Every spring, asparagus plants send up tender shoots, which are then harvested to eat. Most gardeners grow asparagus from crowns rather than seed. For the biggest crops, purchase all-male plants. In cold climates, look for Jersey Giant or Jersey Knight. For climates that don't have deep winter freezes, UC 157 is a good choice.
Once established, asparagus will produce spears for 20 or more years, so choose the site wisely. Because it can grow very tall, many gardeners plant it on the north or west side of the garden where it will not shade other vegetables. Asparagus grows best in full sun and in loose, well-drained soil. Work 3" of composted manure and other organic amendments into the top 15" of the bed. Also work in some 10-20-10 fertilizer at the rate of 1/2 pound per 100 square feet.
In early spring, dig a trench about 8" deep and 8" wide. Place the crowns with buds pointed up on a small mound of soil. Spread out the roots in the trench. Space the crowns about 18" apart. Cover the crowns with 2" of soil and water well.
As the spears develop, gradually fill in the trench by adding an inch or two of soil at a time. Do not cover the foliage, only the shoots. Once the trench is completely filled in, fertilize lightly with slow-release 10-10-10 and mulch the bed well to prevent weeds. Water the plants regularly the first season to get them established.
Do not harvest any spears during the first year. Let all the spears develop into ferny plants, as this allows the plant to develop a vigorous root system. In year two, harvest asparagus spears for just two weeks. After that, let the spears develop into plants. In year three, harvest spears for four weeks. In year four and thereafter, harvest spears for six to eight weeks.
Spears are ready for harvest when they reach 7" to 8" tall and still have tightly budded tips. Use a pair of pruners to cut the asparagus spears just above the soil line. Don't cut below the soil line. Early spears will be rounded and plump, nearly as wide as a thumb. As the season progresses, the spears get smaller. When the spears are thinner than a pencil, it's time to quit harvesting and let the ferns grow.
In the fall, after the plants have turned brown and died back, cut them down to ground level. This prevents insects from overwintering and encourages healthy, pest-free asparagus plants in the spring.