Oh, those delicious spears are one of the great harbingers of Spring in Wisconsin, and it’s a bit heartbreaking when it’s time to draw the harvest to a close! From Diana Alfuth, horticulture educator for Pierce & St. Croix County UW-Extension in Wisconsin, comes the following advice for caring for your asparagus patch.
“You should stop harvesting when the emerging spears are about the diameter of a pencil; this will give the crowns time to rejuvenate for next year’s harvest.
When harvesting is over, fertilize according to soil test results, or with a complete fertilizer such as a 10-10-10, to replenish nutrients used during the harvest season. Let the ferns grow to collect sunlight and restore the root system. In fall, once the ferns have yellowed, cut them back and dispose of them to prevent overwintering of asparagus beetles and rust, two of our most common asparagus pests.
Top-dress your patch with compost or another mulch to reduce weeds. You can eliminate perennial weeds such as quackgrass, with glyphosate (Roundup). For a small patch, put on a rubber glove, then a cloth glove over that. Wet the fingers of the cloth glove with glyphosate and wipe it on the grass blades, avoiding contact with the asparagus. The herbicide will go into the blade and down to the roots, killing the weed, but not harming the asparagus. Tedious, but very effective. If you have a large patch you can try spraying glyphosate in late fall after you’ve cut back the ferns, or in early spring before spears have emerged.”
Diana Alfuth, horticulture educator for Pierce & St. Croix County UW-Extension, teaches the master gardener program and is a frequent speaker throughout the region about gardening and sustainable landscaping. She is a regular guest on WEAU-TV and teaches landscape design at UW-River Falls.