As a gardener, few things are more disheartening than seeing your onion plants prematurely go to seed. After months of careful tending, the thrill of watching those green shoots turn into bulging onions quickly turns to dismay once flowering stalks emerge.
Onion plants going to seed a process called “bolting”, robs your crop of its full flavor and size potential. The good news is that with some planning and quick action, you can still end up with a decent onion harvest. In this article we’ll explore the reasons behind onion bolting and provide tips on what to do when it happens in your garden.
Why Do Onion Plants Bolt?
Onions are biennial plants, meaning they take two years to complete their lifecycle. The first year they focus energy on developing bulbs, while the second year they flower and set seed. However, onions can be triggered to bolt in their first year if conditions become too stressful, whether from weather extremes or other factors like poor soil health.
Here are some common reasons onion plants bolt prematurely:
-
Temperature Extremes – Onions thrive in consistently cool weather. Temperatures swinging up into the 80s or down near freezing will stress plants
-
Lack of Water – Onions require steady moisture. Erratic watering or drought conditions often induce bolting.
-
Nutrient Deficiencies – Poor soil fertility stresses plants. Insufficient nitrogen is a common cause of onion bolting.
-
Day Length – Some onions are triggered to bolt when day length exceeds a certain threshold Planting the wrong varieties for your region can lead to premature flowering
-
Damage: Hail, flooding, disease, and bugs eating onions can all cause them to be stressed. Damaged plants will be more prone to bolting.
-
Small Sets or Seedlings – Onion sets and seedlings that are smaller than ideal lack the stored energy needed for good first year bulb production, making them bolt quicker.
Signs Your Onions Are Bolting
The first sign of onion bolting is the appearance of a flowering stalk or “scape” emerging from the top of the plant. The scape is easily identified by its straight, hollow stem topped by a nascent flower bud.
Left alone, the bud will swell and eventually burst open into a cluster of small white or purple flowers. Once flowering commences, seed production is not far behind.
Along with flowering scapes, other symptoms of onion bolting include:
- Slowing or halted bulb growth
- Soft, thickened neck tissue
- Splitting and doubling of bulbs
- Easily detached and falling over outer skins
What To Do When Onion Plants Bolt
While seeing those premature flower stalks is discouraging, the situation is not hopeless. Here are some steps to take once you notice onions starting to bolt:
Remove Flowering Stalks – Cutting off the scapes as soon as they appear allows the plant to redirect energy back to the bulbs. Use scissors or pruners to remove stalks near their base.
Harvest Promptly – Onions that have bolted will not gain much additional size. Begin progressively harvesting bulbs as they reach good size. Waiting longer increases risk of disease and rot.
Cure Thoroughly – Bolted onions have looser skins and don’t cure well. Take extra time ensuring they are fully dried before storage to prevent rotting.
Use First – Consume bolted onions promptly after curing rather than trying to store them. Their diminished keeping qualities mean they should go from garden to table faster.
If you have more bolted onions than you can use right away, leave some of them where they are to grow seeds for next year’s garden.
Preventing Onion Bolting In Future Seasons
While dealing with current season bolting is important, focusing on prevention for future years will lead to better results long-term. Here are some tips to avoid seeing your onions bolt again:
-
Choose Resistant Types—Look for long-day onions that have been bred not to flower. ‘Copra’, ‘Prince’, and ‘Fortress’ are less prone to bolting.
-
Use Larger Sets & Seedlings – Bigger sets and transplants have more energy reserves to put towards bulbing before flowering.
-
Plant at Recommended Times – Follow planting guidelines for your region, as day length influences some varieties.
-
Use Row Covers – Covering plants protects them from temperature swings. Install covers before cold snaps or heat waves.
-
Water Deeply & Regularly – Onions thrive on consistent moisture. About 1-2 inches per week is ideal, adjusted for rainfall.
-
Test & Amend Soil – Onions prefer fertile, well-drained soils with a pH between 6.0-6.8. Have soil tested annually and correct issues.
-
Control Pests & Disease – Healthy plants are less stressed. Monitor for problems and treat promptly. Avoid overcrowding.
-
Weed & Mulch – Minimize weed pressure, which competes for water and nutrients. Organic mulch helps conserve soil moisture.
-
Top Onions – Removing the top 1⁄3 of foliage mid-season redirects energy to bulbing. Pinch about 6 weeks before harvest.
Using Bolted Onions
While bolted onions may lack ideal keeping qualities, their flavor is rarely affected much. Bulbs remain tasty and suitable for fresh eating. Here are some of the best uses for onions that have gone to seed early:
- Sautéing
- Soups, stews, and chili
- Grilling
- Salads and sandwiches
- Quick-pickling
- Caramelizing
- Onion powder
- Freezing for later use
Avoid long-term room temperature storage or canning bolted onions, as these methods will hasten spoilage. Focus on enjoying those premature bulbs right away!
Though having your onions bolt mid-season is always a letdown, a little planning and quick action once stalks appear can still result in a usable crop. And directing your efforts towards prevention will equip you to avoid many of the triggers that cause premature flowering in future years. Just stay the course – with some patience and diligence, a bountiful, non-bolting onion harvest awaits!
How do I preserve bolted onions?
Use bolted onions right away, just as you would other onions. Bolted onions will not store well, and you need to preserve them differently than onions that did not bolt.
Here are a few ideas for ways to preserve bolted onions:
- Chop and freeze.
- Cut up the onions and dehydrate them. Use dehydrated onions whole, or process them into onion powder. For the strongest flavor, store the dried onions whole. Then, blend a few to make a powder.
- Slice onions and freeze dry them. (This is my FAVORITE way to preserve onions. You can store and use freeze-dried onions “as is” or turn them into a powder. Read this post, Freeze Drying Tips for Beginners, to learn more about freeze-drying.
Onions going into the freeze dryer
Why do onions bolt?
An onion bolts in response to stress. Stress can happen in several ways: too hot, too cold, not enough water, or too much water. Temperature fluctuations can also cause onions to bolt.
Swings in temperature may cause the onion to think it is in the second year of growth when it is supposed to flower.
For example, warm temperatures followed by cool weather can encourage onions to go dormant. Once warm temperatures return, the onion may believe it is beginning its second growing season and produce seeds.
The onion reacts to the stress by putting its energy into reproducing and making seeds.
Grow Perfect Onions – Every Time!
FAQ
Can you eat onions that are going to seed?
A. Yes, Robyn, you can still eat spring onions after they go to seed. Just cook them like you would an onion or spring onion. To get rid of the flower, cut back the leaves of the plants that have gone to seed. This will stop the plant’s energy from going to the flower.
What causes onions to go to seed?
AIt’s common for onions to bolt (run to seed suddenly) when there is a cold snap – it’s as if the plant thinks winter is setting in and quickly throws out some seeds. They can also bolt in very hot weather – they get dry, panic and run to seed.