What Does It Mean When Onions Flower?

QUESTION: What does it mean when onion plants flower? Sometimes my onion plants flower too early in the season. Is this the same as bolting? — Luke C.

ANSWER: It’s natural for onion plants to flower at the end of their season. However, if your onion plants are flowering before it’s time to harvest your onions, this is called bolting. An onion that is bolting will produce a stalk that grows high and is topped with a flower head, which eventually gives way to seeds.

What Causes Onions to Bolt?

Onions usually bolt after a period of hot weather. However, that isn’t the only reason for onions to bolt too early in the season. In fact, anything that stresses the plants can result in them sending up a flowering stalk early and bolting. In addition to hot weather, a few days of chilly weather early in the growing season is another common cause of bolting.

Bolting is a response to stress because the plant responds to the stressful stimulus by going into reproduction mode early. It’s a response to the danger that the plant perceives. Once this reproductive process has started, the plant won’t spend any more energy on developing tasty onion bulbs.

How to Prevent Onions From Bolting

When onion plants go into reproductive mode too early in the season, it can cause the bulb of the onion to lose its flavor. The energy the plant uses to create its flowering stalk and seeds is diverted from making the onion itself grow into a tasty vegetable. Once bolting has started, the onion bulb stops its development. The longer you leave a flowering stalk, the worse the onion itself begins to taste. That’s why you’ll want to prevent your onion plants from bolting if you possibly can.

Cover your onions if cold weather threatens the plants early in their growing season. This will prevent the onions from bolting because a few days of chilly temperatures stressed the plants while they were still young.

When temperatures climb, you can help prevent the kind of stress on your plants that causes bolting by keeping the onions watered well. Not only will this keep the plants well hydrated—making sure your plants have plenty of water in warm weather will also help to lower the temperature of the soil where your onion plants are growing. As water on the surface of the soil evaporates into the air around your plants, it will also help keep things cooler.

Choose the right time to plant your onions if you want to prevent bolting. The recommended planting time is set so that your onions have the right climate and environment to grow healthy and strong. Planting your onions in the garden at just the right time is the number one thing you can do to prevent your plants from bolting.

There are so many different varieties of onion to choose from, but one of the main things you can do to prevent your onion plants from bolting is to choose the right variety for your local environment. Try to find an onion variety that’s developed near you. In the south part of the U.S., choose short-day onions. Long-day onion varieties work best for the northern part of the U.S. For those in the middle of the country, intermediate varieties are the way to go.
If you’re growing green onions, try using larger sets. Choosing larger sets from the beginning means you’ll be ready to harvest your onions before the plants have an opportunity to bolt.

Keep onion sets at the right temperature to keep them from bolting. If they’re stored at lower temperatures, the likelihood of bolting once your sets get into the field increases.

Ensure that the soil around your onion plants isn’t too loose. If your onions aren’t positioned securely in the soil, your onion plants can become stressed because their roots are more easily disturbed. Instead of burrowing through the soil to gain nutrients, the plant can start to starve because it loses its access to the soil and the hydration it contains.

Too much fertilization can be a bad thing for your onion plants and can cause bolting. When onion plants get too much fertilizer at the beginning of their growth cycle, they produce bulbs that are too large. In addition to making sure you don’t exceed the prescribed amount of fertilizer early in the season, you should also make sure to stop using fertilizer on your onion plants once you see that a bulb has developed.

What to Do If Your Onion Plants Bolt

Sometimes even the most careful preventive measures aren’t enough to prevent your onion plants from bolting. If you see that your onion plants are sending up their flowering stalks too early in the season, quick action can save your onion harvest before the flavor is ruined.

Snip the flowering heads off your onion plants as soon as you notice that the onions have bolted. This will prevent the growth process that causes the bulb to split. Then you should go ahead and harvest the bulbs of any plants that have bolted, and eat the onions as soon as possible. The longer you leave the onion plants in the field once they’ve produced that flowering stalk, the more their taste will be negatively affected.

Now you’ve learned what it means when your onion plants flower, but that’s only the beginning. This article has armed you with the knowledge of how to keep onions from bolting. However, sometimes that’s impossible, so we’ve also informed you of what to do if you notice your onions sending up flowering stalks too early in the season. Remember, all is not lost if your onion plants bolt. Simply clip the flowering heads to freeze their production, then harvest and consume bolted onion bulbs as soon as possible to prevent their quality from diminishing.