Family: Liliaceae
Genus and Species: Asparagus officinalis
Climate
Asparagus produces the best in areas where freezing temperatures or drought terminates plant growth and provides a rest period. Without this rest period the asparagus plants experience reduced yields. Asparagus is very tolerant to large temperature variations and therefore well suited to a variety of Zones.
Asparagus can be grown in a wide range of soils and under various climatic conditions, but it thrives in fertile well-drained soils in moist temperate regions that have long growing seasons and sufficient light for maximum photosynthesis. Asparagus likes full sun or at worse, partial sun.
Soil
Attention to selection and preparation of the planting site is especially important. Asparagus performs best if the soil pH is within a range of 6.5 to 7.5. Phosphorous, potassium, and lime amendments - based on a soil test - should be incorporated prior to planting.
If perennial weeds are a problem, a sequence of tillage and cover cropping with sorghum-sudan or buckwheat at least a year in advance of planting will help control weeds. Green manure crops also improve soil structure and enhance soil fertility but be sure to till them in before they reach seed maturity.
Spacing
Plant asparagus with a spacing of 8"-14" between plants and 4' - 6' between rows. At 8" the spears will be more slender and at 14" the asparagus spears will be more robust.
Direct Seeding
Direct seeding is not normally practiced.
Seeding For Transplants
Plant asparagus seeds ½" deep in a cell trays, soil blocks, or 4" pots of potting mix. Soak the seeds in water overnight before planting.
Germination
These seeds germinate best in soils around 60°F - 85°F. Germination will take about 21 days.
Planting Root Stock
Plant the asparagus crowns 2-4 weeks before last spring frost. Asparagus crowns can be purchased from a nursery. Soak the crowns in lukewarm water for a few hours before planting. Plant asparagus in furrows with a spacing of 8"-14" between plants and 4' - 6' between rows. At 8" the spears will be more slender and at 14" the asparagus spears will be more robust.
Transplanting Into the Garden
Transplant asparagus to the garden at 12-14 weeks.
Watering
Asparagus roots can penetrate up to 10 feet to obtain soil water but their greatest water uptake will occur within top 6 to 24 inches of rooting zone. It is very important to ensure the asparagus plants have adequate soil moisture in this zone during the fern stage. Inadequate soil moisture during fern development can cause significant reduction in next spring's spear production. Dry soil conditions during spear growth can also affect quality and yield. Adequate soil moisture is also necessary for newly planted crowns to establish good root development and fern growth. Asparagus planted in sandy soils require frequent irrigation.
Light, frequent irrigation applications should be avoided during fern growth to minimize foliage disease development.
Harvesting
Asparagus planted from seed will take 2-3 years to establish and produce significant yields. Asparagus planted as crowns will begin producing between 1-2 years.
Harvest is done by hand when the spears reach approximately 9". Diameter is not a good indicator of maturity.
Fresh, high quality asparagus will be dark green and firm with tightly closed, compact tips.
Asparagus stalks will be straight, tender and glossy in appearance. The harvest period in a mature asparagus planting lasts about eight to nine weeks. Spears are hand picked by snapping or cutting them just above the ground. Most commercial growers build their own harvest aids to increase harvest efficiency.
These low-lying platforms can either be attached to the front or rear end of a tractor, or are self-propelled. Once harvest begins, picking takes place every other day in cool weather, and every day later in the season.
Be aware that asparagus spears grow more rapidly as temperature increases. Asparagus will grow 7" in a day when the temperatures reach 90°. Also taller spears grow more rapidly than shorter ones.
Post-Harvest Handling
Fresh asparagus is highly perishable and deteriorates rapidly above 41°F and therefore some method of cooling the asparagus after harvest is necessary. Pre-cooling to remove field heat prior to shipment is commonly practiced via hydro cooling. Hydro cooling is the process of spraying or immersing vegetables in chilled water.
Storage
Asparagus can be kept successfully for about 3 weeks at 35°F. High relative humidity (95% to 100%) should be maintained, with good ventilation to reduce carbon dioxide and ethylene buildup. Do not store asparagus in a plastic bag or other non-breathable container. A lack of ventilation will allow the build up of ethylene gas which will cause the asparagus spears to toughen. Asparagus is commonly stored standing on end, bound with a rubber band, and with the butt ends on a wet pad.
Diseases
Fusarium, Asparagus Rust, Needle Blight, Purple Spot.
Pests
Asparagus Beetle, Spotted Asparagus Beetle, and Asparagus Aphid.
Comments
Allow the ferns to grow naturally for the remainder of the season. Don't cut them back until they die naturally. Apply compost or well-aged manure in the fall or spring.
Keep asparagus bed weeded to reduce the possibility of disease and competition for water.
White asparagus has a milder flavor than green asparagus. To create white asparagus, deny the asparagus plant sunlight. Simply mound up soil or straw over the asparagus row and keep the spears covered.
References
Oregon State University, "Asparagus, Commercial Vegetable Production Guide", Last modified 2002-11-12, Oregon State University, http://www.orst.edu/Dept/NWREC/asparagu.html, Accessed 2002-12-30
Marr, C. & Tisserat, N., "Asparagus, Commercial Vegetable Production, Kansas State University",
http://www.oznet.ksu.edu/library/hort2/mf1093.pdf, Accessed 2002-12-30