Asparagus is a highly productive vegetable best suited to cooler areas. Grown for the stems or spears, a well tended planting yields 8 to 10 pounds or more per 100 square feet of bed or 24 to 30 pounds per 100 feet of row. For most home gardeners, one row is adequate.
An asparagus planting lasts 15 to 25 years without replanting if it is well cared for and the climate is suitable. It does not do well if summers are extremely hot and long and winters are mild.
Asparagus is grown from 1-year-old plants or “crowns” planted in January or February. Crowns grow from seed planted in flats or peat cups in October for January transplanting, or they are transplanted from an existing asparagus bed. To get healthy, vigorous plants, buy 1-year-old crowns from a nursery or garden center or order them from a seed catalog. It takes 1 year to grow a good crown.
It requires 3 years from the time the crown is planted until the bed is in full production. Buds arise from the crown when conditions are favorable and develop into edible spears. If these spears are not harvested and are allowed to continue growing, they develop into “fern-like” stalks.
From these “ferns”, the mature plant manufactures food and stores it in “storage roots.” This reserve supplies the energy necessary to produce spears the following year.
Asparagus does best in a deep, well-drained soil with full sunlight.
Since an asparagus planting lasts many years, good seedbed preparation is essential.
In late fall, spread a 3-inch layer of organic matter such as manure, rotted sawdust or compost over the beds. Till or spade to a depth of 10 to 12 inches and turn the soil so all organic matter is covered. Asparagus grows well in high pH soils but does not do well if the soil pH is below 6.0. Test the soil before planting the beds and add lime if needed to adjust the pH to 6.5 to 7.0.
Before planting new asparagus beds, till in 2 to 3 pounds of 10-20-10 or a similar analysis fertilizer per 20 feet of row or as directed by a soil test report.
For established beds scatter 1 to 2 pounds of 10-20-10 fertilizer per 20 feet of row before growth begins in the spring, late January or early February in most areas of Texas. Add an additional 1 to 2 pounds per 20 feet of row after the last harvest. If available, use a nitrogen fertilizer such as 21-0-0 at this time. Water the fertilizer into the soil. Low fertility can cause fibrous spears.
Since asparagus will be in the same place several years, it is important to select the right spot. Asparagus plants make a good border around the edge of a garden or along a fence.
After asparagus beds are tilled, mark rows 4 to 6 feet apart. Dig a furrow 4 inches wide and 6 to 12 inches deep. Place the crowns in the furrow, cover with 2 to 3 inches of soil and firm the soil around the roots. Do not fill the entire furrow at once. Plant crowns 6 to 12 inches deep in loose soils and 4 to 6 inches in heavier soils.
Place crowns 12 to 14 inches apart. Planting too closely can cause small spears. Wider planting results in larger spears but lower total yield. Control weeds but do not injure the crowns. Fill the furrows gradually as the shoots grow. This covers small weeds, and they die from lack of light. By the end of the first season, the furrow reaches its normal level (figure 1). Deep planting of the crowns allows cultivation with garden tools or tiller (do not till too deep) without damage to crowns.
Asparagus plants like frequent, deep watering. Water the beds thoroughly as needed. Allow the top 1 inch of soil to dry before watering again. The time varies from 3 to 5 days depending on temperature. Asparagus roots reach 10 feet deep if the soil is adequate and moisture is available.
Care During the Season
Keep weeds pulled or hoed from the beds. Asparagus beds require little care after the first 2 years. Control weeds without damaging the spears. In early season, till the soil when fertilizer is applied before the spears begin growth (figure 2). Control weeds during the season by raking lightly or mulching. After the last harvest, cut back all top growth. Apply fertilizer and till lightly 1 to 2 inches to kill weeds.
Cover the bed with a 3-inch layer of clean straw, compost or other mulch material, water thoroughly and allow to grow the rest of the year. This helps insure a good harvest the next year (figure 3).
After the first hard frost/freeze of fall, cut fern tops off at ground level and mulch with manure. In southern areas the fern may not be killed by a freeze and should be removed in late November. Any spears which sprout may be removed and eaten.
Harvest asparagus spears from established beds for about 8 weeks. Do not harvest too soon from a new planting.
Harvest spears when they are 4 to 10 inches long. To prevent spears from becoming fibrous, harvest at least every other day. The fibrous condition is caused by overmaturity or inadequate fertility. Spears with loosely formed heads are overmature.
Cut asparagus spears 1 to 2 inches below the soil level. At least one-half the length of the spear should be above the ground. Never cut the spear within 2 inches of the crown to avoid damage to the developed buds. Never cut asparagus spears above the ground and allow stubs to remain (figure 4). Discontinue harvest when spear diameter becomes less than 3/8 of an inch.
Some gardeners prefer white or blanched asparagus. This is grown by shading the spears with mounds of soil or mulch to exclude light.
Home garden asparagus can be damaged by the asparagus beetle in some areas. If you observe insects feeding on asparagus, contact your local county Extension agent for identification and control recommendations.
Asparagus is a good source of vitamin A and C and minerals. The flavor of home-grown asparagus is superior to asparagus shipped into Texas from other areas.
Asparagus loses quality very rapidly after harvest; sugar content declines and the amount of fibrous material increases. Use only spears with compact heads because loose heads do not keep well and are fibrous. Asparagus can be stored up to 3 weeks in plastic bags in the refrigerator.
For longer storage, blanch the asparagus spears 3 to 5 minutes, prepackage and freeze.