Growing Great Onions in a Small Garden

Onions are a wonderful staple crop in our household, and we like to store some of our onion bulbs for 6-8 months over the winter.  We eat a lot of them, and we usually plant over 200 onions each year. If you follow a few simple steps, you can harvest a large amount of high-quality onions from a small garden.

Onions Need High Quality Soil

Bulb onions are a bit pickier about the quality of the soil than some other crops. They grow best in loose, friable, fertile soil with a healthy amount of organic matter.  If your soil is still poor, you might want to wait a year or two to improve your soil before you start growing bulb onions.

compost-enriched soil

Onions prefer loose, friable, and fertile soil. If your soil is poor, you might want to wait a year or two to improve it before growing bulb onions.

Choose the Right Variety for Your Location

It’s important to select the right variety of onions for your climate and latitude.  Short-day varieties, such as Vidalia, are best grown in the South below 35 degrees latitude, which runs roughly along the northern borders of Mississippi, Georgia, and Alabama. Many sweet onions are short-day types, and they aren’t usually good keepers. These plants start bulbing when the day length reaches 10-12 hours in early spring, so it’s best to plant these varieties in the fall.

Long-day varieties are best grown in the northern states. The best storage varieties are often long-day types.  These plants will bulb up during the long 14-16 hour summer days, and produce best north of the 38 degree latitude – which is roughly from the northern half of Virginia west through southern Utah.

Some gardeners, including myself, are located between these two areas. I’m at latitude 37 degrees.  It’s too cold here to overwinter onions outdoors, so I have to look for long-day varieties that will grow well in the upper south.  I’ve had good luck with Copra and Pontiac – both excellent storage varieties. Most good storage varieties have strong, pungent bulbs.

Onions growing in garden bed

Choose the right variety of onions for your location and needs. These are Copra, an excellent storage onion that grows well in many areas.

The better seed catalogs will tell you where each variety will grow well. There are also a few day-neutral varieties available, such as Candy or Stockton Red, which can be grown anywhere.

You Can Plant Onions from Sets or Transplants

Sets are tiny 1-year-old onion bulbs. This is a very easy way to start your onions, especially if they are a minor crop for you and you don’t plan to store them long.  Just plant these sets with the pointy side up so that they are just below the surface of the soil. Avoid planting the largest sets, as they are more likely to bolt (go to flower instead of producing a bulb).

Onion transplants sold commercially are bare-root plants sold in bundles of about 60. They may look half-dead, but they are tough plants and recover quickly after planting.

The Advantages of Planting Onion Seed

However, if onions are a major crop for you – like they are for my sister and myself – you might want to consider starting your onions from seed instead.

You have a wider choice of onion varieties when you use seed, and you can choose between yellow, white, or red varieties. Onion seed is much cheaper than a similar amount of onion sets or plants. In addition, storage onions grown from seed usually keep much longer than the same variety grown from sets.

When and How to Start Your Onion Seeds

Onions are the earliest vegetable seeds that I start for my garden.  For long-day varieties, you need to plant them 8-10 weeks before your last spring frost. As my average spring frost date is around May 10th, I try to plant my onion seeds by March 1st.

They can be planted either indoors under lights, or outside in a cold frame or greenhouse. I’ve had great luck planting mine inside my unheated hoop house, though unusually cold spring weather may slow their growth. If you are in the north, I would recommend starting your seeds indoors under lights instead – though it would be worth experimenting planting some in cold frames, too.

Onions are one of the few vegetables where I will start multiple plants together in one container, instead of starting individual plants in separate pots. They readily tolerate being transplanted as bare-root plants, unlike most seedlings, and it’s easy to separate the onion seedling roots.

Given good growing conditions in the garden, the largest and most vigorous seedlings will produce the largest bulbs. So give your young plants deep soil and enough elbow room to grow. I try to allow each seedling at least 1-2 square inches of space in the seedling flat or containers.

You don’t need to be super exact in planting the seeds. If you’re using 3” square containers, just sprinkle 10-12 seeds fairly evenly over the surface of the soil, and then cover them with a thin layer of more soil.  Your plants will grow OK in a 3.5” deep pot, but they will grow even better in a deeper 5” pot.

Image of onion seedlings ready to transplant

These onion seedlings are ready to transplant. They were grown in large 8″ deep trays in an unheated hoop house.

Since my sister and I grow such a large number of onions, we plant our seeds in our large 8” deep growing trays in our hoop house. When they’re ready to transplant, we just dig them out of the container, shake off the dirt, and transplant them bare root into our garden beds.

Transplanting the Seedlings into Your Garden

You can usually transplant the seedlings into your garden around 4 weeks before your last spring frost date.  It's best to harden off the seedlings before planting them, to get them used to direct sunlight and wind. Another option is to plant them in the garden bed, and then protect them with row cover, gradually exposing them to more sunlight over a week or so.

If you want the highest yields per square foot and don’t mind harvesting smaller bulbs, you can space your plants about 3-4” apart.  I prefer to use large bulbs in my kitchen, so I plant mine about 5” apart. Plant your seedlings at about the same depth they were growing in their containers. If you have more transplants than you need, plant your largest ones and dispose of the weaklings.

Planting onion seedlings in a garden bed at 5" spacing

We space our onions seedlings 5″ apart in rows 5″ apart. We mark the planting spacing on a stick.

Onions don’t tolerate competition from other plants that are growing too close to them.  I once planted some onions one foot away from my row of snap peas, and the onions became very stunted. The next row of onions, just 6” further away, grew to their full size. Competition can cut their yields in half, so keep your onions well-weeded and keep the soil evenly moist – especially when they are first planted, and when the bulbs are starting to size up. We also keep our onions lightly mulched, to reduce weeds and to keep the soil moister.

young onion plants growing in a garden bed

Young onion plants that are a few weeks old. The mulch helps keep the soil moist and reduces weeds.

I also never plant my onions after anything in the cabbage family – such as broccoli, turnips, kale, etc. Your onion yield can be reduced up to 40% in this situation. I’ve noticed this effect in my own garden, and some university studies have found this to be true, too. This may not hold true for all soils and locations, though.  Just be aware of this possible issue.

Onion bulbs grow mostly above the ground.  Don't try to cover the bulbs with soil! It's not necessary, and it can hurt the plants.

How to Harvest Your Onions

Onions are ready to harvest when most of the leaves start falling over just above the bulb. In cooler climates, you can wait until most of the bulbs have fallen over, then pull them up and lay them on top of the soil and let them cure in the sun for a few days before bringing them under cover to dry further. It may take 2-3 weeks in a warm, dry and well-ventilated environment to fully cure the bulbs.

mature onions that are ready to harvest

These onions are ready to harvest, as their leaves have fallen over just above the bulbs.

You’ll know they’re properly cured when the leaves and roots are fully dried and the bulb is covered with a couple of crisp, dried papery layers. You can gently brush off any dirt, and cut off the leaves and roots.  Some people choose to braid the dried onion leaves together, and hang the bundled onions in storage, which can be very attractive. Others hang their onions in mesh bags.

Onions that are fully cured and ready to be harvested

These onions are fully cured and ready to be stored. This 3/4 bushel of onions was harvested from a small 4′ x 4′ garden bed.

In a hot climate, the sun can damage the onion bulbs if you try to cure them in the open. Instead, you should harvest the bulbs when only half the crop has fallen over, and bring all of them into a shady but well-ventilated location to dry out of the sunlight.

Curing onions under a shade cloth in hot weather

We did the initial curing of this onion harvest underneath a shade cloth inside a well-ventilated hoop house.

How to Store Your Onions

Onions store best in a cool, dry location. Around 40 degrees, with low humidity and good ventilation works best.  However, I rarely have perfect storage conditions. My onions are kept in a dry area that averages 55-60 degrees. They would keep better in a colder location, but some of my harvest still lasts over 6 months despite the warmer temps.

Expect to lose some of your onions in storage. Rotting onions really stink, and they can damage any wood or cardboard surface they are sitting on. When I cured my onions on the floor of a spare bedroom, I always spread a sheet of plastic under the onions, to protect the floor.

We store our onions in ventilated plastic crates that are easy to clean out. Look over your stored bulbs at least monthly, and remove any that are becoming soft or moldy.

Onions stored in plastic crates

We store our onions in ventilated plastic crates, in an unheated hallway closet.

Summary

Bulb onions are little trickier to grow than some other vegetables, but by choosing the right varieties, getting the seedlings off to a vigorous start, and giving the plants excellent growing conditions in your garden, you can harvest a large amount of high quality onions from a small garden.

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Leave a Reply 26 comments

Deb - February 15, 2015 Reply

Very informative! Lots of “new to me” info. I plant onions every year and am never real happy with results. Now I have some good knowledge to go with and I think I will plant twice as many this year. Thanks !!!

    Debra - February 15, 2015 Reply

    You’re welcome, Deb! Best wishes with your crop this year!

Joe - February 15, 2015 Reply

Great Article. Perfect timing for me since I am trying onions from seeds for the first time. They are 3 inches tall in trays indoors and now I have a better plan on what to do with them. I ll take your advice and put them in a planter with the best soil. Great Pictures as always.
Thanks

Julie - February 15, 2015 Reply

Thanks for this information! It’s very specific and points out what to watch out for. If you are growing onion from seed, approximately how long until its ready to harvest?

    Debra - February 16, 2015 Reply

    Julie, it depends a bit upon which variety you are growing. In my climate, I transplant most of my onions in mid-April, and harvest them by mid-August. Good seed packets/catalogs should give you their days to maturity (I think from the date of transplant for onions).

Karen Smith - February 15, 2015 Reply

Thank you. Very helpful! I had read that onions were a good companion to cruciferous family, so I had onions interplanted in my garden plan with them. I just removed them.

    Debra - February 16, 2015 Reply

    Hi, Karen. I’ve heard that onions are recommended companion plants for cabbages, but in my own garden, my onions grew terrible if planted after a cruciferous crop. Even Eliot Coleman has experienced this. I’ve wondered why, but I’m suspecting maybe because onions grow much better with healthy soil full of mycorrhizal fungi. Cruciferous crops don’t support that type of fungi. So perhaps a garden bed that has grown a full crop of cruciferous vegetables suffers a low population of mycorrhizal fungi for the following crop. Just a thought.

Catherine Lewis - February 16, 2015 Reply

Thank you! Such great information. Onions are from the Lily family and 4 people like me who is trying 2 heal my immune system, this is such an imp crop 2 learn about. Esp in winter soups. Thank you!

    Debra - February 16, 2015 Reply

    You’re welcome! Yes! Onions are wonderfully healthy food.

LAURA - February 16, 2015 Reply

Hi Deb.
Do you call “long day varieties” onion those that need 14-16 hours of sun a day?
I do not remember any seed cover telling me how many hours of light the plant needs? neither have I seen anything that says “long day” or “short day”? so how to tell the difference?

    Debra - February 16, 2015 Reply

    Hi Laura! Yes, long-day varieties need 14-16 hour days to bulb up. The better seed companies will make it clear what type of varieties they are selling or where they are best grown. I suspect that most varieties sold to home gardeners are long-day types, but it’s best to look it up to be sure. Short-day ones are pretty much restricted to the deep south.

Jacqueline Steudler - February 16, 2015 Reply

Hi Debra, thank you for the very detailed information and the great images. It all helps. Do you have any suggestions for our northern climate in Nova Scotia, Canada with lots of humidity during June and July?

    Debra - February 16, 2015 Reply

    Hi Jacqueline! I would check with regional seed companies, such as Johnny’s Selected Seeds or a Canadian company. Do you have a government agency similar to our Cooperative Extension, that provides gardening/farming information specific to each area?

Donna lee - February 17, 2015 Reply

God Bless_ Diane! Great information in great detail. I’ve never grown onions before! I’m excited because your clarity is so inclusive.

Mike - March 6, 2015 Reply

Hello. This is a great description. I’m intrigued by your system of starting onions in the 8″ deep tubs. I’ve started mine in plug flats under lights, but have been very disappointed with the results this year. Not sure if it’s cold damage (the plant room got down to 35 the other night, right after the stems started poking up through the soil), or if it’s heat damage from the lights. You mention that you start yours in your hoop house. What are the daily highs/lows there? Do you provide any additional heat to get them to germinate? Thanks much.

    Debra - March 7, 2015 Reply

    Hi Mike! A temp of 35 shouldn’t have hurt your onion seedlings, and florescent lights shouldn’t get hot enough to hurt them either. Onion seedlings take a while to size up, and can look a bit scrawny for a few weeks. If they are getting sick, damaged, or dying, though, I would check for damping off or quality of soil issues.

    I planted the onion seeds in my hoop house in mid-February, but the weather has been so cold and dark that I’m only just today starting to see tiny shoots starting to come up (3 weeks later). The temps in the hoop house fluctuate a LOT here in late winter – from 14 F up to 77 F. The seedlings tolerate it pretty well, though they are much slower to germinate than if they had steady, warm temps. They are protected from the wind and quick temperature changes, which helps. Sometimes our weather is mild enough that my seeds will start germinating in the hoop house in mid-February, but I can’t depend upon it. I have a few onion seedlings that I started in the hoop house the beginning of November last year, and they have overwintered there pretty well, and are now about 3″ high. After I plant all of my onion seedlings in my garden, I’m going to compare how those fall-started seedling grow compared to my spring ones. Best wishes!

Debra Singleton - January 31, 2016 Reply

Thanks for the great tutorial. I am going to try starting from seed this year in my little unheated greenhouse. You make it look so easy!

Randy Sutherby - January 31, 2016 Reply

I live in Washington state on the southern end of the Olympic Mountains and about 40 minutes from the Pacific ocean. Also about 35-40 miles south ( as the crow flies) from the wettest spot in the USA,The Hoh Rain Forest.
I give this information as a background to the onions I grow. Candy onions are day neutral. I plant them as transplants. They are sweet like Walla Walla but they last in storage unlike the Walla Walla which doesn’t last long at all. Properly cured Candy onions have lasted 8 months for me. Some will reach 5-6 inches in diameter with nice thick rings.
If you haven’t tried Candy, I urge you to!
1-31-16

    Debra - February 1, 2016 Reply

    Thanks for sharing, Randy! That is great to know. I wasn’t aware that Candy onions could store so well. And the fact that they are day-neutral would allow most gardeners to grow them. Awesome!

john Davies - February 7, 2016 Reply

Greetings Debra,
Being close to Johannesburg at a latitude of 26.5 deg. south, and an altitude of 5000ft, We are towards the end of summer. we are in th southern hemisphere there is a 6 month difference in the planting times.

I thank you for all the little tips and shared experiences, not found in gardening books. I would likewise like to share my experience with onions during the past 2 seasons.

During 2014/15 season, I planted a few short and long day variety seeds, during early August in the house in seed trays. These were planted out after the last frost about middle September. Both grew equally until about the end of November , when the short day variety started forming bulbs, By the end of December we were picking the onions.

The long day variety only started forming bulbs after the summer solstice at the end of December . and produced larger bulbs but later in the season.

This broke the myth that onion seed should be planted only in the fall, and that long day varieties will not grow in our area.

Due to drought conditions this season, I have not continued with the experiments to produce all types of fresh vegetables throughout the year, with plantings of non frost resistant types in my 12 x 12 ft plastic tunnel during the winter. I have concentrated on building new raised beds under 30% white shade cloth.

I have continued with vine type tomatoes with great success. Will share this on the Facebook site.

Thank you for a great service to the vegetable gardener.
John Davies.
Secunda
South Africa.

    Debra - February 8, 2016 Reply

    John, thanks so much for sharing your experience! I love hearing about what other gardeners are doing. I’m a firm believer that we should always be open to experimenting with different varieties and growing techniques. Every location and climate is unique. Best wishes with your garden, and I look forward to hearing more about it in the future!

mark - March 13, 2016 Reply

at what stage of transplanting should I tip off the onion and how far? thanks from N.W pa

    Debra - March 14, 2016 Reply

    Many people trim onion seedlings back to 3-4″ whenever they get tall, sometimes multiple times. It definitely prevents the leaves from flopping over, but I’m not sure it really offers any other benefit. (Some folks believe that it helps the plants to grow more vigorously.) I no longer trim my onions seedlings at all, and my plants grow just fine without it. The only way to find out any difference would be to conduct an experiment. Trim some seedlings, and not others. Treat them both the same otherwise, and compare the final harvest. Good luck!

Evelyn Douglas - March 22, 2016 Reply

Very helpful information. Definitely sharing to my sister because she’s growing onions for first time and she’ll be very glad to have your advises on mind. Found some good ideas for my garden too. Thank you for sharing! Greets, from Evelyn 🙂

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