Asparagus

Introduction

Asparagus is a perennial crop in the lily family. It originated near the Mediterranean and has been used as an agricultural crop since the time of the ancient Greeks. Asparagus beds usually produce well for 10 to 15 years, so choose a site with that in mind. Avoid areas where this tall crop could shade other crops. Select soils that are deep and well drained, such as sandy loams or well-drained loams. However, the water table should not be more than four' below the surface. The site should not have been planted with asparagus for a long perioid, preferably  never for this crop. This is to minimize asparagus crown rot (Fusarium moniliforme) which can survive for a long time in the soil even without a host. Land cropped to corn within 3 years should also be avoided since some strains of F. moniliforme can also infect corn. Avoid areas subject to late spring frosts as emerging spears are easily injured. Site preparation should begin at least 1 year prior to planting in order to properly adjust soil pH, fertility, and eliminate serious perennial weed problems.

Varieties

All-male hybrids that are tolerant to Fusarium crown or root rot should be grown. The varieties listed here are tolerant to Fusarium and to rust. The "Jersey" series are generally all-male hybrids. (Older varieties were half male and half female plants.) Mary Washington and some other old varieties are still available, but are highly susceptible to crown rot and are less productive than all-male hybrids.  Male plants do not expend energy producing seed and are more vigorous than female plants. Also, the lack of seed precludes the growth of nuisance seedlings which are not productive and act as weeds. Within the next few years, Rutgers University will be releasing new purple varieties that have improved uniformity, cold hardiness and disease resistance.

Asparagus Varieties
Jersey Giant*
Jersey Supreme
Jersey Knight
Millennium
Purple Passion (purple)

*Some plants are female.

Soil Fertility

The year before planting,  adjust the pH and build fertility in the soil based on soil testing results (see Table below).  Asparagus does not tolerate acid soils.  Apply lime to maintain soil pH at 6.8 to 7.0.   This may require yearly applications of lime. For new beds, deeply incorporate lime to insure proper pH at crown depth.

Asparagus is planted fairly deeply and the roots are known to penetrate deeper than 6".  Since there is little downward movement of phosphorus in the soil, it is important to get phosphorus into the root zone before planting.  Till deeply and mix fertilizer material well into the deep root zone.

Less nitrogen fertilizer will be needed if manure or legume sod was plowed down (see Table 1, Nitrogen Credits from Manure and Table 2, Nitrogen Credits from Previous Crops).  The second year after planting the asparagus should receive fertilizer in the early spring and late summer.  In subsequent years the bed should be fertilized after each harvest season.  Base fertilizer rates on soil test results.

PLANT NUTRIENT RECOMMENDATION ACCORDING TO SOIL TEST RESULTS FOR ASPARAGUS

ASPARAGUS

NITROGEN (N)* LBS PER ACRE

PHOSPHORUS (P) LBS P2O5 PER ACRE

POTASSIUM (K) LBS K2O PER ACRE

SOIL TEST RESULTS

 

VERY LOW

LOW

OPTIMUM

ABOVE OPTIMUM

VERY LOW

LOW

OPTIMUM

ABOVE OPTIMUM

New Asparagus Beds:

                 

Broadcast and Incorporate

50

150

90

30

0

200

150

75

0

In Bottom of Furrow at Planting

0

30

30

30

30

0

0

0

0

TOTAL RECOMMENDED

50

180

120

60

30

200

150

75

0

Established Hybrid Asparagus Beds:

                 

Broadcast after Cutting Season

75

150

90

30-60

0

300

150

75

0

TOTAL RECOMMENDED

75

150

90

30-60

0

300

150

75

0

Established Non-Hybrid Asparagus Beds:

                 

Broadcast after Cutting Season

50

150

90

30-60

0

200

100

50

0

TOTAL RECOMMENDED

50

150

90

30-60

0

200

100

50

0

Planting

Crowns: Plant healthy one-year-old crowns in raised beds at the bottom of 8 inch deep furrows. Be sure the bud is facing up and roots are spread out. Space crowns 12" apart in rows 54" to 60" apart. Closer spacing produces higher yields in early years, but thinner spears in older beds. This will require 8,712 to 9,680 crowns per acre or 100 crowns per 100 feet of row. This spacing is for hybrids and is somewhat greater than was recommended for less vigorous non-hybrids. Cover with 2" of soil, and during the rest of the season the furrow should be filled in bit by bit being careful not to cover the asparagus foliage.

Transplants: Fields can also be planted with eight- to 12-week-old asparagus seedlings after the danger of frost has passed. Plant spacing is the same as for crowns. Care must be taken in order to prevent the small young ferns from being smothered by soil especially after heavy spring showers. To accommodate the growth pattern of asparagus roots use trays with straight, non-foam, non-tapering cells measuring 2 X 2 X 3 inches. Use a sterilized medium consisting of half sand and half peat or use a commercial seed starting mix. Seed germination will take at least three weeks and the soil must be kept uniformly moist during this time. Young seedlings should be fed with quarter- or half-strength soluble fertilizer solution once each week or as needed. The nitrogen in this fertilizer should be in the nitrate form because young seedlings are sensitive to ammonium sources of nitrogen.

Field Culture

It is essential to maintain healthy fern growth during the first two growing seasons. Weed control is easily accomplished by slowly filling in the trenches over the course of the first season. These cultivations can be timed with flushes of weeds. Be sure ferns are not covered. During the second year the beds must be kept weed free, especially during late summer and fall. Weed competition late in the season will restrict crown growth. Close attention must be given to insects and diseases that attack young ferns. As ferns become vigorous and full, diseases can cause the ferns to die prematurely, especially in late summer and early fall during periods of humid weather. Fungicides should be applied to control this foliage decline.

Mow brush in early spring before spear emergence followed by shallow discing, no deeper than 2" to 3" in order to prevent crown injury. Some growers remove ferns in the late fall or burn the ferns during the winter. This can destroy rust and purple spot inoculum and reduce harboring sites for insects. Beds can also be disced immediately after harvest to control weeds prior to herbicide application.

Harvest and Storage

Spears may be harvested two times at the beginning of the second season. The harvest season is increased one to two weeks in subsequent years and should be six to eight weeks in mature beds depending on plant health during the previous summer and fall. If spears are predominantly small in diameter, harvest should be stopped. Overcutting causes rapid decline in bed vigor. Spears can be snapped or cut at or below the soil surface. Avoid injury to newly emerging spears.

Once spears have been bunched and trimmed, they should be placed upright in shallow trays of water and kept cool. Ideally they should be refrigerated at 32°F in order to maintain sugar content and tenderness.

Mother Stalk Harvest Method: (trial only) In Japan and China, harvest throughout the summer is common. In this method, spring harvest is carried out for two weeks, after which three or four strong spears are left to grow into full ferns. From this point, newly emerging spears can be harvested throughout the season into early fall. Spear production is influenced by soil temperature and nutrient availability. Fertigation is usually practiced with this method. Plants have been shown to have similar longevity as those harvested in the spring only.