Are onions staples in your kitchen? Do you want to grow more of them in your garden, like I do?
We currently have over 300 planted in our garden! After harvest, I store onions whole for a few months and then freeze and dehydrate the rest. Each year I have a goal to grow enough to last me until the next year. Although I haven’t achieved that goal quite yet, I get closer each season.
You make think since I have so many planted that growing onions is a no-brainer for me.
The truth is, onions are a little bit (ok a lot a bit) finicky. I plant so many because no season is the same, and in my Arkansas climate, roller coaster temperatures can cause major setbacks in the size of the bulbs.
But because I’m relentless in my pursuit of more and more onions, I have learned a lot about growing onions the last eight seasons, and I’ve definitely learned a lot of what not to do.
I dive into the details on our latest podcast. You can listen to that below or continue reading.
Common onion growing mistakes
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Planting the wrong onion types
You may be surprised to learn that one of the most common mistakes when it comes to growing onions is planting the wrong type. This is especially true if you’re buying your seeds, sets, and transplants from an online source. You have the option of buying short-day, long-day, or intermediate-day (also called day-neutral) onions, and which ones you choose makes all the difference in whether you harvest bulbs or just green onion tops.
If you are wanting large bulbed onions rather than green onions, you will plant the type of onions depending on your latitude. If you are in the US, find your location on this chart to determine which kind of onion is best suited for you. In many areas, like mine, I can plant both short-day and intermediate-day onions, but long-day onions would never bulb for me.
Planting sets instead of transplants and vice versa
If you are new to onions, sets of onions are those little tiny onion bulbs that look like mini onions. Transplants look like green onions with a long green stem and roots at the bottom. The mistake I personally made my first season was walking into the store and grabbing the sets, hoping to would grow large bulbs. Sadly, all I harvested that year were green onions.
Now, it’s impossible to say for sure, but more than likely those were long day onion sets, and quite honestly, they were more than likely meant to be grown as green onions in my area. They grew very long, beautiful stems…but no onion bulbs. The next year, I learned my lesson, bought the transplants and they grew into huge bulbous onions.
From this experience, made the incorrect assumption that sets are for green onions and transplants are for onion bulbs. But then I started to see northern friends posting about growing sets and having huge success. So, then I started to wonder? What is actually right here?
After digging deep into this subject, I have found that even amongst the credible university extension websites, the answers vary, depending on where the source is located.
This has led me to believe that learning how to grow onions, more than any other crop perhaps, is entirely dependant on the climate you live in. The very best source you can use is your local university extension (find yours here). I — and other gardeners online — don’t live where you live and our experience most likely won’t be the same as yours.
As you’re researching how to grow onions (and which ones to plant, when to plant, when to expect a harvest, etc.), be SURE that you know where the source you’re reading about is located.
But back to what type of onions to plant, the bottom line is this — whether you plant sets or transplants, make sure you choose the right day-length onion.
Planting too large of transplants and sets
Once you know what type of onion to plant, let’s look at some other common mistakes in growing onions.
When you buy your transplants or sets from your local garden supply store or online (this is my favorite source for buying onions), there’s a natural tendency to pick the largest onions.
However, the ideal transplant size is the width of a pencil!
The same is true when it comes to onion sets. Separate your sets and save the biggest ones for green onions and your medium ones for larger bulbs.
Growing from seed
The thorn in my side–growing onions from seed. This year I am hopeful, but up to this point, I’ve not been successful in growing onions from seed. One of the bigger mistakes when trying to grow from seed is that people wait too late to sow their seeds. This should be one of the very first crops you sow seeds for.
While northern gardeners who enjoy a long onion growing season into the summer will have more flexibility with this date, those of us in the South are on the clock since onions start bulbing sooner. Those onions need plenty of time to develop the greens that will nourish the bulbs. Because of that, we need to start our seeds about 10-12 weeks before the average last frost date.
Planting transplants too deep and too close together
Transplants should be planted about one inch deep. A trick I use is I plant them deep enough for them to stand up straight.
Also, after trial and error, I’ve found that planting the transplants 6 to 8 inches apart produces larger bulbs than when spaced closer together. Onions are water- and nutrient-hungry, and they need ample soil space from which to draw water and nutrients.
Not feeding the onions enough
Onions are heavier feeders than you would think for such a small plant. Most reputable onion growers (including the farm where I buy my onion transplants) recommend high-nitrogen synthetic fertilizer. But as an organic gardener, I don’t put any synthetic fertilizer on my garden. This doesn’t mean that I can’t feed my soil and plants organically, though.
Good leaf growth is what feeds your bulbs when the plants switch to the bulbing process. I add Milorganite into the garden ahead of planting because it’s an organic option. In the fall or early spring, I may add chicken manure. I also sometimes add corn gluten meal to sprinkle around the plants. This offers both an extra dose of nitrogen and weed suppression.
Not enough water and/or too much water
Onions love water! They can bolt if they aren’t well hydrated (more on bolting below). So, make sure you make watering onions a regular part of your garden routine if Mother Nature doesn’t provide plenty in the spring.
On the flip side of that, onions don’t love growing in waterlogged soil, so try your best to ensure the soil is well-draining and doesn’t hold water long. If your soil, like mine, contains a high percentage of clay, consider planting onions in a raised bed instead.
Not enough sun
It’s easy to assume (as I did) that onions don’t need as much sun because they aren’t fruiting plants, but in fact, that isn’t true. Onions love full sun, particularly in the early part of their growth. Keep this in mind if you do any companion planting. If you do plant them next to larger plants, try to time the planting where the larger plants are full size later in the onions’ growth.
Competing with weeds
We know now that onions are heavy feeders and need lots of water. This means, they can not be competing with weeds that are looking for the same thing. Make sure you weed often and keep your onion area free of the weeds, especially early on in the planting when the rains are more current.
I have to hand-weed when onions are small, but once they grow larger, a thick layer of mulch is a must. This also helps keep the soil temperature down, which is important to prevent premature bolting.
As a lot of other plants do, onions may bolt. You’ll know it’s starting to happen when the center stalk develops a small tear-drop-shaped white tip. From there, the center stalk grows taller and tougher, and the tip enlarges. This will eventually develop into a flower.
While these flowers are beautiful and feed our beneficial insects, it means that bulb growth has stopped as the plant shifts to seed production.
When an onion bolts, this also means your bulb isn’t a candidate for storage. But all is not lost.
At the first sign of the bolting onion, it’s best to harvest. You can use the onion now or chop and freeze or dehydrate. It won’t store long in its bulb form, and the longer you wait, the tougher the inside of the onion will get. This will make it even harder to use.
Most of the time, bolting is caused by rising temperatures, but often, bolting is triggered by fluctuating temperatures. If you live in my zone 7b, then you know hot to cold temperatures are very common in my area.
There are a couple of ways to try and help your onions avoid these extreme temp changes. One is that you can mulch around your onions after the spring rains but before the weather gets hot. Also, make sure you start watering extra during those hot summer days.
Covering up onion bulbs that have popped out of ground
If you avoid the bolting (which is always my goal!), as harvest nears, the onion bulb starts to pop out of the ground. It’s tempting to cover these back up (like you would potato plants), but this actually can cause the neck to rot, keeping it from being able to store properly after harvest.
Breaking the stems
Often, gardeners break the necks or stems of their plants to lay down on top of the soil at the end of the growing process. They do this in an attempt to get the plant to bulk up the bulb below.
Unfortunately, the opposite occurs. The bulb below the soil is being fed by the sugars that grow in the leafy greens on top. When you damage these greens, you cut off the final stages of bulb production. When the bulb production has stopped, and the onion has reached maturity, the leaves will fall over on their own. It’s at that point we know they are ready to harvest!
To wrap up this discussion, I want to reiterate one thing. Of all the advice you read about growing onions, always consult your local university garden extension website, visit them in person. Or ask local growers. Onions, in my experience, are the most variable in their growth and what they need, based on the location in which they are growing.
And if you’re still in the trial and error camp in your quest to grow large onion bulbs, welcome! You’re in good company. Let’s navigate this together.
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