Growing your own onions is a fun & rewarding project. They’re one of the first plants you can start indoors to kick off the year. Plus nothing compares to the taste of a homegrown onion. We’ll walk you through the planting process & outline some pitfalls you should avoid.
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It’s cold in the Pacific Northwest today. Below freezing and we haven’t seen that thing people call the sun in about a month. On the flip side, it’s the beginning of February, and for someone that loves to grow delicious food that means spring is right around the corner and I’ve got a chore to do…planting onion seeds.
Of course, the word chore is relative. My sister once asked if I enjoyed working so hard on our farm all the time. While it certainly does have its moments, working on a better way of living for the two of us is more a passion than a chore.
I enjoy getting my hands dirty and reaping the rewards that come from doing so. That said, if I had to choose a task that was more on the therapeutic side, it would be planting something.
We were fortunate enough to have planned for just such a momentous occasion, so our grow shelf has been prepped, there is potting soil in the shop and we’re sitting on about 800 seeds all culminating in this moment…let’s get the ONIONS started!
Onions are one of our most treasured vegetables. We put them in most of our recipes, use them as sides, top off a salad and dress up our burgers with them. Aside from garlic, I can’t think of another staple we grow that we never seem to have enough of!
Delicious, fragrant onions…aaaahhh…..
I can smell them sautéing in the cast iron as we speak. And now that I’m hungry, let’s get to the part about growing them so we can get to eating them.
Choosing your Onions
We like a nice variety, and everything we grow has to pass the “does it taste great?” test. Right behind that is the “does it store well?” test. This year, we have chosen…
Long Day vs. Short Day Onions
If you are brand new to growing onions, you should know that there are two basic types dependent upon the length of day in your growing area.
Long day onions require 14-15 hours of light before they will begin to bulb. These onions should be chosen for the northern half of the United States.
Short day onions only require 10-12 hours of light and should be chosen for the southern half.
There are also intermediate onions. You guessed it! They perform well in the transitional areas of the above mentioned.
It is important to buy the correct variety for your locale. Most seed packets and stores will state specifically which zone for which seed.
Planting Onions: Seeds vs Sets
There are two ways to plant onions, from seed or from sets.
Sets are very common, especially for the backyard gardener. They are readily available at most large chain stores or online. We don’t like them and don’t plant them, here is why…
Onions take two years to complete their life cycle.
Their first year they are focused on growing from a seed to a beautiful onion.
In the second year, they’re focused on going from an onion to a flower so the plant can repopulate its own lifecycle.
Sets are young onions that were pulled before maturity, housed, (now 1 year old) and then marketed and sold the following spring (now going into their second year). You can probably see where this is going to lead…
Many of those sets will, in fact, bolt. Bolting is a word used to describe a vegetable that is going to seed. It will put most of it’s energy into the seeds and leave you with close to nothing.
This is not to say that you can’t grow some mighty fine onions from sets, but for us, to grow from seed typically produces much more reliable results.
Start Your Onion Seeds Indoors Now!
Onions grow to their full potential if they are planted early with tons of sun. Some questions to consider…
- Do you have a greenhouse?
- What about a cold frame?
- Built a row cover?
- Maybe just a window sill?
Our biggest concern with seeds is always space. We have a six-shelf grow light system, so planting two flats of onions (roughly 400 seeds) only takes up one shelf. But remember it is only January and they will be there hoarding that space until your last spring frost. For us, that’s is March 25th or 7 weeks from now!
Find more details on our grow light setup here.
What if I Can’t Start Seeds Indoors?
That’s okay! You can still sow them directly into your garden. In this case, it’s best to wait until spring or they won’t have the required temperature needed to germinate. It’s usually spotty below 65 degrees F. Plus they could possibly rot before they ever germinate.
Let’s Get Down to Planting Onion Seeds…
I like to use a 72-cell seed tray and a natural, organic blend of potting soil for my seeds. But what about a seed starting mix? Well, honestly, I have had just as much luck or better with a quality potting mix.
Learn more about making your own potting mix here.
The drive behind seed starting mixes is that they are light weight. Theoretically, the baby roots can grow more easily and the first leaves have a better time breaking through the surface of the medium. However, in my experience, a quality organic potting mix does that just fine.
But guess what? There are millions of growers out there in the world. We can all do it differently as long as we get good results, right!? So go with your gut or experiment!
Fill the tray with your chosen mix, and lightly tamp it down with another tray or your thumb. Don’t pack it down hard, just give the seed a firm bed to lay in to start off its life.
Next, sprinkle your seeds on top. In a 72-cell tray, I will put 1-5 seeds down per cell, depending upon how much of a hurry I am in and how cold my fingers are!
In a 3×3 nursery pot, I might put as many as 20 seeds.
I would recommend more than 1 seed per cell so you can get some serious germination results.
And while other vegetables prefer to have their competitors removed ASAP, onions do thrive with their own brethren in the same pot. So don’t thin them. You’ll do that when you plant them out.
Sprinkle a little bit more potting mix over the top of your seeds to the desired depth of planting.
A good rule of thumb for most vegetables is to plant your seeds 2 to 3 times as deep as the seed is wide. So with a small seed like an onion, an eighth of an inch is good. Though I have buried some and also left some on the surface just as an experiment and most of them sprouted. So don’t stress too much about it!
Water Your Seeds Well
Don’t do this with the pressure on full blast or you could bury the seeds so deep that you can’t get them to germinate. I prefer to water from below. This means that I pour water into the tray to a depth of about 1 inch and wait for the surface to darken with moisture. This usually takes a few hours.
After the cells are sufficiently soaked, don’t forget that plants need oxygen as well. What we do is pour off the remaining water into our watering bucket for use on other plants in the house. If your surface is still not wet, use a small spray bottle dedicated to your grow shelf!
Finally, put your seed tray in a warm spot to germinate. Onions don’t need light to germinate, but they do need moisture and warmth.
I usually put ours on top of our grow shelf so the warmth from the lights below acts as a heating mat. This really jump-starts the germination process.
As soon as the onions begin to sprout, get them into as much light as you can. You can leave them in your greenhouse if it is warm enough, or put them under lights on your grow shelf for 15-16 hours a day.
From this point on you just need to keep the light source in close proximity to your starts, and water periodically. I wait until I see some of the surface dirt drying out, and then wait one more day before I water them again. Always from the bottom now so as to not weigh down any of the new growth.
Onions are Heavy Feeders
However, at this young age, your potting mix should have everything they need to grow into nice healthy starts. If you do feel they need fertilizer at some point, I would recommend cutting the dosage recommended by half or three-quarters, so as not to burn your new babies.
Here’s a nice, mild fertilizer…
Onions are very easy to grow, but you will need to conform to a few basic principles….
As with most plants, they need a sunny spot with rich, well-drained soil.
The onion bulb needs a somewhat loamy soil to be able to expand
Plants need oxygen as well so add a little compost or well-aged manure to your soil if it is full of clay and/or compacted.
Once you have an adequate location chosen, amend your soil as needed in advance so when your starts are ready, you will be too!
Read more about saving eggshells as a calcium garden amendment here.
For more details on the next steps, check out this video…
And that’s all there is to it! Onions are very forgiving and quite hardy. A little TLC in their initial startup and you’ll have a bumper crop ready for transplant by your last frost date. We’ll do another blog post to cover that process as we get closer to spring or check out the video above! Mark it on the calendar and let’s grow some onions together.
Planning your spring garden? Read more about our top plants for beginner gardeners here.
If you’ve tried any of our gardening tips, we’d really love to hear from you! Send us an email or leave a comment below the gardening idea you tried. You can also comment on our Facebook, Pinterest, Instagram or Twitter pages.