Growers assumed for many years that harvesting asparagus the year after planting would severely reduce future yields by reducing the food reserves in the crown.
However, research done by Benson in California, Motes in Oklahoma, and Cantaluppi in Illinois (3,8) found that harvesting one year after planting caused no reduction in subsequent yield, but provided the grower with an income one year earlier than did harvesting two years after planting. The researchers concluded that the plants were not weakened at any of these locations when spears were harvested one year after planting as compared with non-harvested plants the first year after planting. Instead, in the second year after planting, the average spear weight was found to be significantly greater in plants that were harvested the previous year than in plants not harvested the previous year. The increase in spear production may be due to the release of buds from suppression by older shoots.
In contrast to Benson, Motes, and Cantaluppi; Haber in Iowa (16), Lewis in Illinois (25), Shelton and Lacy in Michigan (39), and Lindgren in Nebraska (26) found in their studies a reduced yield from harvesting one year after setting crowns. Except Lewis, their work was done in more northern states with short growing seasons.
Asparagus will respond differently in different regions of the U.S. to first season harvesting pressure, so it might be wise for growers to experiment in regions where there are no recommendations as to how long a grower can harvest the year after planting crowns and not cause a detrimental effect to the plant over the life of the planting.
Benson and Motes (3) state, "The question of how many spears should be harvested the year following planting should be addressed in each asparagus growing region. Asparagus should probably not be harvested as long in shorter, compared to longer, growing season regions, and when asparagus plants are growing under stress from disease, insects, weeds, water, and nutrients. Sufficient growth to build crown reserves is necessary during the first season following planting and the asparagus plant should not be retarded in its growth during the first season. Shelton and Lacy (39) suggest that under Michigan growing conditions, asparagus plants should not be harvested until 2 years after planting. Conversely, our data show that limited harvesting 1 year after planting does not adversely affect asparagus spear production or spear quality in subsequent years. Increased yield early in the production life of an asparagus bed is beneficial to the grower because it represents an early monetary return plus additional returns in subsequent years."
Soil temperature for planting crowns should be at least 50 degrees F so that the crowns can start to grow immediately. There is no advantage to planting crowns in cold soils. In fact, prolonged cool, wet soils might make crowns more susceptible to Fusarium crown rot. Crowns can be planted in mid-April in southern Ohio, and in central and northern Ohio, crowns can be planted in early May if the soil has warmed sufficiently. Growers can have the entire month of May to plant the crowns, if needed. In other states, plant crowns on or after the last mean frost-free date.
Spacing for crowns is the same as spacing for transplants.
Before planting, separate any crowns that are tangled and grown together (Figure 5). It takes about one hour to separate 1,000 crowns. Sort out and discard the extremely small crowns. These will not compete satisfactorily if planted between two larger crowns because the large ones will shade them. Small-sized crowns will produce satisfactorily when planted together in the same row.
A lister plow or middlebuster, which throws soil in opposite directions as it opens a furrow, is ideal for making planting furrows (Figure 6). The planting depth should vary with soil type and probably be no more than 6" deep in a sandy soil and only about 4 to 5" deep on a heavy textured soil (Figure 7).
Work in Illinois and Oklahoma confirmed that shallow planting of crowns promoted production of more spears, but the average spear diameter was smaller compared to deeper planting (8,33). Total yield per acre was reduced when planting depth was increased. The ideal planting depth on a particular soil is that depth where the greatest yield and the highest percentage of the spears produced are of a diameter that can be marketed at the greatest profit. It may take grower experience to determine the optimum planting depth in a specific soil type.
Apply 200 lbs of 0-20-0 or 100 lbs of 0-46-0 fertilizer per acre applied in the bottom of the furrow before planting transplants or crowns. This is in addition to the phosphorus that was incorporated before breaking the furrows. The crowns are then placed into the furrow, right-side up or upside down, on top of the fertilizer. Crown orientation is not important. However, crowns with the buds oriented upward will emerge faster. The fertilizer will not burn the crowns. If phosphorus is not added at this time, it is difficult to get it down to the roots later because it does not move in the soil. Roots literally have to grow through the phosphorus to receive the benefit.
Results of a Michigan State University study (20) indicate that pre-plant applications of phosphorus below the crown are an important factor in long-term asparagus production; probably more important than annual shallow applications. After nine full years of harvests, the in-furrow application of phosphorus still outyields the asparagus given no phosphorus by about 200-500 lbs per acre.
Cover the crowns with a few inches of soil and fill in the furrow gradually, or the furrows can be filled in completely to soil level after planting without damaging the crowns. However, do not drive on or compact the soil over the newly planted furrows or emergence of the spears will be severely delayed or reduced. With good soil moisture, the new spears will break through the soil in 1-2 weeks.
Asparagus is very deep rooted and draws water from a large volume of soil, allowing it to withstand periods of dry weather. Therefore, it may not be necessary to irrigate established plantings in states where the rainfall is 30" or more per year in order to obtain good yields.
However, it is beneficial to avoid drought stress during fern development in the planting year and after harvest during the second year. Dry weather during the harvest season appears to have little effect on yield.
Studies done at Michigan State University (22) showed that after six years of trickle-irrigating asparagus in a sandy loam soil in southwest Michigan, there was no evidence that irrigation benefited asparagus.
The objective during the first two years after planting crowns is to develop maximum fern growth in order to build an extensive storage root system. Any practice that interferes with this objective can have a detrimental effect on yield and may shorten the potential life of the asparagus planting.
After the first planting year, all tillage should stop. Wilcox-Lee (47) found that tillage in asparagus reduces yields, with the yield differences between tilled and no-till plots becoming more significant over time. In addition, asparagus weed seedlings (from female plants) can be controlled more effectively with a no-till system than when soil is tilled. Tilling the soil disperses asparagus seeds and encourages quick germination. Pre- and post-emergence broadleaf and grass herbicides are labeled for weed control in asparagus.
It is interesting to note that Makus (31) observed no increases in spear yield when supplemental nitrogen was applied either before or after the harvest season compared with crowns that received no supplemental nitrogen. Wilcox-Lee (47) also concluded that neither the rate nor timing of nitrogen applications to asparagus had any impact on yields.
This indicates that asparagus is not a heavy feeder of nitrogen and can yield satisfactorily in the absence of additional nitrogen. Nitrogen should be applied according to a soil test recommendation before establishing the planting, but after establishment, it does not seem to influence yield in spite of the lush green color and tremendous vigor of the foliage resulting after application.