The challenge with starting from seeds is that your crop will take up to four months to mature. Gardeners in cold-winter areas will need to start their onion seedlings indoors. Always check a cultivar's day-length requirement or recommended latitudes before you buy, because day length affects how and when onions form bulbs. Short-day onions, such as 'Red Hamburger' , will form bulbs as soon as days reach 10 to 12 hours long.
They're suitable for southern latitudes only. Long-day types, like 'Sweet Sandwich' and 'Southport Red Globe', need 13 to 16 hours of summer daylight in order to form bulbs.
They're the type to grow in more northern latitudes. Onions like cool weather in the early part of their growth, so plant them in spring — except in mild-winter areas, where onions are grown as a fall or winter crop. Generally speaking, onions grow tops in cool weather and form bulbs when the weather warms. Plant onion seeds four to six weeks before the last average frost — or even earlier indoors or in a cold frame. When indoor seedlings are 2 to 3 inches tall, harden them off by exposing them to above-freezing night temperatures.
You can try mixing in radish seeds both to mark the planted rows and as a trap crop to lure root maggots away from the onions. Thin seedlings to 1 inch apart, and thin again in four weeks to 6 inches apart. For transplants or sets, use a dibble to make planting holes 2 inches deep and 4 to 6 inches apart.
Use the closer spacing if you plan to harvest some young plants as green onions. For sets, open a furrow 2 inches deep and place the sets stem pointed end up 4 to 6 inches apart, and then fill in the furrow. One pound of sets will plant about a foot-long row. The practices you follow will depend on the specific crop you're growing. In general, onions grow best if you keep them well weeded. Use a sharp hoe to cut off intruders; pulling or digging weeds up can damage the onions' shallow roots.
Once the soil has warmed, put down a mulch around and between the plants to discourage weeds and to hold moisture in the soil. Dry conditions cause bulbs to split, so water when necessary to provide at least 1 inch of water each week; keep in mind that transplants require more water than sets do. Onions can't compete well with weeds, so it's important to direct water right to the onion roots.
If you've prepared your soil well, no fertilizing should be necessary. Always go easy on nitrogen , which can produce lush tops at the expense of bulbs. New growth from the center will stop when the bulbs start forming.
Egyptian onions, chives, and shallots require slightly different cultivation from regular onions. Here are some guidelines for growing these onion relatives:.
Egyptian Onions Plant Egyptian onions in fall throughout the country; harvest some in spring as green or bunching onions. In mid-summer or fall, miniature bulbs will form at the stem tip, where most onions form flowers. Pick these tiny bulbs when the tops begin to wilt and dry. Use them fresh or store in the freezer.
Chives Plant chives and garlic chives in early spring in rich soil. They will tolerate partial shade put prefer full sun. Seeds are very slow to germinate, so most growers prefer to plant clump divisions, which you can harvest after two months. Space the clumps, each of which should contain about six bulbs, 8 inches apart.
Cut the grass-like, hollow tops frequently to maintain production. The pom-pom-like lavender flowers are very attractive, but always remove the spent flowers to reduce the chance of rampant self-seeding. Dig up, divide, and replant every third year. Transplant to containers and move indoors for winter harvests. Chives are almost as good frozen as they are fresh. Sow them two weeks before the last average frost date in spring, as long as the soil temperature has reached 50 degrees, or sow them four weeks before the first average frost date in fall.
Outdoors, sow them a half inch deep and 1 inch apart. For a shorter period between planting and harvest, you may choose to start the onion seeds indoors eight to 12 weeks before the last frost date for your area, according to Cornell University. Gradually harden off onion seedlings before moving them outdoors. Make sure the soil temperature has warmed to at least 40 degrees and the air temperature is at least 45 degrees. Transplants take about two months to reach full maturity.
Onion transplants resemble tiny scallions. Set starts for scallions an inch apart. If you want these transplants to grow into larger onion bulbs, soak them in compost tea 15 minutes before planting, plant them 1 to 2 inches deep and space them 4 inches apart. If you want larger bulbs upon harvest, according to UC Davis Extension , make sure you look for larger bulbs when buying your transplants.
There are three different types of onions and picking the right type is key to growing a great crop. But, this is only true if you grow onion seeds the right way. Related post: The best way to start seeds: Grow lights or sunny windowsill? Onions are cool-season crops that require 90 days or more to reach maturity. Because of this long growing season requirement and their preference for cooler weather, planting onion seeds directly into the garden in the spring makes it difficult for the bulbs to reach a good size before warm temperatures arrive.
This means the seeds have to be started many weeks in advance of moving the plants outside into the garden. To make matters worse, onion seedlings are also slow growing. But, planting onion seeds indoors under grow lights is a bit more nuanced than growing other vegetables from seed.
When growing the seeds of tomatoes , eggplants, and other veggies indoors under grow lights, the lights should be on for 16 to 18 hours per day. But, if you grow onion seeds indoors under grow lights and leave the lights on for that long, it will initiate an early bulb set and result in puny onions. That means that i f you want to start onion seeds indoors under grow lights, start very early and only leave the lights on for 10 to 12 hours per day.
If you want to skip the hassle of grow lights, heating mats , and other seed-starting equipment, growing onion seeds via winter sowing is the way to go. It works like a charm and is super easy. All you need is a packet of onion seeds, a plastic lidded container, and some potting soil formulated for seed starting.
I start planting onion seeds via winter sowing anytime between early December and mid-February. Once the seeds are planted, put the container in a protected, shady spot outdoors. I keep mine on a picnic table against the back of our house. The seeds will be fine.
Related post: Winter sowing containers. When the temperatures and day length are just right, your onion seeds will start to sprout inside the container.
At that time, you need to start monitoring the moisture level inside the container, watering your seedlings when necessary. Open the lid on warm days and close it at night. If you get a hard freeze in the spring, after the seedlings have germinated, toss a blanket or towel over the container at night for added insulation. Planting onion seeds by winter sowing means the plants are subjected to the natural day-night cycle right from the time of their germination.
This means that bulb set is triggered at the correct time and the plants can form large bulbs before hot temperatures arrive. Try planting onion seeds instead of sets this year, and enjoy a prolific harvest of these beautiful bulbs. Pin it! Give it a try and let us know how it goes. Yes you can, they are even hardier than onions!
When I put shallot sets in the ground, I do it as the same time as I plant garlic in the late fall, not spring! I have a question do you think this sowing of onion seeds in the winter would work on potato seeds? Typically when grown from seed, they need more than one season.
I need to try this method! How fascinating. It will be nice to plant them and leave them to do their thing for a while. Winter Sowing works for most plants, too, in my experience! They grow best when the time is right for them, and they know that time better than any of us and what we try to replicate with grow lights and perfect conditions. Plants are hardy and know what to do to thrive! Even using indoor lights and putting them out in sheltered areas before finally transplanting them, my results were not as good as I had hoped.
The seedlings were somewhat spindly. A couple of days ago I did my winter sowing and placed the plastic container in a shady area. Lets hope things work better for me!! Wish me luck, lol. Love this idea! Thank you. Try it with a few seeds and let us know if your growing season is long enough for it to work.
I keep mine in full shade, though as the spring temperatures warm, I open the lid and gradually start to expose them to more sun in the week or two prior to planting them out into the garden. I planted seeds in an heated propagator in mid-january in a cold but well-lit room. They are now happily sprouting.
Jessica, Thank you for a wonderful, informative website devoid of noisy, blinking advertisements. Will let you know the results this summer. Any suggestions on keeping the onion maggot flies at bay? Thanks, Mary, for your kind words. Report back with how your onion seed planting goes. As for the onion maggot flies, I suggest covering your onions with a layer of floating row cover also called reemay fabric.
It will keep the female flies from laying eggs that turn into those nasty little maggots. Good luck! Water the seeds in right after planting and then leave it go. How large do the seedlings have to be before transplanting?
More like the thickness of embroidery floss. Could you please give me the measurements on your plastic containers. I say No, they are a little bigger than a strawberry container. As you said… about the size of a lettuce container.
Hi Barbara. Thanks Jessca. I was surprised they were that big. My husband will be hapoy he was right. I did plant two packets of onion seed as per your instructions. See photo. My container was about the size you said but not as deep.
It does have a high plastic cover and should work. I have done winter sowing before but never tried growing onion from seed. Are their varieties that can store for longer periods of time? Thanks in advance! Hi Jamie — Welcome to Savvy Gardening! Any of the long-day onion varieties listed in the article will work for your zone. They all store about the same, as long as they are cured properly and you ensure the storage conditions are correct.
Go for it! Still worth a try? Hi Jessica, I live in southern York co. Pa in zone 6b. I planted yellow and red onion seed in the middle of February. Please tell me they will sprout when it warms up and have time to mature.
I followed your directions exactly, even have high mowing seed. Thanks Michael. Hi Michael. Mine have just started to sprout here in Western PA. Would it be to late to try this method in central Wisonsin?
Also, how do you transplant your seedlings? Do you just separate the seedlings a push them in the ground a couple is inches apart? Sorry, seedling myself! You could certainly try it, but I would also start some seeds indoors under grow lights as a back up.
Once the seedlings are a few inches tall, transplant them into the garden, spacing them about inches apart. I had just about given up on my onion seed germinitating but today I checked again and they had finally germinated.
It took 6 weeks. Most perennials are easy to start via winter sowing. You can do tomatoes and other warm-season veggies this way, too, but you should delay planting the containers until early spring and bring them inside if the weather is going to get very cold, especially at night.
How deep do you plant the onions during transplant? Hi Becca — Plant them so the bottom third of the plant is below the ground. The only issue would be if the onions were a hybrid, the next generation would not come true from seed.
Hello Jessica, Great idea! I live in Tulsa, Oklahoma and garden with raised beds. What are your thoughts on that idea? What drawbacks do you see with that approach? I want to use my raised beds as cold frames, but am not sure how, when and what to put in them.
Hi Jessica, I live in north Idaho where we get winter temperatures near zero once in awhile but for the most part temperatures are around 20 degrees at night and low 30s during the day. My garden typically will have at least a foot of snow from Christmas until the spring thaw in March.
Do you think I could sow Walla Walla seed directly into the garden in November? This would save the transplanting step. Great question. Give it a try and let us know how it works out for you. This is how I grow my cilantro, spinach, lettuce, and mache. Jessica, I planted my little onion plants and they did grow. I learned something in the process.
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