Onion seedlings are hardy plants that can withstand cold temperatures to some extent. However, there are limits to their cold tolerance that every gardener should understand when growing onions. In this article, we’ll explore exactly how cold onion seedlings can tolerate before suffering damage.
An Overview of Onion Seedlings’ Cold Tolerance
Onion seeds can be directly sown in the garden bed or started indoors and later transplanted outside. The young onion seedlings that emerge are more vulnerable to freezing injury than mature, established onion bulbs and plants. Here’s a quick rundown of onion seedlings’ ability to withstand chill:
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Most onion seedlings can tolerate short-term temperatures as low as 20°F (-7°C) Prolonged exposure to freezing causes cell damage,
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Temperatures of 25°F (-4°C) or below for an extended time period can be detrimental and may kill the seedlings
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The roots are especially sensitive to freezing. They may rot after thawing from a hard freeze.
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Initial signs of cold damage show up first in the foliage, which may wilt, turn yellow, or collapse.
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Slowed growth and stunted plants are also common symptoms of cold stress in seedlings.
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Freezing that impairs the roots limits water and nutrient uptake, compounding cold injury.
While onion seedlings have some inherent cold hardiness, freezing temperatures persisting more than briefly can overwhelm their defenses. Taking action to modify the environment around seedlings is critical to avoid lasting harm when the mercury plummets.
Protecting Seedlings from Hard Freezes
No gardener enjoys watching helplessly as a cold snap damages tender vegetable seedlings. Here are some techniques for shielding onion seedlings from harsh freezing conditions:
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Cover plants with cloches, cold frames, or fabric row covers to trap protective warmth. Make sure to provide ventilation on sunny days.
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Heavily mulch around seedlings with 2-3 inches of straw, leaves, pine needles or other organic matter. This insulates the soil.
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Water plants thoroughly before an expected freeze. Moist soil retains more heat than dry ground.
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In extreme cold, wrap insulation around containers or move to a sheltered location.
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Avoid over-fertilizing, which leads to tender growth prone to freezing damage.
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Choose inherently cold-hardy onion varieties like Walla Walla, Red Wing, and Candy hybrids.
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Monitor the forecast and be ready to take preventative action before temperatures plummet drastically.
With some simple protective measures, young onion plants can survive bouts of cold weather that might otherwise spell doom. It’s also key to assess for damage afterward and allow time for recovery.
Caring for Seedlings After Freezes
Even cold-tolerant onion varieties can experience setbacks following an unexpected hard freeze. Properly evaluating the damage and responding with care gives them the best odds of rebounding. Here is a post-freeze recovery plan:
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Remove any foliage that is mushy or has collapsed to prevent rot from spreading.
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Check bulbs for soft spots and trim away damaged outer layers if found.
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Thoroughly water to restore moisture lost due to frozen soils.
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Ensure plants receive ample sunlight after several consecutive overcast days to restart growth.
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Apply a balanced soluble fertilizer as directed to aid recovery.
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Be patient. It may take 1-2 weeks for new leaves to emerge and growth to accelerate.
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Watch for ongoing issues like stunted plants or distorted foliage and troubleshoot as needed.
With attentive care and favorable conditions after being struck by a late frost, your onion seedlings can make a comeback. But extended freezing exceeding their tolerance will require reseeding or replanting.
Choosing Cold-Hardy Onion Varieties
One strategy to improve onion seedlings’ odds of surviving cold snaps is to pick adapted, cold-tolerant cultivars. Here are some excellent chilly-weather choices:
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Stuttgarter Giant – Very hardy large storage onion, tolerates down to -20°F (-29°C) when mature.
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Candy – Intermediate-day sweet hybrid with improved frost tolerance, matures in 110-120 days.
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Patterson – Early yellow onion bred for cold climates, ready for harvest in 100 days.
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Super Star – Extremely hardy yellow hybrid onion, withstands temps as low as 10°F (-12°C).
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Red Wing – Purplish-red onion with good frost resistance, stores up to 8 months after curing.
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Walla Walla – Sweet, mild yellow onion surviving temperatures down to 10°F (-12°C).
Seeking out onions specifically developed to perform well in cold conditions gives your crop an advantage when chilly weather hits. Pairing cold-hardy varieties with protective measures helps onion seedlings successfully emerge from spring cold snaps.
Ideal Temperature Range for Growth
While onion seedlings have some tolerance for chilly temperatures, they grow best within an optimum temperature range:
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Minimum Temperature for Growth: 40-50°F (4-10°C)
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Optimal Temperature for Growth: 55-75°F (13-24°C)
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Ideal Temperature for Bulb Formation: 60-65°F (16-18°C)
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Maximum Temperature for Growth: 75-85°F (24-29°C)
Providing warmth early accelerates germination and leaf development. Cooler temperatures around 60-65°F later on produce the largest bulbs. Heat above 75°F can cause premature bolting. Monitoring soil and air temperatures helps predict performance.
Using Protective Coverings
To modify temperatures around onion seedlings, useful season extending techniques include:
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Low tunnels made from hoops and plastic sheeting to retain heat.
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Thick mulch blankets to insulate the soil and protect roots.
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Fabric row covers to buffer plants from wind and cold air.
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Cold frames or cloches to shield vulnerable plants.
These tools create warmer microclimates, boosting growth. Ventilate on sunny days to prevent overheating and allow air circulation. With basic protective coverings, seedlings can thrive despite unpredictable spring weather.
Achieving a successful onion harvest starts with helping young seedlings survive early season cold spells. Understanding the temperature limits seedlings can tolerate guides efforts to safeguard the crop. Onion seedlings can withstand short freezing periods in the 20s°F when established. But extended sub-freezing temperatures below 25°F call for preventative measures like mulch, row covers, or cloches to avert irreparable damage. With thoughtful protection and cold-hardy varieties, your onions can power through cool, frosty conditions on their journey to mature bulbs.
Are Onions Frost or Freeze Resistant? : Garden Space
FAQ
How much cold can onion seedlings take?
We say that onion plants can survive temperatures as low as 20˚F, but what matters more is how long the temperatures are below freezing. Longer periods of freezing temperatures cause more damage to the plants.
When can onion seedlings go outside?
What is the lowest temperature onions can tolerate?
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Short-term cold:Onions can handle brief dips below freezing, but extended periods of cold can damage them.
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Protection during freezes:Covering plants, creating a layer of moist soil for insulation, and watering plants well before a freeze can help protect them.
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Ideal temperatures:Onions generally thrive in temperatures between 50°F and 75°F (10°C to 24°C).
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Hardy varieties:Some onion varieties are more cold-hardy than others, with some able to survive winter temperatures in milder climates.
How cold can seedlings tolerate?
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General Tolerance:Most seedlings will start to show signs of damage when temperatures dip below 32°F (0°C).
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Freezing Point:Temperatures at or below 32°F (0°C) for a few hours can cause damage, and prolonged exposure below 28°F (-2.2°C) can be lethal.
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Species Variations:Some plants, like peas, are more cold-tolerant than others, like tomatoes or peppers, which are very sensitive.
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Harden Off:To acclimate seedlings to outdoor conditions, gradually expose them to cooler temperatures over a period of days.
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Protection:Use cold frames, row covers, or move seedlings indoors during cold spells to protect them.
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Timing:Consider planting dates based on your region’s expected last frost date.
What temperature can onion seedlings tolerate?
Onion seedlings can tolerate temperatures as low as 20°F (-7°C). Onion seedlings can tolerate a cold temperature for several days. Onion seedlings can tolerate light intensity of up to 6,000 foot-candles. Onion seedlings can tolerate various soil types, including sandy, loamy, and clay soils.
Can onion seedlings survive cold?
The ability of onion seedlings to endure cold temperatures varies, but most can tolerate temperatures as low as 20°F (-6°C) for a certain period of time. 10. Can I plant onion seedlings indoors to protect them from cold?
Can onion seedlings withstand freezing?
Generally, cold-tolerant onion seedlings can withstand temperatures below freezing, but only up to a point. Prolonged exposure to temperatures near or below 28°F (-2°C) can cause significant damage to the seedlings. When the temperature dips too low, the seedlings will start to experience an increase in cold stress.
Can onion seedlings survive a light frost?
Yes, onion seedlings can typically survive a light frost, especially if they have been properly hardened off and are otherwise healthy. 3. How can I protect my onion seedlings from cold temperatures? You can protect your onion seedlings from cold temperatures by using row covers, cloches, or other protective barriers to shield them from the cold.
What temperature can onions eat?
When it comes to the ideal temperature for onions, the general rule is that onions can tolerate temperatures as low as 32°F (0°C). This is the temperature at which most onion varieties will begin to experience cold damage.