Revised 3/00 -- Author Reviewed 3/00 HIL-8018-A
The onion is a cool-season crop that will withstand moderate freezes. It may be grown either by seeding directly in the field, or by setting transplants. North Carolina growers have an excellent market opportunity in June and July when very few onions are available.
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.
How to Plant -- Onions may be planted in one of the following ways:
Plant Growing -- Most often, plants are purchased from certified plant growers in more southern states. Growers may raise their own plants by seeding in protected beds in early fall. These seeds are drilled about 1/2 inch deep and in rows about 4 inches apart at the rate of 8 to 10 seeds per inch. About one lb of seed is required to produce plants to set one acre. One acre of plant bed space will produce sufficient plants to set about 10 acres in the field. Seeds should be planted October 1 to 15. Beds should be protected when temperatures reach 200F or below.
Varieties -- Because onions are a cool-season crop, those planted too early in the fall may bolt (go to seed). This results in small bulbs with large necks which are hard to cure and are generally not usable. Onions planted at the time suggested above should not bolt unless extreme weather conditions exist.
Onion varieties are classified into groups according to when they bulb. Regardless of when they are planted, varieties won't form bulbs until the days are long enough for them to do so. Varieties that bulb in a 10- to 12-hour day (short day) are desired in eastern North Carolina for May to June harvest. It is also desirable to have an onion that has a small neck when mature. Juno has high cold tolerance but is more pungent than Grano types. Some new varieties, classed as intermediate or long-day types (14 to 16 hours), have potential for harvest in June and July. Recently, long-day and intermediate-day-type onion varieties have been developed that are well-adapted to N. C. conditions. They all have been very resistant to bolting and have produced good yields of large bulbs when overwintered. Some of the varieties overwinter very well.
See Table 1 to choose your varieties.
Table 1: Recommended varieties for eastern North Carolina.
Short Day* Intermediate Day Long Day Early Grano F Juno F, S, TS Golden Cascade S Texas Grano F Tough Ball F, TS Sweet Sandwich S, TS Texas Grano 502 F Willamette Sweet F Avalanche S, TS Granex 33 F, TS MidStar F, S, TS Magnum S Texas Grano 1015y PrimoVera F, S, TS Yula S
Early Grano F
Juno F, S, TS
Golden Cascade S
Texas Grano F
Tough Ball F, TS
Sweet Sandwich S, TS
Texas Grano 502 F
Willamette Sweet F
Avalanche S, TS
Granex 33 F, TS
MidStar F, S, TS
Texas Grano 1015y
PrimoVera F, S, TS
F = Fall planting held over winter, all varieties
S = Spring planting
TS = Transplant in Spring
Fertilizer -- Apply 400 to 500 lb of 10-10-20 fertilizer per acre, under the seed line, 7 to 10 days before planting. Sidedress with 30 to 40 lb N when plants are about one-third grown or when growth begins in the spring. Make additional applications every 3 to 4 weeks later. If heavy rains leach out the N, apply another sidedressing when plants are about half grown. Heavy N application later in the season may result in necks that are too large.
Spacing -- Row spacing will depend on cultivation equipment available. Seed should be spaced 2 to 4 inches in the row, depending on desired size for market. Plant 2 to 4 rows (10 to 12 inches apart) on beds 36 to 60 inches apart. Transplants should be spaced 3 to 4 inches apart in the row. Planting on shaped beds will ensure better drainage and make possible the operation of pulling the soil away from the bulbs at time of maturity to hasten drying and facilitate digging.
Weed Control -- Growth and yields are considerably reduced by weeds and grasses. Several herbicides are available for onions (consult the current North Carolina Commercial Vegetable Recommendations (AG-586). Shallow cultivation is necessary to break crusts.
Disease Control -- Downy mildew, powdery mildew and tip burn are common onion diseases in North Carolina. Consult the current North Carolina Commercial Vegetable Recommendations (AG-586) for proper control procedures.
Insect Control -- Thrips, onion maggots and wireworms are common onion insects. Consult your county extension agent or the current North Carolina Commercial Vegetable Recommendations (AG-586) for control procedures.
Irrigation -- Properly timed irrigation of 1 to 1 1/2 inches per week will assure larger bulbs and better yields. Irrigating a few days before harvest will make digging easier. Avoid excess irrigation or waiting too late because such irrigations can cause cracking.
Harvesting -- About a month before harvest, it is best to start working the soil away from the bulbs. This process should involve 2 or 3 cultivations so that about 7 to 10 days before harvest time, the bulb is about one-third above ground, which hastens bulb and neck drying. Harvest when 75% or more of the tops fall over. To hasten drying out, some growers use a sub-surface knife (such as a peanut plow) to cut the roots a few inches below the bulb. The bulbs are then allowed to dry for a day in a row. They are then dug by machine or pulled. Tops should be removed by cutting 1 to 1 1/2 inches above the top of the bulb (hand sheep shears work well for this) or machines will remove tops in the digging operation. Bulbs should not be exposed to direct sunlight since they sunburn easily. The tops are cut 1 to 1 1/2 inches from the bulb, the roots trimmed off, the bulbs placed (not thrown) in field crates and transported out of the field within 1 to 2 hours.
Curing -- Curing is very important. If necks are not thoroughly dry, neck-rot results. To store onions, place them in a dry, well-ventilated area.
Published by the North Carolina Cooperative Extension Service