Growing Pearl Onions

Besides being low in calories and free of fat, cholesterol, and sodium, onions contain significant amounts of vitamin C, vitamin B6, potassium, iron, and dietary fiber. That alone would be a good reason to include onions in your diet, but it doesn't end there. Onions also have interesting medicinal properties and are considered by some to be a "nutraceutical" for their disease-fighting properties

True pearl onions are classified as Allium ampeloprasum because they form just one storage leaf. In practice, short-day onion cultivars, such as Grano, Crystal Wax and others, when grown in northern latitudes, will develop pearl-size bulbs and be marketed as such. Most are used in pickling or in frozen mixtures of peas, broccoli and other vegetables.

Varieties

Pearl or cocktail onions - Crystal Wax (also known as White Bermuda), Eclipse (L303). For trial: Barletta (or White Pearl), White Mexican (or El Toro). All these are short-day varieties that bulb shortly after emergence to produce the desired bulb size at the latitudes of Pacific Northwest production areas.

Set onions - Generally long day varieties such as Stuttgart, Yellow Ebenezer, White Ebenezer, and Red Weathersfield are used.

Boiler onions - Small bulbs (1-1 3/4 inches) of any of the varieties listed above may be used. When planting specifically for boilers, Southport White Globe or the yellow types such as Stuttgart, Australian Brown, or Yellow Ebenezer are commonly used.

The optimum temperature range for germination is 48 to 90 F (9 to 33 C). Onions are grown on peat soils or silt loams and sandy loams. For pearl or cocktail onions, soils must be friable to allow rapid mechanical separation of onions from the soil at harvest. Loamy sands or similar sandy soils are best.

Seeding

Onions are easy to grow, although growing mature onions from seed does require some commitment. Since they can take up to five months to mature from seed, in the northern temperate zone onions are usually planted indoors in late January or February, then transplanted into the garden four to six weeks before frosts cease in the spring, when the starts are about ten weeks old.

For normal storage onions, seeds are spaced 7.5 cm apart. When small boiling, pickling or pearl onions are desired, spacing would be reduced to 2.5 cm in the row. Large bulb size is promoted by spacings of 10 cm or more.

Depth of seeding has an effect on bulb shape since the onion stem plate (the base of the onion bulb) forms at the point where the seed germinates. Shallow planting results in flatter bulbs, while deeper seed placement results in taller, and sometimes top-shaped bulbs.

Plant density also has an effect on onion shape, with onions tending to be taller at high density. When round onions are desired at the high densities used for pearl onions, use varieties that tend to be flat-round.

Since onions are a shallow-rooted crop, they don't compete well with weeds. They also need to have consistent soil moisture to produce nice bulbs. Preparing and watering your bed a week or two in advance, then lightly cultivating just before you transplant, can go a long way towards controlling the first flush of weeds. You may also want to mulch your new onions with some grass cuttings to keep the soil damp and help the growth of weeds. 

When at least 50% of the tops are falling over, the crop is getting ready for harvest. If you've mulched, pull it back and let the soil surface dry out. If possible, dry your onions in thegarden. Gently pull them from the soil detaching the root and lay them on the ground. Do not let them get wet from a heavy rain...they may rot.

The onions are cured properly when the neck is dry above the bulb. This will take two to four weeks depending on the humidity. Remove the tops and store ina well ventilated container like a mesh bag. Store in a dark and cool location for maximum usage.