Asparagus - The Perennial Super Food

Introduction & History

Asparagus (Asparagus officinalis) is a member of the Lily family and perhaps the most well known perennial vegetable throughout the world. There are roughly 150 species native to Europe, Asia and Africa. (The asparagus species that we eat today is from the eastern Mediterranean region.) Under cultivation for over 2,000 years, this popular vegetable is prized for its tender, succulent, edible shoots or spears. It is highly popular in home gardens because "fresh homegrown" always seems to taste better than the supermarket version. Commercial production is mainly in California (January–June harvest), Washington (April–June harvest), Michigan and New Jersey (May–June harvest). Imported asparagus comes mainly from Peru, Chile and Mexico with a fall and early winter harvest. Most varieties produce green spears. White spears, which are more tender, are produced by burying the green shoots in soil to prevent chlorophyll formation. There are also purple spear varieties that have a fruitier flavor, although yields are much lower. In addition to its food properties, asparagus is also valued as a medicinal plant.

Climate, Soils, & Site Selection
Asparagus can be grown throughout the United States, however, it is most successful in colder regions that force the plant to become dormant for a significant part of the year. These extended rest periods enable a longer duration of productivity, sometimes up to 20 years, although the length of the harvest season is shorter in these colder regions. In warmer semi-arid and arid regions that have very little winter cold, withholding water for 3 or 4 months during the fall and early winter will also create a dormant rest period that will allow for successful production.

Asparagus tolerates a wide range of soil types, but sandy loam with moderately high fertility is best, and good drainage is essential. Mildly alkaline soils are best, although slightly acidic soils are acceptable. Soil pH less than 6.0 can lead to Fusarium root and crown rot. Generous yearly applications of high quality compost or well-rotted manure are important to maintain long-term plant vigor and health. Select a site that receives full sun and has not grown asparagus before to reduce the chance of Fusarium diseases.

Planting
Asparagus seed can be planted directly, but the seed is slow to germinate and considerable amounts of labor, irrigation and weed control are required to establish plants. Therefore, it is preferable to start with healthy, one-year old fleshy root crowns. In mid-spring when the ground is still cool but not frozen, the crowns are planted into a V-shaped trench 6 to 12 inches deep—deeper for lighter soils and shallower for heavy soils. Plant the crowns 12 to 18 inches apart in the row. Rows should be 4 or 5 feet apart to allow for good fern growth in the summer. Cover the crowns with 3 inches of soil and allow 6 weeks of growth before adding another 3 inches of soil. Do not finish filling up the trench until the fall when the plants have gone dormant.

Weed Control
Young plants are particularly vulnerable to the suppressive effects of weeds from mid-August until frost, so it is essential to keep your patch free of weeds during this time. Competition for light, nutrients and water will greatly decrease asparagus plant vigor and lifespan. When you prepare the site for planting the crowns, avoid areas that are heavily infested with weeds, and especially grassy weeds, which are difficult to control once they are established. Shallow tillage can be effective, but tilling too deeply can damage asparagus roots. Often hoeing or pulling weeds by hand works the best, but be thorough or weeds will come right back and negate all that hard work. Once the plants are weeded, apply a 3–5 inch layer of clean (weed-free) straw or leaves. A yearly application of mulch should adequately control most weeds. Traditionally salt was applied for weed control since asparagus tolerates rather high sodium levels, however this method is not recommended because it destroys soil structure and renders the site useless for planting other plant species in the future.

Insect Control
The major insect pest is the common asparagus beetle (Crioceris asparagi L.). The adult has a slender, 1/4 inch-long blue-black body with a red thorax and lemon yellow and dark blue wing cover. The full-grown larvae is 1/4 inch long, dark gray with shiny black head. The adults feed on spears and the stems of ferns, which weakens the roots. They lay eggs on the spears and the hatching larvae feed on the ferns. Also important is the 12-spotted asparagus beetle (Crioceris duodecimpunctata L.). The adult is broader than the common asparagus beetle, with an orange-red color, and each wing cover is marked with 6 black dots. Full grown larvae are 3/10 inch long and orange. Adults feed on young spears, while adults and larvae both feed on asparagus berries later in the season. Pest damage can be reduced by harvesting all spears every 3–5 days, which removes all eggs that have been deposited. Floating row covers laid on top of the asparagus patch before the spears emerge can help exclude insect pests.

Disease Control
Asparagus rust (Puccinia asparagi) is the most serious disease of asparagus in the U.S. It appears as small reddish-brown spots on the main stems and branches of the ferns. As the disease progresses the entire plant becomes a dark orange or reddish-brown color. This disease weakens the plant and if severe enough will kill it. The best control is to raise rust-resistant varieties All the varieties offered by Seeds of Change are, in fact, either tolerant or resistant to rust. The other key element is maintaining plant health with annual compost applications, good weed control, and avoiding over-harvesting of the spears. Other preventative measures include removing the dead asparagus debris in early winter and composting it, since the debris hosts the rust organism and can carry over into the next year. Avoiding overhead irrigation also reduces incidence of disease. If irrigation is needed, use a drip system. Also, wide spacing of asparagus rows (6 feet or so between rows) will improve air movement and reduce disease.

Another significant disease is Stemphylium Purple Spot (Stemphylium vesicarium), which produces purplish spots on the spears. Although these spots are not harmful and disappear when cooked, this pathogen can develop dark-purplish spots on the ferns, which can kill the plant if the infection is severe. Control measures for this disease are similar to those for rust. The major soil disease is Fusarium root rot (Fusarium spp.). Affected crowns have a brick-red color. Use healthy planting stock and keep asparagus plants vigorous by applying compost annually and maintaining good weed control. These measures will not eliminate the disease but will prevent it from seriously damaging your plants.

Harvesting
After you have received your one-year old asparagus crowns, do not harvest any spears for the next two years. This allows the plant to accumulate carbohydrates and put all its energy into developing a strong root system. Harvest should begin in the spring of the third year after planting. During that year only harvest spears for about 2 weeks. Harvest all spears, regardless of diameter, when they are 8–10 inches tall. The fatter spears are usually more tender, while the skinny spears are more stringy and fibrous. The following year, extend the harvest season to 4 weeks, and then by the fifth year you can harvest for a full season, which is about 7 to 8 weeks long. In warmer regions such as California and the Deep South, the harvest season can be extended a few weeks longer. During warm weather you may be harvesting spears daily, while in colder weather, your patch may only need to be picked once every 4 or 5 days. The best method for picking is snapping the spears off, rather than cutting with a knife, because the point where the spear breaks is right above the tough, woody lower part. After the harvest period ends, allow the subsequent spears to grow into mature tops or ferns. These ferns provide energy for the crown, and sustained production for the next season, so never prune them back. It is, however, not good to allow excessive fern growth, which can deplete energy from the crown. Therefore, starting in mid-summer, stop watering or fertilizing to slow down growth.

Health Benefits
Asparagus is truly a health-giving plant that supplies many important nutrients. The following is a list of its most important nutritional attributes:

The characteristic strong odor from one's urine after eating asparagus is not at all harmful. A class of breakdown chemicals from asparagus, known as mercaptans or thiols (e.g. dimethyl sulfide) cause this smell.

There is one specific health precaution. Anyone suffering from kidney problems or gout should limit their intake of purine-rich foods, such as asparagus.

Preparation
Although asparagus is a prime ingredient in many gourmet casseroles, stir-fries, meat and vegetable dishes, it is probably best enjoyed as a stand-alone dish. The simplest preparation involves boiling or steaming for 3 to 5 minutes and then rinsing in cold water to retain the bright green color. It can also be stir fried with garlic, ginger and sesame oil. If the asparagus spears are particularly thick, a great technique is to roast them in a 500º F oven for 3-5 minutes, or insert bamboo skewers, brush with olive oil and grill over medium heat for several minutes. No matter how you cook asparagus, it is universally loved for its wonderfully succulent flavor and health-giving properties.

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