Q: My husband has a very large asparagus patch. The weeds get in there and are difficult to eradicate. Is there a weed killer that would not hurt the asparagus?
A: According to the Ohio Extension Service, harvesting and weed control go hand-in-hand.
SUMMARY: Harvest asparagus by snapping seven to nine inch spears with tight tips. You can do this regularly for two or three weeks. Stop the harvest when the diameter of most of the spears become less than three-eighths inch.
At this point, snap all the spears off at ground level. Apply one-half pound of ammonium nitrate fertilizer per fifty feet of row . Since no asparagus greenery is aboveground, spray the patch with glyphosate (click for sources). This will kill any existing weeds. New spears will emerge, fern out, and provide a large canopy to cover the space between the rows. Once a dense fern canopy is formed, weed growth will be shaded out.
Original text: Harvest asparagus by snapping seven to nine inch spears with tight tips. There is no need to cut asparagus below the soil with a knife. This may injure other buds on the crown that will send up new spears. The small stub that is left in the soil after snapping, dries up and disintegrates. A new spear does not come up at the same spot, but comes up from another bud that enlarges on another part of the crown.
As the tips of the spears start to loosen (known as “ferning out”), fiber begins to develop at the base of the spears, causing them to become tough. The diameter of the spear has no bearing on its toughness. When harvesting, the asparagus patch should be picked clean, never allowing any spears to fern out, as this gives asparagus beetles an excellent site to lay their eggs.
The year after planting, asparagus can be harvested several times throughout a three-week period, depending on air temperatures. Research shows there is no need to wait two years after planting before harvesting. In fact, harvesting the year after planting will stimulate more bud production on the crown and provide greater yields in future years, as compared with waiting two years before harvesting.
Asparagus spears will start to emerge when the soil temperature reaches 50 degrees F. After this, growth of asparagus is dependent on air temperature. Early in the season, 7 to 9 inch spears might be harvested every 2 to 4 days. As air temperatures increase, harvesting frequencies will increase to once or twice per day, harvesting 5 to 7 inch spears before the tips start to fern out and lose quality. The second year after planting, the length of harvest can increase to about 4 to 6 weeks. The third year after planting and thereafter, harvesting can continue for 6 to 8 weeks. Since the length of harvest season will vary from year-to-year depending on air temperature, stop the harvest when the diameter of 3/4 of the spears becomes small (less then 3/8 inch). Experience gained by growing the crop will make it easier for the gardener to know when to discontinue the harvest.
When harvest is finished, snap all the spears off at ground level. Apply 1/2 lb. of ammonium nitrate fertilizer per 50 feet of row . At this time, a home garden formulation of glyphosate (click for sources) can be sprayed on the asparagus patch. This will kill any existing weeds. New spears will then emerge, fern out, and provide a large canopy to cover the space between the rows. Once a dense fern canopy is formed, weed growth will be shaded out.