What To Do When Onion Plants Flower? Understanding and Addressing Premature Bolting
When onion plants flower, a process called bolting, it signals the plant’s focus has shifted from bulb development to seed production. The best course of action depends on your gardening goals, but generally involves prompt action: you can either harvest the onion for immediate use, or attempt to prevent further bolting, accepting a smaller bulb.
Understanding Onion Bolting
Onion bolting, the premature flowering of an onion plant, is a common issue for gardeners. It occurs when the plant experiences stress, most often due to fluctuating temperatures, particularly a cold snap followed by warmer weather. This temperature fluctuation triggers the plant’s reproductive cycle, causing it to send up a flower stalk (also known as a seed stalk). While flowering is natural for onions in their second year of growth, it’s undesirable when growing onions for their bulbs, as it negatively impacts bulb size and quality.
Why Bolting is Problematic
- Reduced Bulb Size: The plant diverts energy away from bulb development and towards flower and seed production.
- Tough and Bitter Bulbs: Bolted onions often develop a tougher texture and a more bitter taste.
- Shortened Storage Life: Bolted onions don’t store as well as unbolted onions.
Identifying Bolting Onions
The telltale sign of a bolting onion is the emergence of a thick, central stalk from the middle of the plant. This stalk will grow rapidly and eventually produce a flower head at its top. You might also notice the leaves starting to yellow or the bulb becoming less firm.
What to Do When You See an Onion Flower
Immediate Harvest (Recommended): The most effective solution is to harvest the onion immediately. While it won’t store as long as an unbolted onion, it’s still perfectly edible. Use it in cooking as soon as possible.
Cut Off the Flower Stalk (Less Effective): You can attempt to cut off the flower stalk as soon as you notice it. This may redirect some energy back into bulb growth, but the bulb will likely still be smaller and of lower quality than if the plant had not bolted. The plant may also continue to produce new flower stalks. Make sure to use sterile pruning shears and cut the stalk as close to the base as possible without damaging the surrounding leaves.
Let it Flower (for Seed Collection): If you’re interested in collecting onion seeds, allow the plant to flower and mature. Once the flower head dries and the seeds turn black, you can harvest them for future planting. Be aware that seeds from bolted onions may be more prone to bolting in subsequent generations.
Preventing Onion Bolting
Prevention is key to avoiding bolting. Here are some strategies:
- Choose the Right Variety: Select onion varieties that are well-suited to your climate and are less prone to bolting. Short-day onions are best for warmer climates, while long-day onions are better for cooler climates.
- Proper Planting Time: Plant onions at the appropriate time for your region. Planting too early can expose them to cold snaps that trigger bolting. Consult your local agricultural extension for recommended planting dates.
- Avoid Temperature Fluctuations: Protect young onion plants from sudden temperature changes. This can be achieved by using row covers or cold frames.
- Consistent Watering and Fertilization: Provide onions with consistent moisture and nutrients to keep them healthy and stress-free. Water deeply and regularly, and fertilize with a balanced fertilizer according to package instructions.
Comparing Options When Onions Bolt
| Option | Pros | Cons | Best For |
|---|---|---|---|
| Immediate Harvest | Prevents further energy loss; Edible onion for immediate use | Reduced storage life; Smaller bulb | Home gardeners prioritizing consumption over long-term storage |
| Cut Off Flower Stalk | Might slightly improve bulb size | Limited effectiveness; Plant may continue to bolt; Still reduced quality | Gardeners who want to experiment but accept likely reduced yield |
| Let it Flower for Seeds | Collect onion seeds | Significantly reduced bulb size and quality; Seeds may inherit bolting tendency | Gardeners interested in seed saving, understanding potential risks |
Frequently Asked Questions (FAQs)
What does bolting actually do to the onion bulb?
Bolting diverts the plant’s energy from developing a large, firm bulb to producing flowers and seeds. This results in a smaller bulb that is often softer, more bitter, and less flavorful. The texture can also become tough, making it less desirable for cooking.
Can I eat an onion that has bolted?
Yes, bolted onions are generally safe to eat. However, the flavor and texture may be affected. They tend to be more bitter and have a tougher consistency. It’s best to use them in cooked dishes where the strong flavor can be masked.
Will cutting off the flower stalk guarantee a larger bulb?
No, cutting off the flower stalk does not guarantee a larger bulb. While it may redirect some energy back into bulb growth, the plant has already initiated its reproductive cycle, and the bulb will likely still be smaller and of lower quality than if it hadn’t bolted.
What are the best onion varieties for avoiding bolting?
The best onion varieties for avoiding bolting depend on your climate. In warmer climates, short-day onions like Granex, Yellow Bermuda, and White Bermuda are good choices. In cooler climates, long-day onions like Walla Walla Sweet, Yellow Spanish, and Redwing are more suitable. Always check with your local agricultural extension for recommendations specific to your region.
How do I store onions that have bolted?
Bolted onions don’t store as well as unbolted onions. They should be stored in a cool, dry place and used as soon as possible, ideally within a week or two. Avoid storing them near apples or bananas, as these fruits release ethylene gas, which can speed up ripening and spoilage.
If my onions bolted this year, will they bolt again next year if I save the seeds?
There’s a higher chance that seeds from bolted onions will produce plants that are also prone to bolting. Bolting can be influenced by genetics, so selecting seeds from plants that didn’t bolt is generally recommended.
Is there anything else besides temperature that can cause bolting?
While fluctuating temperatures are the most common cause, other factors can also contribute to bolting, including poor soil conditions, insufficient water, and nutrient deficiencies. Stressed plants are more likely to bolt.
Can I transplant bolted onions?
Transplanting bolted onions is not recommended. The stress of transplanting will likely further hinder bulb development and could even kill the plant.
What should I do with the soil where bolted onions grew?
The soil where bolted onions grew is perfectly fine to use for other crops. Consider adding compost or other organic matter to improve its fertility. Avoid planting onions in the same spot for several years in a row to help prevent the buildup of soilborne diseases.
Should I fertilize my onions differently if I suspect they are going to bolt?
Evenly fertilizing your onions can help mitigate the risk of bolting, but it won’t stop it once it has begun. A balanced fertilizer helps provide proper nutrients for overall plant health, which will assist the plant in any stage of growth.
Are onion flowers edible?
Yes, onion flowers are edible. They have a mild onion flavor and can be used as a garnish or added to salads.
Can I compost the flower stalks of bolted onions?
Yes, you can compost the flower stalks of bolted onions. Make sure to chop them into smaller pieces to help them decompose more quickly.