre- and postharvest. The total amount of N should not exceed 80 lb/acre. Every second year, apply potassium at 60 lb K2O/acre or the rate indicated by a soil test. Applying phosphorus after establishment is not beneficial.

IRRIGATION

Irrigate as needed and to keep fern growing vigorously. Six to 8 irrigations may be needed during the first and second year. During the cutting season 1-2 irrigations should be adequate. Refill the soil profile after harvest through several irrigations to promote good fern growth.

Approximate summer irrigation needs for the Hermiston area are: 3.5 inches in May, 5.0 in June, 7.5 in July, and 7.0 in August.

In the Yakima Valley and the southern Columbia Basin, monthly asparagus water usage is reported to average 5.2 inches during the months of April, May and June. Growers sometimes use light, frequent irrigations to reduce wind-blown soil and resultant damage.

Irrigate as necessary to promote and sustain good fern growth after harvest well into the fall. Asparagus water use during fern growth is reported to be 6.8 inches in July, 7.6 in August and 4.6 in September. Fall irrigation is reported to increase yields the following spring and to reduce winter freeze damage.

Soil type does not affect the amount of total water needed, but does dictate frequency of water application. Lighter soils need more frequent water applications, but less water applied per application.

Asparagus is often grown with furrow irrigation in eastern Oregon. Water soluble polyacrylamide (PAM) is useful for flocculating soil particles in irrigation furrows and reducing erosion of soil from the furrow.

HARVESTING, HANDLING, AND STORAGE

Asparagus is not harvested the first year (the year of crown establishment). Second year harvest is usually limited to 4-6 weeks depending on crop vigor. Full-season harvest is conducted the third year but full production usually occurs about the 4th year. Asparagus fields last about 12 to 15 years although some fields may remain productive for over 20 years.

Although there has been much research and testing of machine harvesting, asparagus is currently hand-harvested in the Pacific Northwest. One company advertised (in 1995) an asparagus harvester that is custom built on request. For information contact Steve Raguse, RR 2, Box 24, Wheaton, MN 56296, phone: 612/563-8389.

In Umatilla County asparagus harvest generally begins about the April 10 and may continue to through the end of June. The prime harvest period is from mid-April to mid-June. An acre of asparagus may produce from 125,000 to 150,000 spears, or 25 to 40 cwt/acre per cutting season.

Nearly all green asparagus is harvested with a little white on the butt end. Although some asparagus in the midwestern states is snapped, eliminating any fiber in the harvested product, spears in the Pacific Northwest are hand cut with a special knife and should be 9-10 inches long. At least half that length should be from above ground (green). Length of spear is determined by its intended use and can range from 5 to 10 inches.

Harvest intervals are generally 24-36 hours apart depending on weather. Spear growth begins, but is slow when soil temperatures reach 50 F, reaching a maximum rate at temperatures of 75-85 F and high soil moisture.

Spear length cut on any given day should be set in consideration with the interval to the next scheduled cutting, soil moisture, and air temperatures expected during that interval. If a long harvest interval is expected, and temperature and soil moisture are high, shorter spears should be cut, or else they will be unmarketable by the next cutting. Conversely, if temperatures are cool and harvest interval is short, the shorter spears should be left to the next harvest.

Cut asparagus should be cooled immediately, otherwise quality and food value degenerate rapidly. Control loss of moisture by placing butts in cold water or in contact with other moisture-holding material. Failure to reduce the field temperature promotes growth, causing loose tips.

Understanding what makes asparagus tough.

The following information on toughness in asparagus was provided by Dr. T. Bratsch, University of Illinois:

Asparagus toughness can be a recurring problem for many growers. Though often weather is a significant contributing factor, certain practices can help. The development of toughness in asparagus is due to the formation of fiber cells in the stalk. These cells are thick-walled and contain lignin, a supporting material. They are located in the internal vascular tissues as well as just under the surface of the stalk (the pericycle).

Some facts about fiber in asparagus:

1. The occurrence of fiber cells and toughness is always greater at the base of the spear than the tip.
2. Smaller spears are often perceived to be tougher than larger diameter spears because they contain a higher percentage of fiber on a weight basis.
3. White asparagus generally has a higher fiber content than green asparagus; because of this, it is thought that light decreases fiber formation and content.
4. Due to the narrow genetic base of asparagus varieties, there appears to be little difference between cultivars in fiber content or development.
5. Asparagus developing during cool temperatures (50-55 F) is higher in fiber than spears harvested after warmer weather. This is due to reduced spear growth rate (size), but not reduced fiber cell development which continues during cool temperatures. Thus a fast growing spear out-paces fiber development. This is the greatest contributing factor in asparagus fiber levels.
6. Snapped asparagus (versus cutting) leaves a higher proportion of the fiber-heavy lower stem in the field, and over the period of harvest this method tends to keep overall fiber levels lower.
7. After harvest, several factors contribute to fiber formation. Most post-harvest fiber development occurs within 24 hours. This can be slowed dramatically by cooling promptly to 36 F. There is an increase in fiber with storage, especially at higher than optimum temperatures, but the increase is low under proper storage. Fiber content (or at least its integrity) can even be reduced under CA (controlled atmosphere) storage with low oxygen and high carbon dioxide levels. Water-loss after harvest also increases fiber development, making humidity in storage an important consideration. Film wraps or placing butt ends on water pads also helps reduce fiber development.

To help reduce fiber before harvest:

1. Try to snap spears at ground level versus cutting below ground.
2. During cooler weather, harvest shorter spears. In warm weather, harvest before spears reach 10".
3. Avoid harvesting small-diameter spears (less than 0.25").

To reduce post-harvest fiber development:

1. Cool the crop as quickly as possible after harvest.
2. Storage temperatures should be from 32 F (short-term) to 36 F (long-term).
3. Do not store longer than 2 to 3 weeks in refrigeration. Controlled-atmosphere storage at 2-3% oxygen and 5-10% carbon dioxide can extend storage life to 4-5 weeks.
4. Use film wraps or moisture pads and maintain high relative humidity in storage.

Discontinue cutting no later than June 20 in eastern Oregon to allow for good fern growth and adequate food reserve accumulation for the following season.

STORAGE (Quoted or modified from USDA Ag. Handbook 66 and other sources)

The recommended holding and shipping temperature is 32 F, with a relative humidity of 95%. Keep asparagus upright in containers with moisture pads whenever possible.

Fresh asparagus is highly perishable and deteriorates rapidly at temperatures above 40 F. Thus, the spears should be cooled immediately after cutting, preferably by hydrocooling. In addition to general deterioration, spear growth, loss of tenderness, loss of flavor, loss of vitamin C, and development of decay take place at moderately high temperatures. Asparagus can be kept successfully for about 3 weeks at 34 F and 4-5 weeks in controlled atmosphere storage (see below). It can be held for about 10 days at 32 F, but it is subject to chilling injury when held longer at this temperature.

High relative humidity is essential to prevent desiccation, particularly at the butt ends. Commonly, the desired relative humidity is obtained by placing the butts of asparagus on wet pads. A high relative humidity can also be obtained by prepackaging spears in perforated film. Non-perforated film is not acceptable because the extent of increase in carbon dioxide and decrease in oxygen may be injurious and because enough ethylene may accumulate and toughen the spears.

Asparagus with white butts is less perishable than all-green asparagus. Bacterial soft rot, which can occur at either the tip or butt of the asparagus, is the principal decay.

Asparagus may be damaged by exposure to ethylene, and should not be stored with apples, or other ethylene generating material. Adverse exposure may result in undesirable elongation, curving, and toughening.

Controlled-atmosphere storage is beneficial to asparagus even for a short period because it retards decay and toughening, which occur rapidly after harvest. Gas concentrations should be 2-3% oxygen and 5-10% carbon dioxide at 34-36 F. If temperature control is uncertain and might exceed 45 F, the carbon dioxide concentration should not exceed 7 %; but if the temperature is maintained at 32 F, a 12 percent concentration is suggested. Brief exposure to 20 % carbon dioxide will reduce soft rot at the butt end.

PACKAGING

Asparagus is commonly packaged in 32-lb crates, loose pack; or 15 to 17- lb half-pyramid crates; or 24 to 25-lb cartons holding 16 packs each 1.5 lb.; or, 30-lb pyramid wirebound crates holding 12 2-lb bunches.

FERN INCORPORATION

Fern growth is removed to reduce disease and insect damage. This is done by chopping or shredding in late fall or early spring. Disk or till chopped ferns no deeper than 3-4 inches to avoid damaging crowns. Leaving ferns in the field over the winter helps in holding snow cover, reducing the risk from winter damage, and increasing available spring moisture.