Longevity is a hallmark with an asparagus crop, and once the plants are in the soil they can keep producing for 20 years or more.
Preparing for the perennial crop to remain productive for such a long stretch is imperative, and it all begins with increasing the organic matter in soil before the asparagus roots take hold.
During a March 17 webinar on asparagus production hosted by Penn State Extension, Carl Cantaluppi, a commercial asparagus expert and retired North Carolina State Extension agent, said good organic matter allows roots to grow deep and water to percolate through the soil structure for the long term.
Planting cover crops prior to the asparagus crop is the most effective way to promote long-term organic matter, he said, and it’s important to choose wisely.
Cantaluppi outlined several cover crop options, beginning with a planting of sorghum-sudangrass that is mowed several times before being plowed under.
“It will winter kill very easily, so you can have it there and till it under the following spring,” he said.
Another cover crop option is an early-maturing soybean variety that is plowed under to add nitrogen to the soil. The soybean planting should be followed with a seeding of wheat or rye in the fall, or Austrian winter pea to further augment nitrogen levels in the soil.
While cover crops build organic matter, Cantaluppi said they are not the only step to prepare the soil for asparagus.
Proper soil fertility and pH are crucial, and he recommended applying 250 pounds of phosphorus per acre, 300 pounds of potassium and 50 pounds of nitrogen. Lime should be added to achieve a pH between 7 and 7.5.
“Asparagus does not do well in acidic soils. It definitely will not do well at a pH of 6 or below,” he said, adding a high soil pH lessens the risk of the fusarium fungus. “So get that pH up a year in advance.”
It’s also important to properly store asparagus crowns before planting, Cantaluppi said. To avoid having shoots emerge prior to planting, he recommends refrigerating the crowns at 35 to 38 degrees. He also suggested separating the crowns by size, and planting them together based on those groupings.
“You don’t want to plant a large crown next to a small one because the large one will overshade the small one, and the small one will never gain a foothold. But if you plant all like sizes, you won’t have a problem,” Cantaluppi said.
The soil should be ready for planting when the crowns come.
“If the soil is not ready,” Cantaluppi said, “you don’t want to leave (the crowns) laying in a pile because they will generate their own heat in the pile. They’ll start to grow.”