As one of the few perennial vegetables, asparagus must grow in a permanent location. Weeds may become a problem since the bed isn't tilled yearly. Asparagus also forms roots near the soil surface and doesn't tolerate root damage, which makes cultivating and other weed control practices difficult. Weeding the bed regularly so problems don't get out of control is one of the best defenses in an asparagus bed, though some chemical controls also work well.
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Pull small weeds by hand as soon as they appear during the spring and summer when the asparagus is actively growing. Removing weeds while young prevents them from establishing deep root systems.
Break up the top ½ inch of soil once a week with a handheld cultivator to prevent additional weeds from rooting. Avoid cultivating too deeply, as asparagus roots near the soil surface are easily damaged.
Spread a 2-inch layer of mulch over the bed once the asparagus spears are 5 to 6 inches tall in late spring or early summer. Mulch inhibits weed seed germination.
Harvest the final crop of spears in early to midsummer by breaking them off beneath the soil surface. Apply a preemergent weed herbicide, such as glyphosate, to the bed at the package recommended rate. Allow the spears to regrow and produce foliage, harvesting no more until the following year.
In beds that had a severe weed problem the previous summer, apply glyphosate to the bed in early spring approximately three weeks before the asparagus begins growing.
Asparagus plants readily self seed with the seedlings becoming weedy growth. Plant only male plants to prevent this.