How To Start Onions From Seeds

Learning how to grow onions from seed is my next project in the never-ending journey of gardening. 

We tend to do things the way we have been taught; until we learn a better way. I have always only planted onion sets; until this year.

With our short growing season, growing onions from onion sets seemed to be the only way.

Simple to plant, they can be put into our zone 2 gardens in May, and we have onions by September that we can use. Unfortunately, we also get quite a bit of rain in late August, which seems to cause a lot of onion rot.  

We use quite a lot of onion, and when dried properly, they should keep for several months. However, I have had a lot of problems with onion roots in my garden.

I don’t know if it is because of a deficiency in our soil, the rain in August, or some other mysterious genetic problem. 

This year I am starting onions from seeds. Maybe this will be the answer to my onion woes. I purchased my onion seeds from a local Hardware store, but most places that sell vegetable seeds will have them as well. 

Onions are generally considered a cool-season crop because they like to start their life while conditions are still cool. Once warm weather hits, they start bulb formation.

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    What Type of Onion To Buy

    The three main onion varieties fall into three classifications: short-day, long-day, and day-neutral. 

    Short-Day Onions are perfect for areas where the days are slightly shorter.

    They prefer days that are about 10-12 hours in length. Red Burgundy, Grano, White Bermuda, Southern Belle, and ‘Yellow Granex’ (also known as Vidalia) are all short-day varieties.

    Long-Day Onions prefer about 14 hour long days for bulb formation to begin.

    Some Long Day varieties include Yellow Sweet Spanish, Walla Walla, Calibra, Southport White Globe, Rossa di Milano, Red Baron, Red Carpet, Cortland, and Sweet Spanish White. I’ve planted Yellow Sweet Spanish this year. 

    Day-Neutral Onions comes in right between Long Day and Short Day and prefers about 12-14 hour long days. Day Neutral varieties include Cabernet, Gladstone, Sierra Blanca, Talon, and Red Amposta.

    So what is the right one for you? Day Neutral is great for the mid-section of the US. We have really long days this far north where we live, so I would choose Long Day Onions for our area. 

    Where To Buy Onion Seeds

    Onion seeds can be purchased at garden centers, as well as through seed catalogs, such as T & T Seeds, and Veseys. Here is a list of the best places to buy seeds in Canada.

    When to start onion seeds Indoors?

    Start onion seeds indoors 8-10 weeks before transplanting them out into the garden. My seeds germinated rapidly, and are already growing strong.

    Onion seeds need about 100-120 days to grow, and because we only have about 65, I started my onion seeds in February, 3 months (12 weeks) before they will go into the garden.

    Start With Fresh Seeds And Soil

    Once you’ve chosen your type of onion, and you know when to start your onion, you can get to planting. Buy a fresh bag of seed starting soil, or make your own seed-starter mix. 

    Use seed planting trays, or reuse old fruit containers. Fruit containers work great because they usually have drainage holes at the bottom. 

    If your containers are clear, make a light barrier around the outside of the inside with newspaper. Roots don’t appreciate the light, so clear containers can set them back. 

    Sprinkle your seeds over the soil, and cover them with a ⅛ inch layer of dirt. Mark your trays with variety and planting date.

    Never assume you will remember what you planted! I’ve fone that too often, and always end up forgetting. 

    Cover your trays with a clear plastic bag or lids. Covering them helps to preserve moisture, and I find my germination rate is much higher if I cover them. 

    Onion germination usually takes place within 8-10 days. 

    When seeds have sprouted, take off the lids, and move them to a place where they will have sufficient light. I have one small shelf near a kitchen window, that provides enough light.

    However, as soon as I will start up the rest of my plants, I will move them all under a grow light. Grow lights are amazing if you don’t have a place in your home that gets a lot of light.

    onion seedlings

    Before Transplanting Onions Into The Garden

    Onion seedlings need to harden off before you put them into your garden. Hardening off is just getting them used to the wind and the air outside.

    I always start by putting my seedling trays outside for 2-3 the first day, and then slowly increasing the time they are outside every day.

    When placing them outside, place them in a sheltered place, out of the sun and wind the first several days. Slowly get them used to the sun and the wind.

    If your plants start showing signs of stress, you know they have had too much sun. Decrease the time slightly and continue. They will get stronger. 

    Plants are kind of like us; the more troubles we face, the stronger we become.

    After you have hardened off your onion plants, and you no longer get frost, transplant them into your garden. In early spring, prepare your garden bed by preparing fertile soil for them.

    Compost, worm castings, and a phosphorus fertilizer such as bone meal will help to ensure their health. Plant your onion seedlings ½ inch deep into the soil, 4-6 inches apart, depending on the size of the bulbs.

    Bigger bulbs will need more space. Onion plants need good drainage and direct sunlight. 

    Onions need at least an inch of water every week and full sun. As they grow, brush away the soil from the tops of the onions.

    This will help them to dry out faster, and help ensure they cure well. 

    A lack of potassium is another reason why onions might develop onion rot, and adding compost to your garden will help eliminate this problem. Compost tea and fish emulsion are both beneficial for healthy onion growth.

    Banana peels are another great source of potassium, and making tea from banana peels is an excellent fertilizer. 

    The onions are ready to be harvested when the bulbs have a diameter of 2 to 3 inches, in late summer. You should let the plants go dormant before harvesting, otherwise, they will not store well.

    Wait for a while till most of the onion tops have tipped over and turned to brown, and the bulbs have produced papery skins. Bend the bulbs to the ground to speed up drying.

    Once the tops have withered, you can pull the bulbs out of the ground and cure them in a dry, warm, well-ventilated place. (source)

    It takes around 3 weeks to cure onions. I like to spread mine out on a screen to speed up drying. Make sure you place them somewhere out of the rain. 

    dried onions in a basket

    Can you direct sow onion seeds

    You might be able to, but I can not. Northern growers do not have a long enough growing season to direct sow onion seeds.

    However, if you are in a growing season that has over 100 frost-free days, go ahead. Prepare your gardening bed, and sow onion seeds approximately 1/4 to 1/2″ deep and about 4 inches apart.

    You will need to thin them out to one onion seedling to four inches after they have sprouted. 

    Direct sowing onions seeds can be to your advantage because they don’t have to endure transplant shock, which can set plants back quite a bit. 

    Learning how to grow onions from seed is my next project in the never-ending journey of gardening.

    I am optimistic that learning how to grow onions from seeds will help us be able to buy fewer onions from the store.

    Curing them properly is important for long-term storage, but so is feeding them the right nutrients and amount of water.


    Do you start onions from seeds? Let me know in the comments below.

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