Onion Production Guide (B 1198-2) University of Georgia Extension This publication represents the latest information available on the commercial production of short-day onions in South Georgia. 2017-04-26 16:43:32.793 2008-03-13 10:24:39.0 Onion Production Guide | Publications | UGA Extension Skip to content

Onion Production Guide (B 1198-2)

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photo of onion bulb with stalk

Editors: George E. Boyhan and W. Terry Kelley

Forword

This Extension bulletin is the result of collaborative work across several departments including Horticulture, Plant Pathology, Crop and Soil Science, Entomology, Biological and Agricultural Engineering, Food Science and Technology and Agricultural Economics.

The information in this publication is based on the 2006/2007 growing season, but it can still be applied to the current production of short-day onions in South Georgia. The authors would like to extend their thanks to the many people involved in editing, proofing, and putting this document into its final form.

Introduction

George E. Boyhan – Extension Horticulturist

Onions are one of the oldest vegetables in continuous cultivation dating back to at least 4,000 BC. The ancient Egyptians are known to have cultivated this crop along the Nile River. There are no known wild ancestors but, the center of origin is believed to be Afghanistan and the surrounding region. Onions are among the most widely adapted vegetable crops. They can be grown from the tropics to sub arctic regions. This adaptation is primarily due to differing response to day length. Unlike most other species, day length influences bulbing in onions as opposed to flowering. Onion bulbs are placed into three groups based on their response to hours of day length. The short-day bulb varieties with day lengths of 11-12 hours while intermediate bulb varieties with day lengths of 13-14 hours and are found in the mid-temperate regions of this country; finally, the long-day varieties are adapted to the most northern climes of the United States as well as Canada and bulb with day lengths of 16 hours or greater.

Onions were first brought to this country by early European settlers. These onions were adapted to the temperate climate found throughout the northeast where the first European settlements occurred. Varieties from warmer regions of the Mediterranean eventually made their way to the southeast United States. In particular, varieties from Spain and Italy would become important to the Vidalia onion industry. The first of these varieties came through Bermuda and were thus referred to as “Bermuda onions.”

Yellow Granex, the standard for Vidalia onions, has its origin from Early Grano. The variety Early Grano 502 resulted in the Texas Early Grano 951C, which became one of the parents for Yellow Granex hybrid. The other parent, YB986, was selected from Excel, which in turn was derived from White Bermuda.

The Vidalia onion industry began in 1931 when a grower by the name of Mose Coleman grew the first short-day onions in Toombs County, Georgia. These mild onions were immediately popular with customers. At the beginning of the depression, these onions sold for $3.50 a 50-pound bag, a consider-able amount of money at the time. Soon other growers became interested in these mild onions. The industry grew slowly and steadily for several decades. Its growth was fueled by the fact that the city of Vidalia sat at the intersection of important roads prior to construction of the interstate highway system. In addition, the supermarket chain Piggly Wiggly maintained a distribution center in Vidalia, Georgia. They would buy the onions and distribute them through their stores. Slowly the industry began to gain a national reputation.

In order to help promote the onions further, onion festivals were started in both Vidalia and Glennville in the mid 1970s. Approximately 600 acres of onions were produced at the time. Growth continued during the next decade. In 1986, Georgia gave Vidalia onions official recognition and defined the geographic area where these onions could be grown. There had been some problems with onions being brought in from other areas and bagged as Vidalia onions. State recognition, however, did not give the industry the national protection it needed. The industry obtained Federal Market Order 955 giving the industry national protection in 1989. The Vidalia Onion Committee was formed to oversee the federal market order. Growers are required to register and pay funds based on their production to support the industry. The collected money is used for national and international promotional campaigns and for onion research.

In 1989, the industry began to adopt controlled atmosphere (CA) storage. CA uses a low-oxygen, high carbon dioxide refrigerated environment to store onions. This allows the industry to expand their marketing opportunities well into the fall and winter months. The adoption of the federal market order and CA storage has allowed this industry to grow to its current level of approximately 14,000 acres.

Transplant Production

George E. Boyhan and W. Terry Kelley – Extension Horticulturists

Short-day onions can be grown from both seed and transplants, but the majority are grown from transplants.

Transplant production begins in late summer with land preparation followed by seed sowing in September. Land for transplant production should not have been in onions or related Alliums for at least 3 years. This is not always possible with fixed center-pivot systems. Avoid sites with a history of onion diseases and severe weed problems.

Once a site is selected, take a soil test to determine the optimum level of fertility and soil pH. Recent additions to the soil test recommendations give specific recommendations for plantbed onions. When submitting a soil sample to the University of Georgia’s Soil, Plant & Water Analysis Lab, indicate that they are for transplants or plantbed onion production. The site should be deep turned to bury any residue from the previous crop. Several different seeders are available for transplanting. Set these to sow 60-70 seed per linear foot. Using a Plant-It Jr. four-hopper transplanter, set the plates to No. 24. This should give the needed seeding rate for plantbeds. Vacuum seeders are also a good choice and can accurately deliver seed in the amounts and to the depth required. Other seeders can be used as long as they are capable of sowing 60-70 seed per linear foot and can consistently plant the seed at the proper depth (1/4-1/2 inch).

The plantbed soil should have a pH range of 6.0-6.5 for optimum growth. Soils in Georgia are generally acidic; if your soil pH is low, applications of lime are recommended. Dolomitic lime is preferred over calcitic lime because it supplies calcium and magnesium while adjusting the pH. Changing soil pH is a relatively slow process, so if low pH is suspected early, soil testing and lime application is advantageous to ensure the soil pH is corrected in sufficient time for planting. Soil pH can take several months to change with lime applications.

Nitrogen recommendations on Coastal Plain soils range from 100-130 pounds of nitrogen per acre. On Piedmont, Mountain and Limestone Valley soils, apply 90-120 pounds per acre. Table 1 indicates the phosphorus and potassium recommendations based on soil residual phosphorus and potassium levels.

In addition, apply boron at 1 pound per acre. If zinc results are low, apply 5 pounds of zinc per acre. Sulfur is critical for proper onion production. This is particularly true on the Coastal Plain soils of south Georgia that are very low in sulfur. Sulfur, at a rate of 20-40 pounds per acre, will be required to produce quality onion transplants on these sandy loam soils.

A typical fertility program consists of 300-400 pounds per acre of 10-10-10 with 12 percent sulfur applied preplant. This supplies 30-40 pounds of N-P-K along with 36-48 pounds of S. Follow this with additional applications of P and K according to soil test recommendations. Generally, additional P is not needed, while additional K can be supplied as potassium nitrate (13-0-44). Supply additional N in one to two applications of calcium nitrate (15.5-0-0) applied at 4 and 6 weeks post seeding. Note that any fertilizer that supplies the required nutrients as required by the soil test can be used to produce plantbed onions. More recent work indicates that high P applications at plantbed seeding have no effect. Phosphorus can have limited availability during periods of cool soil temperature. Seeding plantbeds in September, soil temperatures are sufficiently high to avoid P deficiency. However, plantbeds that have not been fertilized properly at seeding may require “pop-up” (high P) fertilizer to over-come deficiencies during the cooler months of November and December.

It is critically important that seedbeds be irrigated regularly to develop a good plant stand. Applying 1/10 inch of water several times a day may ensure consistent soil moisture. See section on irrigation.

Plants are ready for harvest in about 8-10 weeks. Good quality transplants will be about the diameter of a pencil when ready. Transplants are pulled and bundled in groups of 50-80 plants and tied with a rubber band. Approximately half of the tops are cut from the transplants, usually with a machete. Harvested transplants are transported to the field in polyethylene net or burlap bags. Onion transplants can experience a “heat” in these bags, which greatly reduces transplant survival. Take care with transplants so they are not stored for excessively long periods of time in these bags, nor should they be left in the sun for too long. Planning is critical; harvest only enough plants that can be reasonably transplanted that day. Avoid overnight storage in these bags whenever possible but, if necessary, remove them from the field to a cool dry location.

Table 1. Recommendations for phosphorus and potassium based on soil test analysis for plant bed onion production.

N (lb/acre)

Soil Test P & K

P (lb/acre)

K (lb/acre)

pH

Coastal Plain

Piedmont

6.0-6.5

100-130

90-120

Low

120

120

Medium

90

90

High

60

60

Very High

30

30

Overload

0

0

Variety Selection and Characteristics

George Boyhan and W. Terry Kelley – Extension Horticulturists

As mentioned earlier, the type of onion grown in south Georgia is a short-day onion that bulbs during the short days of winter (11-12 hours day length). Although no research has been done in this area, it may be possible to grow intermediate day onions in north Georgia. They would not, however, be as mild as the south Georgia Vidalia onions.

Illustration showing different bulb shapes Figure 1. Bulb Shapes: 1) flattened globe; 2) globe; 3) high globe; 4) spindle; 5) Spanish; 6) flat; 7) thick flat; 8) Granex; 9) top
(Courtesy of Texas A&M University)

The Vidalia onion industry is controlled by a federal marketing order that is administered by the Vidalia Onion Committee and the Georgia Department of Agriculture. This market order defines what type of onions can be grown and marketed as a Vidalia onion. A Vidalia onion must be a yellow Granex type. These onions should be slightly flattened, broader at the distal end (top) and tapering to the proximal end (bottom) (Figure 1).

Recently, additional rules have given the Georgia Department of Agriculture the authority to deter-mine acceptable varieties for the Vidalia industry. Under these rules, the University of Georgia has been mandated to test all onion varieties for 3 years before making recommendations to the Georgia Commissioner of Agriculture. The Georgia Department of Agriculture has already excluded five varieties, ‘Sugar Queen,’ ‘Spring Express,’ ‘Sweet Dixie,’ WI-3115, and WI-609. Varieties the Georgia Department of Agriculture recommends growing as Vidalia onions are listed in Table 2.

Table 2. List of current legal Vidalia onion varieties.

Variety

Source

Season

Georgia Boy

D. Palmer Seed

Mid-

Mr. Buck

D. Palmer Seed

Mid-

Ohoopee Sweet

D. Palmer Seed

Mid-

Sapelo Sweet

D. Palmer Seed

Mid-

Miss Megan

D. Palmer Seed

Mid-

YG 15082

Dessert Seed

Mid-

HSX-61304

 Hortag Seed

Late

Caramelo

Nunhems USA Inc.

Mid-

Nirvana

Nunhems USA Inc.

Mid-

Sweet Caroline

Nunhems USA Inc.

Mid-

Sweet Melody

Nunhems USA Inc.

Mid-

Sweet Vidalia

Nunhems USA Inc.

Mid-

Sweet Jasper

Sakata Seed

Mid-

Sweet Harvest

Sakata Seed

Mid-

XON-403Y

Sakata Seed

Mid-

Century

Seminis Seed

Mid-

EX 19013

Seminis Seed

Mid-

Granex 33

Seminis Seed

Mid-

Granex Yellow, PRR

Seminis Seed

Mid-

Savannah Sweet

Seminis Seed

Mid-

Golden Eye

Seminis Seed

Mid-

Honeycomb

Shamrock Seed

Early

Sugar Belle F1

Shamrock Seed

Early

Honeybee

Shamrock Seed

Early

Candy Ann (SS 2005)

Solar Seed

Early

WI-129

Wannamaker Seed

Early

Onion varieties grown in southeast Georgia fall into three broad maturity classes: early, mid-season, or late. There can be considerable overlap in these categories and not all varieties will perform the same as to their maturity from one year to the next.

Along with maturity, varieties perform differently on a wide range of quality attributes as well as yield. Varieties can differ for pungency, sugar content, disease resistance, seed stem formation, double centers, bulb shape, and bulb size. Consider all of these characteristics when making decisions on variety selection. Growers wishing to try new varieties should consult University of Georgia variety trial results. Trial results should be examined over several years to get a true picture of a variety’s potential. Even after evaluating trial data, growers planting new varieties should grow them on limited acreage. The grower can get a feel for their new varieties’ performance potential under their growing conditions. In addition, growers wishing to grow Vidalia onions should check with the Georgia Department of Agriculture for the current allowed varieties.

Soils and Fertilizer Management

W. Terry Kelley and George Boyhan – Extension Horticulturists

Onions grow best on fertile, well-drained soils. Tifton series 1 and 2 soils are found in the Vidalia onion area and are well suited for onion production. Most sandy loam, loamy sand or sandy soils are also advantageous to sweet onion production. These soils are inherently low in sulfur, which allows greater flexibility in sulfur management to produce sweet onions. Avoid soils with heavy clay content and coarse sandy soils. Clay soils tend to have a higher sulfur content that can lead to pungent onions. Sandy soils are difficult to manage because they require more fertilizer and water.

Always base fertilizer and lime requirements on a recent, properly obtained soil sample. Check with your local county Extension office or crop consultant regarding proper procedures for soil sampling and interpretation of results. Take the soil test a few months prior to crop establishment in order to determine lime requirements and make necessary lime applications in a timely manner. If soil test results show a pH below 6.0, apply and disk in dolomitic lime 2-3 months before land preparation to bring the pH to the optimum range of 6.2-6.5. It is essential to apply sufficient lime to keep the soil pH above 6.0. Low pH can cause nutrient deficiencies during the growing season. Also, high rates of fertilizer used in producing onions cause the pH to drop during the growing season. If the pH is not corrected at the beginning of the onion season, nutrient deficiencies could occur during the year and reduce yields. Calcium and phosphorous deficiencies can often be linked to low pH, even though soil tests indicate adequate levels. Foliar applications of calcium may help overcome calcium deficiencies. But phosphorus deficiencies due to low pH can be difficult to correct during the growing season.

Onions require more fertilizer than most vegetable crops because fertilization of both plant beds and dry bulb onions must be considered. They respond well to additional fertilizer applied 40-60 days after seeding or transplanting. The method of fertilizer application is very important in obtaining maximum yield, with multiple applications ensuring good yields. This increases the amount of fertilizer used by the plant and lessens the amount lost from leaching. More recent research indicates that good results can be obtained with as few as three fertilizer applications. Preplant fertilizer will vary with the natural fertility and cropping history. Proper application methods and function of various nutrients are outlined below. Table 3 shows a suggested fertilizer program for a soil testing medium in P and K.

Table 3. Sample fertilizer recommendations for transplanted onions with a plant population of 60,000 to 80,000 plants per acre. Make adjustments for soil test levels other than medium P and medium K.

Timing

Amount (lb/acre)

Type

Method

N

P2O5

K2O

S

Pre-plant

400

10-10-10 with 12% S

Broadcast & incorporate

40

40

40

48

January

85

0-0-60

Broadcast

0

0

50

 

250

0-20-0

0

50

0

 

200

15.5-0-0

31

0

0

February

520

15.5-0-0

Broadcast

81

0

0

Total

152

90

90

48

With heavy rains, additional nitrogen and sulfur may be warranted. Other fertilizer formulations and application methods may be used as long as the soil test recommendations are met.

Nitrogen (N) especially in nitrate (NO3) form, is extremely leachable. If too little nitrogen is available, onions can be severely stunted. High nitrogen rates are believed to produce succulent plants that are more susceptible to chilling or freezing injury and disease, and to production of flower stalks. Onions, heavily fertilized with nitrogen, are believed to not store well. Finally, excess nitrogen late in the growing season is believed to delay maturity and causes double centers. Make the final nitrogen application at least 4 weeks prior to harvest. Rates of nitrogen vary depending on soil type, rainfall, irrigation, plant populations, and method and timing of applications. Dry bulb production, from transplanting, requires between 125-150 pounds per acre nitrogen. It is usually best to incorporate 25-30 percent of the recommended nitrogen prior to planting; apply the remainder in two to three split applications.

Phosphorus (P) is essential for rapid root development. It is found in adequate levels in most soils but is not readily available at low soil temperatures. Because of these factors, under most conditions, apply all of the P preplant and incorporated before transplanting. Count this amount as part of the total seasonal fertilizer application. Table 4 shows the recommended phosphorous to be applied based on various soil test levels.

Table 4. Recommended potassium and phosphorous applications based on soil test ratings of each nutrient.*

Phosphorous Rating

Potassium

Low

Medium

High

Very High

Overload

(Pounds N-P2O5-K2O per acre)

Low

-120-120

-120-90

-120-60

-120-30

-120-0

Medium

-90-120

-90-90

-90-60

-90-30

-90-0

High

-60-120

-60-90

-60-60

-60-30

-60-0

Very High

-30-120

-30-90

-30-60

-30-30

-30-0

Overload

-0-120

-0-90

-0-60

-0-30

-0-0

*Nitrogen recommendations: Coastal Plain Soils=130-150 lb/acre N. Piedmont, Mountain and Limestone Valley Soils=110-130 lb/acre N.

Potassium (K) is an important factor in plant water relations, cell-wall formation, and energy reactions in the plant. Potassium is subject to leaching from heavy rainfall or irrigation. Therefore, it is best to split K applications by incorporating 30-50 percent of the recommended K before planting and splitting the remainder in 1-2 side dress applications. A low K level makes plants more susceptible to cold injury. Table 4 lists recommended K applications based on soil test results.

Sulfur (S) is an essential element for plant growth. Early applications of sulfur are advisable in direct-seeded and transplanted onions. To minimize pungency, apply fertilizers containing S before the end of January. Research conducted in Georgia on S and onion pungency shows that pungency (pyruvate analysis) of mature onions increases with high rates of S or whenever S applications are made after late January. Therefore, do not apply S to onions after late January unless the onions exhibit S deficiency. Do not completely eliminate S from the fertility program. Apply 40-60 pounds of elemental S with half incorporated at transplanting or seeding and half applied at the first side dress application. Do not apply S in rates higher than 40-60 pounds per acre.

Boron (B) is required by direct-seeded or transplanted onions in the field. If the soil test shows B levels are low, apply 1 pound of B per acre and incorporate prior to transplanting or seeding. Do not exceed the recommended amount since boron can be toxic to onions.

Zinc (Zn) levels determined to be low by soil testing can be corrected by applying 5 pounds of Zn per acre. Excessive amounts of Zn can be toxic, so apply only if needed. Zinc is usually added in the preplant fertilizer.

Magnesium (Mg) levels in the soil must be adequate for good onion growth. If dolomitic limestone is used in the liming program, it will usually supply some of the required Mg. However, if soil pH is adequate and the soil-test Mg level is low, apply 25 pounds of Mg per acre in the preplant fertilizer.

Recently several slow release fertilizers have been introduced to the Vidalia growing region. These fertilizers have performed well and can be considered in a fertility program. These fertilizers, however, have not proven satisfactory for single fertilizer application.

A complete fertilizer with minor elements will provide most of the other required nutrients. Micronutrients can become toxic if excessively applied. Apply them only when needed and in precise amounts. Routine visual inspection of onion fields to watch for nutrient deficiencies is always important. However, during periods of high rainfall or frequent irrigation, be particularly aware of the potential for nutrient deficiencies to occur.

Deficiencies of major nutrients cannot be feasibly corrected through foliar nutrient applications. It is important to properly manage soil fertility to maintain optimum growth and development. Some deficiencies of minor elements can be remedially corrected through foliar applications. Thus, it is always best to supply adequate amounts of these nutrients through your basic soil fertility program. Plants use nutrients more efficiently when the nutrients are taken up from the soil. By the time you visually see deficiency symptoms, you have probably already lost some potential yield.

Plant Tissue Analysis

Plant tissue analysis is an excellent tool to evaluate crop nutrient status. Use periodic tissue analysis to determine if fertility levels are adequate or if supplemental fertilizer applications are required. Tissue analysis can often be used to detect nutrient deficiencies before they are visible.

Plant tissue analysis is accomplished by sampling the most recently mature leaves of the plant. Take a sample of 20-30 leaves fr

Status and Revision History
Published on Mar 13, 2008
Re-published on Jan 24, 2011
Reviewed on Jan 4, 2014