How to Select Onion Sets


Unlike other vegetables, onions aren't always planted from seed. Instead, they are grown from small onion bulbs called sets. Selecting the proper sets for both your climate and your desired product is vital. Some sets are better suited to producing green onions; the edible onion stalk is used as a garnish and to add flavor in many recipes. Other sets produce mature onion bulbs. The day-length requirement is also vital because it indicates whether the onion variety will grow well in your area.

Step 1

Choose long-day varieties of onions if you live in the north and short-day varieties if you live in the south. The north has longer summer days than the south, so varieties that require 14 to 16 hours of sun a day thrive there, while the 12-hour short-day types thrive in the shorter days of the south.

Step 2

Purchase ¾- to 1-inch diameter sets for growing green onions. Choose ½- to ¾ -inch diameter sets for growing full onion bulbs.

Step 3

Inspect the sets for signs of rot or disease. Look for soft spots, mold and cuts in the side of the sets. These sets may rot in the ground before they have a chance to grow.

Step 4

Buy sets from onion varieties that are labeled as slow to bolt. Onion sets are prone to bolting, or flowering, which inhibits the growth of the onion bulb.

Step 5

Plant only sets that are firm. Dispose of any that have already begun to sprout, because these may rot in the ground, especially in wetter regions.

Tips and Warnings

  • Store onion sets in a cool dry place if you can't plant immediately; otherwise they will quickly rot. Place them in a mesh bag and keep them in a 32 F room with a humidity level no greater than 75 percent for two to four months.


  • Purdue Extension Office: Onions and Their Relatives
  • University of Minnesota Extension: Growing Onions
Keywords: choosing onion sets, selecting onions, vegetable garden

About this Author

Jenny Harrington has been a freelance writer since 2006. Her published articles have appeared in various print and online publications, including the "Dollar Stretcher." Previously, she owned her own business, selling handmade items online, wholesale and at crafts fairs. Harrington's specialties include small business information, crafting, decorating and gardening.