Most of this information originated from the University of Michigan and as such it will sometimes talk about growing Asparagus in that state. That’s OK, with few exceptions this same information is applicable to where you live as well.
The information I present has been heavily edited of use on my blog.
Reference Document MSU Extension
Asparagus Plant Once For Years Of Fine Dining Once established Asparagus is easy to grow and harvest and a true luxury make you feel good food. Plant one or more rows and you will be harvesting Asparagus for many years to come with a minimum of effort.
Preparing the Soil For planting asparagus should have begin last year, but that’s no big problem if you use common sense this year. Asparagus has some unusual nutrient requirements and it may take you a while to build your soil up. Shoot for a soil pH of about 7.0. Asparagus will grow at lower pHs, but research shows that lower pHs are more conducive to the growth of the Fusarium fungi. Although asparagus prefers sandy soil, 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, manure would be beneficial as well.
Choosing a variety to plant Mary, Martha or Waltham Washington. These are unimproved, non-hybrid varieties. What hybrid means in the case of asparagus is “all-male” hybrids. In a non-hybrid bed you will have an equal number of male and female plants. While female plants generally produce larger spears, they also produce fewer spears. Gardeners grow mostly hybrid asparagus, chiefly Jersey Giant, Jersey Knight, Jersey Supreme and Jersey Gem.
Increasingly growers are planting more Canadian hybrids, especially one called Teissen, which test show is more productive.
Jersey Knight is what growers here generally use for fresh market. Most of the rest of the varieties mentioned are mostly processing varieties. These varieties are bred for northern climates. I am less familiar with some of the varieties used in the southern United States, but UC 157 is widely grown in places like California and Mexico. It comes from the University of California breeding program.
Transplanting the asparagus Asparagus crown needs to be planted deeply so that you don’t have spindly spears. It is strongly recommend using year old nursery grown crowns. They are small enough that they don’t suffer so greatly from transplant shock.
Asparagus needs to be planted in a trench. In sandy soil, that trench needs to be 8-10 inches deep. Clay soils should have shallower trenches, about 6 inches in depth. Rows are planted from 4 to 5 feet apart to give fern room to grow in the summer. Crowns should be planted between 8 and 12 inches apart on center. A little phosphate fertilizer should be put in the trenches before the crowns are set. Be careful that the fertilizer you use does not also have enough potassium or nitrogen to burn the crown. Triple super phosphate, also known as 0-46-0, is a good choice if you are going to use dry fertilizer.
Do not fill the trenches in completely, although that is sometimes done successfully on very 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 6 weeks and add another 3 inches of soil. Wait until the plants have gone dormant in the late fall or in the spring before growth begins to finish filling the trenches.
Commercial grown Asparagus beds (rows) usually lasts between 12 and 15 years. A few people have asparagus beds that are over 50 years old. However, spear diameter can begin to drop as the bed ages.
Harvesting Asparagus Do not harvest your asparagus the year you plant it or the year following planting. The asparagus plant needs to grow and establish a healthy crown and it will need all of its energy to do that. The third-year after transplanting we generally harvest the field for about two weeks. Try to harvest fields 8 to 12 times the first year of harvest. Which number we use depends on the strength of the field. A picking is taken whenever the spears get tall enough to harvest, usually between 8 and 10 inches, which may be every day in warm weather or every four days in very cool weather. One thing you can use as a guide is the number and diameter of the spears you are harvesting. If the number of spears in a harvest drops off dramatically beyond 15 pickings or so, or if the spear diameter drops, you may want to consider ending harvest early.
Growers should harvest all of the spears that come up until the end of the harvest period, even the small diameter ones call “whips”. You will find that whips are generally higher in fiber and tougher to eat than large diameter spears. That is because most of the fiber in asparagus is in the skins, making the larger spear the more tender.
After the end of the harvest season, the spears should be allowed to grow. A spear is really just a plant shoot, and the shoots will grow into the mature fern that re-charges the crown for the next harvest season.
Insect control Asparagus is attacked by a number of insects. The first one you will notice in the spring is the cutworm. The white cutworm over-winters as a larva and can begin attacking spears as soon as they emerge in the spring. The usual damage that results is that they eat the tip off the spear.
The common asparagus beetle is the next major pest in our timeline. This beetle is uniquely colored with a black and white checkerboard pattern set on a field of maroon. Its chief damage during the harvest season is to glue black eggs to spears. These eggs, which can be numerous, are oblong and stick out from the spear. This pest lasts through harvest season and hatching larvae feed on growing fern, often browning the fern completely off if left uncontrolled.
Dark-sided cutworm also arrives during harvest, usually a couple of weeks after the white cutworm, since in over-winters as an egg. This cutworm feeds on the side of the spear as it grows causing it to bend, often in a corkscrew shape. At present, carbaryl, the active ingredient in most garden dusts, is often used by homeowners to control all of these pests. Follow all label directions when applying any pesticide.
Disease Control Diseases are often the most damaging pests to asparagus plants. There are two major foliar diseases in asparagus rust and Stemphylium purple spot. Sanitation is an important tool in controlling these diseases. Since both of these diseases need moist conditions to grow, another cultural practice can be to plant beds so that prevailing summer winds can blow the length of the row and dry out the fern rapidly. Fern may be treated with a fungicide on a regular basis, every two weeks is often used in preventative treatments, throughout the summer.
Purple spot disease is not generally a problem for gardeners, since cooking usually causes the spots to disappear from the spears. Purple spot during the fern season is more serious. Lesions have a brownish-purple color and are usually irregularly shaped and sunken.
Non-pathogenic asparagus problems Frost can also be devastating to asparagus beds, causing spears to first take on a glassy, dark-green color and then to shrivel and turn black. In both of these situations affected spears should be removed and new ones allowed to grow. Spears can also come up bent and twisted if they are being grown in rocky soil. There is very little that can be done about this situation and the bending does not affect the eating quality of the spear.
Fertilizer Generally do not give asparagus fertilizer unless they are based on a soil test three or less years old. In general, asparagus is a big user of potassium, uses very little phosphorus other than in the year crowns are set, and uses small amounts of nitrogen.
Irrigation Most of the eastern United States, irrigation is completely unnecessary. That is because asparagus is extremely deep rooted. In deep soils, roots often reach 10 feet in depth. In more arid regions some irrigation may be necessary, although overhead irrigation makes an ideal environment for foliar diseases.
White asparagus Contrary to popular belief, white asparagus is not a variety. It is simply asparagus spears grown in the absence of sunlight so that chlorophyll does not develop. White asparagus does have a slightly sweeter taste and has less fiber than green asparagus. In parts of Europe, especially Germany and the Netherlands this is the primary way that asparagus is grown and consumed.
The traditional way to grow it is to plant crowns on the soil surface instead of trenches and to mound dirt up over the rows. During harvest pickers walk between the mounded rows and when they see an asparagus tip just cracking through the soil they dig the spear out of the dirt and cut it off. An alternate way to raise white asparagus was developed by Dr. Jim Motes, an Extension Specialist from Oklahoma State University. His system is to place bent iron hoops over flat rows and cover them with thick black plastic. The plastic blocks sunlight and the pickers can then just lift up the plastic and snap off the white spears.
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