Asparagus picking

David Roseman
November 20, 2007
Last update November 21, 2007
Anna de Mare and Kirsten Kelly produced an excellent documentary about asparagus in Oceana County. Their home page has a link to the film's trailer, which provides a good background. The following are screen shots from that trailer:

Asparagus stalks in the field. Note that they are generally straight, but sometimes curved. They are fairly distinct from the background.


A typical picking machine. It is self-propelled, and steered by the center picker. The pickers' feet are in stirrups that straddle the rows. The stalks are stored in the yellow crates that are behind the pickers.


Carl Fuehring is shown in the film. Here is his photo:


Following are some important facts from John Bakker:

Background:

Asparagus is a perennial crop with a bed life of about 15 years.

Asparagus is planted 8 inches below ground level in rows that are spaced between 48 and 60 inches apart with 54 inches being the most common.

The underground portion of the crop is called the "crown" and is made up of large & long pencil sized storage roots and a mass of buds which produce the spears. As a field ages the center portion of the crown dies and the new buds are produced on the outside portion of the crown. This is important to note because as a field ages the spears emerge further from the center of the row. (for example in a 3 yr old field all the spears will be in a 6-8 inch band whereas a 15 yr old field the spears will emerge in an 18 inch band.

Asparagus spears emerge continually over an 8 week period with the highest number of spears emerging in week 2 or 3.

Spears are pure white, tough and fibrous until they poke above ground level at which time growth speeds up, chlorophyll production turns them green and they become less fibrous. (under optimal growth conditions a spear may go from poking the surface to 10" tall in 24 hours) Profitable asparagus production is possible only if each spear that emerges over the 8 week period is allowed to reach marketable height (specifications following) before being removed.

In Michigan we harvest by hand snapping emerged spears slightly above ground level. Most everywhere else in the world (green) asparagus is harvested by cutting the spear with a knife slightly below ground level. Spears harvested by knife are referred to as having a "white Butt" and this portion of the spear is usually trimmed off in a (fresh) packing shed or processing plant.

Michigan harvests asparagus for three distinctly different markets:
  1. Cut & Tip.(50% of total state production) This asparagus MUST be all green (no white butts), maximum of 8" minimum of 5" and typically is delivered to processors in bulk (500 lb) boxes. This product is dumped into a water bath, conveyed into cutting machines, cut into 1 1/2 inch pieces and either canned or frozen.
  2. Whole Spear. (30% of total state production) This asparagus must have a MINIMUM of 6 1/2 inches all green. Most MI growers snap this product but it could be harvested by cutting. Whole Spear asparagus spears are harvested from 7 - 11 inches tall and delivered to processors in 20 lb containers with all the asparagus pointing the same direction (referred to as "oriented"). This facilitates the placement of the spears on a cutting line. The spears are all trimmed to the appropriate length 5 1/2 to 7 1/2 inches and then either frozen canned or pickled.
  3. Fresh. (20% of total state production) Very similar harvest operation to whole spear but with a slightly longer spear.

Other tidbits;

  1. An acre of asparagus planted on 54 inch centers has approximately 10,000 feet of row.
  2. A prime field can yield a single harvest of 500 lbs/acre.
  3. An average spear weighs 18 grams or roughly 25 spears per lb.
  4. 500 lbs x 25 spears = 12,500 spears per acre.
  5. Assuming approximately 1/2 of the spears would be undersize at any given time a machine would have to "view" 25,000 spears/acre/trip.
  6. A machine traveling at 3 mph (264 ft/min) will have to view 660 spears per minute (2.5 spears/ row ft.) and selectively harvest and place on a conveyor belt 330 of them.
  7. A commercial harvester will need to be able to harvest day and night and in rain and dust.