AGRICULTURE, FOOD AND NATURAL RESOURCES Asparagus production guide Vincent A. Fritz, Carl J. Rosen, William D. Hutchison, Roger L. Becker, Janna Beckerman, Jerry A. Wright, Cindy B.S. Tong, and Terry Nennich Washington, and Michigan, many other areas TABLE OF CONTENTS have great production potential climatically and geographically. The cost to establish an Climate asparagus field is substantial, so the decision Site selection and preparation to grow asparagus is one that should be Soil fertility requirements – new thoroughly investigated. This publication plantings describes the cultural practices that must be Soil fertility requirements – considered to produce asparagus established plantings successfully. Secondary and micronutrients Irrigation Asparagus varieties Asparagus bed establishment Crown plantations Seedling transplants Pest management o Insects Crown and root system of a six-year-old asparagus plant; Weeds o each block represents one foot square. o Diseases Harvesting CLIMATE o Preparing for harvest Production is most successful in areas where o Harvest freezing temperatures or drought terminates plant growth and provides a rest period. o Field maintenance after harvest Without this rest period, reduced yields are likely. Asparagus tolerates great temperature Asparagus is a high value specialty crop and variations: it grows in the Imperial Valley of the earliest producing spring vegetable. It Southern California, where temperatures can currently is priced as a gourmet item and will reach 115° F, and it grows in Minnesota, remain in this category until growing, where temperatures can plunge to -40° F. harvesting, and processing costs can be Asparagus can be grown in a wide range of reduced. Although production in the United soils and under various climatic conditions, States is concentrated in California, but it thrives in fertile well-drained soils in © 2013, Regents of the University of Minnesota. University of Minnesota Extension is an equal opportunity educator and employer. In accordance with the Americans with Disabilities Act, this publication/material is available in alternative formats upon request. Direct requests to 612-624-0772 or [email protected]. moist temperate regions that have long and 3 for suggested rates of fertilizer. For growing seasons and sufficient light for nitrogen, (N) approximately 1/3 to 1/2 of the maximum photosynthesis. recommended rate should be broadcast after planting. The remainder of the N should be In Minnesota, asparagus is susceptible to late sidedressed at the first cultivation. Most of spring frosts that may kill emerged spears, the phosphorus (P) and all of the potassium delaying subsequent spear development. (K) should be broadcast and incorporated Therefore, production fields should not be prior to furrow construction or bed shaping. established in low areas or in other frost- Apply 25-30 lb/A P205 in the trench before susceptible locations. crown setting. If soil test P is high, omit the broadcast application and apply only that SITE SELECTION AND PREPARATION recommended for the trench. Unlike most other vegetables, asparagus is a perennial crop which can be productive for Table 1: Nitrogen recommendations for asparagus 15 years or more. Consequently, it is Asparagus Organic matter level How to apply important to pay particular attention to site selection and preparation for this crop. In Low Med. High Minnesota, asparagus is grown on many N to apply lb/A different soils ranging from sandy coarse- New planting 120 100 80 ½ broadcast, ½ sidedress textured soils to clay fine-textured soils. during cultivation Highest yields are usually obtained on Established 80 60 40 Topdress after harvest medium-textured sandy loam to loam soils. planting Asparagus plants have a deep root system that will penetrate at least six feet. Shallow soils or soils prone to a high water table should be avoided. Asparagus roots will not Table 2: Phosphorous recommendations for asparagus tolerate saturated soil conditions. Phosphorous (P) soil Amount of Phosphate (P2O5) to apply SOIL FERTILITY REQUIREMENTS - NEW test (lb/A) PLANTINGS ppm New Established Field preparation should take place the year 0-10 200 75 prior to planting. Soil tests (0-12") can be 11-20 150 50 used to determine needs for lime, 21-30 100 25 phosphorus, and potassium. Asparagus will 31-40 50 0 not tolerate extreme acid soil conditions and 41+ 25 0 grows best at a pH of 6.5-7.0. The objective during the first 3 years after planting is to encourage maximum fern growth so that plants build extensive storage root systems. Plow down soil amendments before furrow construction or bed shaping. All furrows should be 6 to 8 inches below the normal soil surface. Rates of fertilizer for asparagus are dependent on soil test values and relative organic matter levels. Refer to Tables 1, 2 development. Tables 1, 2 and 3 present Table 3: Potassium recommendations for asparagus fertilizer recommendations for established Potassium (K) soil test Amount of Potash (K2O) to apply (lb/A) plantings. This fertilizer should be lb/A New Established topdressed after harvest to encourage fern growth. 0-50 250 100 51-75 200 75 SECONDARY AND MICRONUTRIENTS 75-100 150 50 Asparagus response to application of 101-150 100 25 secondary and micronutrients is not well 151-200 50 0 documented in Minnesota. Most soils low in 200+ 0 0 calcium (Ca) and magnesium (Mg) are acid and should be limed with dolomitic lime prior to planting. Sulfur may be limiting on For the second and third year following sandy soils with low organic matter. In crown setting, disk in during the spring prior general, asparagus response to to spear development (40-60 lbs. N/A and micronutrients is low. Nutrient ranges from recommended rate of P and K according to a healthy mature asparagus ferns are soil test). An additional 30-40 lbs. N/A presented in Table 4. Suspected nutrient should be applied as the soil warms up. deficiencies should be confirmed with soil tests and/or tissue analysis. SOIL FERTILITY REQUIREMENTS – ESTABLISHED PLANTINGS IRRIGATION Once the plants are established, the primary Irrigation should be used on asparagus fields objective is to maintain plant vigor. containing sandy soils or shallow root Asparagus has a very fleshy root system restrictions in central Minnesota. Inadequate which is capable of storing a large quantity of soil moisture during fern development can nutrients. It has been estimated that the cause significant reduction in next spring's roots can store 150 lbs. N/A, 37 lbs. P/A and spear production. Dry soil conditions during 170 lbs. K/A These stored nutrients, in part, spear growth can also affect quality and can be used for the development of spears in yield. the early spring. The actual amount of nutrients removed by a 2.5 T/A harvest is 23 Adequate soil moisture is also necessary for lbs. N/A, 3 lbs. P/A and 20 lbs. K/A. newly planted crowns to establish good root Generally, it is not necessary to apply development and fern growth. fertilizer for an asparagus crop until after Asparagus roots can penetrate up to 10 feet harvest. Delaying fertilization until after to obtain soil water if not restricted but their harvest can reduce early weed growth. For greatest water uptake occurs from the top 6 sandy coarse-textured soils, 20-25 lbs. N/A in to 24 inches of rooting zone (See cover). the spring may be beneficial for spear Maintaining adequate soil moisture in this Table 4: Nutrient concentration ranges in healthy asparagus ferns Stage of Growth Part sampled N P K Ca Mg Fe B Cu Zn Mn ------------------ % ------------------ ppm ------------------ Mature fern Fern from 18”-36” up 2.4 0.3 1.5 0.4 0.15 --- 50 6 20 20 3.8 0.4 2.4 0.5 0.20 --- 100 11 60 160 zone during the fern stage especially should dioecious (dye-EE-shus) plant, meaning that be the goal of an irrigating producer. there are both male and female plants. Asparagus plants will use .10 to .20 inches of Generally, females produce larger spears soil water per day during fern growth than males, but the males produce greater depending on climatic conditions. numbers of smaller diameter spears. Only female plants produce berries. Breeding work To maintain healthy fern development, soil is in progress worldwide to produce high moisture during this period should not be yielding all male asparagus lines. The main allowed to deplete more than 50 to 60% of benefit from an all-male hybrid is that it the soil's water holding capacity in the active doesn't produce seed, which can later rooting zone or go beyond a soil tension of germinate and create a significant weed 70 centibars before another irrigation. problem in the form of several volunteer Asparagus plants do not generally show asparagus seedlings. Asparagus spears visual signs of wilting when moisture- produced from all male hybrids are usually stressed, so extra care must be exercised to very uniform. For many years, the most ensure there is adequate soil moisture common varieties have been from the throughout the growing season. Washington series (Mary, Martha, Waltham), Several soil moisture monitoring methods are developed by the U.S. Department of available to assist the grower in proper Agriculture which are dioecious. However, timing of irrigation water to maintain healthy several of the all-male hybrids developed in plant growth. A discussion of the typical New Jersey (Rutgers University) offer proven monitoring methods can be found in higher yields and increased rust resistance University of Minnesota Extension article, and tolerance to fusarium crown rot and are Irrigation Water Management Considerations often the preferred choice. 'Jersey Giant', for Sandy Soils in Minnesota. 'Jersey Knight', and 'Jersey Prince' have done well in Minnesota. Other all-male hybrid Light, frequent irrigation applications should varieties released from the Jersey series with be avoided during fern growth to minimize excellent resistance to fusarium include foliage disease development.