Updated at: 24-10-2022 - By: Sienna Lewis

To grow lettuce from seed in the greenhouse, keep an eye on your thermometer and aim for 70 to 75 degrees Fahrenheit. Gardeners may face a quandary when it comes to producing lettuce from seed in a greenhouse: what temperature is best? As a result, you don’t need to be alarmed by the prospect of growing this crop in a greenhouse.

If you want to know if lettuce will grow well in your area, you can consult the hardiness zone map. Keeping this in mind, lettuce crops are best grown in zones 4 to 9, so keep this in mind when deciding whether to grow them. The greenhouse, on the other hand, allows you to have complete control over the inside climate, so you can easily have fresh and nutritious greens in your garden with only a little planning and upkeep.

What Is The Temperature For Growing Lettuce From Seed In The Greenhouse: Pointers To Consider

Seed germination and greenhouse conditions determined the ideal temperature for growing lettuce from seed. Remember to take your growing zone or hardiness zone into account as well, so that you can make the appropriate adjustments based on your specific area. Your greenhouse may require additional greenhouse techniques depending on your location’s climate and temperature.

Seed germination

It’s important to keep in mind that lettuce seed germination is greatly influenced by the temperature. The ideal temperature for seed germination is between 70 and 75 degrees Fahrenheit, but seeds will germinate at temperatures as low as 35 degrees. Even yet, lettuce harvests can be harmed by freezing temperatures, especially if they haven’t yet hardened.

What Is The Temperature For Growing Lettuce From Seed In The Greenhouse - Krostrade

Greenhouse condition

In spite of lettuce’s ability to thrive in freezing temperatures, it is still necessary to keep the greenhouse temperature between 60 and 65 degrees Fahrenheit. 70 to 80°F is ideal for flowering and seeding crops, while lettuce can survive temperatures of 80 to 85°F if necessary for a few days. As a result, temperatures have a greater impact on seedlings’ development.

Lettuce thrives best in temperatures between 60°F and 65°F during the day and 50°55°F at night for upkeep. It’s also a good idea to pick a lettuce variety based on the climate you plan to be in. Heat-tolerant cultivars, for example, are ideal for those who live in a region with a more temperate temperature.

University extensions recommend Leaf and Bibb lettuce types for greenhouses. In the greenhouse, common Bibb varieties include Mirlo, Roxy, Rosaline, and Cegolaine for the former and Ruby Red, Grand Rapids, and Waldmann’s Dark Green for the latter.

When To Grow Lettuce In A Greenhouse?

Starting from seeds, you should sow as soon as the ground is usable or 40 degrees Fahrenheit has been reached. Seven days after planting, germination can occur if the soil temperature is between 55 and 65 degrees Fahrenheit. Sowing before your last spring frost date in a greenhouse will allow you to harvest your crop earlier than usual.

It is possible to seed in both spring and fall in some states like North Carolina. However, according to the NC State Extension Department of Horticultural Science, spring lettuce also tends to fail, so it’s better to use transplants for this season. On the other hand, direct seeding is ideal for fall lettuce, but keep an eye on your greenhouse temperature and watering schedule.

Late January and early February is the average time of year for direct seeding in eastern North Carolina, but late March and early April is the typical time in the west. For a fall harvest, begin sowing 80 days before the first hard freeze. It’s possible to grow a second crop in early winter depending on where you live.

Other Lettuce Growing Requirements

Soil, feeding, and watering

Foliage thrives on a fertile, loose and loamy soil with a pH of 6.0-7.0 and excellent drainage. Sow the seeds half an inch deep, and then cover with another inch of dirt to secure the seedlings in their place. New Mexico State University recommended utilizing a balanced fertilizer prior to planting and weekly nitrogen feedings for the best results.

How much water does lettuce require? Using a misting system to avoid overwatering crops in the greenhouse is recommended. A decent rule of thumb is one inch of water a week to ensure that your leaves are soft and juicy.


Plan on four to six inches of spacing between rows and thin plants by an inch or two. Seed to bed ratio of 6 ounces of seed to 300 square feet of bed works well for lettuce plants being started from seed inside for transplantation later on. With this ratio, you’ll be able to cover an acre with operations.

In the greenhouse, lettuce makes a fantastic companion plant. Aphids can be deterred by the presence of chives or garlic between rows of lettuce. Growing lettuce in a greenhouse can also be done with blocks and containers, but the direction in which their roots grow must be considered.

Step By Step Guide To Growing Lettuce From Seed Indoors

Getting started with lettuce from seed is simple and fast.

  • Growing media is required to germinate lettuce seed. To grow lettuce from seed, you can use any sterile growth mix, but specialized growing mixes can be purchased at your local garden supply store.
  • Fill the growing tray two-thirds full of the growing media and smooth the top slightly before scattering your seeds equally across its surface. Pickling cucumbers demand 100 square feet of space for a single plant.
  • Step 3: Spray them with water and cover them with a thin layer of compost or vermiculite. You should keep a watch on them for the first few weeks because baby lettuce seedlings need damp soil.
  • Preserve optimal growth conditions for your plants during the growing phase (Step 4). Your tiny seedlings will quickly sprout and begin to grow if you follow these instructions. First set of leaves will be ready for transplant in a few weeks, so they can grow in a new container or module tray for a longer period.

If you don’t have enough room on your windowsill to grow your seedlings indoors, it’s best to take them outside as soon as the weather warms up again.

Overnight, if you’ve grown your seedlings indoors for a while, you may want to cover them with some shade netting to help them adjust.

Grow Romaine Lettuce in a Small Container

Growing Lettuce From Seed Outdoors

Remember that the growth space needs to be prepared by spading and adding some sand to the soil before you plant anything!

Transplant your growing plants after you’ve worked the soil to a fine consistency with a hoe or rake. A minimum of 8 inches of depth in your growing pots is required to allow room for the roots to develop.

Once they’re in the ground, make sure to give them plenty of water and watch for the sensitive green shoots to emerge. Keeping an eye on them if there’s a chance of frost could cause them to “bolt” (run up like a flower) rather than mature into a mature plant.

When the weather warms up, you’ll be able to admire the beautiful green leaves in no time! When your lettuce is large enough to harvest, combine it with a nice dressing or dip for a refreshing side dish. The addition of nuts or dried fruit enhances the flavor.

Well, that’s all there is to it — growing lettuce from seed is a breeze if you’re pressed for time but yet want something useful growing on your windowsill. Enjoy!

Check out this guide on growing salad bowl lettuce in containers.

What Is The Right Temperature For Growing Lettuce From Seed In A Greenhouse?

When growing lettuce in a greenhouse, be sure that the temperature is just ideal for your plants.

A minimum temperature of +5°C (41°F) should be maintained overnight when starting lettuce from seed in a greenhouse. Bringing your growing tray indoors if the temperature drops below +5°C (41°F) is a good idea if you want to cultivate plants. Temperatures in the greenhouse should be no lower than +18°C (64.4°F) throughout the daytime hours.

The greenhouse should be kept at a temperature of 20-30°C (68-86°F) on average. Seed-grown lettuce, on the other hand, can endure temperatures up to 95 degrees Fahrenheit (35 degrees Celsius).

How to Grow Lettuce in a Greenhouse | Greenhouse Emporium

What Type Of Fertilizer Does Growing Lettuce From Seed Require?

There are no additional fertilizers needed while growing lettuce indoors. However, you might think about using an organic liquid fertilizer like fish emulsion or seaweed extract + bonemeal before transplanting your young seedlings outside. Use only half of the package’s recommended dosage while growing inside or out.

Growing Lettuce From Seeds In Containers

The amount of time it takes to grow lettuce from seed indoors is really low. A minimum of four hours of direct sunlight each day, and a minimum of twelve hours per day, is required for most houseplants.

Outdoors, you’ll need containers with a depth of about 8 inches; indoors, a depth of around 5 inches is required. Black plastic pots are the greatest because they can absorb the most light and heat, making them ideal for growing vegetables (perfect for plants like lettuce and tomatoes).

In either small individual pots or one large container that is roughly 8 inches deep, plant your seeds about 1/8 inch deep into damp potting soil. These fast-growing plants will thrive if you keep the growing medium damp but not soggy.

What is the Best Temperature for Growing Lettuce?

The ideal temperature for growing lettuce depends on the lettuce’s stage of development, therefore keep this in mind. Even at conditions that would normally cause mature lettuce plants to bolt, seeds from lettuce can successfully germinate (produce seeds and become bitter).

Best Temperature for Lettuce Germination

60 to 86 degrees Fahrenheit is the ideal soil temperature for the germination of lettuce (16 to 30 degrees Celsius). lettuce seeds germinate within 2 to 4 days at this temperature.

Depending on the soil temperature, lettuce seed germination may take longer or shorter than expected. It will take several weeks for lettuce seeds to germinate in soil that is near to freezing, for instance.

University of California Extension data shows the temperature ranges for lettuce seed germination, which include both Fahrenheit and Celsius temperatures, in the table below.

Ideal Temperature for Lettuce to Grow

It is recommended that lettuce plants be grown in temperatures ranging from 55 to 65 degrees Fahrenheit for optimal growth (13 to 18 degrees Celsius). Because lettuce is a cool-season crop, it favors lower temperatures for growth.

As long as the cold does not arrive quickly following warm weather, Texas A&M University Extension says lettuce can even survive a frost or hard freeze.

Lettuce “bolts,” or goes to seed, when the temperature rises. To put it another way, the plant will begin to grow and create flowers, which will in turn generate seed pods.

Lettuce plants go through this process as part of their life cycle. The downside is that the lettuce leaves will get bitter, and as a result, most people won’t want to eat them anymore.

Below you’ll find a list of the ideal temperature ranges for growing lettuce. Depending on the type of lettuce and whatever heat protection (shade cloth, etc.) you have available, this time period can vary.

What Temperature is Too Cold for Lettuce?

As stated by the Michigan State University Extension, lettuce can withstand harsh frosts. A temperature of less than 28 degrees Fahrenheit is considered a “hard frost” (-2 degrees Celsius).

In order for lettuce to survive a strong frost, it must first be properly prepared. In this context, conditioning refers to the plant’s time spent adapting to cooler temperatures rather than being exposed to freezing temperatures all at once.

As an example, lettuce may not survive if a strong frost strikes quickly after a period of mild weather. On the other hand, lettuce can withstand temperatures as low as the 20s Fahrenheit for a long period of time (-6 to -2 Celsius).

How to Protect Lettuce from Frost and Cold

Your lettuce may be able to withstand a harsh frost if it is suddenly forecast. There are a few options if you wish to take further measures to protect your plants.


Protecting plants from cold, pests, and wind is the primary purpose of a cloche. The air and soil beneath a cloche work as a mini-greenhouse, trapping heat from the sun’s rays.

Because it is transparent, a cloche nevertheless enables sunshine to enter, allowing plants to continue growing. With the help of the cap on top, you can cut out a cloche from an empty transparent plastic bottle.

However, a wire cloche can also be made, but it won’t provide any protection from the cold. To keep the plant warm, place a frost blanket or row cover over the cloche.

You can find out more about cloches by reading my article.

Row Cover

A row cover can be used to shield a whole row of lettuce plants from the cold. In order to keep plants safe from the cold and pests, growers use row covers.

As an alternative to using supports along a row, row coverings can be draped over those supports instead. Drive the two ends of a flexible plastic rod into the ground by bending it into a half circle.

You may create a little “hoop house” by placing these half-circles a few feet apart in a row and covering them with a row cover.

When it comes to protecting your lettuce from the cold, row coverings can help. This can make all the difference in the world if they’re heading into a period of intense cold.

Make sure you don’t leave your lettuce plants under excessive shadow all day long.

What Temperature is Too Hot for Lettuce?

When the daytime temperature reaches 70 to 80 degrees Fahrenheit, lettuce will begin to bolt (flower and produce seeds) (21 to 27 degrees Celsius).

After the lettuce has begun to bolt, it will continue to expand. After the plant has bolted, the lettuce leaves will become bitter and unusable for eating.

Varieties within the same species can differ, just like many other crops. Many heat-tolerant lettuce types, for example, can endure temperatures that are higher than those of their relatives without going to seed (more on these varieties later).

How Do You Grow Lettuce In Hot Climates?

The lettuce must be kept a little cooler in warmer climes if it is to thrive. All of the approaches listed here can help in some way with this (pardon the pun!).

For an even longer harvest, you can mix two or more of these approaches with one another.

Choosing lettuce that is heat-tolerant is a good place to start if you want to avoid bolting in the heat.

Choose Heat-Tolerant Lettuce Varieties

Choosing a heat-tolerant lettuce type is an excellent approach to grow lettuce for a longer amount of time in a hot area. Johnny’s Selected Seeds offers a variety of heat-resistant lettuces.

  • Adriana has dark green leaves and is a heat-tolerant butterhead lettuce. It takes 48 days for it to mature and it doesn’t bolt. From Johnny’s Selected Seeds, you can discover more about Adriana lettuce.
  • Known for its ability to withstand the heat, Cherokee is a red lettuce with green veins. It takes 48 days for it to mature and it doesn’t bolt. Johnny’s Selected Seeds has more information about Cherokee lettuce.
  • It is a heat-resistant lettuce with dark green leaves that can be used as heads or as romaine leaves. Coastal Star is It takes 57 days for it to develop. Johnny’s Selected Seeds has more information about Coastal Star lettuce.
  • You can use the brilliant green leaves of Jericho as either a baby-leaf or as a head of lettuce. 29 days later, it is ready to be harvested as a baby lettuce. Johnny’s Selected Seeds has more information on Jericho lettuce.
  • Green and crimson leaves make up the Magenta lettuce. It takes 48 days for it to reach maturity, so you can plant it any time between spring and summer. Johnny’s Selected Seeds has more information about Magenta lettuce.
  • Muir lettuce has light green leaves that can withstand high temperatures. It takes 50 days for it to fully grow. You have the option of harvesting the smaller heads or letting the larger ones grow. Johnny’s Selected Seeds has more information on Muir lettuce.
  • Known as Winter Density, this kind of romaine can handle both heat and cold. Slowly, yet swiftly, it grows into a mature specimen in just 44 days. Johnny’s Selected Seeds has more information about Winter Density lettuce.
Provide Shade for Your Lettuce

During the hottest portion of the day, any lettuce that receives some shade will take longer to bolt. As it turns out, there are numerous ways to protect your lettuce from the sun.

Plant Lettuce Near Taller Crops

In the first place, lettuce can be planted alongside taller plants. You can, for example, allow additional space between tomato plants and plant a lettuce head between each pair of tomato plants.

The lettuce will benefit from a little shade from the tomato plants as they become bigger. Although this is one option, it is by no means the only one.

How to Grow Lettuce in a Greenhouse (Full Growing Guide)

Vining vegetables like cucumbers can be grown at the base of a lean-to trellis. Afterwards, plant lettuce beneath the trellis.

As the cucumbers mature, they will shield the lettuce from the sun. In my essay, you may learn more about lean-to trellises and other styles.

Use Shade Cloth Over Lettuce

To keep lettuce fresh, you can use a shade cloth. In order to keep the plants beneath it from overheating, shade cloth is used.

Your lettuce will still be able to grow thanks to the shade cloth’s ability to let some light through. As much as ten degrees of heat protection for your lettuce is possible depending on the quality of the shade cloth!

With the help of hoops, Gardener’s Supply Company’s shade cloth may be supported. Shade cloth can also keep birds away from lettuce, an extra benefit.

Harvest Lettuce So It Keeps Growing

Harvest lettuce as soon as the leaves are ready, even if they are still small. Finally, keep picking lettuce. It is only when the lettuce leaves have grown large enough for the plant to assume it is “done” growing that it will begin to produce seeds.

The leaves of a lettuce plant will become bitter as they begin to develop seeds. As a result, the leaves are inedible to anyone with the capacity to taste.

You may extend your growing season by at least a few days if you harvest your lettuce as it matures.

Planting lettuce in a greenhouse

  • Lettuce should be planted as soon as soil is workable, ideally one or two weeks before the final spring frost date, but greenhouse conditions provide ample protection from the harsh effects of the environment.
  • If you’re planting lettuce in a seed tray or container, spread the seeds evenly over the soil. Then, add a thin layer of dirt to the seeds and gently press it down with your fingers.
  • You can sow the seeds in rows that are 12 inches apart, or you can spread them out across the field. Depending on the variety, the spacing is different. As an example, leaf lettuce should be planted 8 inches apart, whereas loose-headed and firm-headed kinds should be planted 8 inches apart and 16 inches apart, respectively
  • Get a half-inch of soil on the seeds, then saturate them with water. The soil temperature should be between 65 and 70 degrees Fahrenheit to guarantee optimum germination.

Tips and Tricks

  • To grow lettuce year-round in your greenhouse, you’ll need to use artificial means like heating and cooling.
  • Ventilation systems in your greenhouse can be adjusted according to the outside temperature.
  • Despite the fact that snow isn’t harmful to lettuce, it’s best to keep them out of the freezing cold, which will kill them.
  • Aphids can be controlled by planting rows of garlic or chives nearby.
  • Uninterruptible power supply is critical. To keep your electric heaters and lights running, you may use some extension cords.

Common Problems

Lettuce is vulnerable to earwigs, cutworms, and aphids, among other pests. Rabbits and woodchucks can also be a problem.

Check your lettuce plants daily because as they grow older, their leaves become bitter and woody, and they are more likely to rot.

Before the summer heats up, cover your lettuce plants with shade cloth to keep them from drying out and extending the harvest into the hot months.

Appreciate your efforts? It’s time to pin it!

How to Grow Lettuce – The Requirements


Do not exceed 70 degrees Fahrenheit in the greenhouse at any point during the daytime. When it’s hot outside, throw open the doors to let some fresh air in. Temperatures at night range from 45 to 55 degrees Fahrenheit, which is ideal. It can endure 35-degree Fahrenheit temperatures for a limited period of time, especially if you keep it in a greenhouse. Even if it’s 90 degrees outside, your lettuce won’t be harmed by the heat. The soil should be kept moist, and as much cool air as possible should be distributed throughout the summer seasons.


In order to grow properly, lettuce has to be watered at all stages of development. Spritz the seed tray with a little mist to keep the soil moist and well-drained. A misting system is a great way to automatically humidify lettuces without adding too much water to the environment. Provide a weekly water supply of one inch at a time.

Seedlings benefit from being dusted with a mild solution of seaweed or fish emulsion soon upon transplantation. Because lettuce has shallow roots and grows quickly, it is an ideal green for container gardening. Tender, juicy leaves can only be produced if they have access to a continual supply of water.


Loose, organic soil is ideal for growing lettuce, which thrives on the abundance of nutrients it receives. Use a hand fork to dig fertilizer into the first two inches of soil before planting your seedlings. They thrive in soil that is rich, well-drained, and has a pH of 6.0 to 7.0. Make sure the soil is kept continuously moist to avoid stressed plants. You’ll have more lettuce than you can eat if you plant lettuce seedlings every week. Repeated sowing is the most straightforward method for achieving better outcomes.


Greens need plenty of sunlight to thrive. Choose a location for your greenhouse where it will receive at least six hours of direct sunlight each day, or purchase a lighting kit. The optimum location is one that faces south.


Before they have fully matured, lettuce can be harvested for its finest flavor and tenderness. If you want to get the most out of your romaine and butterhead lettuce, take off the outer leaves first. Early in the morning, before the lettuce leaves have been exposed to sunlight, is the optimum time to select it.


Lettuce is a nutritious and tasty side dish that may be grown indoors for both commercial and personal use. If you’d want to know, what is the ideal greenhouse temperature for growing lettuce from seed? The ideal temperature for germination is between 70 and 75 degrees Fahrenheit, but keep in mind the diverse lettuce needs for a successful growth season.