It won’t be long before asparagus season is upon us. It is important not to mow off the dead fern growth from last year until about three to four weeks before spears normally start coming up. Mowing off the dead fern too early will result in soil temperatures warming up too soon, causing early spear emergence. The dead fern cover keeps the soil temperatures about five degrees colder than bare soil. This will hold back spear emergence and prevent them from starting to grow and then getting killed by frost. After a frost event, it usually takes about one week before new spears start to emerge.

Once the dead fern is mowed, a tank mix of Roundup and Lorox should be applied. The Roundup will kill any existing weeds and the Lorox will be a good pre-emergence for other weeds as they germinate. The dead fern should be mowed as close to the ground as possible to minimize the chance of getting skinned knuckles on the sharp fern stubble while picking spears.

If a grower has problems with soil erosion on hilly or sloping ground, rye can be seeded in autumn to keep the soil from eroding, and this can also delay the emergence of spears early in the spring. It can also improve subsequent crop quality, reduce handling and damage and increase overall monetary returns. Rye provides a cover of mulch residue in the early spring and improves the yield and quality of the spears, and allows better accessibility to fields in wet weather. Growers can mow off the dead fern in the spring while also mowing back the rye cover.

The rye residue that remains after the herbicide treatment will be advantageous for the following reasons:

  • Prevents “goose-necking” or curving of spears by wind or wind-blown sand
  • Reduces soil erosion and the splashing of soil onto spears during periods of heavy rainfall
  • Slows “ferning out” or early opening of spears on hot days because the rye cover will keep the soil cooler
  • Lowers soil temperature and tends to delay the emergence of spears and possibly help avoid late spring frosts
  • Rye residue adds organic matter to the soil

Asparagus Harvesting Techniques

Asparagus spears can be cut or snapped to produce spears of marketable length (usually seven to 9 inches). Spears may be cut below the soil surface with a knife or hand-snapped above the soil surface. Cutting asparagus requires more labor, but increases yield 20 – 25% because spears are longer. (Cutting spears below the soil greatly increases the chance of the knife injuring a bud or emerging spear on the same crown.) When hand-snapping, the spear usually breaks above the area containing fiber – so the harvested spear is more tender and all edible. The small stub left in the soil after snapping dries up and disintegrates. A new spear does not come up at that spot, but comes up from another bud that enlarges on another part of the crown. Snapped, all-green asparagus has no trim-off waste and should command a higher price than cut asparagus with white butts.

To maximize quality, harvest in the morning when the spears are cooler and more easily snapped. Always harvest spears when the heads are tight and before the tips start to “fern out.” In the early, cool part of the harvest season (<70º F), the heads will remain tight on nine- to 10-inch spears. Fiber content will be low in the base of the spears. In warmer weather (>70º), spears will fern out at a shorter height. Therefore, it is necessary to harvest shorter spears during warmer weather to obtain good quality.

To maximize yield, it will be necessary to harvest once or twice per day (morning and evening) when the weather is warm. During cool periods, harvest may not be necessary more than two or three times a week. Spear growth in asparagus, once they emerge, is closely related – about 90% – to air temperature. Spears grow faster at higher temperatures, and the taller the spear, the faster it grows.

Growers can use the following harvesting decision examples to help them determine how and when to harvest:

  • Example 1: The picking crew is about to begin harvesting and the next planned harvest is in 24 hours. The weather forecast is for cool and dry conditions. What instructions should be given to the pickers concerning the minimum spear height selected for harvest today? In this situation, only spears longer than seven inches after harvesting should be picked. All shorter spears should be left for harvesting 24 hours later.
  • Example 2: It is Saturday morning and the weather forecast for the weekend is for very warm, humid and cloudy weather with a high probability of rain. No labor is available to harvest on Sunday so the next harvest is nearly 48 hours away. Under these conditions, even spears that are very short (four – five inches) need to be harvested on Saturday. If the shorter spears are not harvested, they will be 12- to 15-inch spears that have ferned out by Monday morning. It would be best to harvest as late as possible on Saturday afternoon or evening and as early as possible on Monday morning to reduce the time to the next harvest and amount of ferned-out cull asparagus. Even though ferned-out spears are not marketable, they must be cut or snapped to maintain production and to deny insects and diseases a site to get started.

The field should be cut or snapped clean with each harvest. Discard any small, spindly spears or fern growth. Ferns that are allowed to grow during harvest can harbor diseases and insects, especially asparagus beetles. This growth will also slow the emergence of new spears.

An average of approximately two hours of labor are needed to hand-pick one acre of asparagus at each harvest over the course of a picking season. Harvest-aids reduce the labor requirement by 15 – 20%, and workers are usually more content to ride a harvest-aid than to walk and stoop to pick. For a copy of “Asparagus Production From A to Z,” email me at