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How We Grow Our Onions
August 6, 2014

Coming off a year when we grew a fantastic crop of onions in our garden, I thought I'd try to pull together how we grow our onions from our blog postings over the years. It's with a bit of trepidation I write this story, as we may have been extremely lucky this year and in the past. But on the other hand, there may be something of value here for you.

The late Jim Crockett noted in his TV show companion book, Crockett's Victory Garden (pg 18), "There are three ways to grow onions in the garden; from seeds, from transplants, and from sets." While he demonstrated growing onions from sets on the old PBS TV show, he obviously preferred growing his own onion transplants from seed. He wrote, "The advantage to starting from seed...is that seeds are much cheaper than sets, and all varieties are available."

I long ago switched from using onion sets and purchased transplants to growing our own onion plants. As Crockett mentioned, sets can be expensive and definitely limit one to the varieties of sets, usually just two or three, the garden shop sells. Commercial onion transplants, whether purchased by mail order or at a garden shop, were always disappointing to me. Mail ordered plants often arrived terribly dry, and plants from garden centers weren't much better and were also expensive.

Seed Selection and Starting

We order our onion seed from seed catalogs, either by mail order or online. Until this year, we'd settled on four varieties that grew well for us on our ground. With seed for two of the four varieties getting hard to find, I decided to try a number of new-to-us varieties this year and ended up growing a bumper crop of thirteen different onion varieties.

Since I transplant our onions into the garden in April, we generally start our onion transplants in January. I actually started some in December this time around, but that was supposed to just be a germination test. The old onion seed came up, so I was on my way with onion transplants, but onion seed is usually one you don't want to try to save from year to year. Our main onion planting was made in January with one late arriving packet of seed getting started early in February.

Note: Hover mouse over images for labeling throughout this column.

We start our onions in rows lengthwise in seed flats. Since standard 1020 seed flats are rather flimsy and a full tray of wet potting soil is rather heavy, we used to double our seed flats for better strength, using a slotted tray inside a solid tray. A few years ago, we switched to a standard, slotted seed flat in heavy duty Perma-Nest plant tray.

I use a sterilized planting medium for all our plant starts. It's a varying mix of potting soil, peat moss, and a touch of lime, sometimes augmented with powdered seaweed, bone meal, and/or borax. I bake the mix in our oven in a heavy stainless steel pot at 400° F for an hour or so to kill any potential damping off fungus. If you've ever had newly started plants topple over at the base, often with a light circle or thinning at the base of the stem where they fell over, you've probably experienced damping off, a fungus often present in commercial potting mixes. One can get around the problem by using soilless starter mixes or by sterilizing the mix yourself.

Since our starting medium is rich with peat moss, I water the flats with very warm, non-softened water before seeding. Peat moss will absorb warm water, but resists absorbing cold water. I do let the soil cool down a bit before placing any expensive seed in it.

I make four quarter to half inch deep furrows lengthwise down the seed flat with a ruler, or sometimes when the ruler isn't handy, a cheese grater! The tool isn't important. A straight furrow of the proper depth is what you want.

I label each row at either end with an inexpensive plastic label, sometimes labeling half rows when I have a lot of varieties to start. Note that we reuse our plastic plant labels year after year by bleaching the permanent marker labeling on them. Bleach and a little scrubbing removes almost all of the marker, and the bleach sterilizes the labels.

I do my best to space the seed in the rows at half inch intervals. "My best" usually means one could find three seeds on top of each other in places, but almost no gaps in the row. I'd rather thin than reseed.

We usually don't give our onion flats any bottom heat, allowing them to germinate at the ambient 65° F temperature in our basement. We do cover the flats with a clear humidity dome to hold in soil moisture, sometimes having to mist with Captan to hold back moss and mold on the soil surface. The slender onion plants agreeably pop up in 4-7 days.

Care

Since we grow our onions under plant lights, less charitably called old shop lights, we have to keep the lights just an inch or so above the tops of the tallest onion plants. Even with regular bottom watering and keeping the lights properly adjusted, our onions always get leggy, too tall, and top heavy. When that happens, I harden my heart, take a sharp pair of scissors, and give the onions a haircut, cutting them off to around three inches tall. I have to do so two or three times before transplanting, or I end up with a tangled mess of fallen over, intertwined onion leaves. The pruning doesn't seem to hurt the onions terribly. We do lose a few plants, but the survivors form sturdier plants than would happen without the trimming.

The pile of onion trimmings at right go only into our compost bucket. While they look like they could be used as chives, many of the leaves still have a seed hull attached, some of them that had been treated with Thiram, Captan, or some other chemical that wouldn't do a human digestive system any good!

We don't mess around with the temperature in our plant room. When the ambient temperature is 65° F, the onions seem to like it. When it rises to 70° F or more, they still seem happy.

An open flat of onions can dry out rather quickly. While I usually water our plants on our basement plant rack about once a week, the onions seem to require more water than the other flowers and vegetable starts. With double trays, I can often lift the top tray and bottom water the lower, solid tray, lessening the chances of washing away an onion seedling or two.

Sometime in March, often a week or so too early, I move the onion flats outside under our cold frame. I say "too early," as we often get a really hard frost once or twice in late March that requires either bringing everything indoors for a night or two or covering the closed cold frame with tarps, blankets, or whatever other insulating material I can find. Onions can stand a bit of a light frost, but won't handle the occasional 20° F March nights we experience.

Getting the onions outside is important to harden off the plants. If moved directly from our protected plant room in the basement to the garden, the onions would probably die from the harsh sun, UV, and wind they've not experienced. Sitting a week under a partially opened cold frame and then another week or so on our back porch gives the plants time to toughen up a bit before going into the garden.

Planting

Onions love rich soil. If you have it, great. If not, you do the best you can.

Before we had our current raised garden beds, we created "softbeds." They were areas where we never stepped into the bed, preventing soil compaction. We heaped up the soil and added all the organic matter we could to the small areas, including compost and peat moss. While we couldn't make all of our garden soil rich at that time, we could at least make our onion (and carrot) softbed a rich growing environment.

We now grow our onions in raised garden beds that have had truckloads of compost and peat moss lavished on them. But we continue to treat the area where we grow our onions as softbeds, never stepping directly into the bed after it has been tilled for planting. When we grow our onions in our 4' x 16' raised beds, we just work from the outside of the bed. When we grow our onions in interior areas of our large, 16' x 24' raised bed as we did in 2014, we use walking boards outside the rows to spread my considerable weight and prevent soil compaction.

We usually grow our onions in intensive plantings side-by-side with our spring carrots. We've also grown them in the past around lettuce, beet, and spinach rows. Since we were trying a lot of new-to-us onion varieties in 2014, we did a later, extra planting that year on either side of where a row of bell pepper plants would eventually go to have space for all the new onion types. The peppers went into the ground two weeks after the onions.

We plant a double row of onions with the rows spaced about four inches apart, leave a foot of space before planting a double row of carrots whose rows are also spaced just four inches apart. I leave another foot of space before adding another double row of onions. Growing the carrots between the onion rows seems to help deter insect pests.

The carrots usually get seeded first, just to get that out of the way so I don't have to reach over onion plants to seed the carrots. But the carrots are another story, so let's get to transplanting the onions.

The areas where we'll grow onions and carrots usually get fall tilled with whatever peat moss I can afford. I add a bit of lime if I've added peat and also sprinkle a bit of Muriate of Potash (0-0-60) over the area. Muriate of potash is hot stuff, so it's best to add it in the fall.

If I don't get to rototill again in the spring, I start our planting by loosening the soil with a garden hoe and then rake the bed smooth. I mark my planting rows with stakes and string and spread a little (about 3-4 handfuls) 10-20-20 fertilizer on the outside of the onion rows, working it into the soil with the hoe.

I start at one end transplanting the onion plants we've grown from seed two at a time. Keeping the plants in row and making sure I leave around 3-4" between plants is the hardest part of the planting for me. I dig a deep, wide hole across both rows with a good garden trowel, press the onion transplants into the wall of soil on one side, and pull soil up to them with my trowel, making the next planting hole. Every few plants, I go back and firm the soil around each onion plant.

Separating the onion plants in the flat they were grown in often loses most of the soil off the roots. Fortunately, onions seem to tolerate being bare rooted into the ground. They recover from the transplanting shock in about a week as long as they're well watered.

When I'm done planting, I pull my row marker stakes and string. I replace the wooden stakes with flower transplants, as they're lots more attractive than wooden stakes. While the onions and carrots will be out of the ground by mid-summer, the flowers remain, edging the raised bed in glorious color.

Let me add here right in the middle of this story that we have a neighbor "around the corner" who grows his onions in widely spaced rows with the onions a foot apart in the row. He uses a large, pull-type rototiller to keep the aisles between his plantings clean, hoeing in the row. It works for him, and he grows gorgeous, huge onions. But his method just wouldn't work for us.

Planting Sets

If you chose to go with onion sets, the soil preparation is the same as for transplants. With sets, you just push the sets into the ground a couple of inches apart in the row and then wait for them to grow.

Care and Mulching

As soon as the onions get established (about a week or so), I begin to mulch the rows with grass clippings. The grass clipping mulch holds back weeds and helps retain soil moisture. I'm careful not to use fresh, green grass clippings close to the onions, as decomposing grass clippings can give off enough heat to cook young seedlings. I have to go back and re-mulch the onions (and carrots) later in the season, as the clippings decompose and weeds begin to pop through the thinning mulch.

How quickly one mulches is really a trade-off of how much weeding you're willing to do until you think your plants can handle having grass clippings up against them. As you can see from the images above, we had four double rows of onions to be mulched, along with a double row of carrots and a late planted row of pepper plants. I really got serious with the mulching that year two weeks after transplanting the first of our onions.

One of the reasons we're big on mulching is that our well really won't support a lot of irrigation of the garden. Since we usually get good rainfall in the spring, mulching then allows us to slip by with little to no watering when things begin to dry out towards the end of June and early July.

One of the advantages of an intensive planting becomes apparent when the onions and carrots and to a lesser extent, the onions and peppers, almost canopy, keeping light from hitting the ground. Most weeds need light plus oxygen and water to germinate. But if you don't mind weeding and have a good water supply, mulching may not be necessary. There is something really pretty, in my mind, about a nice row of well weeded onions growing in an unmulched row. Either way, onions don't need a lot of care once established. You just stand back, pull an occasional weed, re-mulch where necessary, and watch them grow.

I should add that in wet seasons, one may need to spray the onions with a fungicide to prevent mold from growing on the bulbs. Some folks have to spray for insects as well. We've been lucky with that one and seem to get by each year without the need for pesticides on our onions.

Harvest

It always seems to take forever before our onions begin to bulb. They put on luxurious leaf growth, but eventually begin forming the onion bulbs we want. Sometime in late June, some of the leaves begin to brown, and early onion varieties may start to topple over, a sign they're close to being ready to pull.

Since we live in a windy area, our onions get blown over prematurely sometimes. Short of planting a windbreak in the farmer's field west of us, I really don't have an answer for that one. Fortunately, wind toppled onions usually only occur close to the time when the onions would naturally fall over.

When about three-fourths of our onions have tipped over, I bend over any plants that haven't yet toppled over. In some cases, it may be necessary to pull some varieties of onions well before other varieties are done bulbing. But at some point, all the onions need a week or so with their tops bent over to begin the end of the season.

As the onion tops dry down a bit and the bulbs get even larger, it's time to pull the onions. I like to let our pulled onions just sit on the ground and dry in the sun for a day or two when I can. We were able to do that with several of our onion varieties in 2014, but had some immature Walla Walla sweet onions that probably needed another couple of weeks of growth to reach optimum size. Since we had rain on the way, and I wanted to bring in all of our onions at once, the Walla Wallas got pushed over and only cured in the sun for a few hours.

Curing

When you get your onions out of the garden, they'll need to cure for some time before being ready to store. Obviously, sweet varieties like Walla Wallas need to be used within two months of harvest, as they don't keep well. But most of the onions we grow are storage varieties of one sort or another, so we need to thoroughly cure our onions.

I've let our onions cure in the past on our back porch, but sometimes wind will blow rain under the porch roof, wetting the onions which can lead to mold and rot. We now cure our onions on a makeshift table made of a sheet of plywood stretched across some old furniture in our garage. Curing them on the garage floor would be an option, but our dogs have full run of the garage!

I first lay our onions out on the table with their leaves attached. Since we grew so many onions in 2014, the onions were crowded and the air circulation around them, critical for curing, was poor. Rather than add another drying area to spread them out, I cut the tops off our onions to within 3-4 inches of the bulb. I don't like to cure that way, but with over a hundred pounds of onions to cure and nowhere else to go with them, that was my only option. In years since, we've grown less onions and had room to let them dry down normally on the table without trimming.

I also use an old fan to create some air movement across the onions in the garage. Since it wasn't rainy, I was able to open a couple of the garage windows and leave the walking door open without letting in too much light.

The important thing is to try to give your onions a week or more in a preferably somewhat dark, dry area with good air movement. The leaves will dry down, allowing you to cut or just twist off the dried leaves from the onions. After a couple of weeks of such curing, onions with tops near the bulb that are still squishy should be used if possible and definitely not stored.

At this point, one can move the onions into permanent storage. We added an extra step of curing in 2014 for the first time, bagging and hanging the onions from the garage rafters for a week or so before they were to go into our basement for long-term storage. It didn't seem to help in making the onions store better over the winter.

Note that at each step in harvesting and curing the onions, I carefully culled out any doubled bulbs (two onions in one bulb), soft bulbs, and onions that in any other way suggested they might not store well. While we brought in well over a hundred pounds of onions from the garden, we only hung just over eighty pounds of bagged onions from the rafters. Some of the culls got used or given to family. And some were so bad they went directly to our compost pile.

Let me add here that we've had lots of black mold on some of our onions for years. One can carefully peel an onion around the black mold which only occurs on the outer surfaces of the onion, but it's messy. I was prepared to spray our onions this year with the nastiest of fungicides to prevent the mold, but we just didn't have any. I had treated the soil with a biofungicide, Serenade. It's available in large quantities under the name Serenade Soil as a soil treatment fungicide for onions, potatoes, and lots of other plants. Whether it made the difference or not, I don't know, but we haven't seen any black mold on our onions so far.

Storing Onions

If you don't grow a lot of onions, storing them may be just a matter of popping them into the pantry. For us, we try to grow enough onions to last us throughout the winter. We store our onions in our basement plant room. It is somewhat dark, despite our plant rack with its lights being there. We hang the onions from hooks on the ceiling.

Obviously, a better storage area might be darker (doesn't have to be pitch black), but with good air circulation. Temperatures around 45-55° F would be ideal for onions. Our basement runs 60-65° F through the fall and a bit cooler in the winter, and our onions, garlic, potatoes, sweet potatoes, and butternut squash store fairly well there.

Possibly as important as light, humidity, or temperature considerations is regularly checking your onions for rot. I try to check our onions once a month. I pour each bag of onions into a plant tray and sort through them, throwing out any onions that are sprouting or showing any sign of softness or rot. Even under the best storage conditions, some onions will sprout or rot, causing nearby onions to rot...and so on until you have a smelly, gooey mess instead of usable onions.

With careful monitoring, we sometimes have onions well into the next spring...sometimes. We had a lousy year for onions in 2013 (last year at this writing). Our dogs dug up lots of our carrots and onions and it was very wet when we got our onions out of the ground, leading to a lot of mold and rot. (Sh)it happens! We were buying onions at the grocery by February!

I hope you've found some useful information here.

Update 1/24/2015:

I just realized that I hadn't mentioned the differences between short, intermediate, and long day onion types here. It's something that can make a difference in your success growing onions, as day length is one of the factors that trigger onions to bulb. At our latitude, most of the onions we grow are either intermediate or long day, reflecting the long hours of sunlight we receive in June and July. But rather than get into a discussion of that here, let me share some links to good pages on the subject:

• Burpee: All About Onions
• Weekend Gardener: Gardening Fast Facts - Onion Types
• Dixondale Farms: Short, Intermediate, and Long Day Onion U.S. Map
• Bonnie Plants: Which Onion Is Right For You?
• Food Network: White Versus Yellow Onions: What's the Difference? A guide to 7 different types of onions.

Since we did our Onion Trials in 2014, several of our favorite hybrid onion varieties have been discontinued. Seed for the excellent Pulsar and Red Zeppelin varieties is no longer available. In looking ahead to 2018, we'll be growing Clear Dawn and Milestone for our yellow storage onions. Southport White Globes will give us a nice white storage onion. For red onions, we're going to go with the Rossa di Milano variety. And of course, we'll grow some large Walla Walla onions for a sweet onion.

Fall Planting Onions 7/2/2023

I ran across a page on the High Mowing Organic Seeds' site last summer, Time to Plant Fall Onions for Overwintering. I decided to give it a try. So in mid-September, I direct seeded some Walla Walla onion seed. Our spring transplanted Walla Wallas never seem to achieve full size. So I was pleased to see that we're getting some full sized Walla Wallas from the fall planting.

About the only trick to fall planted onions seems to be mulching them over the winter.

Overwintered Onions 7/20/2023

Our experiment with overwintering onions turned out to be a smashing success. While I'd used some of the onions for cooking, our take was about eight pounds of lovely Walla Walla sweet onions.

Early this spring, I did transplant some of the onions, as there were big gaps in the planting. That didn't seem to negatively affect the plants.

As sweet onions don't keep well beyond a month or so, I selected the worse looking onions and chopped, blanched, and froze them. Two of the onions I selected had serious rot and had to be pitched. Another had to have some rot trimmed. But I still froze a half gallon of chopped sweet onions for future use.

Some random notes follow:

For 2014, we ended up with four 14+ foot double rows of onions, equivalent to around 112 footrow of onions. We harvested well over a hundred pounds of onions from those plantings. During the growing season, we liberally pulled and used onions for cooking and gave away a good many as well. We used almost half of our Red Creole onions, a new-to-us, early maturing heirloom variety we were trying, well before any of our other varieties began to bulb!

We hung 81 pounds of onions in the garage for final curing. Of those, about a third went into our basement for winter use. There was some serious culling when we moved the onions to their final storage location, but most of the excess went to family, neighbors, and area food banks.

We grew so many onions this year because we were trying some new varieties. You can read about the various onion varieties in Onions We Grew in 2014.

Our intensive planting method works well for us on some fairly rich soil in our raised beds. Your mileage may vary.

I referenced Crockett's Victory Garden early in this column. The book has been out of print for a long time but is still available used for around $5 shipped from book vendors such as Amazon or Alibris. While you're thinking about Crockett, writing and suggesting WGBH release the old Jim Crockett episodes of The Victory Garden on DVD might just move them to action.

If you're looking for suppliers of quality seed, we maintain a Trusted Suppliers page of good seed houses. We rate them based on our experiences with them over the years, but also link to The Garden Watchdog ratings from Dave's Garden.

Disclaimer

Just because a retired, old guy has a web site on gardening doesn't mean he knows jack about it. I have absolutely no degrees in agriculture or horticulture or any other special training. At 75 years old, I'm still learning, so there may be tragic errors in the information above. It's just what has worked for us.

From Steve Wood, the at Senior Gardening