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Asparagus (Asparagus officinalis) is a fern-like, perennial vegetable grown for its delicious young shoots (spears). This high value specialty crop and the earliest producing spring vegetable, has dark green foliage in summer and bright yellow in fall.
Asparagus is probably native to the seacoasts of Europe and eastern Asia, although it grows wild in many areas around the world so it is difficult to pinpoint its place of origin. It has been grown in Syria and Egypt since ancient times and was cultivated by the Greeks and Romans. In the sixteenth century, it appeared in France and England, and has been grown in America since colonial times.
United States asparagus production is concentrated in California, Washington, and Michigan, but many other areas have production potential.
Asparagus may be eaten fresh, frozen or canned. Asparagus is low in calories with each serving of four spears containing only 10 calories. Asparagus is a good source of thiamine, vitamin A, B vitamins, vitamin C, calcium and iron.
'The first major task in asparagus production is to select a site. A well-prepared asparagus bed in good soil could produce abundantly for fifteen to twenty years or more so the initial site selection and land preparation is of utmost importance.
Asparagus can be grown in a wide range of soils and climatic conditions and is typically planted in the spring. Asparagus thrives in fertile, well-drained lighter soils that warm up quickly in the spring. In Minnesota, asparagus is grown on sandy to heavy clay soils with the highest yields obtained on deep sandy loams. The asparagus root system will penetrate at least six feet, so shallow soils should he avoided. Standing water should also be avoided because it will quickly rot roots.
Asparagus can tolerate some shade, but full sun produces more vigorous plants and helps minimize diseased Production is most successful in areas where freezing temperatures or drought halt plant growth and provide a rest period. Without this rest period, reduced yields are probable.3
In the fall, prior to planting crowns or transplants, remove all perennial weeds and till in a rich organic material such as manure or compost, or sow a green manure crop. This will add organic matter and nutrients to the soil. In early spring, till or cultivate deeply to destroy all the weeds and to work in the manure crop prior to planting. Have soil tested for fertility so that the proper amount of manure or compost to add can be determined.
Asparagus plantations can be established using direct seeding, transplanting, or crowns. Growers may purchase transplants and crowns or grow them in a greenhouse or crown nursery. Growing asparagus from seed is difficult, while growing from either transplants or crowns is more expensive but allows you to harvest a year earlier. Producers should purchase seeds and plants that have been produced in their area and are suited to the local climate and conditions.
When raising asparagus, growers should eliminate female plants or purchase all male hybrid seed. Female plants put their energy into forming berries, leading to lower yields and unwanted seedlings. A bed of all male plants may produce as much as 25 to 30 percent more spears than a mixed bed of male and female plants.2
The slow rate of germination is a problem with direct seeding of asparagus in Minnesota. Although lower soil temperatures slow germination, asparagus seed should be planted as soon as the soil is workable. Early spring seeding will allow germination to occur as soon as the soil environment becomes favorable. Asparagus seed should be treated with fungicide to prevent infection by soil-borne pathogens.
Transplanting seedlings into the field is an increasingly popular option for growers. Seedlings are started in a greenhouse and transplanted into the permanent field when they are ten to twelve weeks old. Planting costs are reduced because the seedlings can be mechanically transplanted. Plant spacing is the same as for crown plantings.
Crown nurseries offer growers an opportunity to produce the crowns needed to start a permanent planting. A one acre crown nursery can produce enough crowns for a ten acre permanent planting. The seeds are started on a temporary site, usually sandy for easy plant removal, then crowns are harvested the following spring and replanted into the permanent site. Growers purchasing crowns should choose large one year-old crowns, with many storage roots and buds (each bud will produce a spear), which transplant easier and are generally cheaper. Because of the size of two and three year old crowns, the roots may be damaged in digging, causing considerable plant shock.
Crowns usually are hand planted with buds up, spaced 18 to 24 inches apart within rows in furrows four feet apart. Six to eight inches is the optimum depth for crown planting in sandy soils and five to six inches in heavier soils. Shallower planting depths cause production of spindly, thin spears, whereas deeply planted crowns produce fewer spears of larger diameter and emergence is delayed. Planting crowns closer than 18 inches results in reduced spear size and quality. Spacing crowns farther than 24 inches apart may result in larger spears but fewer spears per acre. Growers should add phosphorus at planting.
After placement in the furrows, cover the crowns with two to three inches of soil. Gradually fill in the furrow as shoots emerge. The furrows should be filled in by the end of the season, although the developing asparagus fern should never be buried.
Asparagus does not wilt like other crops and can easily suffer from drought, so it is important to monitor the moisture level in the root zone and irrigate when necessary.
Controlling weeds during the first two or three years of an asparagus planting is crucial. Weed control during flue first year is accomplished mainly by cultivation. Cultivation should be shallow to prevent injury to the crowns.
After the first full year of growth, several pre-emergence herbicides are labeled for asparagus. These can be sprayed on the shredded old fern growth after it has been mowed in the spring, about three weeks before new spears emerge.
Asparagus grown in Minnesota is relatively free of insect pests compared to many other vegetable crops.3 The asparagus beetle, which chews on spears in the spring and attacks summer foliage, is the most common insect that attacks asparagus. Control asparagus beetles by hand picking; spray or dust seriously infested plants. Destroy any infected ferns.
The main diseases of asparagus are Fusarium crown root rot and asparagus rust. Fusarium crown root rot is present in all asparagus growing regions in the U.S. Infected plants wilt, turn yellow, and are stunted. Spears may turn brown, rendering them unmarketable.
If an asparagus bed does become infected by disease organisms, the best option is to start a new bed in a distant location using newly purchased or grown plants.
Depending on the planting method, asparagus beds require two to three seasons to become established. Transplants and crowns require two years for establishment before first harvest begins, whereas asparagus started from seed takes three full growing seasons before harvest.3
Waiting until the second year after planting to harvest spears allows plants to develop strong, healthy tops. Limit harvest to two weeks in the second year and one month in the third year after planting. Over-harvesting one year will decrease the following year's yield.
Hand harvest spears when they are six to eight inches long. Approximately two hours of labor are needed to hand-pick one acre of asparagus. Spears may be harvested by cutting the spear below the soil surface or snapping the spears at the surface. Cutting must be done carefully to avoid damaging developing spears and the crown below the soil surface.
To improve quality. harvest in the morning when the spears are cooler and more easily snapped. Harvest spears when the heads are tight and before the tips begin to spread out. Freshly harvested asparagus is highly perishable and loses quality rapidly at temperatures above 40°F. Collect the harvested spears as soon as possible, protect them from the sun, immerse them in ice-cold water or shower 32 to 400F water on them. Wash the asparagus and discard spears that are too slender or those with open heads, insect eggs or other damage.
Growers can expect yields of about 500 Ibs. per acre during the second year following establishment. This can increase to 1,000-1,500 Ibs. per acre during the third year, and 2,000 Ibs. per acre during the fourth year.
Asparagus plants need stored nutrients and time to recover from harvests. They also need weed-free environments, moderate soil fertility, and adequate moisture to build up food reserves in their crowns. Neglecting asparagus fields after harvest is complete is a more significant contributor to poor yields in subsequent years than insect or disease damaged
The major expense in asparagus production is the initial cost to establish the crop. Initial expenses include site preparation, weed control, asparagus seed or crowns and fertilizer. The cost of maintaining the crop after establishment is primarily labor-related.
Growers should have a market for their asparagus before beginning asparagus production. Selling asparagus wholesale requires competitive marketing efforts on the part of the grower but also lower returns. Pick your own, farmer's markets and direct sales to grocery stores and restaurants offer greater opportunities for increased profits. Asparagus is currently priced as a gourmet item and will remain in this category until growing, harvesting and processing costs can be reduced. As with any new enterprise, asparagus production should be thoroughly investigated before beginning production.
by B.A. Davidson, The Center
1. Higgins, M. 1981. Grow the Best Asparagus. Storey Communications, Inc.
2. Asparagus Tips. 1994. Minnesota Horticulturist. Aug/Sept.
3. Dufault, R.J., et al. 1988. Growing Asparagus in Minnesota: A Production Guide. Minnesota Extension Service, AG-OF 1861.
4. Anderson, L. and C. Tong. 1993. Commercial Postharvest Handling of Fresh Market Asparagus. Minnesota Extension Service, FS-6236-A.
5. Rutherford, P. 1995. Asparagus Culture: Production, Management, and Marketing. Small Farm Today. December.
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