May 13, 2021

How to grow asparagus

By Ken Johnson

Asparagus is one of the few perennial vegetables that is commonly grown in gardens. Like many vegetables, asparagus can be somewhat polarizing; either you love it or hate it. If you’re in the love category, it is a relatively easy crop to grow. However, you’ll need to exercise some patience when growing asparagus.

When growing asparagus, you’ll have a choice between planting seeds and crowns. Most people tend to plant one-year-old plants, which are referred to as roots or crowns, and for a good reason. While asparagus seeds will be much less expensive than crowns, it will take much longer to get your plants established.

Asparagus plants are dioicous, meaning they are either male or female. While female plants tend to produce larger spears, they produce fewer of them. Additionally, female plants will produce fruit and seeds, which take considerable energy from the plant and sprout new seedlings, which may cause overcrowding.

While male plants tend to produce smaller spears, they will also produce more of them. Since they aren’t producing seeds, you won’t have to contend with seedlings becoming weedy. Because of this, male plants are the preferred choice for home gardens.

Asparagus does best in well-drained soils that are in full sun. It can be planted as soon as the ground can be worked in the spring (typically March 15-April 15). When planting, dig a trench that is 12-18 inches wide and 6 inches deep. Place the crowns 9 to 12 inches apart in the trench, making sure the bud side is up. Once the crowns are in the trench, you don’t want to completely fill the trench with soil. Instead, cover them with 2 inches of soil and continue to fill the trench as the plants grow taller during the growing season.

Weed control is very important when establishing asparagus as well as to develop a good crop. Early in the season, before asparagus shoots emerge, shallowly cultivate your soil to eliminate weeds. Then add a layer of mulch to help suppress weeds.

During the first three years, plants should be fertilized in the spring with a balanced fertilizer at a rate of 2 pounds per 100 square feet. Starting in the fourth year, apply the same amount of fertilizer, but wait to apply it until you are done harvesting (June or July).

Now that you’ve gotten your asparagus planted and cared for, when can you begin harvesting? The year you plant, you should not harvest any asparagus. Let the spears grow and develop “ferns” (leaves). The year after planting (second year), you can begin harvesting when the spears reach 5 to 8 inches long for two weeks, although many people opt to skip harvesting the second year to allow their plants to build up reserves. In the third year you can harvest for up to four weeks. Finally, in year four and onwards, you can harvest through May or June (up to eight to 10 weeks).

Even though it can be a bit unsightly, it’s best to leave the fern-like growth until it begins to die back in the fall. Like spring bulbs, the foliage of asparagus helps generate energy for the following year.

Good-Growing Tip: White asparagus isn’t a special variety of asparagus – it’s asparagus that has been blanched (grown in the dark). This is done by burying the crowns in more soil, straw, or covering rows with row covers that don’t allow light in.

Ken Johnson is a University of Illinois Extension educator.