When growing asparagus in a no-till system, the dead ferns from the previous year's growth can be mowed as close to the ground as possible two to three weeks before spears emerge. In central Ohio, spear emergence should occur from around April 7 to April 15. In other areas, mow the fern about three weeks before the mean spring frost-free date.
Immediately after mowing, apply an approved pre-emergence herbicide over the shredded fern. Some growers rake the shredded fern out of the field before applying herbicides for better herbicide effectiveness. Others let it lie on the soil surface to provide soil organic matter.
Growers who have planted crowns the previous year might want to drag the field to eliminate any uneven terrain due to the newly made furrows. Smooth fields are also easier to harvest. Dragging should be done about two to three weeks before new spears emerge.
Leaving the old fern growth intact until 2 to 3 weeks before new spears start to emerge will keep the soil temperature at crown depth several degrees colder than adjacent bare soil, thus delaying spear emergence. It also holds moisture, snow, and reduces wind erosion. Spears emerge earlier when ferns are mowed too early, and may possibly be damaged by early spring frosts.