Growing lettuce is a lot like getting along with people. You want to be careful not to expect too much, without expecting too little, either.
Some gardeners want this cool-season vegetable to keep producing in hot weather, for example, and that’s just not possible.
But you may not be aware you can rely on most varieties of Lactuca sativa to keep growing as freezing temperatures set in, with some support from you, the gardener.
You will need to protect most types from frost. But when you do, you can expect this species to produce baby leaves and even full-size heads well into late autumn or winter, times of year when fresh greens are so welcome.
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I’d like to encourage you to ask more from your lettuce in the cool months, but only after giving it what it needs to resist frost or survive light freezes.
You’ll be happy to hear it’s much easier to get your crop to meet the expectation that it will survive through a frost than it might be to get a human to start picking up their socks or waking up on time!
Lettuce is a cool-weather loving plant that thrives in chillier temperatures. As a frost-hardy vegetable, lettuce seedlings can withstand colder conditions than many other crops. However, lettuce growth and development are affected once temperatures drop below optimal ranges. Understanding lettuce’s cold tolerance at various growth stages enables gardeners to better protect their crops.
Lettuce Prefers Cool Conditions
Lettuce grows best in cooler temperatures between 45-75°F (7-24°C). Temperatures on the lower end of this range are ideal for lettuce germination and seedling growth. As lettuce matures, it can withstand chillier temperatures.
Mature lettuce heads tolerate light frosts in the low 30s°F (-1°C). Brief freezes rarely damage mature plants, although growth will slow. Prolonged freezing temperatures below 30°F (-1°C) can injure or kill mature lettuce.
Lettuce seedlings are more vulnerable to cold conditions. However, they are among the most cold-hardy vegetables started from seed. Understanding lettuce seedlings’ unique cold tolerance aids gardeners in protecting their crops.
Optimal Temperatures for Lettuce Germination
Lettuce seeds germinate best in cool soil between 40-75°F (4-24°C). The optimal temperature range is 70-75°F (21-24°C) for quick, uniform germination. Temperatures above 80°F (27°C) inhibit lettuce seed germination.
While lettuce seeds can sprout in chillier soils down to 35°F (2°C) germination is slower and uneven. Temperatures below 40°F (4°C) often result in spotty germination over extended periods.
Lettuce Seedlings Tolerate Light Frosts
Young lettuce seedlings tolerate light frosts better than most vegetable transplants. Their small size and frost-hardy nature give them an advantage over other tender vegetables.
Most lettuce varieties tolerate temperatures as low as 20°F (-7°C) when young plants are properly hardened off. Hardening involves gradually exposing seedlings to cooler temps, wind, and sun to toughen them up before transplanting outdoors.
Butterhead and romaine lettuce varieties are more cold-tolerant than delicate leaf lettuces.cold-tolerant than delicate leaf lettuces.These types better withstand light frosts during early spring.
Direct-sown lettuce also demonstrates good frost tolerance when soils are cool. Plants started outdoors from seed acclimate as they sprout and grow.
Ideal Temperatures for Lettuce Seedling Growth
Lettuce grows best when daytime temperatures reach 60-70°F (16-21°C). Cool nights around 55°F (13°C) are preferable. Temperatures up to 80°F (27°C) are tolerated if plants receive ample moisture.
Seedlings grow poorly once daytime highs exceed 80°F (27°C), or nights stay above 70°F (21°C). Hot temperatures cause bitter, bolted lettuce before plants fully mature.
For best growth, lettuce seedlings prefer consistent temperatures between 60-75°F (16-24°C). Avoid large day/night temperature fluctuations that stress young plants.
Protecting Lettuce Seedlings from Cold Damage
Lettuce seedlings need protection when temperatures drop below their hardy range. Use floating row covers or cold frames to shield plants from freezing conditions.
For short cold snaps, a blanket or sheet can conserve warmth overnight. Remove coverings during daytime to prevent overheating.
Wait until after the final spring frost to transplant lettuce starts outdoors. Harden off seedlings for 7-10 days to enhance cold tolerance before placing them in garden beds.
Choose cold-tolerant lettuce varieties like Arctic King, Brune D’Hiver, North Pole, or Winter Density. Start seeds indoors 3-4 weeks before transplanting into the garden.
Lettuce can be direct-sown in very early spring once soils reach 40°F (4°C). Use season extension devices to protect outdoor seedlings from cold damage.
Identifying Frost Injury on Lettuce
Frost damage causes several symptoms on lettuce plants. Leaves turn limp and often appear water-soaked. Prolonged freezing may cause dried, browning leaf edges.
Leaf tips and margins are most susceptible to frost injury. Inner leaves are often protected and remain usable. Remove any damaged outer leaves promptly.
Severe frost can kill young seedlings outright. Entire plants collapse and decay due to the extensive destruction of tender tissue. Surviving lettuce may exhibit stunted, malformed growth.
Growing Lettuce Successfully in Cool Weather
Lettuce thrives in chilly spring and fall temperatures. To grow lettuce successfully:
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Select appropriate lettuce types for the season. Grow heat-tolerant varieties in warm weather.
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Start seeds indoors for early spring transplants. Harden off seedlings before garden planting.
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Time outdoor sowing carefully around frost dates. Plant very early in spring or late summer for fall crops.
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Use season extension devices to protect seedlings from extreme cold and frost.
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Monitor weather forecasts when cold conditions threaten. Shield plants or provide emergency covers as needed.
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Harvest lettuce promptly before hot weather causes bolting and bitterness. Make successive plantings for continual harvests.
With proper planting schedules and cold protection methods, gardeners can grow lettuce successfully despite chillier temperatures. Lettuce’s natural frost tolerance also makes it an ideal cool weather crop.
The Takeaway
Lettuce seedlings tolerate colder temperatures than many vegetable crops. While mature lettuce withstands light frosts, seedlings are more prone to injury. For best results, grow lettuce seedlings at optimal temperatures between 60-75°F (16-24°C). Shelter plants from extreme cold and hard freezes. With care, gardeners can cultivate lettuce effectively even during cool spring and fall weather.
Is Lettuce Cold Tolerant?
Lettuce is no Russian kale, which can grow merrily along when temps plummet to -10°F. It’s also less cold-hardy than most other cole crop leafy greens, including spinach, some mustards, and baby leaf brassicas.
But it is a quintessential cool-season crop, and some varieties grow quite well even if the temperature dips below freezing.
Jim Myers, plant breeder and researcher at Oregon State University, describes lettuce as “semi-hardy” vegetables, ones that will do okay in light frost, when air temperatures range from 28 to 32°F.
Most types grow best in temperatures from 55 to 65°F, but if you “harden” the plants by introducing them gradually to progressively colder temperatures, many leaf varieties and some butterhead and crisphead types will withstand the cold down to 20°F.
There are also numerous cultivars that have been bred or selected to survive really low temperatures, like -30°F, and I’ll share a couple of those varieties here in a minute.
But first let’s consider the average lettuce. Most types can usually sail through the occasional light frost, which occurs when temperatures are at or just a little below 32°F with a low dew point, and ice crystals begin to form.
But they require special measures on the part of the gardener to withstand hard frosts, when the air is colder than 28°F, or during hard freezes, when temps below 25°F last for four or more consecutive hours.
If you’re growing your average garden variety lettuce, stay tuned for frost protection tips.
If you haven’t decided what to grow yet but are serious about growing salad greens well into the frosty months, you may want to look into some of the veggies that can be harvested as baby leaves for salad, even in chilly weather.
Does Lettuce Need to be protected from Frost?
Growing your own lettuce is a beautiful thing. Not only is it rewarding to pick your own fresh produce, but once picked, lettuce will continue to grow, giving you successive harvests of fresh greens. But what happens when temperatures dip toward the freezing mark? Does your lettuce need to be protected from frost? Lettuce seedlings will generally tolerate a light frost and, unlike most vegetables, continue to grow through the fall when the possibility is a probability in some regions. That said, cold, clear nights may create frost damage in lettuce, especially if the duration of the cold snap is lengthy.
How cold can lettuce plants tolerate?
FAQ
At what temperature should I cover my lettuce?
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Frost Tolerance:Lettuce is generally considered a cool-season crop and can handle a light frost. However, prolonged exposure to temperatures in the 20s (Fahrenheit) can cause damage, especially to young seedlings.
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Covering for Protection:When frost is predicted, you can cover your lettuce plants with row covers, frost cloth, or even old blankets to create a barrier against the cold.
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Timing:Cover your lettuce plants late in the day, when the temperature is beginning to drop. Leave the cover on overnight and remove it when temperatures rise the next day.
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Other Protection Methods:Besides covering, you can also protect your lettuce from frost by mulching the soil, which can help to insulate the roots and keep them warmer.
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Varietal Considerations:Some lettuce varieties are more cold-hardy than others. If you’re growing a variety known for its cold tolerance, you may not need to cover it as early as a less cold-hardy variety.
When can I put lettuce seedlings outside?
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Timing:Start thinking about moving seedlings outdoors once you’ve reached a point where the soil temperature is consistently above 50°F (10°C). In Los Angeles, this is typically around late March to early April.
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Acclimatization:Before moving seedlings outdoors permanently, you need to harden them off. This means gradually exposing them to the elements to help them adjust to the changes in temperature and light.
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Gradual Exposure:Start by bringing the seedlings outside for a few hours each day. Gradually increase the time they spend outside each day, up to several hours, says the Beginner’s Garden with Jill McSheehy.
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Protect from Cold:Even though Los Angeles has a mild climate, it’s still possible for temperatures to drop below freezing, so it’s important to protect your lettuce seedlings from frost, especially in the first few days after transplanting. You can do this by covering the seedlings with row covers or by bringing them back indoors overnight.
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Soil Preparation:Make sure your garden bed is well-drained and prepared with compost or other organic matter before transplanting your seedlings.
What is the night time temperature range for growing lettuce?
Lettuce is a cool-season crop with distinct temperature requirements. The optimal growing temperatures are 73ºF (23ºC) during the day and 45ºF (7ºC) at night. Most California growing regions have daytime temperatures from 63º to 83ºF (17º to 28ºC) and night temperatures from 37º to 53ºF (3º to 12ºC).
How to protect lettuce seedlings from frost?
Young seedlings can be protected from light frost with an old sheet or piece of row cover spread over the ground.Mar 9, 2023
What temperature does lettuce grow?
Lettuce is adapted to cool growing conditions with the optimum temperatures for growth of 60 to 65°F. At 70 to 80°F, the plants flower and produce seed. Lettuce can tolerate a few days of temperatures from 80 to 85°F, provided that nights are cool.
What is the best type of lettuce?
The purple lettuce. Because it has a purple color, in addition to all the vitamins and minerals found in other lettuces, it also contains anthocyanin – a substance that, in addition to being responsible for the purple pigmentation, also has an antioxidant action to prevent premature aging and other complications in the body.
Can lettuce grow in cold weather?
Temperatures above 80°F will cause lettuce to bolt and become bitter. Below 55°F, growth will slow down. According to the University of California Cooperative Extension, lettuce seeds germinate best when soil temperatures are around 75°F. Lower soil temperatures will delay germination. Mature lettuce plants can tolerate cold better than seedlings.
How much frost can a lettuce plant tolerate?
Lettuce can usually tolerate at least a couple of hard frosts, especially if you’ve taken steps to harden off the seedlings and keep the soil warm. A light freeze is defined as any time temperatures are in the 28 to 32°F range, and a hard freeze occurs below 28°F.
What kind of lettuce is cold tolerant?
Good options include: Romaine lettuces – These have great cold tolerance. Try cultivars like Winter Density, Flashy Trout Back, or Cimmaron. Leaf lettuces – Green leaf and red leaf lettuces are also quite cold-hardy. Good options include New Red Fire, Red Sails, or Salad Bowl.
Do different lettuce varieties have different temperature tolerances?
Yes, different lettuce varieties have varying temperature tolerances. Selecting types based on their tolerance can significantly enhance your chances of a successful harvest. For example, Leaf Lettuce does better in moderate heat conditions.