Planning an Onion Crop

Although we’re in the midst of winter, it is never too soon to think about next growing season. This is particularly true if you want to grow onions.

Onions are a good crop for Kentucky farmers. Typically in late winter it takes eight to ten weeks to produce a reasonably sized transplant. If you want to plant in late March or the beginning of April, you should have seeded your transplants in late January. If you have not already seeded, it’s not too late for an onion crop this year. You can purchase transplants.

Be sure to buy intermediate day-long or day neutral onion varieties. Onions can typically be categorized into short, intermediate and long day types.


Onions will bulb in response to day length. Short-day varieties need 11 to 12 hours of
sunlight per day to bulb, intermediate-day varieties bulb with 12 to 13 hours of sunlight, and long-day varieties bulb with 13 to 14 hours. The types of onions grown during the winter in the Deep South, such as Vidalias, are short-day types. Unfortunately, Kentucky is far enough north that if planted here short-day onions will bulb very early in the spring when plants are still small. The result will be small golf-ball or tennis ball size bulbs.

Instead, try to buy intermediate-day types such as the popular Candy onion. These will begin to bulb in mid-May and should mature by early- to mid-July.

Many growers report bulbs the size of softballs when growing Candy onions. If you decide to plant a long-day variety, such as Walla Walla or Sweet Spanish, your plants will begin to bulb in June and continue until early August when they will be mature. Although long-day types yield well in Kentucky, high summer temperatures may lead to an increased disease risk.

For more on growing onions and other vegetables, contact your local Cooperative Extension Service.

Submitted by Tim Coolong, Extension Horticulturist, University of Kentucky