Growing asparagus

By Ken Johnson

Asparagus is a relatively easy crop to grow, however, you’ll need to exercise some patience if you want to be successful. According to University of Illinois Extension Educator Jennifer Nelson, if you decide to grow it from seed you can “expect to harvest asparagus 1,095 days (three years) after planting from seed”. Because of this, people tend to plant one or two year old plants, commonly referred to as roots or crowns.

Asparagus should be planted as soon as the ground can be worked in the spring. Plants will have compact buds in the center (crown), with numerous dangling, pencil-sized roots. Asparagus plants are naturally either male or female. The female plants bear seeds, which take considerable energy from the plant and sprout new seedlings, which cause overcrowding in the bed. Male plants produce thicker, larger spears because they put no energy into seeds and have no weedy seedling problem. Because of this, male plants are the preferred choice for home gardens. There are some varieties that are all male such as Jersey Knight, Jersey King, and Jersey Giant. In addition to being male hybrid plants, they show resistance to rust and fusarium, common fungal diseases in asparagus.

Asparagus does best in well-drained soils. Weed control is very important when establishing asparagus as well as to develop a good crop. Many people believe that adding salt to asparagus plantings is a good way to control weeds. While asparagus can tolerate higher salt levels than many plants, it’s not a good idea to add salt to the soil. Excess salt will destroy the soil structure and inhibit water penetration into the soil. The salt can also leach out of the asparagus planting area and affect other nearby plants.

Instead Jennifer Nelson suggests that early in the season before asparagus shoots emerge, cultivate shallowly to eliminate weeds, and then follow up with three to four inches of mulch. Pre-emergent herbicides such as trifluralin (the active ingredient in Preen) or corn gluten meal (an organic alternative) can be applied at this time, as well. It is also possible to apply non-selective herbicides such as glyphosate to an asparagus bed before the shoots emerge, or after the last harvest, as long as all asparagus spears are removed, as glyphosate will potentially kill the asparagus if it makes contact with green portions of the plant. This method is particularly effective when perennial weeds are a problem. As with any type of herbicide use, make sure to read and follow all of the label directions.

During the first three years plants should be fertilized in the spring with a 10-10-10, 12-12-12 or 15-15-15 fertilizer at the rate of 2 pounds per 100 square feet. Starting in the fourth year, apply the same amount of fertilizer but delay application until June or July (immediately after the final harvest).

Even if you plant crowns, harvest should still be delayed a year or two to allow the plant to build up reserves (once plants are three years old). During the first harvest only do so for a month, again allowing the plant to build up its reserves. Once the plant is four years old, and thereafter, spears may be harvested from their first appearance in the spring through May or June (as long as 8 to 10 weeks).

Harvest spears 5 to 8 inches in length by cutting or snapping. Cut shoots will need to be trimmed before cooking to remove the tough fibrous ends. To snap a spear, grasp it near the base and bend it toward the ground. The spear breaks at the lowest point where it is free of fiber.

Leaving some shoots in the ground will maintain quality over time. Nelson recommends that home growers leave a portion to develop ferns, which will fuel the next year’s harvest. A well-maintained bed will keep producing each year for 20 years or more. It is also a good idea to leave the fern-like growth intact until it turns brown in the fall. Like spring bulbs, the foliage of asparagus helps generate energy for the following year.

Asparagus beetles are a common insect pest on the foliage, but they can be controlled per label directions with an insecticide specifically labeled for these beetles.

For more information on growing asparagus at home, visit University of Illinois Extension’s “Watch Your Garden Grow” website at

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