As an Amazon Associate I earn from qualifying purchases.
You can read my full disclosure statement here.
Today I am excited to share with you how to start onion seed indoors in January! I hope you will pick up some helpful tips and tricks, and learn how we grow enough onions to use for most of the year!
Today I will go over when and how to start onion seed indoors step by step! Starting onion seeds indoors, is not difficult at all. By starting onions from seed, you will have many more varieties to choose from.
When to Start Onion Seed Indoors in January
January is the month my fingers get itching to plant onion seed. Luckily there are a few things you can plant by seed as early as January here in the PNW, even earlier in milder parts.
Onion seed is usually the first thing I plant in the dead of winter. Other things that may be started this month by seed are celery, artichoke, asparagus and hot peppers.
Different Methods for Sowing Onion Seeds
I sow most of my seeds using two methods, Winter Sowing and also indoors using your standard seed starting Equipment. Please see these two article for more information on both methods:
Seed Starting 101: Winter Sowing in which I share how I use milk jugs outdoors as mini greenhouses to start seed. Winter sowing is a great option for starting onion seed if you don't have a lot of room indoors. Plant the milk jug with the seed as set it outside, simple as that.
Watch for the seeds to germinate, and you can open the lid and leave it open once the seedlings need their first trim, (see below for more info on that!). Onion plants don't mind the cold once they have germinated, but I might still bring them inside if it gets below freezing.
Seed Starting Equipment lists more details about equipment needed to start your seeds indoors. It also covers what type of soil I use for starting seeds. I will go over how I plant onion seed indoors using this equipment set up in more detail down below.
Choosing Which Onion Varieties to Plant
I chose several varieties of onion seed to plant, with my primary focus being on onions that are excellent keeping onions or also called storage onions. These types of onions will last in storage all through winter after harvesting and curing them.
Sweet onions like Walla Walla and Vidalia are delicious, and I usually grow a small amount for fresh eating. But if you want to keep onions for a long period of time, these are not the best for that.
Onion Seed vs Onion Sets
When trying to grow most of our own produce for the year, it is essential to look at varieties of food that keep well. For this reason, I choose not to start my onions by onion sets.
Often onion sets will bolt very early, as they are actually onion that was grown from seed the previous year. Their main objective is to reproduce, so all their energy goes into making seed, not into making a large onion bulb.
There are usually not many varieties to choose from when using onion sets either. By planting from seed, you can plant any varieties of onions including leeks, shallots or heirloom varieties using the process I outline below.
Storage Onions aka Keeping Onions
This year for storage onions, I will be growing Talon, Cortland and Red Bull F1. I have grown all of these before and they have all grown well for me. Other varieties that I have grown that have done well for me are Patterson and Red Wing.
The Red Bull kept the longest in storage before sprouting, so I always grow a lot of it, even though we prefer the yellow onions.
The Walla Walla's are a sweet onion, and will only be used for fresh eating.
Viability of Onion Seed
Onion seeds are one type of seed that do not store well. I learned that the hard way one year. I planted 2 yr old left over seed, and had less than 10% germinate.
Now I always buy fresh onion seed as a result. So be sure you are using fresh seed. If in doubt how old the seed is, buy new. I would not get onion seed from a seed swap for this reason.
Long Day Onion vs Short Day Onions
When you plant onion seed, be sure you are choosing the correct onions for your area. There are long day onions which do best in the northern half of the states and need daylight for longer than 12 hours a day. Then there are short day onions which do better in the southern half of the states and require less sunlight hours during the day.
How to Start Onion Seed Indoors
For planting onion seed, I like to use seed tray inserts that are approximately 4" x 6" or 5"x5". Draw 4 furrows about a ½" deep the length of the tray. Plant the onion seed down the line, maybe 1 seed every quarter inch or so. I use a chop stick to help place them.
You could also use 4" pots and just sprinkle about a ½-1 teaspoon of seed on top and cover gently with soil. Don't be worried about planting onion seed too close together.
There is no need whatsoever, to plant one or two seeds per each little cell pack if you are using 6 packs, throw 6-10 seeds in each cell. Once the plants are mature, it is easy to pull them all apart and they don't mind being snuggled up close.
Than gently cover the seed with soil and press down all the soil in the tray firmly with your palm and fingers. Spray with water, enough water to get the top inch or so of soil damp.
These would probably germinate fine without a heating mat as the ideal germination soil temperature is 55-75 degrees. But I have seed mats on hand so I place the flat on the heat mat when done.
If you don't have a heat mat, try placing the flat in a warm area such as on top of the refrigerator. Watch that the soil doesn't dry out, and spray when necessary to keep the seed in a damp soil medium.
Caring for the Onion Seedlings
Once the majority of the seeds have germinated, it is safe to take the plastic dome lid off. This is only used to ensure that the soil stays damp for germination.
From this point onward, water from the bottom, by filling the flat about halfway with water. Onions are heavy feeders, so I like to feed them with Fish Emulsion Fertilizer in the water, using a highly diluted amount of 1-2 TBSN's per gallon of water.
It is a good idea to place a gentle oscillating fan pointed at the seed starts. This helps prevent mold and fungus from growing on the top of the soil which can harm the plants. It also helps to create a stronger stem on the plant.
At this point, they can also be taken off the heat mat if you are using one. Onions don't mind the cold, and it will free up your heat mat for growing another crop that needs it like tomatoes or peppers.
Ideally the plants should also be under grow lights, placed about an 1" above the plants, raising the light as needed to stay close to the tops of the plants.
I keep them under the grow lights for the first few weeks, and then if you live in a mild enough climate like I do, they can move outside in a sunny sheltered area if warm enough. Just watch the weather and bring them in if it gets to freezing or below.
Trimming your Onion Seedlings
As your onions starts grow, they may get long and scraggly. It is perfectly ok to give them a "haircut" to neaten them up. I trim them down to 2-3" high.
Trim them pretty regularly, every few days or at least once a week. When the plants are flopping over on top of themselves, they don't get as much air circulation which is unhealthy for them and will cause rot.
Preparing your Onion Seedlings for Final Transplant
Keep watering, feeding and trimming them until you are ready to plant out in the garden. This is usually around April 1st or so here in the PNW. Ideally they should be as thick as a pencil, but I have planted them when thinner. Ideally they should also have their third "leaf" in.
If it is going to be really wet out, I suggest waiting as the smaller plants may rot if it is too wet out. Also, be sure to harden the plants off over a week or so, as they slowly need to adjust to living outside. Putting them straight in the garden without hardening them off, will put them into shock which is not good.
See my article on How to Harden Off Your Seedlings.
See more information on How to Transplant Onion Seedlings.
Don't forget to consider other onion plant family varieties when you plant onion seed. You could also start leeks, chives, white onions, Spanish onions, or choose from a vast assortment of heirloom onions.
Want to Remember This?
As you can see, starting onion seeds indoors is not that difficult! I hope this help you understand better how to start onion seeds indoors and the benefits from doing so, and that you can grow some unique to you varieties of onions this way. Happy planting!