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Chapter 21: Onions

21.1 Varieties

Growers should test new varieties routinely to determine which perform best on their farms, choosing those with tolerance or resistance to diseases such as pink root and Fusarium basal rot if their fields have a history of these diseases.

Tables of Disease Resistant Varieties

21.2 Planting Methods

Onions are a cool-season crop that requires a long growing season to produce good bulb yields of high quality. In New York, most dry bulb onions for commercial production are grown on muck soils because of the advantages offered by these soils. These include a uniform water supply, early crop establishment, and ease of mechanical harvesting. Most mineral soils require irrigation to produce a good yield.

Because onion plants begin to bulb in early summer when days reach sufficient length, it is important to establish the crop early to assure that plants are large enough to develop a large bulb. The crop also must mature early enough to allow curing of the bulb before cool, wet weather arrives in the fall. Onions may be grown from seeds, sets, or transplants, but because of economics direct seeding is the usual practice in New York. Row spacing varies considerably depending upon weed and foliar disease management, seeder capability, and harvesting equipment. In-row spacing also varies depending upon variety, desired bulb size, row spacing, soil type, and other management considerations. To ensure good quality bulbs for storage and to produce acceptable yields, plants must not be spaced too far apart in the row.

Onion yields in New York vary considerably from year to year and from field to field. Average yields are around 300 to 350 cwt per acre but can reach 500 cwt or more per acre when growing conditions are good and proper management is practiced.

21.3 Fertility

Maintain a pH of 6.0 to 6.8 on mineral soils. Consider liming muck soils when pH is 5.2 or below. See Table 21.3.1 and Table 21.3.2 for the recommended rates of nitrogen, phosphorus, and potassium.

Table 21.3.1 Recommended nutrients based on soil tests for onions grown in mineral soils

N pounds/acre P2O5 pounds/acre   K2O pounds/acre Comments
  Soil Phosphorus Level   Soil Potassium Level  
  low med. high   low med. high  
90-120 150 100 50   150 100 50 Total recommended.
30-40 100 50 0   100 50 0 Broadcast after plowing
30-40 50 50 50   50 50 50 Apply in band at seeding or transplanting.
30-40 0 0 0   0 0 0 Apply at 4 to 5 week stage.

Table 21.3.2 Recommended nutrients based on soil tests for onions grown in muck soils

N pounds/acre P2O5 pounds/acre   K2O pounds/acre Comments
  Soil Phosphorus Level   Soil Potassium Level  
  low med. high   low med. high  
100-1251 150 100 50   150 100 50 Total recommended.
100-125 150 100 50   150 100 50 Broadcast after plowing
1: On deep well-drained mucks, 50 pounds per acre may be sufficient for best yields, but higher rates may accelerate seedling growth and maturity of later hybrids. Muck onions have not responded to nitrogen sidedressings except in rainy seasons.

21.4 Harvest

A high percentage of onions grown in New York are stored for marketing throughout the fall, winter, and early spring. Late, hard, pungent varieties with good skin retention are preferable for storage after January 1. Undercutting several days before harvesting can improve keeping quality. To develop best skin color, onions should be cured for two weeks at temperatures between 75° and 80°F and relative humidity of 70 to 80 percent. After curing, temperatures should be lowered gradually to as near 32°F as possible for best keeping. Rapid cooling followed by a sudden warm period might break dormancy and cause onions to sprout early. A sprout inhibitor should be applied to all onions intended for sale after mid-November. Apply when about 50 percent of the tops are down, bulbs are mature, necks are soft, and five to seven leaves are still green. This treatment is not recommended if Botrytis leaf blight is moderate to severe because it destroys leaf tissue before the the sprout inhibitor can be absorbed.

21.5 Disease Management

21.5.1 Bacterial Soft Rot, Slippery Skin, Bacterial Canker, Sour Skin
21.5.2 Fusarium Basal Rot
21.5.3 Botrytis Leaf Blight
21.5.4 Botrytis Neck Rot
21.5.5 Damping-Off
21.5.6 Downy Mildew
21.5.7 Flower Blight
21.5.8 Nematodes
21.5.9 Pink Root
21.5.10 Purple Blotch
21.5.11 Smut
21.5.12 Stemphylium Leaf Blight and Stalk Rot
21.5.13 Onion Yellow Dwarf Virus
21.5.14 Iris Yellow Spot Virus


21.6 Insect Management

21.6.1 Onion Thrips
21.6.2 Onion Maggot
21.6.3 Seedcorn Maggot
21.6.4 Bulb Mite
21.6.5 Cutworms
21.6.6 Leek Moth
21.6.7 Allium Leafminer


21.7 Weed Management



Maintained by Abby Seaman, New York State IPM Program. Last modified 2019.