Planting & Harvesting Onion Sets

What Are Onion Sets?

Onion sets are small, young onion bulbs that are planted in the early spring and then harvested in late summer or early fall. The onion sets look like small bulbs and, once they mature, they will develop into a full-size onion bulb that you would purchase from your local market.

Why Plant Onion Sets?

Onions are surprisingly easy to grow! They are planted early in the spring and harvested from midsummer through the fall. And since they come pre-sized and pre-packaged, they're a cinch to plant.

Plus, onions are incredibly versatile. You can use them in savory dishes or sweet dishes, and they add flavor and nutrition to any meal. So if you're looking for an easy way to add some fresh produce to your garden, onion sets are a great option.

When to Plant Onion Sets

When to plant onion sets is dictated by your climate. In spring, plant onion sets outdoors as soon as the ground can be worked, usually in late March or April, when temperatures are no longer likely to dip below 28°F. However, a fall-planted crop of onions needs at least 4 to 6 weeks of warm temperatures to become established in the ground. Onion sets planted in the fall will remain dormant during the cool season, as the temperatures and soil warm again in early spring, the onions come back to life.

How to Plant Onion Sets

When it comes to planting onion sets, there are a few things you need to keep in mind. Onion plants are heavy feeders and require constant nourishment to produce big bulbs. At planting time, add nitrogen fertilizer.

Many organic gardeners will add an inch of compost to the bottom of each row before planting. Or, dig a trench in the soil about 2 inches deep and 3 inches wide, and then fill the trench back in with about an inch of compost.

Bury onion sets 2 to 6 inches apart, gently pressing them into loose soil no more than 1 inch deep. Space transplants 4 to 5 inches apart and rows 12 to 18 inches apart.

Set the bulbs with the point end up. Again, don’t bury them more than 1 inch under the soil. It’s important that onions aren’t planted too deep, as this can affect bulb development.

How to Harvest Onion

Onion harvesting is a task that should be done with caution. You don't want to damage the bulbs in any way, as this will lead to rotting. The best way to harvest onions is to wait until they are yellow and the tops have fallen over. At that point, you can cut the roots and trim the tops back before storing them in a cool, dry place.

When it comes to planting onion sets, timing is everything. If you plant them too early, they may not produce onions; if you plant them too late, the onions may be small and poor in quality.