When asparagus spears start poking their heads out of the ground, it is an exciting time of the year. It’s also when you need to start careful monitoring so you can efficiently manage asparagus harvests.
Usually asparagus harvests start in the third year after planting, although there are studies that suggest harvests could begin the first year after planting. This could stimulate more bud production on the crown and provide greater yields in future years, as compared with waiting two years before harvesting. If growers chose to harvest the year after planting, it should be done sparingly to allow more spears to fern out and provide photosynthates to the crown below.
Asparagus harvest starts at the end of April and usually lasts for three to four weeks depending on air temperatures. In some years, I’ve seen the cool Iowa spring weather delay harvests by one to two weeks.
Spears start to emerge when the soil temperature reaches 50°F. After this, asparagus growth depends on air temperature. Early in the season, you might harvest 7- to 9-inch spears every two to four days. As air temperatures increase, harvesting frequencies will increase to once or twice per day. You can have up to 24 harvests per season, after which you can allow crowns to fern and grow out.
There is always a debate on how to harvest asparagus: snap vs. cut. It’s important to note there are no benefits or advantages of cutting asparagus below the soil with a knife. On the contrary, this may pose risk of injury to buds on the crown that will send up new spears. Snapping a 7 to 9 inch spear slightly above the ground level is the ideal harvesting procedure. The small stub of asparagus that is left in the soil after snapping eventually dries up and disintegrates.
Timing Is Everything
It is critical to harvest asparagus at the right stage. Prolonged harvesting intervals lead to reduced spear quality. Tips of the spears start to loosen, also known as “ferning out,” and fiber begins to develop at the base of the spears, causing them to become tough.
Asparagus heads ferning out. Photo credit: Ajay Nair
You should harvest all of the spears that come up until the end of the harvest period, even the small diameter ones. If you don’t, asparagus beetles will lay their eggs in those ferns. Since the length of the harvest season will vary from year-to-year, depending on air temperature, you should stop harvesting when the diameter of 75% of the spears becomes small (less than 3/8 inches).
Another indicator is the number of spears harvested. If the number of spears in a harvest drops off significantly beyond 15 to 16 pickings or so, you may want to consider ending harvest early. After the end of the harvest season, allow the spears to grow. A spear is really just a plant shoot. And the shoots will grow into the mature fern that recharges the crown for the next harvest season.
When harvest finishes, snap all the spears off at ground level and apply fertilizers (organic or synthetic). Also start actively managing weeds until the new spears emerge, fern out, and provide a large canopy to cover the space between the rows. Once a dense fern canopy is formed, weeds are shaded out.