Ask a Master Gardener A Cool Spring Helps Delay Asparagus Planting

Over the past week I have had a few small asparagus harvests. I always look forward to spring asparagus in my garden and a few wild sprouts in the rows of fences. Although it’s a bit late to plant, most of the garden work has been delayed by our cool, wet spring, so I’d say give it a go.

David Trinklein from the University of Missouri Plant Science & Technology had a great article to get you started, here are some highlights:

March to mid-April is the perfect time to establish an asparagus plantation in Missouri which, with proper management, should last 10 to 15 years or more.

Since asparagus is a perennial vegetable, care should be taken in choosing the best planting site. Like most vegetables, asparagus will not tolerate wet, soggy soil. Choose well-drained soil or use raised beds to promote drainage. Since weeds are a major problem, try to choose a site with as few weeds as possible.

A soil sample should be taken in the fall or spring before planting to determine its nutrient status. The optimal pH for asparagus is 6.5-7; it may be necessary to incorporate lime into the soil before planting. Before planting, spread and incorporate approximately 20 pounds of 10-20-10 or similar fertilizer per 1,000 square feet of garden area.

For best results, asparagus should be planted in the spring as soon as the soil in the garden or field can be worked. In mid-Missouri, it’s usually early to mid-April.

Normally, asparagus is started using dormant crowns. When available, male crowns should be used as male plants are up to three times more productive than female plants. Examples of all-male asparagus varieties include Jersey Giant, Jersey Supreme, and Jersey Knight. Select healthy one-year-old crowns from an inspected nursery. Separate crowns by size and plant similar sized crowns together to promote even growth. If the crowns cannot be planted immediately, store them in the refrigerator.

To plant, make a furrow 4 to 6 inches deep. Cover the fertilizer or mulch with an inch of soil and space the crowns 12 to 18 inches in the furrow. If a variety produces large diameter spears, you should reduce the spacing in the row to reduce the spear size. Each row should be no closer than 5 feet apart so the ferns can close the canopy and shade the weeds during the summer. If the rows are too close together, the spear size can be reduced. Cover the crowns with about 2 inches of soil and as the plants emerge and grow, gradually fill in the furrow throughout the summer.

Weed control is the most difficult part of successful asparagus production. Asparagus is a poor competitor to weeds. On small plantings, very light work with a hoe can be used to remove weeds, but avoid using a tiller or any other tillage tool which can damage the crown, reduce yields and promote disease. Organic mulches such as grass clippings, wood chips, straw/hay or compost can be applied 4-6 inches thick for weed control.

Several herbicides are labeled for weed control in asparagus. Glyphosate can be used as a contact spray to control winter annual and biennial weeds in early spring before spear emergence and after final harvest. Cover crops such as rye or wheat can be sown in the spring in the middle of the rows to suppress weeds. Common rock salt was once used to control shallow rooted weeds in asparagus because asparagus has deep roots and can tolerate some salt. This practice is no longer recommended because salt can damage the soil structure by creating a crust that prevents water infiltration.

Asparagus can be harvested for a limited time (two weeks) in the second year after planting the crowns. Over-harvesting one year can weaken plants and reduce yields the next year. Three years after planting the crowns, the asparagus can be harvested for five to eight weeks. Each year, during the first years of production, yields will increase if the plantation is well managed.

Asparagus spears are best harvested by breaking them by hand near ground level. Most gardeners prefer to snap off asparagus spears when they reach 7-9 inches in length in cool weather (less than 70 degrees), or 5-7 inches in hot weather (over 70 degrees), and the tip of the spear is tight. Cutting with a knife is generally not recommended as it can spread disease. Expect to harvest every one to three days as temperatures rise. Harvesting should stop when the majority of spears are pencil diameter (less than 3/8 inch). A longer harvest will weaken the plants and lead to poor production the following spring.

After the harvest season is over, the asparagus planting should be fertilized to stimulate fern growth in the summer and fall. A complete and balanced fertilizer (such as 13-13-13) can be applied at the rate of approximately 1.5 cups per 10 feet of row. Herbicides can be applied after harvest to control weed growth. Frost will dry out the ferns and they can then be cut in late fall or early winter. Do not mow ferns in early fall while they are still green as this will reduce the harvest the following spring.

It may seem like a lot of work, but once you start the asparagus bed, it will bring years of rewards. Happy gardening!

Peter Sutter is a lifelong gardening enthusiast and a participant in MU Extension’s Callaway County Master Gardener program. Gardening questions can be sent to [email protected]