Wednesday, January 21, 2009

How to go about planting onions from seed

After some poor onion results last year I decided to grow my own onions from seed. I started to research how to grow onions and what a mountain of information there was. I found most of my information on Dixondale Farms page, they provide a lot of information on onions as well as grow and ship transplants within the USA.

First off onions are day light sensitive and consist of Long Day, Intermediate Day & Short Day varieties. I am in the northern section of North America so I have to grow Long Day varieties which need 14-16 hours of day light to start developing bulbs. With them needing such long daylight hours to start developing bulbs it gives them a longer season to grow leaves and get big. The more leaves and the bigger the plant, the bigger the bulb will be when it starts developing.

This year I am growing Prince F1 for a large yellow storage onion and Armador F1 Shallots for a small storage onion.
Planting Onions Seeds

There is a couple ways of growing onions, the first being in a community pot or flat. They don't mind growing close together and a community pot makes them very easy to look after. You can also plant them in cell packs and thin to 3 plants per cell. I choose to use terracotta half pots so I can use them year over year, those cell packs don't seem to hold up well for reuse.

Now fill your container of choice with potting soil, pack it down and water until the soil is completely saturated. Potting soil has a tendency to repel water so if it is not saturated to begin with it can be problematic to get wet later. Once the soil is good and wet, let the excess water drain out for about 10 minutes.

With the soil wet, start to broadcast your onion seeds over the area. I usually use extra seed and then thin when they germinate. You can use the extra sprouts to transplant into bear spots and eat the left over as onion sprouts.

Once your seed is in place top dress your containing with about 1/2" of soil and gently tamp the soil down. From this point no more watering is needed. The top dressing will become saturated from capillary action from the moist soil below.

Then label your pots and place them in a seed propagator. Place the propagator under a grow light or on a window sill and make sure that the light is on for less hours then need to produce bulbs. For the Long Day onions I am growing I will leave the light on for 8-10 hours a day.

The seeds should germinate within 4-13 days depending on soil temperature and need little care well in the seed propagator. Once most seed has germinated and grown a little bit, remove the pots from the seed propagator to avoid any mold growth. Once the onions start to look crowded thin to approx. one plant every 3/4" and the tops can be trimmed to 4"-5" to bulk the seedlings up as well as control leggy growth. When the weather is better I will move these into my cold frame and then transplant them into the soil once my area is frost free.


  1. Well, that was very informative. Thanks, Dan! I bought some sets the other day, and will plant into the garden this coming weekend. Have you ever grown green onions from seed. I have some, but got them out too late last year. Thanks again for the tutorial. I really enjoy those kinds of posts!


  2. EG - I did the same thing with green onions last year so I have yet to try them. I ordered them for my cold frame but it was then way to late to start anything. I think green onions can be plant any time except the dead of winter. You could start some in your propagator and then plant them out a few weeks after they sprout.

  3. Thank you for this! I have stumbled your article and will be saving it in my collection of "usefull things for our garden project"

  4. Great job .... you just have so much info in the head of yours.... LOL

  5. Looking forward to seeing them grow Dan.

  6. I never have luck with starting from seed but as you know, I will be trying my hand at purple tomato seeds soon! I like the info you passed along and it will be helpful with hopefully a success for me!

  7. Dan, what brand of potting soil do you buy? I've tried a couple different ones this past year and been very unhappy with them. Of course, I didn't note what brands they were, so I'm likely to buy them again.


  8. dormouse74 - Glade I could help!

    Hendria - The brain was firing on all cylinders this particular day :-)

    Tina - me too.

    Skeeter - I tried growing walla walla onions once from seed and they didn't do so well. That was before I knew anything about growing onions, lets hope it turns out better this time.

    Granny - I use Pro-Mix as long as I can find it. They have many different mixes, I just go with their general purpose 'potting & seeding' mix. This link will take you to their page so you can find a retailer in your area.

  9. Darn, not a retailer within 100 miles of either my AZ or WA home! But thanks for the link, Dan.

  10. I had no idea that onions had different day lengths.

    I just bought a bunch of Egyptian walking onions. Even if they do flower, the tops are edible or can be planted to produce more!

  11. I'm curious to see how the onions turn out. I'd like to try to grow them someday. How many weeks do you plan to grow them indoors?

    I've tried growing the the basement, but I sometimes forget to go down and tend to them. Out of sight, out of mind...

  12. Red Icculus - Neither did I until I started reading about them last fall. Complex little creatures.

    Sally - I will grow them inside until early April. From that point I have read conflicting information. Some say to plant onions out as soon as the ground can be worked well others say to plant out after the last frost. So in April they will either go in the ground or go into my cold frame.

  13. The conflict in planting out time has to do with concern about bolting or premature flowering caused by a sustained period of stress (in this case cold). You could probably plant out a month or so before last frost, covering at night with a row cover or something to keep the wee ones happy.

    There are lots of perennial onions such as shallots which can be replanted to produce divided bulbs again in the following year rather like garlic and many others: potato onions, bunching onions, wild onions blah blah blah blah blah...

    I have been intrigued by what I belive is called the Winter Party Mix at Salt Spring Seeds this year with a colour mix of winter keeping onions.

  14. Ottawa Gardener - Thanks for the information, that explains why there is conflicting information.

    I have followed a few bloggers that plant potato onions and can harvest them over the winter. They intrigue me but I have yet to find any.

    I will have to try replanting some of the shallots I grow this year!

  15. Hi Dan,
    I propagate many of my vegetable seeds. However, when I did not have a propagator, instead of taking a trip to the DIY store, I built my own, saving me time and money.
    How to make a simple seed propagator has plans on building one of these, as well as other tips on buying them, using them and getting the best out of them.