Growing Onions

Supermarkets offer three choices of onions: yellow, white and red. Grow your own and you can pick from of a wide variety of pungent and sweet alliums right outside your back door.

Onions take up little space and can be harvested and used at different stages of growth, from young, green scallions to fully mature bulbs. They’re also easy to dry, providing onions for all your cooking needs until the following spring.

Types of Onions

Although onions may be yellow, red, or white, seventy percent of onions grown are yellow. Yellows are good all‐purpose onions and the best winter keepers. They also have tougher skins and are more disease‐resistant and less susceptible to insects. Reds are the sweetest but are generally the worst keepers. Whites make the best scallions, harvested as “green onions” before their bulbs form.

Bulb formation is affected by temperature, light intensity, and the amount of light and darkness. Once the balance of daylight and darkness reaches a certain point, leaf growth ceases and bulb growth begins. Onions are classified as short‐day, intermediate‐day and long‐day:

  • Short‐day onions start forming bulbs when days are 11‐12 hours long.
  • Intermediate‐day onions need days that are 12‐14 hours long.
  • Long‐day varieties need days longer than 14 hours.

It’s important to choose the right type of onion for your area. Pick the wrong variety and you’ll still get onions, but they probably won’t be as big as you’d like. In general, long‐day onions grow better in northern climates and short‐day onions are better suited to southern gardens. Intermediate or day‐neutral onions will grow anywhere. Growing short‐day varieties in the North will result in leaf growth stopping too soon to produce a large bulb.

Each leaf of the onion plant corresponds to a ring in the onion itself? More leaves mean more rings, larger leaves mean larger rings and both mean larger onions. Under ideal conditions, onions will have thirteen leaves and thirteen rings.

Onions may be grown from seeds, transplants, or sets, which are immature onion bulbs. Growing from sets is the easiest and most foolproof method. Onion sets are not as finicky about soil and are better for short growing seasons and cooler climates. The disadvantages are that there is less selection and sets are more expensive to buy than seed. You can, however, grow your own sets from seed and save them to plant the next season. Seeds can be started indoors and set in the soil as transplants or sown directly in the garden. Transplants may also be purchased in bunches from garden centers or seed catalogues, but they’re expensive. Direct‐seeding is impractical for long‐season onions in most home gardens, but is suitable for scallions.

Varieties of onions to grow from seed include:

  • big sweet ‘Ailsa Craig’ (long‐day, yellow, 105‐110 days)
  • large mild ‘Super Star’ (day‐neutral, white, 109 days)
  • heirloom ‘Red Weathersfield’ (long‐day, red, 110‐115 days)
  • ‘Walla Walla’ (intermediate‐day, white, 90‐110 days) produces huge 5‐7″ (12‐18 cm) onions that are exceptionally sweet, but they are not good for storage.

Varieties to grow from sets are limited. Most common are ‘Stuttgarter’, ‘Yellow Ebenezer’, ‘White Ebenezer’ and ‘Red Wethersfield’.

Growing Requirements

Onions are frost‐tolerant and like cool, wet spring weather. These light feeders prefer rich, well‐drained soil with a pH of 6.2 to 6.8. Add lime if necessary. Onions are best grown in raised beds about 4 inches (10 cm) high and 20 inches (51 cm) wide with one to two inches (2.5‐5.1 cm) of compost worked into the soil. Be sure to provide consistent water and keep weeds under control while onions are maturing.

Planting Onions

Plant onion sets two to four weeks before the last frost and use bulbs that are less than ¾ inches (19 mm) in diameter. Onion sets should be spaced from 4‐6″ (10‐15 cm) apart, depending on the size of the mature bulb. Press bulbs gently into the soil about an inch (2.5 cm) deep so that their pointed tips just break the surface.

If planting onions from seed, wait until the soil temperature is 50°F (10°C). Sow seeds ¼ inch(6.25 mm) deep, ½ inch (12.5 mm) apart, with 12‐18 inches (30‐45 cm) between rows. Thin to 4‐6 inches (10‐15 cm) for large bulbs or 1‐2 inches (2.5‐5.1 cm) for scallions.

To grow transplants, start seeds indoors about eight to ten weeks before last frost. Sow seeds in flats ¼ inch (6.25 mm) deep about ½ inch (12.5″ apart). Thin to one inch (2.5 cm). Harden off and transplant in the garden when plants have two true leaves and temperatures reach 40°F (4.5°C), two to four weeks before last frost. Set transplants about one inch (2.5 cm) deep, 3‐4 inches (8‐10 cm) apart.

Mild, sweet, or pungent, try growing a new variety of onions in your garden this spring.

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