Growing Asparagus in North Carolina for Direct Market
Carl Cantaluppi recognizes that asparagus is not a traditional Southern food and, therefore, not a garden staple in North Carolina. However, with residents relocating to North Carolina from northeastern states and the revival of culinary sophistication and healthful eating prompted in part by the local foods movement and the emergence of self-proclaimed “foodies,” Cantaluppi suggests that N.C. farmers give asparagus a closer look as a high-value, low-input specialty crop ideal for direct market.
Cantaluppi is an N.C. Cooperative Extension area horticulture agent with the Granville and Person County Centers. He has been evaluating asparagus trials in North Carolina since 1994. He first began working with the crop in the early 1980s as an Extension agent in Oklahoma and also conducted trials in Illinois and Ohio prior to arriving in North Carolina. During his work with the crop, he has seen the development of male hybrid varieties which demonstrate superior yield compared to open-pollinated varieties, such as Asparagus officinalis ‘Martha Washington’. For North Carolina growers, he recommends ‘Jersey Giant’ as the highest yielding and most widely adaptable variety. Other selections that perform well here include ‘Jersey Supreme’ and ‘Jersey King’. He is still evaluating varieties from California, but has observed that they may have less longevity over time as compared to the Jersey series released from Rutgers University.
The asparagus season starts in mid-March in the eastern part of the state and early April in western North Carolina. Harvest continues for two months in an established field. Asparagus is a perennial that will produce acceptable yields for 15 to 20 years. The yield peaks from year 7 to year 12. After year 15, the yield decreases by five percent annually. A mature field has an expected yield of 3,000 pounds per acre.
Growing for Direct Market
Cantaluppi suggests a direct market price of $3 to $4 per pound. He does not recommend large-scale, wholesale asparagus production due to price competition from California growers.
The product from California is harvested by cutting the spears below the soil line. The end of the spear is fibrous and unpalatable and must be removed by the consumer. This harvest method is used to prolong postharvest life and quality during shipping. Harvesting with a knife could also lead to damage of the emerging buds and possibly reduce yields. Cantaluppi recommends harvesting by hand-snapping the spear from the crown. For maximum tenderness the tip of the spear must be tight. Once it begins to open, known as “ferning out,” the tissue becomes fibrous and less palatable.
Immediately following harvest, place the asparagus spears, in an ice bath or a cold-water bath for 10 minutes to remove the field heat. Cut asparagus has a high rate of respiration, similar to cut flowers. Store fresh cut asparagus at 36 degrees F for up to two weeks. In cold storage, do not immerse in water since the cold, moist environment is ideal for the growth of white mold.
For retail display, bunch the spears into one-pound bundles and position them upright in a tray of shallow water. Be aware that asparagus is phototropic, meaning that it will grow toward a light source (the sun). If the spears seem to be bending in one direction by the end of the day, they may have elongated toward a light source.
Plant asparagus crowns in the spring and do not during the planting year. Beginning in the second year, the harvest period will increase with each passing season. In the second year, harvest for two weeks; in the third year, harvest four weeks; in the fourth year, harvest six weeks; and in the fifth year, harvest eight weeks. Asparagus is a drought-tolerant plant requiring no irrigation. It also has few pest pressures. However, Cantaluppi reports, it is difficult to grow as an organic crop due to weed control. Harvest should cease when three-fourths of the spears are pencil-diameter or smaller.
Despite between-row spacing of five to six feet and in-row spacing of 12 inches, field cultivation (or tilling) is not an acceptable weed control measure for asparagus. Even light, shallow cultivation has been detrimental to the asparagus root system, ultimately resulting in higher susceptibility to root diseases. Pre-emergent herbicides are the suggested weed control method. Those attempting organic production should use an abundant supply of heavy mulch, supplemented by hand weeding.
Fusarium root rot and crown rot are two disease issues problematic for asparagus growers. Prevention is the best defense. Adequate soil fertility and resisting the urge to overharvest are two key measures of prevention. Cercospora needle blight is an asparagus-specific disease that is problematic in North Carolina due to the high humidity through summer. Cantaluppi recommends application of a fungicide every two weeks from early July through late September. Failure to control Cercospora needle blight can lead to a 40 percent yield loss the following year.
Once harvest stops, the spears are allowed to fern-out, creating a canopy over the field. The fern growth should not be removed until approximately one month prior to spear emergence. Through the winter, the fern growth helps regulate the soil temperature protecting the crowns and developing buds with as much as a five degree temperature cushion.
White asparagus and purple asparagus are two variations of the typical green asparagus that can be found in the marketplace. In some markets, these oddities can command a higher price. Purple asparagus is a variety selection, A. officinalis ‘Purple Passion.’ The burgundy spears have a higher sugar content lending this asparagus a unique flavor. However, ‘Purple Passion’ is lower yielding than the Jersey hybrids and the spears lose the purple pigment when cooked.
White asparagus, sometimes referred to as “blanched asparagus,” is produced by excluding sunlight during production. In the absence of sunlight, no chlorophyll is produced. Chlorophyll is the green plant pigment that is used during photosynthesis. Cantaluppi suggests using an opaque 55-gallon drum cut in half lengthwise to cover the rows during spear growth. White asparagus is a lucrative crop for growers who supply specialty restaurant chefs. Bunches of white asparagus may be valued at 3 to 4 times the value of green asparagus.
Cantaluppi, and Robert Precheur, Ohio State University Extension, have published an Extension Bulletin, Asparagus Production Management and Marketing, that focuses on production in the northeast, Midwest and southeastern U.S. This publication is available online or e-mail firstname.lastname@example.org to order a hard copy.