Ten Top Tips for Growing Onions from Seed

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Onion seedlings being raised in paper cups

In the past year, both Ben Vanheems and I have written about the virtues of growing onions from seed. We left out many small details, which I've been keeping track of in recent weeks as I've been growing onions from seed myself. Please bear in mind that I am an onion maniac, and I have no explanation for my obsession with growing onions and shallots from seed to table year after year. I am driven to do it, which explains the evolution of these ten guidelines for growing onions from seed.

1. Start with fresh seed and seed starting mix

Onion seeds can be kept for two years in a cool, dry place such as a properly monitored seed storage box, but fresh first-year onion seeds germinate best. Germination rates fall as the seeds age, and though I have had three-year-old onion seeds that sprouted well, germination is always highest with fresh seeds. I also purchase a fresh bag of seed-starting mix each spring as a safety precaution against soil-borne diseases. My onion seedlings stay in pots for up to 10 weeks, so I like to use a soil medium that's unlikely to host diseases.

2. Provide bottom heat

The tops of my florescent plant lights are flat, and they give off just the right amount of bottom heat needed to help onion seeds germinate quickly. Onion germination is fastest as 68-77°F (20-25°C), with slight temperature drops at night. Before I started using the top of my plant light, I found that the top of the refrigerator was a sufficiently warm place to germinate onions. I enclose newly seeded containers in a plastic bag to maintain moisture, provide them with bottom heat, and the onion seeds germinate in about 8 days.

Trimming onion seedlings
Trimming onion seedlings

3. Clip off seed husks

Soon after germination occurs, my indoor-grown onion seedlings often do a poor job of pulling away from the seed. The stuck seedling looks like a little green loop. Eventually the smaller end pulls out of the soil, weighted down by the black remains of the seed husk. To shorten this drama and encourage the seedling to get on with growing into an upright onion, I often "rescue the chick" by snipping the loop in half, pulling out the smaller end, and discarding it.

4. Keep under lights and trim back

At this point growing onions from seed requires bright supplemental light, which I provide with a two-bulb florescent fixture. I keep the lights on my onions for 12 hours a day, and position them within 1 inch (2.5 cm) of the bulbs. Every day or so I trim the onions back to about 3 inches (7-8 cm) tall, which keeps them from falling over. Use scissors to get a clean cut.

5. Transplant when the third leaf appears

When an onion seedling has three leaves, I gently transplant to containers that are at least 4 inches (10 cm) deep. In my experience, onion seedlings that are given plenty of vertical root space grow much more rapidly than those confined to shallower quarters. They may not be pretty, but containers made from the bottoms of milk cartons or large paper cups house the majority of my adolescent onion seedlings.

Onion seedlings to transplant

6. Trim off seeding leaves

Soon after transplanting, my onions often shed the seedling leaf (sometimes called the flag leaf). I snip it off and remove it to keep the containers tidy. Onion seedlings respond to transplanting by making strong upright growth, which I keep trimmed back to about 5 inches (12 cm) high.

7. Provide maximum light

The best light of all is found outdoors on sunny days, so my adolescent onions get moved outdoors whenever we get warm sun. I shield them from wind by using my cold frame or a plastic-covered tunnel for my onion day care center. They love it!

8. Harden off, but protect from chilling

Eventually the onion seedlings stay outdoors 24/7, provided temperatures are well above 46°F (8° C) at night. Consistent exposure to temperatures below 50°F (10°C) for more than 10 days can cause onions to bolt rather than producing big bulbs.

9. Band composted fertilizer in the planting trench

Onion roots are concentrated in the area just below the bulbs. As I prepare the planting bed, I make deep planting trenches and line them with rich compost and/or composted organic fertilizer. This technique, called banding fertilizer, places a cache of organic riches where the onions can utilize it early on, during the plants' most active period of growth. Providing bioactive compost is important when growing onions, because onions take up much of the phosphorous they need through partnerships with soil-borne mycorrhizal fungi.

Curing onions after harvest
Curing onions after harvest

10. Sow leafy greens between rows to suppress weeds

Once my onion seedlings are in the ground, the war with weeds gets into full swing. Skinny onions are notoriously poor competitors with weeds, so they require a certain level of tending. Each year I find myself interplanting more arugula, lettuce and other leafy greens among my little onions grown from seed. Employed as smother crops, salad greens are much more fun to pull compared to weeds, and onions grown from seed seem to like their company.

By Barbara Pleasant

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Comments

 
"Should I trim the tops of my leek starts too? They seem to be doing the same thing. Making the little green loop and some have even pulled away with the husk still attached. This is the first time I've started leeks from seed. They were started almost a month ago and are 3-4 inches tall. Thanks!"
Rachel on Friday 9 March 2012
"Yes, treat leeks from seed just like onions when they are young. Your early start should give you a nice crop! "
Barbara Pleasant on Friday 9 March 2012
"When transplanting to deeper containers, can I plant more than one seedling in each container? For instance, if I am using 3" square pots, how many seedlings can I transplant to that conainer without crowding them too much? I guess I'm wondering what kind of spacing the seedlings require before being planted out. Thanks!"
Kelly on Friday 9 March 2012
"Thanks for all this information, Barbara! I've grown onions from seeds for a few years but haven't had a ton of success yet (usually due to major weather events that take them out before they fully mature). I'm hoping to do better this year. I've never trimmed the onions before - do you believe it's better to trim them to 5" than let them grow to full vertical height? And this is just during the seedling phase? Thanks again!"
Melissa on Saturday 10 March 2012
"Kelly, I often grow two, three or even four seedlings in a container. Onion seedlings are easy to pull apart for transplanting to the garden, especially if they have good vertical growing space. In a 4-inch diameter half-gallon milk carton bottom I would plant 4 seedlings, but only two in a 3-inch pot. If the roots of neighboring plants become extremely intertwined it can get ugly on transplanting day....Melissa, trimming back your onion seedlings regularly until they are almost ready to set out will help them bulk up faster and keep them from falling over. After the seedlings have four leaves they seem to need less frequent trimming compared to when they have two. Good to hear from fellow onion lovers!"
Barbara Pleasant on Saturday 10 March 2012
"I was wondering if it is necessary to "start" your onion seeds indoors or if direct sow was an option? If not, is it too late to start the seeds indoors this year? I live in Utah so our "last frost" isn't until mid May. This is my first year doing onions."
Rebbi on Sunday 11 March 2012
"Mike, onion seeds that are not up in 2 weeks are not going to germinate. Pitch them and start over if your frost date is not until May, or work with purchased sets and seedlings this year...Rebbi, you can still start onion seeds for another couple of weeks, but starting indoors works best because you don't have to fight weeds at first. Stick with long-day varieties, which won't mature until late summer in your climate. "
Barbara Pleasant on Monday 12 March 2012
"Here in the West midlanmds we are plagued with onion Leaf minor on both onions and leeks- this is a pest which appears to be steadily spreading across England. I was thinking of trying to control them using a neem oil spray- has any body tried this? Many thanks, Joyce."
Joyce on Tuesday 13 March 2012
"Thanks for bringing the allium leaf miner to my attention, Joyce. It's a recent invader, first appearing in the UK in 2003 after wreaking havoc in Poland, Germany, other places for some time. The best control according to the RHS is to use fleece (row cover) from late February through April, when the adult flies are seeking their favorite host plants - leeks, chives and garlic. The second frequently-recommended control is to delay planting until May, after the spring leaf miner season has ended. In the US, neem is allowed to control other leaf miner species on organically grown onions, but I can find no information suggesting it would work on this pest. Leaf miners in general are difficult to treat with pesticides because they feed inside leaves. Commercial growers use systemic pesticides (another reason to grow your own or buy organic. Good luck! This link gives more details: http://apps.rhs.org.uk/advicesearch/Profile.aspx?pid=643"
Barbara Pleasant on Tuesday 13 March 2012
"Thankyou Barbara. I will cover the onions with enviromesh- but find it difficult to ensure that I leave no gaps for the tiny flies to get at my onions!I will try planting sets in May in the hope that I miss their invasion. Going home to give my seedling onions a haircut- I was wondering why they were falling over!Best wishes, Joyce."
Joyce Langan on Tuesday 13 March 2012
"Love this. I am starting onions from seeds for the first time this year and was so lost about what to do. This will be a big help. Thanks so much."
Anita on Wednesday 14 March 2012
"I've tried for a couple years to grow Japanese long onions where the white is about 30cm. long and is supposed to be mounded with soil around them, similar to leeks. I've had virtually no success. Can I start and trim them the same as you've described?"
Denese on Friday 16 March 2012
"What about chives? I started my chives the same time as my onions. All of my onions have started sprouting and I gave them their first trimming today (thanks to your article). I only have two small sprouts to my chives its been almost two weeks should I toss them and start over? My husband is the one who sowed them so I don't know how deep he went, from what I have read they only need to be surface sown. Please Help..."
Alecia on Friday 16 March 2012
"Alecia, chives are enthusiastic growers once they are established, but that often takes a year. Keep your two tiny sprouts, but also ask around about local nurseries that sell herbs. With chives, it's easier and much, much faster to start with a purchased clump. Chives multiply primarily by division, secondarily by seeds. "
Barbara Pleasant on Friday 16 March 2012
"My 9onion sets are now up to 5", can I cut them back to 2"?"
Julie Hungerford on Sunday 18 March 2012
"Julie, cut them back only to 3-4 inches. As it is, onions have very little leaf area for photosynthesis, so you want them to hold as much green as possible. Good luck!"
Barbara Pleasant on Sunday 18 March 2012
"Here in the deep south we take the root end of green onions and plant them around the perimeter of the garden. They seem to grow like weeds. When they get to full, we just dig some of them up and cook with them. I'm not sure why people plant them around the perimeter though, someone told me they're supposed to help ward of pests. Is this true?"
Darlene on Tuesday 27 March 2012
"Onions may deter grazing pests like deer and rabbits, which would be a good reason to grow them around the outside edge of the garden. "
Barbara Pleasant on Wednesday 28 March 2012
"Here in Ohio we start them in late December and start hardening them off in early March in a cold frame. Ours get a lot of time in freezing temps (both in the cold frames and after they are transplanted) and do just fine with very little bolting (we do around 15K and maybe 10 will try to bolt)"
Boulder belt on Thursday 26 April 2012
"A good estimate, assuming reasonable soil quality, would be a handful of good compost beneath each onion plant. "
Barbara Pleasant on Tuesday 29 May 2012
"my onions have grown very tall this year and have a small bulb on the top of many of the stalks.Is this normal or should they be 'deadheaded'?"
Keith on Saturday 21 July 2012
"When bulbils form at the top, the plant has flowered while you were not looking. Or, you may be looking at an unopened flower bud. Onion flowers are edible, but in general they are removed in hopes of sending more energy to the bulb."
Barbara Pleasant on Sunday 22 July 2012
"I want to grow onions from seed for my own consumption. I use about 3-4 onions a week. Would staggering seed planting (ie. 10 seeds planted every two weeks) work? What is the best way to store your fully grown onions? And thank you for the info you've presented - a big help!! "
Trish Morrison on Monday 20 August 2012
"oh, and I forgot, how will the onions bolt? How do I collect seed for the following year? Again, thank you!"
Trish Morrison on Monday 20 August 2012
"Planting different varieties can help, but not staggering planting dates, because onions bulb in response to day length. Onion self sufficiency is not easy, and I think the quest is best pursued using high quality purchased seeds. If seed-saving is in your long-term future, work with open pollinated varieties. This time of year, you can start seeds of "Japanese" onions, which winter over and bulb in late spring. They work great in the UK, and to Zone 5 in the US. "
Barbara Pleasant on Monday 20 August 2012
"I'm a novice gardneer, have just caught the passion of growing your own food recently. Apart from seeming to feed half of the snails in the country, I'm not doing too badly except for my onions. They started off great as seedlings, I planted them out in big potato sacks but they have done nothing (a bit like my teenage son). They haven't grown, they haven't died, they just sit there as if to say, 'you're doing this ALL wrong'. Seedlings I gave to my friend are thriving. I have given them plant food, etc. They are about 5 inches tall. Outside so they are getting the sunshine. I haven't trimmed them, could that be an answer?"
Brigid on Thursday 23 August 2012
"It sounds like there is something about the site or soil the onions find objectionable. Are you growing them in potato sacks filled with soil, while your friend has them in the ground? That may be the crucial difference."
Barbara Pleasant on Thursday 23 August 2012
"No, the funny thing is, he potted them out in the same good quality compost I did but in less shallow pots. I've been giving them feed every week, he hasn't. Have just read back on some older posts and think they may not be getting enough sun light as the potato bags are quite tall. Should I plant them out in the garden now? See how they go? "
Brigid on Thursday 23 August 2012
"When a gardener's patience wears thin, a rescue replanting is in order. Good luck!"
Barbara Pleasant on Thursday 23 August 2012
"hello i used your guid. thanks"
abraham on Wednesday 3 October 2012
"i have my onions covered with underheat ant present onions are starting to pop through .when should i take my cover off and put lights on"
bryan on Monday 14 January 2013
"Today! Your little seedlings no longer need warm, moist conditions, but they must have as much light as you can muster. "
Barbara Pleasant on Tuesday 15 January 2013
"Thank you for all of the useful information. It's been a big help. My onions have germinated and seem to be doing well. I have them under lights 18 hours, but see that you recommend 12 so will cut back. I had to run a heater to maintain the temps for germination, but now that I'm using lights only the temp ranges from between 64 degrees when the lights are off and 74 when they're on. Are these temperatures ok? Also, how moist do they need to be and what about fertilizer at this stage?"
Vicci on Tuesday 12 February 2013
"Vicci, you can stay at 18 hours and it will be okay for now. Might be a good idea to gradually cut back when you get ready to start exposing them to natural sun. Your temps are okay, too. Onions need a bit more moisture than other seedlings but will rot if kept too wet. I like to water them well every other day, and let them dry out a bit in between. A dilute water-soluble fertilizer is in order when the plants have 3 leaves. Good luck!"
Barbara Pleasant on Wednesday 13 February 2013
"Wow! Thank you for all of your great advice! This is my first growing from seed attempt, and lacking all knowledge, I pulled (ever so gently) the seed hull/husk off of the tips of my onions seedling when they started to weigh them down. Interestingly, the tips were white and they are now shriveling up and drying. Should I snip it off? They now all have two leaves, are growing upright and otherwise appear happy. Thanks again for this great article!! It seems most of the advice on other sites is on growing sets only (helpful for when I get to that stage at least). "
Kelly on Wednesday 20 February 2013
"Kelly, that first leaf with the shriveled end can be trimmed, but don't snip it off completely until it turns tan. This happens about when the third true leaf appears. Your seedlings will not become sets, but will proceed straight to bulbing in midsummer. "
Barbara Pleasant on Wednesday 20 February 2013
"Howdy from Calgary. Great advice which I'll need as we are fighting high altitude, heavily alkaline soil, and huge day time/night time temperature differentials and very drying winds here. Just learned that to get good size bulbs I have to start onions from seed so thanks for your info."
Val on Friday 22 February 2013
"Hi there just reading your great advice Im in south west Ireland and am making my very first attempt at growin onions from seeds mine will go into raised beds!I didnt realise you could start from seeds as Ive always seen sets!hope I can ,manage,your advice is great!"
Julie Grey on Thursday 28 February 2013
"Hello Barbara When my onion seed have three leaves and I need to pot them on into larger pots, will it matter if the roots of the young onions are exposed and disturbed whilst transplanting, or do I have to ensure the soil around the seedlings is intact to avoid disturbance. Many thanks Ade"
Adrian Blake on Thursday 28 February 2013
"Hi Barbara. I live in the Vancouver / Seattle area and have been putting off starting my seedlings until now. Will I just end up with small onions because I'm starting so late?"
Warren Williamson on Thursday 7 March 2013
"Warren, because you live so far north, long-day onions will not bulb until late summer, so they are a good bet if you start seeds right away. "
Barbara Pleasant on Thursday 7 March 2013
"Thank you Barbara."
Warren Williamson on Thursday 7 March 2013
"Hi my seeds are comming along nicely on my window sill it is really unseasonably cold here for March at least 10 degrees colder than usual Ive a feeling it could be the middle of April before we even reach cold frame stage,will it matter that final planting could be much later than expected?"
Julie Grey on Monday 25 March 2013
"Julie, as long as you live in the north where long-day onions are grown, having planting run a little late won't hurt. See if you can set up some supplemental light to keep your seedlings growing strong."
Barbara Pleasant on Monday 25 March 2013
"Hi Barbara. My onion plants don't seem to be doing much of anything. I transplanted them to 4 1/4 inch deep containers on April 3rd (from 2 litre juice and ice cream containers). Since then they've remained as thin as when they were seedlings, they've barely got a third leaf going (most of them seem to be down to two), and they grow maybe 1/4 inch a day. Could it be the pH of the soil? I used equal parts peat, perlite, topsoil, and chicken compost. Are they even worth saving? Thanks again for your post."
Warren Williamson on Sunday 14 April 2013
"Also I forgot to mention, I have 2 6500k fluorescents an inch or two above them about 15 hours a day."
Warren Williamson on Sunday 14 April 2013
"Onions accept artificial light, but what they really want is sun. Can you rig up a protected space outdoors for them? Soon after the seedlings start getting natural light you should see new upright leaves. At six weeks, onion seedlings are still small."
Barbara Pleasant on Sunday 14 April 2013
"Thank you, that gives me hope. We are getting our first sunny day in a little while so will se what I can do."
Warren Williamson on Sunday 14 April 2013
"I live in Nashville, TN. Our last frost date is, I think, April 15. I want to plant onions from seed directly in the ground. Your thoughts?"
Loren on Wednesday 17 April 2013
"Many people direct-seed scallions (green onions) because they germinate fast and grow quickly. Bulb onions, unfortunately, grow very slowly for the first couple of months, and are thus very easily overtaken by weeds. In Nashville you should be putting well grown seedlings in the ground now. If I were you, I would buy seedlings this year, and get an early start next year by starting seeds indoors in January or February. "
Barbara Pleasant on Thursday 18 April 2013
"hi my onion seedlings have two leaves at the moment, you mention repotting when they have 3 leaves into 4inch tubes. i have a 80cm trough planter, how far apart do my onions need to be? i also have 3 different size potatoe sacks if they will be better than the trough. thanks"
Laura McDowell on Wednesday 24 April 2013
"Laura, this late in spring you can transplant little onion seedlings into any type of container at least 8 cm deep. Or, as long as you keep them weeded, you can harden off the seedlings and set them out in the garden. Onions run on sun, and the sooner they get abundant sunlight, the better. Good luck!"
Barbara Pleasant on Wednesday 24 April 2013
"I've grown my onions (Red Brunswick and Spanish White) in deep root trainers so I didn't pot them on. They were started indoors and are now in a polytunnel. Thanks for the tip on trimming as they are falling over. I wanted to plant out this weekend but we are still due our last frosts in May. Is this OK or should I cover them with a polythene cloche/hoops?"
Vanessa Burholt on Saturday 27 April 2013
"I've grown my onions (Red Brunswick and Spanish White) in deep root trainers so I didn't pot them on. They were started indoors and are now in a polytunnel. Thanks for the tip on trimming as they are falling over. I wanted to plant out this weekend but we are still due our last frosts in May. Is this OK or should I cover them with a polythene cloche/hoops?"
Vanessa Burholt on Saturday 27 April 2013
"Three to four weeks before the last spring frost is usually a good time to set out onion seedings. The main reason for covering them is to reduce stress for a couple of weeks. When the plants perk up and show new growth, they won't need protection from wind and cold anymore."
Barbara Pleasant on Sunday 28 April 2013
"Thanks for all your help Barbara. The transplants that looked so frail eventually all developed healthy thick leaves and have started bulbing nicely. Unfortunately a number have succumb to onion maggots. I have no idea where these came from since I started with seeds, used a sterile soil, and don't know of any onion gardeners around here. Have you encountered this problem?"
Warren Williamson on Tuesday 2 July 2013
"I occasionally have a bulb onion plant fail due to onion maggots, which are the larvae of a small fly. If they appear to be established in your area, you could cover your bed with a rowcover tunnel until the plants start growing vigorously. My worst problems have been with perennial onions. If I do not lift and move my multipliers in the fall, they become magnets for onion root maggots. "
Barbara Pleasant on Tuesday 2 July 2013
"I have planted my onion sets quite deeply in the soil- they are totally submerged and invisible! The leaves are growing really well but do I need to uncover the onion itself or will they swell without sunlight? Do garlic bulbs and elephant garlic need to have their bulbs on the surface- again mine are planted deeply. Any information would be appreciated! Thankyou, "
Joyce Langan on Tuesday 2 July 2013
"Joyce, the garlic should be deep, with the tops of the bulbs covered with 3 inches or more of soil. The onions are different, in that they will push up toward the surface as they swell, often ending up sitting almost on top of the soil. Some gardeners do loosen the soil around onions as they bulb, but it is really not necessary. "
Barbara Pleasant on Tuesday 2 July 2013
"Thank you for providing such useful tips..."
Malik deenar on Monday 2 September 2013
"I'd like to plant garlic for next year. I'm in southeastern Wisconsin - zone 4 or 5. Any information on when to plant and/or good types to plant in my area? Never done garlic before but my onions are wonderful! "
Vicci Hubbard on Monday 2 September 2013
"Vicci, there are a couple of blogs on growing garlic here. In your area, you can plant in late September, using mostly hardneck varieties from Northern Europe. These are not the same as supermarket garlic! You will need to look for seed garlic at local farmers markets or order by mail. "
Barbara Pleasant on Tuesday 3 September 2013
"Vicki, I'm growing autumn onions from seed, sown in a coldframe, and a few in the greenhouse. They're doing well, but only a few are starting to show their third leaf. I'm worried that the weather is getting colder, our average first frost is the middle of October. Is it OK to transplant as soon as the third leaf is up? Do I need to cover? By the way, you didn't mention how many hundreds of seeds you get in a packet! I sowed white and red, and I must have about 3-400 seedlings!"
Helen on Thursday 26 September 2013
"Helen, with overwintering onions you will need to provide a row cover tunnel if you are north of Zone 7. In Zone 5 a layer of plastic is added, over the row cover, for the months of Dec-Jan. The little plants start growing vigorously first thing in spring."
Barbara Pleasant on Thursday 26 September 2013
"great info will now grow my own onions and garlic thank you "
mr fawcett ( dave) on Thursday 26 September 2013
"Thank you for all your help this past year Barbara. I wasn't able to transplant my onions until late in the season so they weren't very large but still I harvested more than enough fresh sweet onions for my needs. I have my Walla Wallas in the ground for next year which are doing well and should be a good crop."
Warren Williamson on Thursday 26 September 2013
"I too would like to start fall onions from seed. Here in this part of the Atlanta area we are in zone 7B, not far from zone 8A. Typically first frost is in mid-November. How much protection do scallions need here? I can plant in heavy red clay soil or raised beds. Are row covers helpful to onions through the winters here?"
Mark O. on Saturday 28 September 2013
"Mark, you can grow scallions with no winter protection. Planted now, even rooted ones from the store may multiply before winter. The clay soil may help the scallions to stand a little stiffer. I would use the better-drained raised beds for short-day bulb onions."
Barbara Pleasant on Saturday 28 September 2013
"Hi I am interested in growing onions in Uganda. I have come across a type 'Jambar F1' and I am wondering if any one knows its other name by which it is known in Europe. Thanks"
nassib on Wednesday 13 November 2013
"Nassib, that variety is widely promoted by Monsanto Africa. Many gardeners in other parts of the world choose not to support Monsanto because of GMO and economic issues. Should you wish to look elsewhere, there are many other excellent short-day hybrid varieties from which to choose."
Barbara Pleasant on Friday 15 November 2013
"I am intrested to grow onion in my place. I wanted to know what is the right altitude to grow and how to rease onion nursery?"
Roshan kafley,Salami Tsirang Bhutan. on Tuesday 26 November 2013
"I claim no expertise in Bhutan onions, but you would need short-day varieties to grow through winter, similar to those grown in Texas and Georgia in the US. The onions would be harvested before the rainy season begins. In the US Grano or Granex hybrids are widely planted, but where cold winter weather requires more bolt resistance, "Japanese" onions like Bridger and Desert Sunrise are preferred. With either type you would start seeds in September or October for harvest in late spring. "
Barbara Pleasant on Tuesday 26 November 2013
"Hi Barbara. I am an Englishman living in Ukraine. I notice you have followers from around the world. The wealth of information given by you has made me determined to grow onions from seed next year. Keep up the good work"
Robin A J Attryde on Monday 23 December 2013
"Hello Barbara, I've had very little success in the 3 yrs I've tried growing from seed but at least now I can see why thanks to your far more detailed advice - thanks ! Having said that I'm still snookered as I only have my allotment greenhouse to sow in (Birmingham, UK). I want to grow a lot of onions and so I do not have enough space at home. Am I flogging a dead horse until I can get the seedlings under artificial light? If not when should I sow? Thanks."
Togalosh on Saturday 4 January 2014
"Hi Barbara, Thanks for the fantastic info you made available here on starting onion from seed. I'm in USDA Hardiness Zone 6A -10F to -5F the average last frost occurs between April 11~20 2014. I've followed your instruction and my onion seeds came up - the tallest currently being about 3". Many still have the seed hulls attached. Some of the smaller ones are still stuck in the "hoop phase" and I will snip them loose with scissors in next few days. I have a couple of questions if you don't mind answering them for me. 1) When should I start spraying diluted liquid fertilizer and what N-P-K ratio should I use? 2) When should I transplant the seedlings from the flats into deeper containers - I plan on using paper cups. 3) I'm in the process of building a cold frame to free up seedling table space and also harden off the onion seedlings. When would you recommend setting the transplants into the coldframe? 4) Finally my understanding is I should transplant into the garden 4 week before the last frost. So around the middle to the end of March - is this correct? Growing Intermediate Day Ruby Ring (Red), Candy (Yellow) and Sierra Blanca (White) Thanks again for the great information."
Jeff Mills on Tuesday 7 January 2014
"I would not start feeding the onions until they show their third leaf, which is also the best time to transplant them to deeper containers. Until then, you depend on intense light to support new growth. As you will see when you transplant them, the seedlings have 2-3 main roots with minimal branching. Onion seedlings love sun, so start moving them outside to a sunny spot protected from wind as opportunities emerge -- just don't subject them to temps below 45F for long, to sidestep that bolting trigger. Your planting dates look good to me. "
Barbara Pleasant on Sunday 19 January 2014
"Hello Barara, I grew onions from seed for the first time last year....WHAT A BUZZ!! Just eating the last of them from store and the beauty of each one still amazes me (note to self: must get a life!). My question is, is there any reason why I shouldn't start the seeds individually in root trainers and continue growing them on in there until planting out? Also, I can't imagine what your lights look like....do I need to buy these or can I rig something up myself. Would a chick heat lamp work maybe? Thanks "
Helen, Kent (England) on Monday 3 February 2014
"My question also can you sow seed in individual deep cells instead of transplanting after starting into flats. After transplanting over 500 seedlings this past weeked into paper cups from flats, i am looking to bypass the transplanting step next year for sure."
jeff mills on Monday 3 February 2014
"If the cells you are using are small, less than 3 inches deep, you can so individual onion seeds in them provided you use seed starting mix. Using containers too large invites problems with root rot and damping off. The good thing about transplanting young onion seedlings is that you should only have to do it once. I use a two-bulb florescent fixtures with new bulbs this year. They are bright!"
Barbara Pleasant on Friday 7 February 2014
"When the onion seedlings are ready to transplant outside, what is the procedure for getting them from the pot to the garden? Do you remove them completely from the soil or do you keep as much soil as possible around each seedling?"
Dennison on Friday 21 February 2014
"Barbara, thank you for all the great advise. i moved my onion seedlings out into the cold frame yesterday. i was growing weary of having to trim them back every other day. they are doing well about the size of a pencil now and coming into their 5th true leaf. i'm hopeful they will do well when I transplant them into the garden in 3 to 4 weeks."
Jeff Mills on Saturday 22 February 2014
"Hi Barbara- Thanks for all the great advice, keep up the good work! I am attempting to grow onions from seed for the first time this year- I sewed them into inside seed trays in about late February or March and they have just been growing steadily since April in an outdoor greenhouse. During this time I also moved the 'strongest' plants to small plastic pots and have only recently (in the last week or so) done a 'test run' of putting several into the ground. I only did a few due to the fear of them all dying if I put them out Into the veg patch. I would say they have about 3 leaves each and are probably about 6-7" tall, but are still very thin (I'd say about the thickness of a feather quill). Having read the information on here do I need to trim them to promote bulb growth? I say this mainly because when I transplanted them, there was barely a bulb on the end- I wasn't sure if they needed to have a little bulb before planting out?- Thanks!"
Mary, (UK) on Wednesday 11 June 2014
"Mary, at this point the best thing you can do is to put your onions in the ground where they can stretch their roots. They need to make quite a bit more green growth before they will grow big bulbs. The bulbing process comes last, just before the onion goes into dormancy, so you want to see vigorous leaf growth and little or no bulb until mid to late summer. Good luck!"
Barbara Pleasant on Wednesday 11 June 2014
"Hi - I was enticed by Burpee to order onion seeds and potato tubers, and it is June in zone 7, Should I wait until next year or start now for fall harvest? Thank you!"
Theresa keefe on Friday 13 June 2014
"Theresa, I would go ahead and plant the potatoes, because they will shrivel and rot if you don't. Keep the onion seeds in the fridge or freezer until late winter, and start them then. Good luck!"
Barbara Pleasant on Tuesday 17 June 2014
"Greetings from Tasmania, Australia, Am growing both brown onions (Creamgold) and red (Early Californian Red) and am following your instructions as closely as possible, My previous experience with growing onions is not to transplant too deeply, basically, just covering the roots. When I come to transplant after the third leaf, and ultimately into the ground, does this philosophy still apply? It seems to me that the plants may well fall over, especially in the first transplant stage. Your advice would be appreciated."
Wilfred Knight on Monday 21 July 2014
"Wilfred, I favor letting the seedlings get bigger before setting them out. When possible, you can grow them for 8 weeks or so, until they are almost the thickness of a pencil, and set them out then. Tiny seedlings would have a hard time competing successfully with weeds. "
Barbara Pleasant on Monday 21 July 2014
"Thanks for the quick response Barbara, I may have inadvertently misled you. My query is this, When the third leaf develops is the recommended time to transplant. Then how deep do I need to transplant the seedlings? Then, when ultimately I plant outside, which may be several weeks later, again, how deep should I plant? "
Wilfred Knight on Monday 21 July 2014
"I find that having the onions planted one-half inch deep, so that the base of the white shank is covered with soil, helps the plants stay upright better than shallow planting. In the garden onions use their contractile roots to settle at that level, so I think that's what they want."
Barbara Pleasant on Tuesday 22 July 2014
"Barbara, great information. I'm planning to overwinter onions from seed this year and I have a question about trimming the tops once the seedlings are transplanted into the ground. I kept the seedling trimmed at about 3.5" when they were in the nursery containers. I transplanted the seedlings into the ground several weeks ago. Do I continue to trim the tops or should I let them go wild? I've read some sources that say continue to trim the tops until winter comes to promote root growth and then let them go gangbusters in the spring. Other sources suggest to not trim the tops once the seedlings are in the ground because the leaves are their energy factory. I would prefer to trim the tops because it also helps from having them fall over, but I don't want to do anything to negatively impact their growth potential. What do you suggest?"
PJ on Saturday 13 September 2014
" I had no idea, but intend to cultvate onion during this season in fields."
A. Ikhlaas on Thursday 12 February 2015
"how many onions do you put in a tall 4" pot when transplanting? Or in a plastic milk carton with the top cut off?? I'm new to onions and a bit lost!"
Alyssa on Sunday 22 March 2015
"You can keep onion seedlings in random containers for quite a while, even if they are crowded. I would not hesitate to hold four to six in a 4-inch pot -- just be sure they get as much light as possible. When you transplant them to the garden, the seedlings will pull apart easily. "
Barbara Pleasant on Monday 23 March 2015
"This year I sowed a few seeds in deep cells. Trimmed the tops back a few times. Once they got their 3rd or 4th leaf I moved to the cold frame and they are doing great. I will be setting them out in the garden in the next few weeks I'm just waiting for the garden soil to dry out some first. Right now the leafs are long but I'm not going to trim them back until I set them out in the garden."
jeff mills on Tuesday 24 March 2015
"Greetings, I live in central Maine and I planted onion sets in the spring. I harvested about a month ago. Today, I prepared the bed for next spring. I noticed many very small onions. These were even smaller than the sets that I planted. I would guess that the onions propagated. Now I have onion sets. How can I store these for next year? Can I plant them now ( Nov ) for next fall harvesting? How can I do this again? Thanks,"
Angelina Levino on Saturday 7 November 2015
"I think you may have little bulbils, which can be replanted but are probably dormant right now. I would keep them in a cool place until early spring, and plant them then. They may or may not produce a good crop, though, so plan to repeat your success with purchased sets again next spring. "
Barbara Pleasant on Monday 9 November 2015
"I plant the onion, growing very well, but few weeks later the greens are broken and not growing further. I take that onion bulb it spoil inside the soil. I pour water in daily basis is it correct or not"
SureshBabu Janarthanam on Monday 28 December 2015
"I think it is likely that the plants developed a root rot disease, which also killed the little bulbs. Too much water often contributes to this problem, because very moist conditions favor the growth of fungi in soil and on roots. "
Barbara Pleasant on Tuesday 29 December 2015
"Hi Barb - I've been following this article for going on three growing seasons. Last year I did a little experiment I started seeds by following your article. When it came time to transplant into the gardeb I bought bulbs from the local farm store also. When setting out I set a row of transplants raised from seed and a row of bulbs or sets as they call them. I cared for the traansplant and set rows exactly the same - Guess which gave me the biggest onions? Well the transplants started from seed of course :) I do have a question for you though I have chickens which I deep bed (don't change bedding but keep adding more bedding and a layer of barn lime) during the winter what's your thoughts of lining the bottom of the trench with this come spring. It will be good and composted by then. Chicken manure is high in nitrogen. Thanks"
Jeff Mills on Monday 11 January 2016
"Hello, 1 thing i'm confused about is this...i live in England and sowed a packet of Bedfordshire Champion seeds a couple of weeks ago. Most of them are growing (about 200 seedlings) and will soon need transplanting. So firstly, do i keep them in containers for all of the first year and plant them outside next spring? Or do i plant them outside this year? If planting outside, are they ok to be left over winter until harvest next year with no protection? Sorry for so many questions but i'm a novice at onions. I do have about 50 Stuttgarter sets growing now which should be ready to plant out in a couple of weeks, these'll be my 1st attempt at onions and the seedlings should hopefully give a good harvest next year if i do it right. Thanks for this informative website. "
Jason on Wednesday 23 March 2016
"Jason, both of your varieties will bulb this year if they have good conditions. The Bedfordshire should get plenty of sun but not be subject to chilling. As light intensity increases -- plus exposure to gentle wind -- you will see stiff new growth. At that point, think about transplanting them to the garden. Good luck! "
Barbara Pleasant on Wednesday 23 March 2016
"Thanks Barbara for answering. Wow i thought onions were a 2 year grow, like the way sets are a year old. If the Bedfordshires bulb this year i'll have about 200+ onions ! I'm confused as to why sets are last years plants but seeds planted around the same time can grow as big as the sets, if i understand that correctly. Oh well, i hear they store well. I do use lots in Indian cooking but if i have too many i can just give them away to neighbours."
Jason on Wednesday 23 March 2016
"Hello! Thank you for this article it has been very helpful! I've recently tried my hand at starting onion seeds (and other veggies) for the first time indoors. I didn't find this article until after my onions were started. There are some things I didn't do, like provide heat and artificial light. That being said, I planted on 3/5 and my first one popped up on 3/11, all were looking great. They are abut 3.5 weeks old now and all have 2 leaves. I have trimmed them back to 3 inches because they started to tip. Now, the first leaf is browning at the tip and yellowing a bit down its body and looking like it's going to die. Is this ok? Is there something else I should be doing? I am in zone 4b and have just had them in a big south facing picture window where they get full sun as long as it shines. And I planted Spanish yellow onion seeds. Thank you! "
Erica on Wednesday 6 April 2016
"Erica, those first leaves are wimpy seedling leaves that die off naturally, usually as a new leaf is emerging. The more light your seedlings get, the stronger they will grow. Be patient for a while yet, and they will thicken up in a few weeks."
Barbara Pleasant on Wednesday 6 April 2016
"Awesome! Thank you so much Barbara! I'll try to be patient! :)"
Erica on Wednesday 6 April 2016
"Hi Barbara, This is a fantastic site, so much info!! I am writing from Kingston Jamaica West Indies,we don't have to contend with snow and frost. Jamaica is a tropical country with temperatures ranging 90-100 degrees ALL YEAR LONG!!. Do I still have to plant my seeds in a covered nursery or plant directly in the soil? I am a rookie. Just bought seeds for the first time 2 days ago to sow them this morning. Regards, Donna"
Donna on Saturday 23 April 2016
"Donna, the best onions for your climate are short-day varieties that are planted in the fall, so that they grow during the slightly shorter, milder days of winter. This time of year you can start scallions from seed, and visit local markets in search of "tropical shallots" -- bunching onions that are adapted to hot climates and grow as perennials. Good luck!"
Barbara Pleasant on Monday 25 April 2016
"My seed onions are about 2 inches tall now. Should they be transplanted outdoors now or left to get a little bigger in the greenhouse?"
Simon Newman on Wednesday 4 May 2016
"Very small onion seedlings are easily swamped in the garden, so you might give your plants more time before setting them out. Good luck!"
Barbara Pleasant on Thursday 12 May 2016
"Hi Barbara, Can I just say - you're incredible for answering all of these comments, 4 years on! Thanks so much for your in-depth, step-by-step article, and for all of your personalized advice."
Cait on Wednesday 22 February 2017

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