Asparagus can be started from seed but by planting one year old roots, called crowns, you can harvest a year earlier. Before planting, mix manure, compost, or other organic matter into the first foot of soil. If you live in a warm climate and have a well drained soil, dig a trench 8 inches deep and 12 inches wide to plant the crowns in. For each 10 feet of row, scatter 1/2 pound of a 5-10-10 fertilizer in the bottom of the trench. Cover the fertilizer with about 2 inches of soil, then set the crowns in the trench 12 to 18 inches apart and cover them with 2 more inches of soil. As the new shoots emerge, gradually fill in the trench until it is even with the surrounding ground. Asparagus roots spread widely, so if you plant more than one row, space them 4 to 6 feet apart.
To prevent root rot in rainy climates or on clay soil, do not dig a deep trench. Instead, plant the top of the crowns only 2 inches below the soil surface. The following fall, cover them with 2 more inches of soil and repeat this again the following year. The roots will then be covered with 6 inches of soil. You may have to put boards along the sides of this raised bed or gently slope the soil to keep the roots covered. Water asparagus well during the first year. After that, water during the "fern season" but not during the harvest season. Cultivate lightly to keep weeds under control.
Do not harvest any spears the first year. The second spring, harvest for 2 or 3 weeks then allow the remaining spears to develop into ferns. This will encourage the roots to store food for the next year’s growth. In the third year, and thereafter, you can harvest for a period of 8 to 12 weeks.
Spears are ready to harvest in early spring when they are about 8 inches long. Cut the spears 1 to 2 inches below ground level or about 2 inches above the ground. They can be eaten immediately or kept for 3 to 4 weeks in the refrigerator, or frozen for longer storage. Do not wash the spears before storing them in the refrigerator.
Each year after the harvest period, apply 3 pounds of ammonium nitrate or 5 pounds of ammonium sulfate in a furrow several inches deep to the side of the row. Scatter the fertilizer evenly in the furrow, cover it with soil, then irrigate. In the fall, when the ferns turn brown, cut them off at the ground.
A few insect pests occasionally attack asparagus, but prompt harvesting of the spears and disposal of the ferns in the fall will help to minimize their damage. Since early pest detection and treatment results in better control, inspect your plants frequently.