Asparagus Growing Guidelines
Apply mulch to smother weeds, which compete with the young spears and reduce yields. Carefully remove any weeds that do appear. Water regularly during the first 2 years after planting. As asparagus matures, it crowds out most weeds and sends long, fleshy roots deep into the earth, so watering is less critical. Fertilize in spring and fall by top-dressing with liquid fertilizer (such as compost tea) or side-dressing with a balanced organic fertilizer.
Leave winter-killed foliage, along with straw or other light mulch, on the bed to provide winter protection. Remove and destroy the fernlike foliage before new growth appears in spring; it can harbor diseases and pest eggs.
If you want to grow white asparagus, which has a slightly milder flavor than green asparagus, blanch the spears by heaping up soil or mulch over the bed before they emerge.
Starting Asparagus from Seed
It takes patience to start your asparagus patch from seed, but there are advantages to gain from the extra wait. Seed-grown plants don't suffer from transplant trauma like nursery-grown roots, and you can buy a whole packet of seed for the same price you'll pay for one asparagus crown. Most seed-grown asparagus plants eventually out-produce those started from roots. Growing from seed also allows you to selectively discard female plants and plant an all-male bed, no matter what variety you choose to grow.
In the North, start seedlings indoors in late February or early March. Sow single seeds in newspaper pots, place the pots in a sunny window, and use bottom heat to maintain the temperature of the mix in the pots at 77°F. When the seeds sprout, lower the temperature to 60° to 70°F. Once the danger of frost is past, plant the seedlings (which should be about 1 foot tall) 2 to 3 inches deep in a nursery bed.
When tiny flowers appear, observe them with a magnifying glass. Female flowers have well-developed, three-lobed pistils; male blossoms are larger and longer than female flowers. Weed out all female plants. The following spring, transplant the males to the permanent bed.
Healthy asparagus foliage is necessary for good root and spear production. Asparagus beetles, which chew on spears in spring and attack summer foliage, are the most prevalent problem. The 1/4-inch-long, metallic blue-black pests have three white or yellow spots on their backs. They lay dark eggs along the leaves, which hatch into light gray or brown larvae with black heads and feet. Control by hand picking; spray or dust seriously infested plants with insecticidal soap. These methods also control the 12-spotted asparagus beetle, which is reddish brown with six black spots on each wing cover. Asparagus miner is another foliage-feeding pest; it makes zig-zag tunnels on the stalks. Destroy any infested ferns.