It has been said that the Ancient Greeks and Romans relished asparagus. This is evidence that asparagus is a good, reliable crop to grow in many climates and throughout the ages.
Even with a great reputation, today’s asparagus needs to be planted, cared for and harvested correctly to maximize profit and yield. If done correctly, income can be upwards of $6,000 per acre, according to the Agricultural Marketing Resource Center (AgMRC).
Approximately 23,000 acres of asparagus were harvested in the U.S. in 2016, according to AgMRC. Most of these commercial acres are in California, Washington and Michigan. In 2015, total asparagus production was 63 million pounds with 84 percent (53 million pounds) marketed as fresh and 10.4 million pounds and 4.6 million pounds frozen or canned, respectively.
The value of the 2015 U.S. commercial asparagus crop was approximately $62.9 million. With such little preplanting requirements and a reliable harvest, getting part of that $62.9 million is obtainable, but not without some work first.
1. Ground prep
Before planting, the soil must be prepared about a year before the planned planting date. Asparagus has a somewhat unusual pH level that is needed for proper growth.
According to the Michigan Asparagus Advisory Board (MAAB), a pH of 7 will do the job but a little higher won’t hurt the crop. To get the proper pH, adding lime to the soil can increase the pH and the deeper you apply the lime, the better it works, according to MAAB.
Apply lime the first year by spreading it on the surface and moldboard plowing the field to a minimum of 10 inches. Plowing will incorporate the lime to the deeper levels where it is needed.
Do not disk or harrow the lime before plowing, so that it can be incorporated through the plowed layer. Lime should be applied as early as possible and preferably six months before planting time. Lime should be applied every other year,” advised experts at NCSU.
Sandy soil is preferable but according to MAAB, “Anything you can do to raise the organic matter of the soil before planting will also pay big benefits.”
Compost is probably the easiest way to do this but manure is beneficial as well.
Keep in mind that good drainage is important for control of problems like crown rot disease of asparagus. “Commercial plantings of asparagus should not be made in soil that is heavier than a sandy loam,” NCSU noted.
Given the correct soil type and a pH of at least 7 or higher, it is time to plant.
When planting, the timing is as important as how to plant. University of California (UC) Small Farm Program said planting can be done any time in the spring after the soil warms to 50 degrees Fahrenheit.
Asparagus should not be planted in cold, wet soils, which can harbor Fusarium crown rot disease.
When planting, only a 6-inch deep trench is needed, and no deeper. To get this depth, a lister plow or middlebuster that throws soil in opposite directions can be used. Be careful not to go deeper though. “The deeper the plant, the lower the yield,” warned the UC Small Farm Program.
The crowns being used should go 1 to 1.5 feet apart in a row. This takes between 5,800 and 8,700 crowns per acre.
Rows should be established at least 5 feet apart. This will allow for good air circulation that will help stop onset of foliar fungal diseases.
Asparagus is generally planted using 1-year-old crowns. At planting, 200 pounds of 0-20-0 or 0-46-0 fertilizer per acre should go in the furrow.
Crowns placed in the trench should have the crown buds facing up with the root systems spread out as much as possible. Cover the trench with soil up to the original soil level. However, do not compact the soil over the row, or spear growth will be seriously delayed.
MAAB recommended not filling the trenches in completely, although that is sometimes done successfully on sandy soils. The best approach is to cover the crowns with about 3 inches of soil. Let the new plants grow through that soil for about six weeks and add another 3 inches of soil.
Wait until plants have gone dormant in the late fall or in the spring before growth begins to finish filling the trenches.
Costs run about $130 per 1,000 crowns or from $780 to $1,170 per acre, including fertilizer and lime (if needed). Add in the cost of soil preparation, and the total cost should be about $1,500 per acre.
With good soil moisture, new spears emerge in about a week. If proper soil preparations are taken and proper plant spacing occurs, the asparagus will be plentiful come time to harvest and will be a great source of revenue as planting costs are relatively low.
3. Deadly diseases
Just because weeds are taken care of, the fight is not over. There are several deadly diseases that can drastically decrease crop yield if not handled properly.
The first is fusarium diseases. Fusarium oxysporum, aka crown rot, is a type of devastating fusarium disease. According to NCSU, the crown rot fungus is found in most soils but at very low levels. If asparagus crowns are planted that have crown rot they will not produce for more than four to seven years, and this is not profitable.
To prevent this disease, do not plant asparagus in soil and do not purchase crowns grown in soil where the asparagus was grown in the last five years. Purchase only certified crowns.
If these practices are followed, the asparagus should be healthy enough to fight off the disease, since as of now there are no proven practices to kill the disease after it has attacked.
Next, consider root rot. According to MAAB, “Asparagus is an excellent host for this disease and populations grow steadily in your asparagus bed over time. At present the only control is to keep asparagus crowns healthy so that they can successfully fight off the disease as long as possible.”
Affected crowns will have a brick-red rot that works from the outside of the crown in until the crown is killed. This disease also explains why it is not a good idea to plant a second crop of crowns in an old asparagus bed. Because levels of Fusarium are already high, the yield and life expectancy of the new bed is much less.
Similar to crown rot, there is not much that can be done once asparagus are infected except to let the asparagus fight off the disease naturally. Although letting the crop defend itself may sound risky, if the proper planting precautions are followed, the asparagus will be strong enough to defeat both crown rot and root rot.
4. Beating bugs
Another threat to asparagus is insect damage. The main threatening insects are beetles and aphids. Asparagus beetles and asparagus beetle larvae attack spears and ferns. To kill them, spray Sevin at 1 to 1.5 pounds active ingredient per acre at first observation to control this insect.
Armyworms can be especially bad on young ferns but can be controlled by Lannate or Nurdin at 0.9 pound active ingredient per acre.
European asparagus aphid can be a problem in certain years. This blue-green aphid forms colonies some years in August or September. When the aphid forms colonies, it causes “Christmas tree” or bonsai effect; the new fern becomes shortened or stunted and new needles look like they are clustered. The entire fern takes on a blue-green color. The following year spears and fern are stunted and often die. These aphids can be controlled with insecticides, according to NCSU.
If the weeds are controlled and insects and diseases are properly eliminated, it is time to harvest.
Harvest time is like Christmas: you want to open up all the presents at once but, in the end, they must be handled one at a time. Harvesting asparagus is similar.
The proper harvesting technique for any field of asparagus will change year to year. According to NCSU, “Asparagus can be harvested on (a) limited basis (two to three weeks, or eight spears per plant) during the first year after planting. Harvesting should be limited during the second year.” Watch for a slight reduction in spear size as an indication of when to stop cutting. It takes a long time for asparagus to develop a large root system, which is necessary for a healthy bed of asparagus to produce for many years.
Do not over-harvest in early years because bed life can be shortened and total yield and profit drastically reduced. Harvest six to eight weeks during the third year of growth. This is generally until mid-May in the east and mid-June in western North Carolina.
Allow spears to reach 8 inches tall and then cut with a knife or hand snap at the soil surface. Spears should not be allowed to get taller than 9 inches. The decision on when to harvest is based on having an average of one harvestable size spear per foot of row.
When temperature exceeds 80 degrees Fahrenheit, it may be necessary to harvest daily.
After harvest, the spears should be held in a cool shaded place and sprinkled with water to prevent shriveling and wilting. A single irrigation sprinkler over the boxes works well. Asparagus should be hydro cooled before packing.
The payoff comes when it is time to sell. The “look” of the product in the market is important. Spears should be uniform in length. Tie in bunches of 1 to 2 pounds or pack loose in a carton. Present standards allow lengths of 7 to 10.5 inches.
Even though it may look good, how it tastes and freshness are the main factors in how much will sell. “Asparagus loses edible quality rapidly and should be cooled as soon as possible. After bunching, place the butts of the spears in damp peat moss or blotter paper in a crate or carton. Pack 15 or 30 pounds in special pyramid-shaped crates.
Cooled asparagus will remain saleable for three weeks or more if held at 32 degrees Fahrenheit. Asparagus should always be shipped under refrigeration, experts noted.
Overall, asparagus is a profitable crop to grow; fairly easy to care for; and, with proper care, has a good track record when it comes to the final quality and quantity of the product.