What To Do When Your Onion Plants Start Going To Seed

Seeing your lovingly tended onion plants shoot up a flower stalk can be disheartening for any gardener. This process known as “bolting” turns your prospective big bulbs into disappointing greens destined for the compost heap. But bolting doesn’t have to spell disaster for your onion patch. Read on to understand why onions bolt, what it means for your crop, and most importantly, what you can do about it!

What Is Bolting and Why Do Onions Bolt?

Onions and other alliums like garlic and shallots are biennial plants, meaning they take two years to complete their lifecycle. The first year they grow foliage and swell their underground bulb, storing energy for the next phase. The second year, they use that reserved energy to rapidly shoot up a tall central stalk and produce flowers, seeds, and then die back.

This is all part of the natural lifecycle. However, when onions “bolt” prematurely in the first year, it means something triggered the early formation of that flower stalk. This diverts energy away from bulb growth, resulting in stunted onions.

Onions bolt in response to stress, which causes a survival mechanism to kick in and skip to the reproduction phase Key stressors include

• Temperature extremes – prolonged cold or sudden heat waves
• Drastic temperature swings – warm days and cold nights
• Lack of water during hot, dry periods
• Excess moisture from heavy rains, irrigation, or over-wet soil
• Damage to the bulb and roots from cultivation, transplanting, or pest attacks
• Excess nitrogen fertilization later in the season

What To Do With Bolting Onions

When you spot an onion plant shooting up a developing flower stalk, take these steps:

• Remove the stalk. Cut or snap off the stalk at ground level. This won’t restart bulb growth, but it stops further energy drain.

• Harvest ASAP. Use, preserve, or process the onions right away. Bolted onions won’t size up anymore or store well.

• Leave some stalks. Allow a few bolted onions to fully flower and set seed. Collect these for planting next year.

• Chop and freeze. Diced onions freeze nicely for later cooking use.

• Dehydrate. Dried onion slices or powder are great pantry staples.

• Freeze dry. Freeze dried onions retain excellent texture and flavor for soups, stews, etc.

Preventing Onions From Bolting

While you can’t control the weather, using good cultural practices can help minimize bolting:

• Choose adapted varieties. Pick long day, short day or intermediate onions suited to your climate.

• Use seeds or transplants. Sets (small bulbs) are prone to bolt, especially in hot areas.

• Time planting carefully. Follow local guides for best windows to plant fall or spring onions.

• Water consistently. Ensure onions get 1-2 inches of water per week, more in extreme heat.

• Avoid damaging plants. Be gentle when weeding, hilling and cultivating around onions.

• Go easy on nitrogen. Reduce high-nitrogen fertilizers when bulbing begins.

• Monitor for pests. Prevent damage from onion flies, maggots, nematodes, etc.

• Cover with soil. Hill up soil or mulch around the bulbs to protect from sunscald.

When Bolting Spoils Your Onion Harvest

Even if you do everything right, some onions may still bolt, especially during periods of abnormal weather. While disappointing, bolting doesn’t have to mean a total loss. Adjust your plans, use the greens, and preserve the bulbs for later use in your kitchen. Taking notes on which varieties did best can guide future plant choices too.

Most importantly, don’t let a bolting year discourage you from growing onions again. Collect some seeds and start planning next season’s onion crop wiser and better equipped to avoid potential pitfalls. With a few lessons learned, you’ll be back on track to big, beautiful bulbs once again.