Unlike most other vegetables, asparagus (Asparagus officinalis) is a perennial, and plants can produce for as long as 20 years or longers after the first harvest. That first harvest is a long time in coming, however, because it doesn't occur until three years after seeds are planted. That's why most gardeners plant crowns instead of seeds; it cuts the time to the first harvest by a year.
Asparagus grows well in U.S. Department of Agriculture zones 2 through 8. People in colder climates benefit by planting 'Guelph Millennium,' a variety that emerges late, while those in warmer climates should plant 'Apollo' or 'UC-157,' which produce before the onset of hot weather. 'Jersey Knight' is a hybrid that grows especially well in USDA zones 4 through 6.
Germinating and Transplanting
Asparagus seeds take a long time to germinate, which is one reason many gardeners prefer to grow the plants from crowns. Depending on the temperature of the soil, it can take asparagus seeds up to two months to germinate. Time the planting to be ready to transplant the shoots 10 to 12 weeks later. The best time to plant the shoots is in early spring, after all danger of frost has passed. Asparagus thrives in cool temperatures and full sun, and the pH of the soil should be between 6.5 and 7.5.
Gardeners should perform a soil test approximately six months before planting the asparagus as it takes this long to adjust the soil's pH. If the soil's pH tests too high, apply 1/4 pound of sulfur for every 100 square feet of garden bed. If the results of the soil test states the pH is too low, adjust by applying 5 pounds of lime for every 100 square feet of garden bed.
Soak seeds for two hours prior to sowing.
Place each seed in a separate 2-inch pot filled with sterile sowing mix. Sow the seed 1/4 inch below the surface. Make sure the container has bottom drain holes so it doesn't retain too much moisture and the seeds rot.
Place the pots in a warm place and keep the soil moist. Sprouts should appear in two to eight weeks, depending on the soil temperature; they'll sprout faster if the soil is warm.
Prepare a well-draining soil bed by removing all the weeds and working in 1 to 2 pounds of 5-10-10 fertilizer per 100 square feet. Water the fertilizer into the soil after applying. Transplant the shoots into holes about 4 inches deep and cover the crown with more soil as it grows. Space holes in each row 18 inches apart, and space rows 3 to 6 feet apart.
Care and Maintenance
Fertilize the plants in the early spring, using 1 to 2 cups of 5-10-10 fertilizer per 10 feet of row, which amounts to a handful of fertilizer per plant. The best time to do this is after you've finished harvesting the spears. Avoid high-nitrogen fertilizers, as well as "hot" ones like hog, sheep or poultry manure. Instead, use bone meal and high dolomitic limestone. Water the fertilizer into the soil after applying.
Give each plant 1 inch of water every week. To help plants retain moisture, mulch them with straw. Mulch also helps control weeds and protects young shoots in the event of a late frost. Even with mulch, it's important to control weeds growing around the young plants by pulling them by the roots. Weeds will gradually get fewer as the asparagus plants grow and become bushier.
Trim the ferns down to about 2 inches in the late fall using hand pruners and throw them away to help prevent disease and control pests, such as the asparagus beetle, which overwinters in the top fronds. If pests aren't a problem, consider leaving the fronds -- they transfer energy to the roots.
It takes three years for asparagus plants to be strong enough to harvest. If the plant is growing vigorously, spears will appear in the first spring after planting, and for about two weeks you can break these off if they grow longer than 4 inches. That encourages the plant to produce more. In the second year, extend this harvest period to four weeks, and in the third year, extend it to six weeks. In the fourth year, when the plant is mature, you can harvest spears for up to eight weeks.