Texas Cooperative Extension,
Texas A&M University, College Station, Texas

January-February 2006


Plan for Onions Now


by Dr. Douglas F. Welsh, Horticulturist,
Texas Cooperative Extension

Perennial shallots & garlic
Perennial shallots & garlic

Success with onions under Texas climatic conditions depends upon knowing the right varieties to use, and the correct time of the year to get them started. Listed below are some good guidelines taken from the Texas Master Gardener Handbook:
  • Light: Sunny (green onions tolerate partial shade)

  • Soil: Well-drained loam

  • Fertility: Medium-rich

  • pH: 5.5 to 7.0

  • Temperature: Cool (45 to 60F) during development; medium-hot (60 to 75F) during bulbing and curing

  • Moisture: Moist, but not waterlogged

  • Planting: Use sets, seeds or transplants in spring for bulbs and green or bunching onions; seeds may be started indoors 8 weeks before setting out; use sets in fall for perennial or multiplier onion types

  • Spacing: Standard - 1 to 4 inches X 12 to 24 inches; wide row - 4 inches X 4 inches in rows up to 2 feet apart; plant close, then thin; use thinnings as green onions

  • Hardiness: Bulb onions - hardy biennials; green or bunching - hardy biennials; Egyptian or Perennial Tree and multiplier - hardy perennials

  • Fertilizer needs: Heavy feeder; apply 4 to 5 pounds of 10-10-10 per 100 square feet before planting and side-dress 3 weeks after trans-planting and again when bulb enlargement begins (2 or 3 tablespoons of 21-0-0 per 10 feet of row)

Onions are often grouped according to taste. The two main types of onions are strong-flavored (American) and mild (often called European). Each has three distinct colors; yellow, white and red. Generally, American onions have smaller bulbs, denser texture, stronger flavor and better keeping quality than European types. Globe varieties tend to keep longer in storage.

Onion varieties also differ in the number of daylight hours required to make a bulb. If the seed catalog lists an onion as a long-day variety, it bulbs when it receives 15 to 16 hours of daylight. Long-day varieties are used in the northern United States to produce onions in summer. Short-day varieties bulb with about 12 hours of daylight; they are used in southern areas for winter onion production.

For green or bunching onions, use sets, seeds or transplants in spring. In fall, use Egyptian (perennial tree) and yellow multiplier (potato onion) sets.

For bulb production, set out transplants in early spring, spacing them 4 to 6 inches apart and 1 to 2 inches deep in the row. Planting too early and exposure to cold temperatures causes seed stalk development. Egyptian tree or multiplier onions should be set in late October or early November. Plant 4 inches apart in rows 1 to 2 feet apart. Distance between rows is determined by available space and cultivating equipment.

Onions have shallow root systems and compete poorly with weeds. Shallow cultivation is necessary; do not mound soil on onions as this may encourage stem rot. Ensure ample moisture, especially after bulbs begin to enlarge.

Onions should be harvested when about two-thirds of the tops have fallen over. Careful handling to avoid bruising helps control storage rots and thorough curing increases storage life. Onions can be pulled and left in the field for several days to dry, then cured in a well-ventilated attic or porch for 1 or 2 weeks where they are not in direct sunlight. Tops may be left on or cut off, but leave at least 1 inch of the top when storing.

Diseases:
Neck or stem rot; bulb rot; pink root

Insects:
Thrips; onion root maggots

Cultural:
Bulb rot from bruising or insufficient drying; split or double bulb from dry soil during bulb formation; very small bulb from planting too late or inadequate soil moisture

Days to maturity:
100 to 120 (mature bulbs)

Harvest:
Harvest green onions when tops are 6 inches tall and bulbs after two-thirds or more of the tops have fallen over. Do not wait more than 1 or 2 weeks after this occurs; allow time for thorough drying before storage.

Approximate yields (per 10 foot row):
10 to 15 pounds

Amount to raise per person:
10 to 15 pounds

Storage:
Cool (32F), dry (65 to 70 percent RH) conditions for 6 to 7 months

Preservation:
Onions can be stored dry or pickled and canned; they freeze well if chopped and covered with water. For fresh storage, maintain good air circulation. An effective storage method is to place an onion in a nylon hose, tie a knot and add another onion. When the hose is filled, suspend it from rafters in a storage area.

Perennial onion relatives such as shallots, multiplying onions and garlic, once planted, will last for many years in the well-tended garden.


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