It is universally conceded that a strong one-year-old crown is superior to older crowns. The roots of two-year plants are seriously mutilated when dug, and the younger plant becomes established more quickly and grows more rapidly. The best cultural conditions must be provided to grow strong crowns in a single season.
The richest garden soils should be selected for this purpose, and the seed sown in the spring as soon as the ground can be prepared. As the seed germinates very slowly, an early start is important to have the benefit of a long season. If hand wheel hoes are to be used, the rows should be not less than 15 inches apart; while for horse tillage 30 inches is not too much space. A pound of plump, fresh seed should produce at least 3,000 plants. The propagator should aim to have a strong plant every 2 inches, though 3 inches apart in the row is better spacing to produce the most vigorous crowns.
Thinning is often necessary to prevent crowding and the production of weak plants. As the small plants are very delicate, the depth of covering over the seed should not be more than 1 l/2 inches to insure germination. Since asparagus seeds germinate very slowly, a few radish seeds should be sown with them to mark the rows, so that tillage may begin as soon as the radish plants appear. The button-shaped radishes should be used because they will be ready to pull in four weeks or less and may be removed without any detriment to the asparagus plants. The most thorough tillage should be given the nursery plat throughout the season. Nitrate of soda can generally be employed very effectively, by applying as a top dressing at frequent intervals during the summer. One hundred pounds an acre may be applied each time, sowing broadcast or along the rows.
The Missouri Experiment Station recommends sowing the seeds in hotbed or greenhouse during February or early March, transplanting the best when 3 inches high into small pots. Later the plants are shifted into larger pots, so they may make a good start before being set in the field. By this method very strong plants are secured the first season, and a larger percentage of marketable shoots become available during the early life of the plantation.
Asparagus may also be propagated by dividing the crowns. This method, however, is not satisfactory and it is seldom, if ever, practiced by commercial growers.