Growing Asparagus in Minnesota

Harvesting

Back to Table of Contents

Preparing for Harvest

In earliest spring. mow or chop the old asparagus fern with a brush hog mower or flail chopper. Add phosphorus and potassium fertilizers and give the entire field a shallow disking. Do not delay disking. Doing so can cause considerable damage to the developing but unemerged spears just below the soil surface. Wounds also provide a portal for disease organisms.

Apply a preharvest herbicide at this time. The advantage of an early season herbicide application is that it reduces or even prevents the establishment of winter annuals and other weeds not controlled by cultivation.

Harvest

Spears are hand harvested when they are six to eight inches long. A special pronged knife can be used to cut the spears below the soil surface. or they may be snapped at the soil surface. Cutting must be done carefully to avoid damaging developing spears and the crown below the soil surface. The knife should be placed near the spear, tilted on a 45 degree angle, and directed to cut the spear about two inches below the soil surface. Shoots injured by cutting will not develop properly and should be culled. Spears may be hand snapped just above the soil surface. Snapping severs the spear at the junction between the green tender tissue generally above ground and the white woody tissue below ground. The advantage to cutting spears is that the woody base restricts water loss, which preserves spear quality.

Depending on the planting method, asparagus beds require two to three seasons to become established. Transplants and crowns require two years for establishment before first harvest begins, whereas asparagus started from seed takes three full growing seasons before harvest. During the establishment years, fern growth, plant vigor, and health should be optimized with careful cultural management. For areas with short growing seasons, the USDA recommends a light harvest (two to three weeks) during the first season after plant establishment. A full harvest season of six to eight weeks may begin the following season, although the harvest should be terminated immediately any time spears are reduced to pencil size. Harvesting may have to be performed every two days at the height of the harvest season. Spear emergence greatly increases in response to warm temperatures and slows considerably with cold temperatures.

Overharvesting greatly reduces the vigor of the asparagus plant by seriously draining the sugar reserves in the crown. Remember: next year's yields and profits are determined by how well the asparagus is treated this year.

Field Maintenance After Harvest

Asparagus plants need stored nutrients and time to recover from harvests. They also need weed-free environments, moderate soil fertility, and adequate moisture to build up food reserves in their crowns. Neglecting asparagus fields after harvest is a more significant contributor to poor yields in subsequent years than insect or disease damage.

After harvest, add nitrogen fertilizers according to soil test results. Since the asparagus plants will now be left to fern out, they need nitrogen to encourage maximum fern development, photosynthesis and storage of sugars in the roots for next year's crop. Research has consistently shown that the bushier the asparagus plant the better the yields will be the next season. Nitrogen should be incorporated very shallow. A postharvest herbicide application is necessary to extend weed control full season. A contact herbicide may be necessary to kill perennial weeds prior to fertilizer incorporation. In times of severe drought or if the asparagus is grown on sandy soils, use irrigation to maximize subsequent yields.

Asparagus is a rewarding crop to grow. But it is a perennial plant that will cause perennial problems if its culture and maintenance schedules are ignored.

Produced by Communication and Educational Technology Services, University of Minnesota Extension.

In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request. Please contact your University of Minnesota Extension office or the Extension Store at (800) 876-8636.

University of Minnesota Extension is committed to the policy that all persons shall have equal access to its programs, facilities, and employment without regard to race, color, creed, religion, national origin, sex, age, marital status, disability, public assistance status, veteran status, or sexual orientation.