7 Reasons Your Onions Aren’t Forming Bulbs
Putting time and energy into a patch of onions can reap great rewards, but it’s a bummer to pull one at harvest only to find a tiny bulb. Experienced gardener Sarah Jay covers 7 reasons your onions haven’t formed those luscious, layered bulbs.
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No kitchen is complete without onions. Growing them is fun, and the result is a healthy harvest of bulbs with a much more pungent flavor than what you can get at the grocery store. However, if you’ve encountered onions not forming bulbs, you know how big of a letdown it can be.
The reasons for a lack of bulb formation range from user error to environmental factors. If it’s your first time growing onions, there could have been one misstep that threw off your onion patch. If you’re experienced, it could be completely out of your hands, and the season just wasn’t right.
Knowing what’s going on when you find onions not forming bulbs will help you determine whether or not you can remedy the problem. Sometimes there’s no problem at all, and all it takes is a little patience!
Flat of Italy Bulb Cipollini Onion
Flat of Italy Bulb Cipollini Onion Seeds
Wrong Type
There are three types of onions grown across the world: day-neutral, long-day, and short-day. Long-day onions need at least 14 hours of sunlight to fully form and grow along the earth’s latitudes from 37 to 47°. Short-day onions need 10 to 12 hours and do best at 25 to 35°F. Day-neutral onions form bulbs between those two light exposures at 32 to 42°.
If you live in Michigan, where sunlight isn’t as plentiful as it is in Texas, growing a long-day variety, like ‘Yellow Sweet Spanish Utah,’ won’t work out. Instead, opt for a short-day onion, like ‘Yellow Granex PRR,’ which can handle the limited daylight hours that occur in the north. If you’re lucky enough to live in that intermediary zone, try the lovely red Flat of Italy.
These are just a few examples of the varieties out there. If you’re new to growing onions, you’ll be in awe of the selection available, no matter where you live. If you’re not sure how to look, go to your local farmer’s market and find some sets. These are most likely attuned to your region’s climate and light availability.
Improper Fertility
Sometimes the reason for onions not forming bulbs has less to do with the type of onion and more to do with the quality of the soil or the additional fertility needed as you grow them. You need a good foundation for onions. Start with a loose, well-draining soil that has a pH between 6.0 and 7.0. You want a loamy or sandy soil, as opposed to heavy clay.
You should always start with a soil test. Once you’ve done this and you’ve amended as necessary, plant your onions. Then throughout the onion season, feed them. Start by adding a small amount all-purpose organic fertilizer to the soil at planting if your soil test indicates this is needed. The initial feedings should include nitrogen, which contributes to leaf growth.
After you have a good set of roots and leaves, skip the nitrogen and start fertilizing with organic liquids that are higher in phosphorus and potassium. However, note that any additional feeds should always correspond to your initial soil test. Your soil may already have the nutrients available for proper bulbing. Overfeeding can also stunt bulb growth, so always consult the soil test to determine if more nutrients are needed.
Pests
Say you’ve done your soil test, you’ve picked the right type, and you’re working with the right nutrients, but you still see onions not forming bulbs. There are pests that limit your onions’ ability to grow, and there are some that are not visible above ground.
The most likely culprit in the case of bulbs is the onion maggot. These guys pupate in the soil during winter, emerge as adult flies in spring, and lay their eggs at the base of onion plants. Their larvae hatch and burrow into the bulb, limiting the nutrient and water uptake.
Prevent them by delaying planting until later in spring in temperate regions, where the season is long enough. Rotate your onion crops every year, avoiding planting after legumes. Plant onions in a covered area where the flies can’t get to them. In infestations, use spinosad to keep their numbers down.
Other pests are only likely to limit bulb growth in infestations, but keep an eye out for leaf discoloration to stay abreast of their numbers.
Diseases
There are times when onion tops wilt, leaves take on striping or mottling, and disease sets in. The most common of these is root rot, which originates from poorly draining soil. When the soil compacts and water can’t drain freely, fungi, bacteria, and water molds take hold, feeding on the sugars bulbs provide. With this disease, you’ll assuredly find onions not forming bulbs.
Purple blotch can also limit formation, as leaves take on lesions that block photosynthesis. Avoid neck wounds and plant healthy sets or seeds from reliable sources to prevent this. Infected soil can cause white rot (Sclerotium cepivorum) or sour skin (Pseudomonas (Burkholderia) cepacia).
The best way to keep diseases from taking hold of your precious onion bulbs is to ensure you’re cultivating in the best possible conditions. Always use bulbs and seeds from reliable sources, and avoid planting alliums repeatedly in the same area year after year.
Dense Plantings
While dense plantings are great for lettuces, herbs, and other crops, onions need space to grow those healthy, happy bulbs. Sometimes you’ll find onions at the store in starter pots. And maybe you sowed them in your Epic cube pot this way. Purchasing potted sets is a great way to get started without devoting the entire time to growing the seeds.
However, before you plant those stuffed starter pots, separate them to give each plant the room it needs to grow. Just rehydrate the entire root mass, and gently pry them apart. Similarly, don’t plant too many seeds in one area. If you do, then thin them to the recommended spacings.
Start by consulting the seed packet or information on the variety you’re growing, and use those spacings. In later years, when you’re more experienced with onion-growing, you can experiment with closer spacing if you’d like.
It’s Been Overcast
We’ve discussed your onion type and how growing the wrong kind can lead to onions not forming bulbs. Overall, onions need tons of sun, at a rate of 10 to 16 hours per day based on their day length. But there are times when the season is just cloudy and rainy, and this stunts them.
There’s really no getting around a super cloudy season. If your season allows, you can leave the onions in the ground a bit after their days to maturity expire to let them grow larger. If you can’t do this, you could harvest them and just have smaller bulbs than you expected.
It’s Early
If you’ve pulled an onion and it’s tiny, it could be too early to harvest them. Onions need 85 to 185 days to fully develop. Larger bulbs need more days in that range than small bunching onions do. Always consult your seed packet to determine approximately when your harvest will occur. Start checking your onions somewhere in that range. Feel free to let them continue maturing if there are no looming weather conditions that would negatively affect them.
Another thing to consider at planting time is whether you want to grow seeds or sets. Sets have a shorter maturation period than seeds do, as they’re already a couple of developmental stages ahead. If you are growing sets, do some research to figure out how many days to pull an onion from the ground and check it.
[div]Key Takeaways
Reading all this, it may seem that growing onions is hard, and there’s a lot to consider. While that is sometimes the case, as long as you start with good soil, the right nutrients, and with reliable seeds or sets, you’re likely to succeed!
Sometimes things happen that are out of your control, but the most probable outcome for someone with a good foundation for growing onions is tons of healthy, juicy bulbs.
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