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Commercial Production of Bulb Onions in Mississippi
printable version (2 pages)Onion is a cool-season crop that will withstand moderate freezes. It may be grown by seeding directly in the field or by setting transplants. Onions grown from sets do not make the best bulbs, are rather costly, and are not recommended for commercial plantings.
Soils
Any fertile, well-drained, loamy soil, fairly high in organic
matter with a pH of 6.0 to 6.5 is suitable for onion production.
Varieties
Varieties are classified into groups according to when they
will bulb. Regardless of when they are planted, varieties won't
bulb until the days are long enough for them to do so. Shortday
varieties that may be harvested in May or June include
Granex-33, 1015Y, and any variety on the approved Vidalia
variety list.
How To Plant
Method 1. Sow seed in early October about 1/2 to 3/4 inch
deep, with about 15 to 25 seeds per foot of row (thinning necessary).
This will require 3 to 4 pounds of seed per acre. Plant
two rows spaced 12-14 inches apart on 38-inch beds (depending
on equipment).
Method 2. Set transplants in December. Plants should be about 6 inches high and about the thickness of a lead pencil at time of transplanting. Set plants at a uniform depth, with the bottom of the plant about 1½ inches below the soil surface. Set three plants per foot of row. Plant two rows 12 to 13 inches apart on a 38-inch bed (depending on equipment).
Bolting
Bolting, or seed stalk formation, occurs only from fall-planted
onions grown through the winter for spring harvest. The size
of the overwintering plant and the exposure to cold temperatures
are the most critical factors in determining whether the
plant will bolt. Early plantings in late August and September
are more likely to bolt than are the later plantings in October
and November. An extended warm period following planting
produces a larger overwintering plant (more than ¼-inchshank
diameter), which results in a high percentage of bolting
when exposed to extended temperatures below 50 °F.
Fertilizer
Apply 200 pounds of 0-46-0 fertilizer per acre to fall-seeded
onions. Apply as a band 2 to 4 inches directly below the seed
or transplant. When active growth begins in the spring, sidedress
with 30 to 40 pounds of nitrogen and 75 pounds of
potassium. Make two additional nitrogen sidedressings at the
same rate at about 3-week intervals, or apply all P and K
from soil test recommendation preplant. Sidedress with N
when actively growing in the spring. Avoid N application
within 3 weeks of harvest.
Irrigation
The seedbed is usually irrigated immediately after planting,
and then as necessary to maintain a moist condition until
emergence. Irrigate seedlings as soon as possible after transplanting.
Irrigate 1 inch every week during bulbing if necessary,
but do not irrigate when plants start to mature.
Weed Control
Weeds can seriously reduce yield. For preemergence weed
control in onions, use 5 to 6 pounds of Prefar or 11 to 12 pints
of oxyfluorofen (Goal) on broadcast basis. Prefar performs
best when incorporated 2 to 3 inches deep with the soil before
planting. Do not incorporate Goal. Apply it to the soil surface
after planting and just before planting transplants. You can
also apply Goal postemergent to onions during the growing
season to extend preemergent weed control to harvest. Follow
labels carefully when using
any herbicide.
Disease Control
Diseases of onions include pink root, botrytis blast, downy
mildew, purple blotch, white rot, and neck rot. Pink root is
caused by a soil-borne fungus. Prevent problems by buying
disease-free seed or transplants, growing in disease-free fields,
and when possible, planting resistant varieties.
Leaf diseases include botrytis blast (numerous white specks), downy mildew (pale green, oval sunken spots), and purple blotch (purplish lesions with yellow margins).
White rot can be identified as a white fungal growth on the base of the onion. Apply control before seeding.
Neck rot occurs during or following harvest. The disease can be recognized by the grayish mold on the surface of the infected area. Bulbs that are well dried are less likely to succumb to the disease. They should be dried at 90 to 120 degrees Fahrenheit for 2 to 3 days and then stored at 32 °F. There should be adequate ventilation to maintain a dry atmosphere during storage.
Consult “Southeast U.S. 2010 Vegetable Crop Handbook” for more detailed information on pest control.
Insect Control
Onion thrips and onion maggots are important, widespread
pests. Onion thrips are similar to other thrips. Onion maggots
are larvae of a small fly that lays its eggs near the base of the
plant. The small maggots burrow into the stem and bulb and
kill the plants. Control both with pyrethroid sprays according
to manufacturer's instructions.
Harvesting
Harvest when 75 percent or more of the tops fall over. To hasten
drying, some growers use a subsurface knife to cut the
roots a few inches below the bulb. The bulbs are then allowed
to dry for a few days.
After this preliminary curing, the tops are cut 1 to 1½ inches from the bulb. This may be done by hand with shears or by a topping machine. Roots are trimmed off and the bulb placed in field sacks.
During extremely hot weather, it is desirable to place the onions into sacks almost immediately after pulling. These are then stacked in the field for curing. Such a practice avoids sunburn. The curing process is usually completed by keeping the bulbs for several weeks in slatted crates or trays. These are stacked in open sheds or in any place where there is free circulation of air.
Do not store onions permanently until thoroughly cured. Remove loose material such as dirt. Sort out all soft and immature specimens and bulbs with thick necks. These will not keep in storage.
Grading
Onions are graded according to size and quality. A high-quality
pack is obtained by eliminating immature, decayed, sunburned,
and mechanically injured bulbs, double bulbs, and
bulbs that have started a second growth.
Marketing
Buyers usually specify minimum sizes of the onions they will
buy. This minimum is usually 2 inches in diameter, with bulbs
greater than 3 inches bringing a much better price. The famed
"Vidalia" onion is a Granex grown in low-sulfur soils near
Vidalia, Georgia. The combination of low sulfur and favorable
climate is responsible for the sweet taste. Mississippi onions
can be of the same sweetness if the right variety is grown with
no sulfur and no stress.
Yield
A 2007 trial of yellow Granex onion at Delta Branch
Experiment Station yielded 20,000 pounds per acre of onions
that were 2 or more inches in diameter.
Costs
Production Costs: Rough estimate per acre based on yield of
400 50-pound bags.
The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended of other products that may also be suitable.
By Dr. David Nagel, Extension Professor, Plant and Soil Sciences
Discrimination based upon race, color, religion, sex, national origin, age, disability, or veteran’s status is a violation of federal and state law and MSU policy and will not be tolerated. Discrimination based upon sexual orientation or group affiliation is a violation of MSU policy and will not be tolerated.
Information Sheet 1506
Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture.
Published in furtherance of Acts of Congress, May 8 and June 30, 1914. MELISSA J. MIXON, Interim
Director
POD 04-10