Planting Onions


There are several ways to grow onions. You can grow them from sets, seedlings (transplants), or seeds.

Growing Onions from Sets

Sets are defined as onions bulbs that have reached about one inch in diameter. These small bulbs are conditioned to be planted later in gardens. After planting them, they immediately grow to form larger onion bulbs, although sets are sometimes appropriate for growing both bulb onions and green onions.

Gardeners growing onions in a small garden plot are advised to try growing them in sets. Onions planted in sets grow very hardy and mature quickly for easy harvesting.

When you go to the nursery, you may see onion sets sold only by their color. White sets of onions are some of the best for green onions. Please see our list of onion varieties to get an idea of the best onions to grow from sets.

Buy your sets early in the growing season and if you’re not going to plant them right away you’ll need to store them somewhere cool and dry, preferably a dark garage or storage shed.

If you plan on growing green onions, break up the sets appropriately. Sets for green onions should be about ½ inch in diameter or more. The smaller sets will make the best bulb onions. The rounder sets grow flatter onions. Round onions typically come from longer, tube-shaped sets.

Plant the onion sets about 1 ¼ inch deep. Space the rows out about 16 inches apart. If you choose, you can plant the sets pretty close together in the rows. As they grow you can thin out the green onions and let the rest develop as bulbs.

Growing Onions from Transplants

Onion transplants (seedlings) are defined as small plants that have been growing for roughly two months. They have not yet formed bulbs. However, when planted at the correct time they work very well to form bulb onions.

Onions grown from seedlings are a good pick for growing larger bulb onions. You can get them from nurseries and on-line catalogs. Buying from your local nursery is generally less expensive than purchasing onions through catalogs as the shipping can be pretty pricey. Your local nursery should also have a better idea what varieties of onion grow best in your area.

Remember to pick long-day varieties for northern states and short-day varieties if you live in a southern state. Please see our list of recommended onion varieties for a list of short and long-day onions that will work for your region.

Early April will work for planting onion transplants in most regions. Plant your transplant about 1 inch deep. You should place the transplants about 4 ½ inches apart in your rows. This spacing will help you grow larger onion bulbs. About half this spacing will allow you to grow green onions. Space the rows about 16 inches apart. If you prefer to grow onions in garden beds instead of rows, give them about seven inches of space on all sides.

Growing Onions from Seed

If you grow onions from seeds planted directly into your garden, plant them about 3/8 of an inch deep and space your rows at least 1½ feet apart. In general, wide rows work very well for onions.

You can also sow seeds to transplant in a greenhouse, hotbed, cold frame, or specially prepared beds at the rate of 3½ or 4 pounds for each acre of land to be planted.

When the seeds are grown under a cover, they are typically easy to care for and provide with the proper water and ventilation. The seedlings need to be “hardened” before planting though.

When ready to transplant, the seedlings should be somewhat smaller than a lead pencil and rather stocky. Begin by exposing them gradually to cooler temperatures and a little less water.

The advantages gained by transplanting seedlings grown indoors are an earlier crop, a uniform stand, and bulbs of a more regular size. Where a small area of onions is to be grown, the transplanting method is ideal, but for large garden plots which may require more time and labor, transplanting seedlings may be impractical.

After transplanting, the seedlings will require rain or watering in order to start growing in the garden plot, so you may be limited in growing where you have ready access to irrigation.

To transplant, lift the onion seedlings from the seed bed and trim the roots and top a little. As soon as the plants are up and the rows can be followed, a cultivator can be used to break up the soil a little.

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