University of Illinois Extension

Growing Asparagus

“Growing asparagus is best reserved for patient people.
The crop cannot be harvested for three years after planting,” said Jennifer Schultz Nelson, University of Illinois Extension horticulture educator. “This frustrates many home gardeners, and is one factor that makes asparagus more expensive in stores, since commercial growers must spend time and money to weed and maintain plots before they yield any asparagus.”

Asparagus starts as a seed. The first year, the plant primarily develops a crown, or growing point with an extensive root system. The second year, the crown begins to produce a few tiny spears that develop into fern-like portions above ground.

“It isn’t until the third year that the characteristic asparagus spears emerge from the crown in the spring and early summer in numbers high enough for harvest,” she said. “A well-maintained bed will keep producing each year for 20 years or more.”

Spears, she noted, are harvested by hand even in commercial production fields.

Botanically, asparagus is in the lily family, as are onions, leeks and garlic. The plants are also dioecious, meaning there are separate male and female plants. The female plants typically yield less and have thinner spears because they channel energy into producing seed. All male cultivars are available which produce relatively greater numbers of thicker spears.

“When growing asparagus in the home garden, look for all-male hybrids such as Jersey Knight, Jersey King, and Jersey Giant,” said Nelson. “These were developed in New Jersey, the fourth largest producer of fresh asparagus. Not only do these all-male hybrids yield more, they show resistance to rust and fusarium, common fungal diseases in asparagus.”

Asparagus grows best in well-drained, even sandy, soil. Weed control is crucial to developing a good crop. Many myths circulate about applying table salt to asparagus plantings to control weeds.

“Although it is true that asparagus will tolerate higher salt levels in soil than most weeds, this is a poor weed management strategy,” she said. “The excess salts inhibit water penetration into the soil, potentially stressing the asparagus plants. It is also likely that excess salts will leach out of your asparagus bed and affect other plants.”

Asparagus should be planted at the edge of the garden so it is not disturbed when the garden is tilled each spring.

“A western exposure is the best place for asparagus, so that the tall ferns that develop after the spears do not shade the rest of the vegetable plants,” Nelson noted. “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, and can be controlled by handpicking adults and eggs or treating with an insecticide specifically labeled for these beetles per label directions.

“The beetles are only about one-quarter of an inch long, but may cause enough damage to asparagus spears and ferns to affect the next year’s harvest,” she said.

Plants should be fertilized each spring before spears emerge with 20 to 25 pounds per 1,000 square feet of a balanced fertilizer, followed by another dose after the last harvest. Maintain quality in the harvest by never harvesting every spear. Let a portion develop ferns to fuel next year’s harvest.

“Occasionally, you may see a purple or white asparagus for sale and wonder what variety it is,” she said. “Purple asparagus are specific varieties, such as ‘Purple Passion’ that produce a purple pigment.

“But for the white asparagus, the difference is not in variety, but in how it is grown. White asparagus is regular green asparagus that has had soil loosely mounded over the top as spears emerge. The spears remain milky white without exposure to sunlight. Producing white asparagus takes a lot of extra labor, which translates into higher costs for consumers.”