What To Do When Onions Bolt

What To Do When Onions Bolt: A Comprehensive Guide to Handling Bolting Onions

Wondering what to do when onions bolt in your garden? This comprehensive guide provides valuable insights, practical tips, and expert advice on how to handle bolting onions. Learn about the causes of bolting, preventive measures, and steps to manage bolting effectively.


Onions are a versatile and essential ingredient in the kitchen, adding flavor to countless dishes. However, gardeners may encounter a common issue known as “bolting” with their onion crops. Bolting refers to the premature flowering and seeding of onions, which can negatively impact their taste and storage capabilities. If you’re facing this predicament, worry not! In this article, we’ll explore everything you need to know about what to do when onions bolt. From understanding the causes to taking preventive measures and managing bolting effectively, we’ve got you covered!

What To Do When Onions Bolt

What To Do When Onions Bolt

When your onions start bolting, it’s essential to take prompt action to ensure a successful harvest. Here’s a step-by-step guide on what to do when onions bolt:

1. Identify Bolting Signs

Identifying bolting signs on onions is crucial for gardeners to take timely action and prevent further complications. Here are some key indicators to watch out for:

  • Visible Flower Stalks: The most apparent sign of bolting in onions is the appearance of tall, slender flower stalks rising from the center of the plant. These stalks can reach several inches in height and are a clear indication that the onion is transitioning to its reproductive phase.
  • Bulb Enlargement Slows Down: When onions bolt, their energy is redirected towards flowering and seed production, causing the bulb’s growth to slow down significantly. If you notice that the onion bulb stops increasing in size or becomes smaller, it may be bolting.
  • Formation of Flower Buds: Prior to the emergence of flower stalks, you may notice small, greenish flower buds forming within the center of the onion plant. These buds will eventually develop into the flower stalks.
  • Leaves Turn Yellow: As onions bolt, the leaves may start to turn yellow or even brown. This yellowing of the foliage is an indication that the plant is shifting its focus from vegetative growth to reproductive functions.
  • Softening of the Bulb: The onion bulb may become softer to the touch when it starts to bolt. This change in texture is due to the shift in the plant’s physiological processes.
  • Shortening of Day Length: Onions are sensitive to day length, and bolting is often triggered by the length of daylight hours. If you observe that the days are getting shorter, be vigilant for signs of bolting.
  • Stress Factors: Environmental stressors such as extreme temperatures, water scarcity, or nutrient deficiencies can also encourage onions to bolt. Keep an eye on the overall health of your plants to detect any stress-related issues.
  • Observation of Flowering: As bolting progresses, the onion plant will eventually produce flowers. The appearance of blooms in the onion bed confirms that bolting has occurred.

By paying close attention to these signs, you can identify bolting onions early and implement appropriate measures to manage the situation effectively. Remember that not all onions will bolt, and by selecting the right varieties and providing optimal growing conditions, you can minimize the risk of bolting in your onion crop.

2. Understand the Causes

Understanding the causes of onions bolting is essential for gardeners to prevent this phenomenon and ensure a successful onion harvest. Several factors contribute to the onset of bolting in onions:

onions Temperature Fluctuations
  • Temperature Fluctuations: Onions are cool-season crops and prefer moderate temperatures for their vegetative growth. Sudden and significant fluctuations in temperature, especially prolonged periods of high heat, can trigger bolting. The plant perceives such conditions as a sign of the changing season and initiates the reproductive process.
  • Day Length Sensitivity: Onions are photoperiodic, meaning their reproductive behavior is influenced by the length of daylight hours. When the day length reaches a critical threshold (typically 12-14 hours for most onion varieties), the plant interprets it as a signal to start flowering and seed production, leading to bolting.
  • Onion Variety: Different onion varieties have varying levels of susceptibility to bolting. Some cultivars are more genetically predisposed to bolt under certain environmental conditions, while others are more resistant. Choosing the right variety for your climate and growing conditions can reduce the likelihood of bolting.
  • Environmental Stress: Stress factors, such as water scarcity, nutrient imbalances, or physical damage to the plant, can stimulate bolting. When an onion plant faces adverse conditions that threaten its survival, it may prioritize reproduction as a means of preserving its genetic material.
  • Planting Time: Timing is crucial when growing onions. Planting too early or too late in the season can affect the plant’s growth cycle and increase the risk of bolting. Properly timing your onion planting ensures that the plant establishes itself before encountering the critical day length for bolting.
  • Seed Quality: The quality of onion seeds used for planting plays a role in determining the likelihood of bolting. Using seeds from reputable sources and ensuring their viability can influence the overall health and resilience of the onion plants.
  • Soil Conditions: Onions thrive in well-draining soil with sufficient nutrients. Poor soil conditions, such as compacted or waterlogged soil, can stress the plants and trigger bolting.
  • Cultural Practices: Improper cultural practices, such as excessive fertilization or inadequate thinning of seedlings, can create stress on the onion plants, encouraging them to bolt.

3. Preventive Measures

Preventive Measures

Preventing onions from bolting requires a combination of proactive measures and careful management. By implementing the following preventive strategies, gardeners can significantly reduce the risk of onions transitioning to their reproductive stage prematurely:

  • Choose the Right Onion Variety: Select onion cultivars that are known for their resistance to bolting in your specific climate. Consult with local gardening experts or seed suppliers to identify varieties that are well-suited to your region’s day length and temperature conditions.
  • Optimal Planting Time: Timing is critical when planting onions. Start your onion crop at the appropriate time for your location, considering the average date of the last frost in the spring. Planting too early or late can increase the chances of bolting.
  • Manage Day Length: Keep track of the daylight hours in your area. If you are growing onions from seeds, you can start them indoors under controlled lighting conditions to delay exposure to the critical day length for bolting. Alternatively, choose varieties with longer maturation periods that align with your region’s day length.
  • Provide Adequate Water: Consistent and sufficient watering is vital for preventing bolting. Onions require regular moisture, especially during dry spells. Avoid water stress, as it can trigger the reproductive phase in the plants.
  • Mulching: Apply a layer of organic mulch around the onion plants to help regulate soil temperature and moisture levels. Mulching also prevents weed growth, reducing competition for nutrients and water.
  • Fertilize Wisely: Provide a balanced fertilizer with appropriate levels of nitrogen, phosphorus, and potassium to support healthy vegetative growth. Avoid excessive nitrogen, as it can encourage bolting.
  • Thinning Seedlings: If you start onions from seeds, thin the seedlings to the recommended spacing to avoid overcrowding. Crowded plants can experience stress and are more prone to bolting.
  • Companion Planting: Consider companion planting with other crops that may provide some shade to the onion bed during hot periods. This can help regulate soil and air temperatures and reduce stress on the onions.
  • Monitor Environmental Conditions: Keep a close eye on weather forecasts and be prepared to protect the onion crop during extreme temperature fluctuations. Consider using shade cloth or row covers to shield the plants from excessive heat.
  • Pest and Disease Management: Healthy plants are better equipped to resist bolting. Implement proper pest and disease management practices to prevent stress on the onions.
  • Harvesting Promptly: For onions that do bolt, harvest them promptly to prevent the energy loss from the bulb. Use bolting onions as soon as possible, as their quality may not be as good as non-bolting onions.

4. Managing Bolting Onions

Managing bolting onions involves a combination of preventive measures and specific actions to address the issue once it occurs. If you spot signs of bolting in your onion crop, here are some steps to effectively manage the situation:

  • Early Detection: Regularly inspect your onion plants for any signs of bolting. Detecting bolting at an early stage allows you to take appropriate action before it progresses further.
  • Harvest Early: If you notice a few onions in your crop starting to bolt while others are still growing well, consider harvesting the bolting onions early. While these onions may not store as long as non-bolting ones, you can still use them fresh in various dishes.
  • Remove Flower Stalks: For onions that have partially bolted but still have a substantial bulb, promptly remove the flower stalks. Snip or cut the stalks at their base to redirect the plant’s energy back into the bulb, enhancing its quality.
  • Allow Bolting to Complete: If a significant portion of your onion crop has already bolted, you may choose to allow the bolting process to complete. The flowers produced will eventually turn into seeds that you can use for future plantings.
  • Save Seeds: To collect seeds from bolting onions, let the flower stalks fully mature and dry out. Once the seed pods turn brown and dry, harvest them and store the seeds in a cool, dry place for next year’s planting.
  • Adjust Planting Time: For future plantings, consider adjusting your planting time to avoid the onset of bolting. Plant onions early enough in the season so that they mature before reaching the critical day length for bolting.
  • Companion Planting: Companion planting with other crops can provide shade to the onion bed during hot periods, helping to regulate temperatures and reduce stress on the onions.
  • Mulching: Apply a layer of organic mulch around the onion plants to help maintain soil moisture and temperature levels, reducing stress on the plants.
  • Water Management: Ensure consistent and sufficient watering for your onion crop. Proper irrigation can help prevent bolting caused by water stress.
  • Address Stress Factors: Identify and address any environmental stress factors that may be contributing to bolting, such as nutrient deficiencies or pest infestations.
  • Rotate Crops: Practice crop rotation to prevent the buildup of pathogens or pests that could stress the onion plants and trigger bolting.

5. Transplanting Onion Seedlings

If you’ve started onions indoors from seeds and they begin to bolt, you can transplant them outdoors. Harden the seedlings before transplanting to minimize transplant shock. Ensure the outdoor location provides the right conditions for onion growth.

6. Companion Planting

Employ companion planting strategies to deter bolting in onions. Planting onions with other compatible crops can help create a more favorable environment for onion growth.

7. Crop Rotation

Rotate your crops annually to reduce the risk of soil-borne diseases and nutrient imbalances that can lead to bolting.

8. Mulching

Apply organic mulch around onion plants to regulate soil temperature and moisture, reducing stress and bolting risk.

9. Irrigation

Provide consistent and adequate irrigation to prevent water stress, a common trigger for bolting.

10. Fertilization

Apply balanced fertilizer to ensure your onion plants receive essential nutrients for healthy growth.

11. Pruning

Prune any competing plants that might shade the onion crop, as excessive shade can lead to bolting.

12. Shade Cloth

During periods of intense heat, use shade cloth to shield onions from scorching temperatures and minimize bolting.

13. Harvesting and Storing Onions

Harvesting and storing onions properly is essential to preserve their quality and extend their shelf life. Here’s a step-by-step guide on how to harvest and store onions:

Harvesting Onions:

  1. Timing: Onions are ready for harvest when their tops start to turn yellow and fall over. Typically, this occurs in late summer or early fall, depending on the onion variety and planting time.
  2. Loosen Soil: Before harvesting, gently loosen the soil around the onions using a garden fork or shovel. Be careful not to damage the onion bulbs during this process.
  3. Lift the Bulbs: Carefully lift the onion bulbs from the soil, leaving the tops intact. Avoid pulling the onions by the tops, as this can lead to bruising or damage.
  4. Cure Onions: After harvesting, place the onions in a well-ventilated, shady area to cure. Spread them out in a single layer on a clean, dry surface, such as a wire rack or a well-spaced mesh screen. Curing allows the outer layers of the onion to dry and toughen, enhancing their storage potential.

Storing Onions:

  1. Cleaning: Once the onions are cured, gently brush off any loose soil and trim the roots, leaving about 1 inch of the roots attached to the bulb.
  2. Inspect for Damage: Discard any onions with visible signs of damage, disease, or soft spots, as they will not store well and may affect the quality of neighboring onions.
  3. Storage Location: Choose a cool, dark, and dry storage location for your onions. A well-ventilated basement, pantry, or garage is ideal. Avoid areas prone to high humidity, as this can cause onions to sprout or rot.
  4. Storage Containers: Use breathable storage containers such as mesh bags, old pantyhose, or wooden crates. Avoid using plastic bags, as they can trap moisture and promote rot.
  5. Layering: Place the onions in the storage containers in a single layer, making sure they do not touch each other. Overcrowding can lead to bruising and spoilage.
  6. Check Regularly: Periodically check your stored onions for any signs of spoilage, rot, or sprouting. Remove any affected onions to prevent the issue from spreading.
  7. Separate Varieties: If you have multiple onion varieties, store them separately, as each variety may have different storage requirements.
  8. Freezing or Drying: If you have an abundance of onions, consider freezing or dehydrating some for long-term storage and use.

15. Onion Bolting FAQs

Let’s address some common questions about what to do when onions bolt:

FAQ 1: What causes onions to bolt? Bolting can occur due to temperature fluctuations, day length, and plant stress.

FAQ 2: Can bolting onions be eaten? Yes, bolting onions can still be eaten, especially the green tops.

FAQ 3: Can I save seeds from bolting onions? Absolutely! Allow some bolting onions to mature and produce seeds for future planting.

FAQ 4: How can I prevent bolting in onions? Choose the right variety, plant at the appropriate time, provide adequate nutrition, and ensure proper spacing.

FAQ 5: Should I remove the flower buds on bolting onions? Yes, remove the flower buds to redirect the plant’s energy into bulb development.

FAQ 6: What can I do with onions that have bolted? Consider using bolting onions in recipes that call for green onions or chives.


Bolting onions can be disheartening, but with the right knowledge and proactive measures, you can minimize its impact and still enjoy a bountiful harvest. In this guide, we’ve covered various aspects of what to do when onions bolt. From identifying bolting signs to managing the situation and even harvesting seeds for future planting, you now have the expertise to handle bolting onions like a pro.

Remember, preventing bolting is key, so choose suitable onion varieties, provide proper care, and monitor your plants regularly. With dedication and attention, you’ll have a thriving onion crop and delicious homegrown onions to savor throughout the year!