Ultra-Niche Crops Series: Asparagus

Ultra-Niche Crops are defined as exceptionally high-value crops that can provide a significant source of income to the farmer while using minimal land area.

Asparagus (Asparagus officinalis) is a perennial crop that can thrive for 15 years or more when well-cared for. However, asparagus requires a high initial investment and ongoing maintenance costs and offers no net income until the third or fourth growing season. After the field is established, maintenance costs are minimal compared to annual vegetables. Therefore, it is essential to carefully plan your marketing, production, and harvesting goals to establish and sustain a financially successful long-term asparagus operation on a small acreage farm.

Marketing

Who Will Buy the Crop?

It is important to recognize and understand your target customers and base the size of the asparagus acreage on market potential. Asparagus may be marketed successfully through roadside markets, pick-your-own, restaurants, CSA programs, or farmer's markets. The number and quality demands of targeted customers must be considered to determine acreage. Asparagus attributes such as spear length, diameter, tip quality, and spear color must also be taken into consideration.

How Suitable Is This Crop for Agritourism?

Asparagus is an excellent crop to offer to roadside stand and farmer's market customers because it is one of the early season highlights in New Jersey. Asparagus helps to sell and compliments other early crops such as strawberries and bedding plants.

How Well Does This Crop Withstand Shipping?

Asparagus withstands shipping well when cooled and boxed correctly.

What Packaging Should Be Used?

Asparagus should be packed vertically into ventilated shipping containers that can withstand moisture and prevent the spears from damage. Allow space between the top of the spears and the box cover. The spears will continue to grow in the box and if head space is not provided, the spears will curve.

Farmer's Tool Box

Essential Equipment/Supplies

1. Certified or disease-free crowns
2. Furrow opener/middle buster
3. Ridging discs
4. 5-foot field cultivator or 4-foot rototiller
5. Air blast sprayer (3 pt. hitch)
6. Low pressure boom sprayer
7. 4 or 5-foot brush hog
8. Overhead or drip irrigation
9. Asparagus knives
10. Harvest containers
11. Packing area

Optional Equipment/Supplies

• Cooling or storage facility

Crop Requirements

Soil

Asparagus is most productive when grown on deep, well drained sandy loam soils. Asparagus plants lose vigor, become more susceptible to root rot, and ultimately die in poorly drained areas or following prolonged high rainfall. The soil pH should be maintained between 6.5 and 6.8. Medium to high fertility produces the highest yield and quality asparagus.

Water

Adequate soil moisture is important during the first growing season. Weekly applications of irrigation sufficient to wet the soil 8 inches deep should be adequate. After the first growing season, asparagus plants do not require frequent irrigation because of the deep and extensive root system. Thorough watering (2 inches of water) slowly applied every two weeks during dry weather is usually sufficient. Insufficient soil moisture in periods of dry weather may result in subsequent reductions in yield.

Light

Asparagus grows best under maximum photosynthesis conditions: a long growing season and sunny days in full sunlight. Ideal daytime temperatures during the growing season are 75° to 85° F with night temperatures from 60° to 70° F.

Frost Damage

Early spears can be frost damaged which results in dark-colored spears that collapse within 24 hours after frost exposure. Frost injury can be reduced by ridging soil onto raised beds when preparing the field in the spring, selecting a variety that emerges late, or selecting a site that has heavier soils that warm more slowly, thus delaying spear emergence beyond the threat of frost.

Growing the Crop

How Is Asparagus Started?

Plant healthy, certified 1-year-old crowns; never use 2- or 3-year-old crowns. Crowns should be kept cool (under 40° F) to prevent dehydration and bud growth during storage. An alternative to purchasing commercial asparagus crowns is to grow your own crowns from seed. Select and obtain high quality seeds or crowns of a male hybrid variety that has been tested and performs well in the Mid-Atlantic area. Avoid inter-planting small and large crowns because the large crowns will tend to out-compete small crowns and may prevent the long-term survival of the small crowns, leaving gaps in the stands. If crowns vary in size, sort small and large crowns, and plant like-size crowns in blocks.

What Is the Optimal Number of Plants per Acre?

A 12-inch spacing on 60-inch row centers results in 8,712 crowns/A. A 15-inch spacing on 66-inch centers gives 6,336 crowns/A. The closer in-row spacing usually produces a higher yield during the first two or three harvest seasons.

Management

Year Prior to Planting Asparagus

1. Take a soil sample and obtain a complete analysis including pH, major, secondary, and minor nutrients.
2. Consult the 2019 Mid-Atlantic Commercial Vegetable Production Recommendations (PDF) for details on rates and timing of all nutrient and pesticide applications suggested in the following management sections.
3. Apply the amount of lime (calcitic or dolomitic) recommended by a soil test to bring soil pH to 6.7–6.8. Apply potassium and other recommended amendments according to the soil test.
4. Deep rip or sub soil the field to eliminate compaction and break up any hard pan. Plant a soybean cover crop and then incorporate it into the soil when it is mature and green. Plant a fall wheat cover crop, and plow it under in the spring as soon as soil conditions are favorable.

Year of Planting

1. Make a 7-inch deep furrow with a middle buster or specially-designed furrow shaper in early April.
2. Apply super phosphate in the furrows based on soil test results.
3. Place crowns in the furrows with the apical buds oriented upward, 12 to 15 inches apart in the row.
4. Cover the crowns with 2–3 inches of soil from the berm, and top dress 25 lb. of nitrogen/A from calcium nitrate over the furrow.
5. Apply pre-emergence herbicides.
6. Install overhead or drip irrigation, and maintain favorable soil moisture conditions with irrigation as needed.
7. After about 4 weeks, side dress with 25–50 lb. of nitrogen/A.
8. Observe plants for the presence of insects, and apply recommended controls as needed.
9. When weeds first appear, cultivate to destroy weeds, and till soil in the furrow, being careful to avoid covering asparagus foliage.
10. Apply fungicides in late July and again in mid-August and early September to control foliar diseases, including asparagus rust, purple spot, and cercospora leaf blight.
11. Till soil, and fill in furrows so that furrows are level with beds by mid-September.
12. After the ferns turn brown (late October or November), use a ridging disc to form a 2–3-inch ridge over the top of the asparagus row. This will help excess water drain away from the crown during the winter.

Year Two

1. Early in the season, while asparagus shoot buds are still dormant (late February or early March), mow off the brush from the first growing season with a rotary mower. Apply a glyphosate herbicide to control perennial weeds that have emerged.
2. Apply 50–75 lb. nitrogen/A plus phosphorus, potassium and boron as recommended based on the soil test from the season prior to planting.
3. When soil moisture is favorable and before spears begin to emerge (usually mid-March) use ridging discs to form a 4 to 6-inch ridge of soil over the asparagus row. Smooth the ridge with a 5' wide field cultivation tool set at a height to avoid damaging the underlying crowns or emerging spears.
4. Apply the recommended pre-emergence herbicide at the full season rate.
5. Apply fungicides in late July and again in mid-August and early September to control foliage diseases.
6. Observe plants for insects and apply recommended controls. Maintain good soil moisture through early September with irrigation (approximately 2 inches of water every 10–14 days) as needed.

Year Three and Beyond

1. Mow brush from the previous season and apply glyphosate. Then apply fertilizer, ridge the rows, and prepare the soil as directed for year two.
2. Apply the pre-emergence herbicides at half the full season rate.
3. Harvest all spears for 2–3 weeks from first spear emergence during the third growing season, 4–6 weeks during the fourth growing season, and 6 weeks during the fifth and subsequent seasons. Base the duration of harvest on the vigor of the brush in the fall of the previous growing season. Reduce the duration of harvest if brush vigor was low in the fall of the previous growing season. Over-harvesting depletes the crown of photosynthetic energy reserves, reduces foliar vigor, and decreases spear yields in subsequent years.
4. After harvest, apply 50 lb. nitrogen/A followed by post emergence herbicides.
5. Apply fungicides in late July and again in mid-August and early September to control foliar diseases.
6. Observe plants for insects during the growing season, apply recommended controls, and maintain good moisture through early September with irrigation as needed.

How Is Harvesting Performed?

Spears grow 3–5 inches per day when temperatures are 80–85° F. Harvest all spears that are more than 9 inches above the soil level by cutting just below the soil surface with an asparagus knife. Some growers snap the spears just above the soil level. Unmarketable, small, and defective spears are cut and left in the field.

How Is Asparagus Graded?

The USDA has established size and quality standards for asparagus. High quality spears have tight bracts at the tip. Most markets prefer the standard 9-inch long, all-green spear. Spears for commercial markets are usually trimmed at the cut or butt end; sized by diameter into small, medium, large, and jumbo categories; and bundled into 1 or 1.5 pound bunches for retail sale. Some markets prefer spears of other lengths and diameters. Be sure to check with your buyer or customers to determine their preferences.

What Are the Postharvest Cooling and Washing Requirements?

Asparagus loses quality rapidly after harvest. Sugars are respired and converted to lignin fibers resulting in a loss of sweet flavor and an increase in toughness. It is essential to shade harvested asparagus and quickly move it to a cooler environment or the packing house to prevent moisture loss and heating. If spears are washed, the wash water should contain an EPA-registered sanitizer. Washed, trimmed, sized, and bunched asparagus spears should be placed at 35° F and cooled as quickly as possible following harvest. Asparagus can be stored up to 10 days if held between 32–36° F at 90–98% relative humidity. Maintain temperature at 35–40° F with high humidity during transit and display prior to sale.

Diseases and Controls

The most serious disease of asparagus is Fusarium root and crown rot, a soil-borne disease. Only disease-free seeds or crowns should be used. Planting infested seed or infected crowns can lead to a rapid buildup of the pathogen in the soil and crowns that will drastically reduce yields of the asparagus and permanently contaminate the field for asparagus planting in the future. Fusarium infects the root system, kills the feeder roots, and causes collapse of the storage roots and rot of the crown. As a result, shoots and ferns wilt, turn yellow, and die. Plant vigor declines, spear size and yield decreases, and weaker plants may die.

Fusarium can be identified by the reddish-brown color of the feeder roots, reddish-brown spots and streaks on the storage roots, large reddish lesions on the base of the spears and stalks at or below the soil line, and wilting and die-back of maturing shoots.

These symptoms are much more severe when the plants are under stress due to excessively long harvests, poor drainage, competition from weeds, and damage from insects and foliage diseases. Planting new vigorous asparagus varieties that are adaptable to local conditions and reducing plant stress will help minimize the damage from Fusarium root and crown rot.

Asparagus rust is another common fungal disease. The fungal pathogen appears on the surface of stems and branches as small rust-colored elliptical spots containing spores that facilitate the spread of the disease. The asparagus rust fungus causes premature yellowing and death of the foliage. In the fall, the rust-colored areas produce black, overwintering spores that can infect the plant the following year. Severe rust infestations can destroy much of the foliage and reduce the yield of the next year's crop. Rust can be partially controlled using fungicides. New hybrid varieties that have some rust resistance will reduce reliance on fungicide applications.

Insects and Controls

Several species of aphids, mites, and thrips are often a serious problem, especially on smaller or younger plants. They damage plants through feeding, sucking plant juices, and causing the green needles and stems of the young plant to turn dull gray-green, yellow, and die. Insecticides can be used to control aphids and thrips.

The common asparagus beetle (Figure 1) is a serious pest every year. Adult beetles are ¼ inch long with shiny black wings that have red margins and three yellow spots on each wing. They overwinter in debris in and around the field. In the spring they emerge, feed on spears, and lay rows of small, black elongated eggs on the spears and foliage. Spears contaminated with beetle eggs may be unmarketable. The larvae (small, dark green worms) do the actual damage by eating the green fern, thus reducing photosynthetic area, plant vigor, and yield. Beetles can kill very young seedlings and seriously damage ferns of mature plants. Asparagus beetles can be controlled by insecticides.

Considerations for Organic Production

Can Asparagus Be Grown Organically?

Organic production of asparagus is challenging due to increased time commitment and high labor costs associated with weed control and the lack of effective organic pest controls.

Organic Weed Control Considerations

1. Perennial weeds must be eliminated by tillage prior to planting the crop.
2. Annual weeds should be controlled with a combination of cultural and mechanical methods.
3. Shallow cultivation should be used to control winter annual weeds in the spring.
4. Between-row cultivation can be conducted during the growing season, if care is taken to avoid compaction damage to plants in the production rows.
5. Weed management within rows is imperative and can include hand-weeding, mulching, or flame weeding.

Organic Insect and Disease Considerations

1. The asparagus beetle is the most damaging insect to asparagus. Sanitation of the crop in the fall by removing plant debris from the field (and mechanical tillage in the spring) may be helpful in reducing overwintering populations of the pest. There are several OMRI approved pesticides available, and natural predators support asparagus insect control.
2. Several diseases impact asparagus, and the purchasing or production of certified crowns is a priority. Avoiding overharvesting, reducing crop stress, and managing weeds can dramatically reduce the impact or severity of diseases.

Critical Considerations

One of the biggest issues farmers need to consider when growing asparagus is site selection. Asparagus can be productive for 15 years or more, so the investment in land, time, and location is critical to success. Asparagus should be planted in sandy loam or loam soils with very good surface and internal drainage. Select a field that has not previously been planted in asparagus for at least ten years. Evaluate the field for perennial weed populations as they can seriously affect the quality and quantity of the crop and harvest.

1. Selecting the correct variety is critical for the success of your operation. Acceptable varieties for the Mid-Atlantic U.S. include Jersey Deluxe, Jersey Supreme, Sequoia, Greenox, Greenix, Millennium, and Spartacus. These green-speared varieties vary in color, size, earliness, yield, disease resistance, and spear tip quality. The variety Purple Passion has large purple spears with a sweet flavor but is less resistant to foliage diseases than most hybrid green varieties.
2. Proper field preparation the year prior to planting asparagus is critical to the success of the crop. Test your soil, and apply lime if need be to adjust soil pH to 6.7–6.8. Weed management must be planned prior to planting the crop. An understanding of the types of weeds to control and a plan of action for each weed type is recommended to ensure effective control and high yields of a high-quality asparagus.

Resources

1. C.A. Wyenandt. (ed) 2019 Mid-Atlantic Commercial Vegetable Production Recommendations (PDF), Rutgers Cooperative Extension Publication E001.
2. Cantaluppi, C. J., and Precheur, R. (1993). Asparagus production, management and marketing, Ohio State University Extension Bulletin 826 (USA).
3. Dean, B. B., Boydston, R., Cone, W., Johnson, D., Ley, T. W., Mink, G., Parker, R., Stevens, R., Sorensen, E. and Van Denburgh, R. (1993). Washington asparagus production guide. Washington State University Extension Bulletin, 997.
4. Putnam, A. R., Stuckey, R., Lacy, M. L., Cress, D. C., Bird, G. W., & Dover, M. J. (1976). Know your asparagus pests. Ext Bull Mich State Univ Coop Ext Serv.
5. Sandsted, R. F., Wilcox, D. A., Zitter, T. A., & Muka, A. A. (1985). Asparagus information bulletin. Information bulletin 202. Cornell University Cooperative Extension, Ithaca, NY.
6. Tetrault, R., McNab, A.A., Ferretti, P.A., and Orzolek, M.D., (1986) Asparagus Production for Small-Scale Growers and Gardeners, U/Ed/ 86–601.

Photo credits: Top row l - r: Tom Orton (asparagus), Tom Orton (asparagus field), Fred McGrady (asparagus harvest); Rick VanVranken (Figure 1).

March 2019