The most critical time in the life of an asparagus bed is the first two to three growing seasons, especially the period from mid-August until frost. Competition with weeds for light, nutrients, and moisture will greatly reduce vigor the following year. A significant amount of food is stored in the crowns during the latter part of the growing season. Damage or early fern removal before frost during the first year results in visibly reduced fern height and vigor at the beginning of the following growing season. Therefore, it is important to minimize any stress from the plants caused by weeds, insects, or diseases.
In some states, pre-emergence broadleaf and pre- and post-emergence grass herbicides are labeled for asparagus during the planting year. After the first full year of growth, there are more pre- and post-emergence herbicides labeled for asparagus in all states. These pre-emergence herbicides are applied generally about three weeks before new spears emerge, over the shredded old fern growth after it has been mowed in the spring. Currently labeled herbicides are listed in Bulletin 672, Ohio Vegetable Production Guide, available through your local county Extension office. In other states, contact the local county Extension office for vegetable crop herbicide information.
Using salt to control weeds in asparagus is not recommended. Salt will kill weeds and not harm asparagus because of its high salt tolerance. However, salt tends to "seal" the soil surface and inhibits water penetration into the soil. Salt can also leach laterally through the soil and kill or injure other close-planted vegetables that are not as salt tolerant as asparagus.