Beloved for its delicious young shoots, asparagus is one of the first crops of spring harvest. The perennial vegetable is rich in B vitamins, vitamin C, calcium, and iron. And it just so happens that fresh-picked spears are far more tender and tasty than store-bought.
Asparagus thrives in any area having winter ground freezes or dry seasons. In fact, the mild, wet regions of Florida and the Gulf Coast are about the only places where it’s difficult to grow.
Select and prepare your asparagus bed with care—this crop will occupy the same spot for 20 years or more. It can tolerate some shade, but full sun produces more vigorous plants and helps minimize disease. Asparagus does best in lighter soils that warm up quickly in spring and drain well; standing water will quickly rot the roots. Prepare a planting bed about 4 feet wide by removing all perennial weeds and roots and digging in plenty of aged manure or compost.
Asparagus plants are monoecious—meaning each individual plant is either male or female. Some varieties of asparagus, such as Jersey Knight and Jersey Giant, produce all male or primarily male plants, so they’re more productive—male plants yield more harvestable shoots because they don’t have to invest energy in producing seeds. Choose an all-male variety if high yield is your primary goal. If you like to experiment, you may also want to grow an heirloom variety or a purple-stalked variety like Purple Passion. With an all-male variety, twenty-five plants are usually adequate for a household of four; plant double that amount for standard varieties. (Ardent asparagus lovers recommend tripling these quantities.)
Starting asparagus from 1-year-old crowns gives you a year’s head start over seed-grown plants. Two-year-old crowns are usually not a bargain. They tend to suffer more from transplant shock and won’t produce any faster than 1-year-old crowns. Buy crowns from a reputable nursery that sells fresh, firm, disease-free roots. Plant them immediately if possible; otherwise, wrap them in slightly damp sphagnum moss until you are ready to plant.
To plant asparagus crowns, dig trenches 12 inches wide and 6 inches deep (8 inches in sandy soil) down the center of the prepared bed. Soak the crowns in compost tea for 20 minutes before planting. Place the crowns in the trenches 1½ to 2 feet apart; top them with 2 to 3 inches of soil. Two weeks later, add another inch or two of soil. Continue adding soil periodically until the soil is slightly mounded above surface level to allow for settling.
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.
Avoid asparagus rust, which produces reddish brown spots on the stems and leaves, by planting resistant cultivars. Minimize damage from Fusarium wilt, which causes spears, leaves, and stems to be small with large lesions at or below the soil line, by purchasing disease-free roots and using good garden sanitation. Crown rot causes spears to turn brown near the soil line. Prevent crown rot by planting in raised beds, maintaining good drainage, and keeping soil pH above 6.0.
If your asparagus bed does become infected by disease organisms, your best option is to start a new bed in a distant part of the garden, using newly purchased or grown plants.
If young spears turn brown and become soft or withered, they may have been injured by frost. Cover spears with mulch or newspaper when freezing nights are predicted.
Don’t harvest any spears during the first 2 years that plants are in the permanent bed. They need to put all their energy into establishing deep roots. During the third season, pick the spears over a 4-week period, and by the fourth year, extend your harvest to 8 weeks. In early spring, harvest spears every third day or so; as the weather warms, you might have to pick twice a day to keep up with production. Cut asparagus spears with a sharp knife or snap off the spears at, or right below, ground level with your fingers.