Weeds compete with asparagus for soil nutrients, water, and light, so managing weeds will help support a more bountiful yield of spears. Removing weeds by hand is still one of the most effective methods, especially in smaller asparagus beds. Additional methods include well-timed hoeing, flame-weeding, cover crops, and careful use of select herbicides.
Perennial weeds like Canada thistle and quack grass thrive in asparagus because it is a perennial crop that is rarely cultivated or tilled.
Reading: How do I grow asparagus
In larger asparagus gardens with multiple rows, managing weeds between the rows is relatively easy compared to managing weeds in the asparagus rows themselves.
Non-chemical weed management
Cultivation (hoeing and tilling): Cultivation is an effective weed management tool for vegetable gardens in general, but be cautious when using it in asparagus. Cultivating too deep, or at the wrong time in the season, can damage the crowns and emerging spears.
There are two times when asparagus beds can be cultivated: Before the spears come up in the spring, and after all of the spears are harvested but before ferns come up in late June. At both times, the cultivation must be very shallow, less than 2 inches deep.
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Cultivating in the spring allows for the addition of fertilizer to the soil, but can also stimulate the growth of weed seeds that were previously buried. Therefore, gardeners should only cultivate in the spring if it is truly necessary for removing the weeds in their patch, and if they need to add fertilizer.
Do not cultivate the asparagus rows during the harvest season, when new spears are coming up every day. In larger patches with multiple asparagus rows, cultivation can be used at any time between the rows.
Cultivation is most effective on small, young weed seedlings and is not likely to control perennial weeds or large, established annual weeds.
Cover crops: In larger patches, perennial cover crops (groundcover plants) can be planted between asparagus rows. Healthy, dense cover crops can help outcompete weeds, without disturbing the soil through cultivation. Use a perennial cover crop mix including species like fescues, perennial ryegrass, and clover that are hardy in Minnesota.
Flaming (propane weeding): Flame weeders, also called propane weeders, emit heat and flames from propane-powered torches. Despite the name “flame weeder” this tool is not meant to burn the weeds. Instead, it is meant to kill the weeds by heating them to high temperatures. Small scale flame weeds for home gardens are available.
Hand-removal: In small asparagus patches such as home gardens, hand weeding can actually be one of the most effective and efficient ways to remove weeds. Hand removal is necessary to manage large annual weeds and perennial weeds. Hand removal is also the safest way to keep weeds out of the rows during the harvest season (May-June). Hand-removal can also be used to eliminate any weeds that escape through cover crops and mulches.
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Hand-removal is the most efficient way to eliminate stubborn perennial weeds like Canada thistles and quackgrass in asparagus. Flaming and mowing are not effective tools for managing Canada thistles in asparagus, because the plants will continue to reproduce even if the tops are removed or burned.
Mulching: Straw and leaves can be used for mulch in asparagus beds to help smother weeds. However, these mulches also keep the soil cooler and wetter, potentially delaying or reducing asparagus spear emergence in the spring. Therefore, push the mulch away from the rows in the early spring to allow the soil to warm and encourage spear growth. In larger patches with multiple rows, the aisles between the rows can be mulched using wood chips, straw, or landscape fabric.
New Crown Plantings
Good weed management is critical for establishing high yielding, healthy new asparagus beds. As described previously, most new asparagus patches are established by planting one-year-old crowns into deep furrows. The newly planted crowns have very small root systems, so just a few weeds around each plant can cause the plants to grow slowly and produce fewer spears later on.
Using herbicides in garden-scale asparagus patches
Home gardeners can use glyphosate (i.e. Roundup) in and around asparagus at certain times in the season. They can be used in the early spring before spears have started emerging, or after all spears have been harvested in late June and no ferns are present. Do not use herbicides when spears or ferns are present, as this will damage the plants. Read the label of the herbicide carefully before applying it to ensure that it is permitted for use in asparagus, and follow all label instructions for application.
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