How To Plant Fall Onions

There is little doubt that fall is our favorite time of all for planting onions in the garden. And for so many great reasons!

For starters, it’s simply refreshing to finally be planting in the cool autumn air. Especially after spending so many days tending, weeding and harvesting the garden in the hot summer sun.

But even more, planting onions in the fall is the secret to creating an earlier harvest of bulbs next summer. And even better – onions that are larger, sweeter, and filled with more flavor than ever!

Why Plant Onions In The Fall

Although onions can be planted in either the spring or fall, autumn has a few big advantages over spring planting. One of the biggest being warmer soil – which just happens to be perfect for fast growth.

*Planting fall onions can lead to larger bulbs for harvesting next summer. Our fall bulbs outpace our spring planted bulbs in size usually by 1/3 or more.*

Unlike early spring when the soil temperatures are still cool from winter’s chill, the ground in fall is warm and toasty. And that allows onion sets or seeds to germinate fast. Even better, it also means they can grow and quickly establish a strong root system before winter sets in.

Fall onions grow in much the same fashion as a fall crop of garlic (See How To Grow Garlic This Fall).The bulbs sprout and establish in the soil, and then the cold chill of winter arrives, and the crop goes dormant.

And just like fall planted garlic, as the temperatures and soil warm again in early spring, the crop comes back to life. But it does so with a strong root system already developed from the previous fall. The result is fast, strong growth that can helps develop larger, full-bodied onions, and an onion filled with big flavor.

The Proof Is In The Garden

We have always planted both spring and fall onion crops. And without a doubt, our fall crop always seems to bring a much larger and better tasting onion than our same-year planted onions.

Fall planted onions also mature earlier. In fact, some of our fall onions can usually be harvested at near full size as early as the following June.

red yellow and white onion sets — We plant a mix of yellow, red and white onions in both the fall and the spring. We use our fall planted onions to grow larger, full-sized bulbs. Our spring planted bulbs tend to be smaller and are great for both spring or young onions.

With those advantages in mind, here is a look at how to plant for success when it comes to fall onions:

When To Plant Fall Onions

A fall-planted crop of onions needs at least 4 to 6 weeks of warm temperatures to become established in the ground. It is important to note these are long-day onion varieties.

Here in the Ohio, we usually plant our fall onion sets during the middle portion of September. That gives plenty of time for growth before winter.

We prefer planting onion sets over seed. For starters, they establish quickly in the soil and are easier to plant. Seeds can be hard to plant evenly. In addition, they sprout and grow so thin that they can easily be overwhelmed by weeds.

Finally, onion sets simply grow larger bulbs. Onion sets are in essence, onion seeds that have already sprouted and grown a bit. By their very nature, they will mature faster and to a larger size.

We usually plant a mix of white, yellow and red onions each fall to have a good variety the following year. Product Link : Mixed Onion Sets

If you do want to go the seed route, you will want to plant them in the ground 3 to 4 weeks earlier than onion sets. This allows them to get a bit of a head start and develop a root system before going dormant in the fall.

Soil Preparation – How To Plant Fall Onions

Growing great onions, whether in the spring or fall, all starts with great soil. Onions, grow best in loose, fertile, and well-drained soil. And that means adding compost before planting is a BIG plus! (See : How To Make Great Compost – Fast!)

No matter if you plant in long rows, or with individual holes in raised beds, adding compost to the bottom of the planting hole is a must.

As with nearly every vegetable and crop in the garden, adding compost prior to planting can go a long way towards success. Compost not only adds nutrients to the soil, but it also helps to give better drainage and holds moisture close to the roots.

We like to add about an inch of compost to the bottom of each row before planting. This gives the onion bulb loose, nutrient-filled soil to establish quickly.

Amending your soil is even more important if your soil is hard or clay-like. The harder the soil, the less likely root crops can reach their full potential. For hard soils, add in equal amounts of compost and sand prior to planting. This will help with both drainage and root growth as the bulbs sprout.

Planting – How To Plant Fall Onions

For our onion bulbs, we dig a trench in the soil two inches deep and a few inches wide. For this task, a mattock (often called a garden pick) is the perfect tool.

It can easily be drawn through the soil, and makes a perfect 2″ wide trench with ease. We actually use our mattock for all of our trench planted crops like corn, beans and garlic.

Before planting, we fill the trench in with about an inch to and inch and a half of compost. Next, we plant the bulbs into the trench, setting them into the compost a bit. Always plant your bulbs with the pointy end facing up. This helps the bulbs sprout quickly through the soil.

We like to space our bulbs about 4 to 6 inches apart. This spacing allows plenty of room for growth. This is important for fall planted bulbs, which grow larger than spring planted bulbs. We finish by covering the bulbs with an equal mix of soil and compost to fill the trench.

Long Term Care – How To Plant Fall Onions

Once the crop is planted, we mulch over top with a 1/2″ layer of straw or shredded leaves. This helps to keep out weeds and keep in moisture. Keep the covering light to allow the crop to germinate and sprout through the earth.

how to plant onions - mulching — *Mulch is critical for helping conserve moisture in the soil, and for keeping competing weeds out of the rows. Straw, shredded leaves, and grass clippings all work well for mulching onions.*

Once the onions have grown through the surface, add a few more inches of straw or shredded leaves on top. This helps blanket the crop from the deep freezing and thawing cycles winter brings. Before winter arrives, your crop should have about 4 inches or so of mulch to help protect it.

A thicker layer of mulch also helps keeps competing weeds at bay. Keeping weeds out of your onion rows is vital to their development. The more weeds that are present, the smaller the onion bulbs will grow.

Watering Your Onions – How To Plant Fall Onions

As soon as you finish planting, water your bulbs in. It is better to water the onion sets once the mulch is down. This sets the bulbs into the soil and keeps the mulch down. It will also help to hold moisture in for germination.

Autumn usually provides adequate rain for an onion crop. As long as you have rain weekly, the crop should be fine. If you do experience extended dry periods, water as needed to provide moisture to the crop. Once the crop goes dormant for the winter, there is no need to water.

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As spring rolls around, your onions will come back to life. They can be harvested at any point as smaller onions, or allowed to grow to full size for a mid to late summer harvest.

Here’s to planting a great fall crop of onions this year, and being rewarded with an earlier and tastier harvest next year. Happy Gardening! Jim & Mary

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