An asparagus planting will produce good crops for 15 to 20 years when given good care. Proper cultural practices include a limited harvest season, fertilization, and insect and weed control.
Discontinue harvesting of well-established asparagus by early June in southern Iowa and mid-June in northern areas of the state. If harvested over a longer period, the plants may be weakened which can seriously reduce future yields. Allow the asparagus to grow after the last harvest. The top growth can be removed after it has died in late fall or early the following spring.
Two species of asparagus beetle feed on the spears, stems, leaves, and berries of the asparagus plants. The adults are oval- shaped beetles approximately 1/4-inch long. The spotted asparagus beetle is reddish-orange with 12 black spots. The other asparagus beetle is blue-black with 6 square yellow markings. Female asparagus beetles lay eggs on the growing tips. The eggs are black in color, football-shaped, and attached by one end to the spear. The larvae are orange or dark gray.
Asparagus beetles can be controlled by destroying weeds in and around the asparagus planting and by promptly harvesting the spears in spring. If a large population of adults or larvae are present, the insects can be controlled with malathion, rotenone, or Sevin.
Perennial weeds, such as quackgrass, can be controlled after the last harvest of the season. All asparagus growth should be cut back to ground level prior to the herbicide application. Then spot treat the weedy areas with glyphosate (Roundup). Glyphosate is a non-selective systemic herbicide. The herbicide is absorbed through stem and leaf tissue and then translocated to the root system, killing the entire plant. The herbicide is not absorbed by plant roots so the asparagus will be unharmed.
Asparagus may also be fertilized after the final harvest. Apply 1 pound of 10-10-10 complete fertilizer per 100 square feet of garden area.
Proper care of the asparagus planting should allow gardeners to harvest a good crop for many years.
This article originally appeared in the May 19, 1993 issue, pp. 1993 issue, pp. 71-72.