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Home Garden - Onion in Fall

 5 Reasons to Plant Onions in Fall + How to Do It

A few years seem to fall in the blink of an eye. There are green leaves on the trees for a week, then, unexpectedly, the cold nights come, the color explodes, and then the show is over. Not for this year's harvest, but for next year's. So, when you're harvesting the last vegetables in your garden beds, it's time to plant onions, garlic, and carrots. While you're at it, you might want to dig up your horsetail and transplant it when the soil is moist from the rain.

Reasons for your onion crop to fail

Generally, gardeners plant onion seeds or sets in the soil and can work the ground in late March or April. That is the norm. However, we don't all garden in the same climate. Onions can be grown year-round in some states, such as California's central coast. To make growing onions even messier, it's certainly possible to plant onion sets in the fall and let them cross under a layer of mulch. This way you can harvest mature onions in spring.

That's what we did this year, planting our onions in the fall - pictures to be continued below.

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In a nutshell, here's why you should plant onion clusters:

Warm soil = faster growth.

Both onion sets and onion seeds can germinate in already warm soil and establish their roots quickly.

Strong roots.

Onions grow much like garlic – when planted in the fall, they set deep roots, lie dormant through the winter months, and then spring back to vigorous life with warmer weather.

Big onion.

It goes without saying that more established plants have a big advantage when high temperatures roll around. Instead of putting energy into growing roots, all they have to do is gain weight and girth. It makes a beautiful, full-bodied onion.


I'll let you be the judge of this, but some gardeners, including us, find that fall-planted onions have a better flavor.

Fall-planted onions mature earlier.

Several months early, some fall-planted onions can be harvested in June of the following year. Combine that with spring planting and harvest all summer long, and you've got a nice onion succession. If you haven't tried the falling method of planting onion sets yet, it's definitely worth a trip, regardless of the weather. But to be successful, you need to know the difference between onions.

Finding the best onions for your location

Most onions will work for fall planting, but not every bulb will thrive, and if you're approaching your garden as an edible experiment, go ahead and plant onion sets or seeds you have. If you don't have a tunicate bulb to eat, you will surely be blessed with green onions. Sometimes you are happy with what you have.

So, which onion is best for your garden?

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For starters, onions like full sun, which is a given.

From there, you need to decide whether your belly prefers green onions or bulbs. Bulbless green onions, for example, are very easy to grow. They don't care one bit about the time of day. If you're not sure about soil conditions, daylight, water requirements, etc., they're the perfect onion to grow. Then there are short-day onions, long-day onions, and day-neutral onions. Let's take a quick look at some of the categories in each package.

Short day onion

Short-day onions develop bulbs as daylight increases from 10 to 12 hours each day. White Bermuda, Southern Belle, and Red Burgundy are ideal for planting in southern gardens. If grown in northern states, they may flower and go to seed very quickly. Any plant that blooms too quickly will be stunted. Still tasty, but smaller than average.

Long day onion

Walla Walla, Red Baron, Sweet Spanish White, and Rosa de Milano are onion varieties that need 14 hours or more of sunlight each day. If this amount of sun doesn't cover your garden, it's a good idea to try a short-day or a day-neutral onion variety instead.

Day-neutral onions

It is special that other onions are ordinary. Day-neutral or intermediate-day onions produce bulbs regardless of the sun. They grow well anywhere and are especially sweet in the Midwest. They still prefer 10 hours of sunlight, but hey, no vegetable grows to full size in the dark. Try Cabernet, Red Amposta, Sierra Blanca or Monatrall.

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How to Plant Onions in the Fall

Mid-September to early October is an excellent time to plant onions in the fall. The planting date depends on soil conditions (hopefully not too wet), as well as the first expected frost. Generally, fall-planted onions take 4-6 weeks before winter sets in.

Sets or seeds?

Seeds are always cheaper and perhaps more readily available, but whether you plant your onions in fall or spring, sets have a clear advantage. If you choose to go with onion seeds in your garden, spacing is important, but it's more difficult to achieve than if you're planting sets. Another minor drawback is that the early growth of onion seeds is easily overrun by weeds. If all you have are seeds, plant them according to the instructions on the package.

On the other hand, the set is already ready to grow into bulbs.

Onion sets are simply seeds that have germinated and grown to a certain size. If onion sets are not available in the store, you can certainly grow them yourself. It gives you a wide variety to choose from. Be aware, however, that this part of the growing process also takes time. It takes about 60-80 days to grow your own set of onions. Again, gardening is as layered as an onion. If you don't have onion sets for fall planting, seeds may still be a better option.

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Planting onion seeds in autumn

With a packet of onion seeds in hand, head to your prepared garden beds on a nice dry fall day and sow those little black seeds half an inch deep in rows 8″ apart. Since the germination rate of onion seeds is very low, sow the seeds densely. Then those seedlings should be thinned out to about 4″ apart, but you can do this gradually and pick the weakest ones first. Onion seeds should be planted 3 to 4 weeks earlier than onion seeds. This is four to eight weeks before the first frost date. But you can plant them at the same time if the weather is right.

Autumn planting onion sets

Although onion sets establish quickly in the soil, they are more prone to bolting. This can lead to underdeveloped bulbs. When an onion molts, it sends out a flower stalk for the rest of the season trying to make seeds. If this happens, remove it as soon as possible unless there are seeds you want to save. At the same time, onion bulbs that bolt will develop a hard brown core. You can easily remove this before consuming it, but the onion is much more desirable when it's healthy inside.

As for planting, plant onions 3/4″ deep in the ground two to four weeks before the last frost date. The pointed end of the bulb should peek out of the soil. Space 4-6″ apart. While it's tempting to choose larger sets, these are the smallest ones you'll want to grow. Smaller sets are less likely to bolt and tend to get bigger sooner.

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Whatever you do, grow more than one variety. Red, yellow and purple onions. For both taste and beauty. Don't forget to add compost to your soil when you plant - if your garden needs it. As a no-dig gardener, I cannot stress enough the importance of mulch in the garden.

When planting onions in the fall, even if you haven't moved your garden yet, you can add a half-inch layer of shredded leaves, leaf mold, grass clippings, or straw to the newly planted onion bed. This will prevent weeds from sprouting and retain moisture in the soil, creating optimal growing conditions for your onion seeds or sets. Once your onions are green and out of the ground, slowly add another few inches of mulch. This winter blanket protects from freezing in winter.

Here are before and after pictures of a small patch of fall-planted onions.

Irrigation fall planted onions

If your soil is as wet as our mountain soil is after 3 weeks of rain every day, you may not need to water it after planting. You can set it and forget about it, maybe even until spring. If your soil is on the dry side, it's best to water your sets or seeds after covering them with a layer of mulch. Fall rains usually provide an adequate source of water for onion growth. Once your onions begin to go dormant (go dormant), you no longer need to water them. All that needs to be done is to wait for them to emerge in the spring.

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