When Do You Plant Onions? General Growing Tips On How To Grow Onions

Onions (Allium cepa) are one of the most versatile cooking vegetables. Most of the best delicious dishes in the world begin with a handful of diced onions. This makes onions a must-grow vegetable.

But most people don’t know that onions are easy to grow in the garden. 

In fact, achieving success with growing onions in the garden starts when you know when to plant, whether to plant onion sets or the seed, and how to prepare the soil.

In this post, you will learn about when and how to plant onions to get the best and biggest harvest you can. Read on.

When Do You Plant Onions?

When to plant your onions largely depends on the type of onion you want to grow and the climate of your location.

For instance, the best time to plant short-day onions is late winter to early spring in southern regions, while the best time to plant long-day onions is early spring in the northern areas where days are longer during summer.

For spring planting, onions are mostly planted in early spring for most regions, about four to six weeks before the last expected frost date. This planting period is best suited for bulbing or green onions.

You can also plant your onions in the fall, especially in milder climates. Planting onions in the fall enables the onions to have established roots before winter and start growing in early spring.

When planning to plant your crop of onions, ensure that you consider the onion type and your local climate.

Generally, you can plant your onions almost any time of year, but know that your timing will have a significant impact on the size of the onions you would harvest.

However, early to mid-spring is the best time to plant onion sets. Although you can grow some onion varieties in autumn for an early summer harvest, there is a possibility that the bulbs may rot in wet heavy soils during the colder months. 

We recommend that you plant onion sets outdoors in spring, usually in late March or April, as soon as you can work the ground. At this period, it is not likely that the temperatures would dip below 28°F (-2°C).

Suppose you wish to plant onion seeds instead, plant them indoors for about six weeks before transplanting them into your in-ground or raised garden bed once the soil’s temperature is at least 50°F (10°C).

Note that onions planted in fall need at least four to six weeks of warm temperatures to become established in the ground. 

During the cold season, the onions planted in fall will remain dormant, and as soon as the temperature rises in early spring, the soil would warm up, and the onions would come alive.

Planting Onions From Seed, Sets, Or Transplants?

There are three methods to plant onions – seeds, sets, transplants, and all of these three methods work really well.

Planting Onion Seeds

Planting onion seeds is the most affordable way to grow your onions. This method also enables you to grow a wider selection of onion varieties.

However, this method requires a bit more work because you would have to thin the onions out once they sprout. 

More so, this method is incredibly slow-growing as sowing to transplanting requires about 12 to 16 weeks. This method also takes a longer time to form bulbs than the other methods.

Nevertheless, planting onion seeds is a good option to grow onions indoors or in a greenhouse before the ground thaws.

Planting Onion Sets

Onion sets are onions grown from seeds in the previous season but later harvested as immature bulbs.

Onion sets are easy to work with and very affordable. This makes them the most common way to grow your onions without worrying about thinning later on.

They also grow relatively quickly. However, they are limited in variety.

Instead of buying onion sets, you can save money by growing your own onion sets to plant the following year.

Planting Onion Transplants

Planting onion transplants or onion starts is the easiest and fastest way to grow onions, especially if you are running a bit late on your planting schedule. 

However, they come in limited availability. More so, planting onion transplants is the most expensive of the three methods.

Transplants are sown the same way as onion sets and do not need to be thinned out.

Is It Better To Grow Onions From Sets Or Seed

You can choose to grow your onions from either seeds or sets, both methods are fine.

However, we recommend that you start onions from seed only if you are well-experienced in gardening and have a greenhouse. 

This is because starting onions from seeds is more complex and takes more time. Nevertheless, planting onion seeds is the most cost-effective way to grow onions.

When you start your onions from seeds, you can later transplant them into your garden. 

If you need a quick and convenient way to grow your onions, try growing from sets. Onion sets are young onion bulbs, so they don’t need a greenhouse and can be planted directly into your garden in springtime.

Best Way To Plant Onions

Onions are relatively easy to grow and do not require a large space. To thrive, onions need good drainage, plenty of water, and full sun. They also need constant nourishment to produce big bulbs.

Preparing Your Soil

Just as with any other plant, soil preparation is important prior to onion planting. Onions love loose, well-draining soil that is slightly acidic (pH between 6.0 and 7.0) and high in organic matter.

Dig over your garden soil to loosen it up. Boost your soil’s organic matter by adding an inch of cured manure or compost. 

If you have a limited supply of organic material, you can dig a trench about two inches deep and three inches wide along the row you intend to plant your onions in and fill it with organic materials.

Planting Your Onion Seeds (Sets Or Transplants)

Sow your onion seeds in a two-inch wide band, ¼ to ½ inch deep. Space the rows 12 to 18 inches apart. Once the seeds have sprouted, thin them to about three to four inches apart.

You can check your seed packets for any specific recommendations.

Onion sets and transplants can be planted the same way. Gently bury them one to two inches deep into loose soil, two to six inches apart, 12 to 16 inches apart in rows. 

Use closer spacing for the transplants if you wish to harvest immature onions. Don’t forget to trim the roots to about two inches and the tops to about four inches.

Also, make sure that the sets are pointed up when planting them, and do not bury them deeper than two inches into the soil. 

Note that planting your onion sets too deep into the soil can affect bulb development.

As said earlier, onions are heavy feeders. So, it is advisable to add nitrogen fertilizer at planting time, in addition to the organic material/compost added during soil preparation.

After planting, mulch with straw in between rows to help stifle weeds and retain moisture content.

Caring For Your Growing Onions

Onions are shallow root veggies. So, make sure that immature bulbs are lightly covered with mulch to protect them. But be careful not to cover emerging onions.

Onions also need a lot of water for optimal growth and to prevent bolting. They will be happy if you soak them up once a week (or more if your garden soil is sandy).

To get big bulbs, apply Nitrogen fertilizer to your plant every few weeks. You can stop fertilizing once the plant pushes the soil away and starts bulbing.

At this period, don’t cover the onions back with the soil as the bulbs need to emerge above the soil.

Finally, onions are ‘photoperiodic.’ This means that they grow in response to the amount of day length they receive.

For instance, short-day onions bulb when the day length reaches 10 to 12 hours. Intermediate or day-neutral onions bulb when day length reaches 12 to 14 hours. Long-day onions bulb when the day length reaches 14 to 16 hours. 

However, do not try to outsmart nature, planting short-day onions in a long-day zone will lead to small onion bulbs and not an early harvest. 

Conclusion

We hope this post helps you get started on your onion vegetable garden.

Once you are able to choose the right variety of onions for your local climate, nail down the proper timing, and meet the necessary soil requirements, you are sure to achieve a successful onion crop. Happy onions growing!

If you have any questions or need more help or tips to grow your onions, don’t hesitate to contact us.

Frequently Asked Questions (FAQs)