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If you are looking to grow the biggest and most beautiful onion bulbs this year, bolting can throw a big wrench in those plans. Fortunately, there are several ways to handle bolting in your onion crop and steps you can take to prevent it from happening next year.
To prevent your onions from bolting, make sure they have plenty of water and are covered when the temperature outside gets too cold. If your onions do bolt, be sure to remove the onion scape so the bulb won’t split, and plan to harvest the onion as soon as possible.
In this article, we will dive deeper into the best preventative measures for onion bolting, what you can do with them if they already have, and the most bolt-resistant varieties. As a bonus, I’ll share some tips on how to save onion seeds once they have flowered.
Why is onion bolting bad?
Onions that have bolted will struggle to keep growing as all of their energy is now being directed toward producing seeds. This can leave you with much smaller onion bulbs than anticipated. While small onions may not bother you that much, onions that have bolted are also more susceptible to rot and will not store as long as an unbolted onion.
If you find rot on any of your onions, the best thing you can do is remove and compost that plant. By putting a rotting onion into storage, you run the risk of spreading that rot to the rest of your beautiful onions as well. If rotting onions in storage are something that you struggle with, check out this article on how to fix it.
Bolted onions are also much more likely to split leaving you with two smaller-sized onions instead of one large onion.
Why do onions bolt?
Onions are biennial plants meaning that their life cycle spans across two years. The first year is when the onion produces its bulb – the part we eat – and the second year is when it flowers and goes to seed. Most onions don’t see their second year of life because they are harvested before then.
Onions will bolt when they experience stress from unideal conditions. When the temperature outside gets too hot or too cold, it sends the plants into “panic mode” and makes them think that they need to quickly reproduce before they die.
Onions will do this by sending up a scape with a seed pod at the end. If left alone, this pod will eventually open to reveal a flower that will create seeds after it’s been pollinated.
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If you notice that your onions have bolted, here are some next steps you should take:
Remove the onion scape
When an onion starts to bolt, all of its energy is going towards producing seeds. By cutting the scape, you can give your onion a little more time in the ground. But, don’t throw your onion scapes away! Scapes are completely edible and delicious and can be used just like a conventional green onion.
Harvest the onion
If you have removed your onion scapes, you will want to harvest those onions sooner rather than later. As previously mentioned, bolted onions will not store well. At this point, they are much more susceptible to rot in and out of the ground.
Consider seed saving
Maybe you already have plenty of good onions and can spare losing a few to premature flowering. In that case, try saving the seeds! Seed saving is a fantastic way to ensure seed supply for the next growing season. Letting crops flower will also increase pollinator traffic to your garden. At the end of this article, we’ll explain the best way to collect onion seeds.
How to prevent bolting in onions
If you are concerned about your onions bolting, have no fear! There are several preventative measures you can take to ensure this does not happen:
As temperatures start to warm and precipitation frequencies decrease in the summer months, most of the plants in your garden will need more water. This includes onions. Making sure your onions have ample water supply is crucial in keeping them from becoming stressed. The water will also cool the onions as it evaporates.
During the colder months, onions should be covered with some type of row cover or gardening fleece to keep them warm. Depending upon the weight of the row cover, it can provide your onions up to 10 degrees of protection. The heavier the cover, the warmer it keeps the plants.
Choosing the right varieties
When it comes to choosing onion varieties, you have 3 types to choose from: long-day, intermediate-day, and short-day. If you live in a more northern region, long-day onions are your best bet as the longer days of summer will trigger bulbing. As you get further south consider choosing an intermediate or short-day variety instead.
Choosing what onion variety is best for your garden can be overwhelming but here are some bolt-resistant varieties to help you get started:
- Walla Walla Sweet
- Sierra Blanca
- Sweet Vidalia
- Texas Early Grano
Another thing to take into consideration is whether to start your onions from sets, seeds, or seedlings. While onion sets are more resistant to pests and disease, they are also more likely to bolt due to the sets technically being in the second year of their life cycle. Check out this article on the difference between sets, seeds, and seedlings to help you decide which onion start is the best for your garden.
How to remove onion scapes
To remove onion scapes, all you need to do is cut the scape at its base where it starts coming out of the plant- it’s that easy! You can also snap the scape off with your finger if you don’t have any tools handy. Once you have removed the onion scapes, feel free to compost them or save them to eat.
Similarly, you may want to consider topping all of your onions to improve bulb size. Check out this great article for more information on how to top your onions.
How to collect onion seeds
Onions are pollinated through insects and can sometimes be difficult to keep pure. If you are interested in saving a lot of seeds, try keeping the flowers covered and pollinating them by hand. As the flowers ripen, they may need to be staked as they will become heavy with seeds.
Once the flowers have become brown and dried out, you’ll want to cut them off. Place your flowers in a brown paper bag and keep the bag somewhere cool and shaded until the flowers are completely dry. This part may take a couple of weeks.
Last comes the fun part. All you need to do to remove the seeds from the flower head is shake the bag. Once, you’ve given the bag a few good shakes, dump the contents out onto a plate and collect your seeds.
Having onions bolt can be disheartening for any gardener – but all hope is not lost. As long as you take special care to protect the onions from extreme temperatures and plan to remove the scapes at the first sign of bolting, you are sure to have a fantastic onion harvest.
At the end of the day, almost all parts of the onion plant are edible. If your onions bolted this year and you did not end up getting the bulb harvest that you expected, try eating the green leaves! Maybe you’ll discover a new favorite garden treat.
Check out these must-have gardening products
You don’t need much to start gardening, but some tools and products will make a difference in how comfortable and effective gardening can be for you. Here are my favorites:
- Garden Trowel. A good garden trowel will last you many years. I love how sturdy this hand trowel from WOLF-Garten is, the metal doesn’t bend and it has a nice grip.
- Trimming Scissors. I use them for delicate pruning and harvesting all summer long, and they’re super handy. These Teflon Trimming Scissors are extra nice because they don’t rust as easily.
- Dutch Hoe. Dutch hoes may seem old-fashioned, but there’s nothing like a quick sweep through the topsoil to get rid of small weeds – no bending required. I love WOLF-Garten’s selection: this dutch hoe coupled with their universal handle.
- Grow Lights. These grow lights from Mars Hydro are super strong, yet dimmable, so they fit every stage of growth. They don’t put out too much heat and are very economical.
- Seedling Trays. There’s an art to choosing the best size for seedling trays so that it holds the perfect amount of water and gives the roots enough room to grow. These germination plugs are perfect when coupled with 1020 bottom trays.
- Liquid Fertilizer. You’ll need to feed your plants from the seedling stage, all the way to fruiting. This organic fish & seaweed blend is a very versatile option. Use it half-strength for young plants and full-strength for established plants.
Browse our list of tools, fertilizers & pesticides, indoor growing products and seed shop recommendations – we hope you find our selection useful and it saves you some time!