How to Grow Short-Day Onions: From Transplants to Huge Bulbs & Harvest
Growing big, beautiful onion bulbs starts with something many gardeners don't realize: choosing the right type of onion for your climate. Onions are sensitive to day length, and planting the wrong type is one of the most common reasons gardeners end up with tiny bulbs instead of the large onions they were expecting.
For gardeners in Florida and other areas with mild winters and hot summers, short-day onions are usually the right choice. They're planted during the cooler months, spend the winter developing a strong leafy plant, and begin forming bulbs as the days lengthen in late winter and spring.
In this complete guide, I'm going to walk you through the entire process—from choosing and planting short-day onion transplants to watering, fertilizing, troubleshooting pests and diseases, harvesting, curing, and storing your homegrown onions.
Watch the video version of this guide:
What Are Short-Day Onions?
Bulbing onions are generally divided into short-day, intermediate-day and long-day varieties based on the amount of daylight that triggers them to begin forming bulbs.
Short-day onions begin bulbing at approximately 10–12 hours of daylight, which makes them well suited to southern areas with mild winters. Long-day onions require much longer summer days, while intermediate-day onions fall somewhere in between.
Here in Florida, I grow short-day onions because our summers are simply too hot to grow traditional bulbing onions through the summer. Instead, we plant during the cooler fall and winter months and harvest in spring before our intense summer heat and rainy season arrive.
Choosing the correct day-length variety is extremely important. If you plant an onion that requires more daylight than your location provides at the appropriate time of year, you can grow plenty of green tops but end up disappointed by the bulb size.
Quick tip: Look up an “onion growing map” for your region and choose varieties based on your day length zone.
When Should You Plant Short-Day Onions?
In warm climates, short-day onions are planted during fall and winter so they have plenty of time to grow before spring.
Remember that onions are a long-season crop. If you're growing from seed, you'll need to start well ahead of your intended transplanting date. Commercial growers may start onion seeds approximately 10–12 weeks before transplanting because seedlings take quite a while to reach transplant size. Onions top 5 tips
If you've already reached your ideal planting window, I recommend using onion transplants instead of starting seeds too late. This gives the plants the head start they need to produce plenty of foliage before bulb formation begins.
Why Starting Early Produces Bigger Onions
This is one of the most important concepts to understand if your goal is to grow large onions.
Before an onion begins forming its bulb, it spends its energy producing leaves. Each onion leaf corresponds to a layer, or ring, in the developing bulb. That means the more healthy leaves your plant can produce before bulbing begins, the greater its potential to produce a large onion.
This is why timing is so important.
We want our short-day onions established early enough that they have a nice long vegetative growing period before increasing day length triggers bulb formation.
Once that bulbing process starts, you can't simply make up for months of lost vegetative growth.
Ideal Growing Conditions for Short-Day Onions
Sunlight
Plant onions in full sun. Even here in Florida, where many vegetables benefit from some afternoon shade, I give my onions as much sunlight as possible.
All of those leaves are essentially little solar panels collecting energy that the plant can eventually put toward developing a large bulb. My goal is at least 6–8 hours of direct sunlight per day, with more being perfectly fine during our cooler growing season.
Soil
Onions have relatively shallow root systems, so I want the upper 6–8 inches of soil to be loose, fertile and well drained. Short Day Onions Planting 2025 …
Heavy, compacted or waterlogged soil can make it harder to grow healthy plants and increases the potential for disease and bulb rot.
I like to amend my planting area with biologically active compost, worm castings or insect frass to add organic matter and support the soil ecosystem.
If you garden somewhere with extremely wet or humid conditions like I do here in Florida, raised beds, grow bags and containers are excellent options because they make drainage much easier to control. I've even grown surprisingly large onions in GreenStalk garden towers. Onions top 5 tips
Water
Onions like consistent moisture, but there's a big difference between moist soil and soggy soil.
As a general starting point, approximately 1 inch of water per week works well, adjusting for rainfall, temperature, soil type and container conditions. Onions top 5 tips
I use drip irrigation because it delivers water directly to the root zone without constantly wetting the foliage. My drip tape happens to have emitters every 6 inches, which also makes spacing my onions incredibly easy.
If you're watering overhead, water early enough in the day that the foliage has time to dry. Prolonged leaf wetness and excessively wet soil can encourage disease. Extension recommendations similarly emphasize good drainage, proper spacing and watering at the root zone as important disease-management practices.
Here is my video tutorial on how I installed drip irrigation along with the supplies I used:
How to Plant Short-Day Onion Transplants
When your onion transplants arrive, plant them as soon as you reasonably can. These are essentially bare-root plants without soil protecting the roots, so I don't want them sitting around drying out.
If absolutely necessary, you can temporarily wrap the roots in damp paper towels and keep them somewhere cool for a very short period, but planting them promptly gives them the best chance of establishing quickly. Short Day Onions Planting 2025 …
Onions should be planted surprisingly shallow.
Make a hole approximately 1 inch deep and place the transplant so the white portion at the bottom is just beneath the soil. Don't bury the green foliage deeply.
Gently firm the soil around the plant and water it in well.
Space bulbing onions approximately 4–6 inches apart. I personally prefer about 6 inches because I'm gardening in a humid environment with significant pest and disease pressure. The additional space provides better airflow and plenty of room for large bulbs to develop. Short Day Onions Planting 2025 …
One more tip: I don't trim the green tops when I plant my transplants. I want to preserve as much healthy photosynthetic leaf area as possible.
How to Fertilize Onions for Bigger Bulbs
Onions are fairly heavy feeders, and fertilization should change as the plant moves through different stages of growth.
Stage 1: Grow the Leaves
During the early vegetative stage, my primary goal is leaf growth.
Nitrogen is especially important during this stage because it promotes leafy green growth. Remember: more healthy leaves before bulbing means greater potential for more layers in the finished onion bulb.
When planting, I like to incorporate organic matter such as worm castings and use a nitrogen-rich fertilizer. One organic option I use is blood meal. Conventional onion growers commonly use fertilizers such as ammonium sulfate, which contains substantially more nitrogen.
After the plants establish and begin producing new leaves, I continue feeding nitrogen periodically during the vegetative stage. In my garden, that's generally around every 2–4 weeks depending on the fertilizer I'm using. Always follow the application rate for your particular product rather than assuming every fertilizer should be applied at the same rate.
Stage 2: Bulb Formation
Eventually you'll notice something exciting happening at soil level: the bases of your onions will begin swelling.
This is your signal that the plant is transitioning from primarily producing foliage to developing its bulb.
At this point, I stop pushing nitrogen. In my own garden, I transition away from nitrogen-heavy feeding and focus more on overall bulb development rather than trying to force additional leafy growth.
Your plants have spent the previous months building their solar panels. Now it's time to let them put that accumulated energy into the onion.
Stage 3: Approaching Harvest
As harvest approaches and the foliage begins naturally falling over, yellowing and drying, I stop fertilizing.
At this point, we're no longer trying to stimulate new growth. We're allowing the plant to complete its natural maturation process.
Weed Control Is More Important Than You Think
Don't let weeds take over your onion bed.
Because onions have relatively shallow root systems and don't create a dense canopy over the soil, weeds can compete heavily with them for water, nutrients and sunlight.
I like using mulch to reduce weed pressure, but I still regularly check around the plants and remove weeds while they're small. Be gentle when pulling or cultivating close to your onions so you don't damage their shallow roots.
Common Onion Pests
Thrips
Thrips are probably the onion pest I would watch most closely.
These tiny insects feed on onion foliage and tend to hide deep inside the folds and neck of the plant, so they can be easy to miss. Feeding damage can reduce the plant's ability to photosynthesize and, under significant pressure, ultimately reduce bulb size. UF/IFAS identifies thrips among the most common insect pests of Florida onions and notes that some species can also transmit plant viruses.
Regularly inspect the newest leaves and the tight areas where leaves meet. Because thrips develop resistance to insecticides readily, I wouldn't automatically spray simply because you see one insect. Accurate identification and an integrated pest-management approach are preferable.
For home gardeners, if you're unsure what you're seeing, take clear photos or a sample to your local Extension office before treating. And if a pesticide becomes necessary, use only a product specifically labeled for onions and the pest you're treating, following the label exactly.
Caterpillars and Cutworms
Caterpillars and cutworms can occasionally damage young onions, especially newly established plants.
Regular scouting is usually the easiest way to catch the problem early. In a small backyard planting, caterpillars can often simply be removed by hand.
Common Onion Diseases
Disease prevention is especially important for me because Florida's humidity can create ideal conditions for fungal and bacterial problems.
The best defense starts before you ever see disease: provide good airflow, don't overcrowd plants, use well-drained soil, avoid keeping the foliage unnecessarily wet, rotate crops when possible, remove diseased plant material, and don't overwater.
Leaf Blights and Leaf Spots
Several pathogens can cause spotting, lesions, yellowing or dieback of onion leaves. Botrytis leaf blight, purple blotch and other foliar diseases become more problematic when foliage remains wet for extended periods. UGA Extension notes the strong relationship between onion leaf diseases and prolonged leaf wetness.
This is another reason I prefer drip irrigation.
If you're hand watering, aim the water toward the soil instead of repeatedly soaking the foliage.
Bulb and Bacterial Rots
Soft, slimy or foul-smelling tissue is a warning sign that you're dealing with rot rather than normal onion maturation.
Excess moisture, poor drainage, plant injuries and warm conditions can all contribute to problems. Avoid damaging bulbs and foliage, particularly as plants approach harvest, and don't leave mature onions sitting in saturated soil.
Never store a rotting onion with healthy onions. Remove it immediately because disease can spread during storage.
Pink Root
Pink root is a soilborne fungal disease that causes onion roots to turn pink or purplish before eventually deteriorating. Heavily affected plants may become stunted and produce small bulbs.
Long crop rotations away from onion relatives can help reduce losses, and good soil, fertility and water management help minimize plant stress.
How Do You Know When Onions Are Ready to Harvest?
One of the great things about onions is that technically you can harvest them almost anytime.
If you pull them before they've formed bulbs, you can use the greens like green onions. If you need an onion for dinner and the plant has already formed a usable bulb, you can pull one early.
But if I'm growing bulbing onions, my goal is usually to let them get as large as possible.
The classic indicator is when the green tops begin falling over at the neck. The neck tissue of a mature onion becomes softer and more flexible than that of an immature onion.
In my own garden, I often allow the foliage to progress even further and begin drying and turning brown before harvesting because I want to give the bulbs as much growing time as conditions safely allow. Onion Harvest and Curing
There are, however, a couple of important exceptions.
If your onion sends up a flower stalk, or bolts, I recommend harvesting it rather than expecting the bulb to continue getting dramatically larger. The plant has shifted into reproduction.
The second exception is weather.
Here in Florida, I don't want mature onions sitting in the ground as we move into our summer rainy season. Excessive rain around mature bulbs can greatly increase the chance of rot. One of the advantages of growing short-day onions during fall and winter is that we're usually harvesting in spring before that intense summer rain arrives. Onion Harvest and Curing
Should You Bend Onion Tops Over?
You've probably seen the advice to manually bend onion tops over to supposedly force the plant to put more energy into the bulb.
I would not consider this necessary.
Natural top fall is a useful indicator of maturity, but deliberately bending healthy green foliage isn't something you need to do to successfully grow large onions. In one of my earlier videos, I mentioned this as an experiment I wanted to try because some growers claim it increases bulb size, while others say it doesn't. Onions top 5 tips
Rather than manually damaging healthy foliage, I prefer to let the plant mature naturally.
How to Harvest Onion Bulbs
Whenever possible, harvest onions on a warm, dry day.
If the soil is loose and dry, I can often gently lift the onion without much effort. If the soil is holding tightly around the roots, loosen it first with a hand shovel or garden fork rather than pulling aggressively on the foliage.
The main goal is to avoid damaging the bulb.
Cuts, bruises and damaged necks can create entry points for decay organisms and shorten storage life.
If an onion already has a broken or soft neck, set that one aside and use it first rather than putting it into long-term storage. Onion Harvest and Curing
And don't wash your onions before curing them. We're trying to get the outer surface dry.
How to Cure Onions After Harvest
If you want onions to last beyond the immediate harvest, curing is one of the most important steps.
Curing dries the outer scales, roots and neck while helping protect the moisture inside the bulb. Properly cured onions develop those familiar dry, papery outer skins that protect them during storage.
For the home gardener, choose a dry, shaded location with excellent airflow and arrange your onions in a single layer so air can circulate around them. You can also hang them if that's more convenient.
I generally allow mine to cure for about one to two weeks, watching the onions rather than relying only on the calendar.
They're finished when the outer skins feel dry and papery, the roots have dried, and the neck is thoroughly dry.
Avoid getting the onions wet during curing. If rain is coming, move them to a protected, well-ventilated area. Onion Harvest and Curing
Preparing Cured Onions for Storage
Once the onions are completely cured, I trim away the dried roots and tops. I leave approximately an inch or a little more of dried neck above the bulb rather than cutting directly against it.
Then I inspect every onion.
Any bulbs that are damaged, soft, bruised, diseased or have questionable necks go into my "use first" pile.
Healthy cured onions can be stored in mesh onion bags, baskets, crates or cardboard boxes with ventilation holes. The important thing is airflow.
Don't seal onions inside an airtight plastic bag.
How Long Do Short-Day Onions Store?
This is an important distinction with short-day onions.
Many short-day varieties grown in warm climates are sweet onions, and sweet onions generally don't have the extremely long storage potential of some pungent long-day storage varieties. UF/IFAS specifically notes that the sweet short-day onions commonly grown in Florida do not store as well as long-storage onion types.
So although proper curing absolutely extends their useful storage life, I recommend enjoying your short-day onions rather than expecting every variety to sit in the pantry for six months.
Storage potential depends heavily on variety, growing conditions, bulb health, curing quality, temperature and humidity.
Check your stored onions periodically and remove any that begin softening or rotting.
From Transplant to Harvest
The biggest lesson I've learned from growing onions is that producing a large bulb isn't about one magic fertilizer or trick at the end of the season.
Success starts months earlier.
Choose the correct onion type for your climate. Plant early enough to give it a long vegetative growing period. Give it plenty of sun. Plant shallowly in loose, fertile, well-drained soil. Keep moisture consistent. Give the plant the nutrition it needs while it's producing leaves. Keep weeds, pests and diseases under control. Then recognize when the plant naturally transitions into bulbing and eventually maturity.
Do all of those things well, and you're setting your onions up to produce the largest bulbs they're genetically capable of producing.
And if you're a warm-climate gardener like me, short-day onions are one of those crops that can completely change what you thought was possible to grow through fall and winter.
Once you've tasted a freshly harvested homegrown onion, you'll understand why I make room for so many of them every year!