If you are planting (or have already planted) lettuce seeds, you are probably wondering just how long they take to sprout. You may also be curious about how you can speed up the seed germination process.
So, how long do lettuce seeds take to germinate? Lettuce seeds take 2 to 15 days to germinate. Lettuce seeds germinate faster with optimal soil temperature, humidity, and air circulation.
Of course, you can germinate lettuce seeds indoors and transplant outside later, but it is preferable to germinate lettuce seeds directly in the soil outdoors.
Let’s take a closer look at some of the factors that affect how long lettuce seeds take to germinate. We’ll also see how we can optimize these factors to encourage faster seed germination.
How Long Do Lettuce Seeds Take To Germinate?
According to the University of Michigan Extension, lettuce seeds will take 2 to 15 days to germinate. Of course, this will vary based on soil temperature.
The University of California suggests that it will take lettuce seeds around 2 days to germinate at a soil temperature of 77 degrees Fahrenheit (25 degrees Celsius).
On the other hand, lettuce seeds will take around 15 days to germinate at a soil temperature of 41 degrees Fahrenheit (5 degrees Celsius).
It will also depend on various other factors that affect time to seed germination – let’s get into some of those now!
What Factors Affect Seed Germination?
The time a seed takes to germinate depends on several important factors, such as soil temperature, humidity levels, and air circulation. Let’s dive into more detail on these factors that affect seed germination.
The temperature of the soil (growing medium) will affect the time it takes for seeds to germinate. Soil temperature will also have an effect on germination rate, or the percentage of seeds that sprout.
***Note: You can find the germination rate on the seed packet itself. For example, if the germination rate is 95%, then you would expect 95 seeds to sprout out of every 100 seeds that you planted.***
The minimum temperature for lettuce seed germination is 32 degrees Fahrenheit (0 degrees Celsius). If the soil is any colder than this, you will see low germination rates – that is, if you can get any seeds at all to germinate! This is nature’s way of protecting lettuce seeds from sprouting at a time when they will be unable to survive.
The maximum temperature for lettuce seed germination is 85 degrees Fahrenheit (29.4 degrees Celsius). If the soil is any warmer than this, germination rates will decrease.
Combined with high humidity, high temperatures can encourage the growth of mold, which is another threat to your plants.
The ideal (optimal) temperature for lettuce seed germination is between 60 degrees Fahrenheit (15.6 degrees Celsius) and 75 degrees Fahrenheit (23.9 degrees Celsius).
Keep in mind that these temperatures refer to soil temperature, not air temperature. If you want to find out the soil temperature, use a probe-type thermometer to check.
If the thermometer reads a temperature that is too low, then you have some options. One option is to wait until the sun warms up the soil.
To speed up this process, clear away any debris, such as leaves or grass clippings, from the soil surface. Also make sure to choose a location for planting that gets plenty of sun, so that it can warm up the soil faster.
If you are worried about a short growing season, you can also use a cloche (a plastic or glass cover) to trap some heat and warm up the air and soil near your lettuce seeds.
For more information, check out the table below, and check out this article from the University of California on ideal seed germination temperatures.
|Ideal||60 to 75||15.6 to 23.9|
Humidity is another important factor to consider when germinating lettuce seeds. If the air is too dry, then the soil will dry out faster, and the seeds will have trouble germinating – they may even die!
If the air is too humid, then the soil will stay too wet, especially if you over water the soil. This can lead to damping off, which occurs when mold or other pathogens affect seeds or seedlings.
Damping off is more likely with high humidity levels, in moist soil, and at cooler temperatures.
For more information, check out this article on damping off from Wikipedia.
If you find that you have trouble keeping the air and soil humid enough, you do have some options. One option is to use a cloche (mentioned earlier).
A cloche, if sealed, traps moisture in the air and soil so that seeds have the humid environment they need to germinate properly. A cloche will help your seeds to germinate faster, increase germination rates, and cut down on the time and effort needed to keep soil moist.
Seeds need air, just like seedlings and established plants. If the soil is too wet and there is too little air circulation, it can spell death for your seeds before they even have a chance to sprout.
To keep your seeds from suffocating due to lack of air, there are two key things you can do.
First, keep the soil moist, but not wet. Do not over water the soil, and consider using a cloche to help you to get the right moisture level.
Second, keep the soil loose. Do not compact the soil by pushing down on it either before or after planting your seeds. When there is more space between soil particles, there is more space for air and water, both of which are necessary for seed germination.
How Do I Make Lettuce Seeds Germinate Faster?
If you want to make your lettuce seeds germinate faster, there are several important actions you can take.
First, protect your seeds from extreme heat and cold – anything below freezing (32 degrees Fahrenheit or 0 degrees Celsius) is too cold for lettuce seeds. As mentioned earlier, temperature is one of the most important factors that affect seed germination.
If it is too cold to plant seeds outside, then start your seeds indoors. This gives you a head start on the growing season, and minimizes the danger of late spring frosts killing your seedlings. This is especially helpful if you live in an area with a short growing season.
Second, ensure that the soil is moist (not wet!) and the air is humid. Seeds will not germinate if there is not enough moisture in the soil and air. Consider a cloche for this purpose.
Third, make sure that the soil has enough air circulation. This means that you should avoid compacted soil both before and after planting. It also means that you should avoid over watering your soil.
Fourth, remember that lettuce seeds need light to germinate, which is why they are planted in shallow soil. If you start lettuce seeds indoors, give the seedlings bright overhead lights during germination.
Fifth, make sure to plant your lettuce seeds according to the proper depth and spacing. Lettuce seeds should be planted at a depth of ¼ to ½ inch (0.64 to 1.27 centimeters). The seeds should be 12 inches feet (30 centimeters) apart, to allow each seedling its own space in the soil to grow roots.
Finally, you can scarify (scratch the surface) of your seeds in order to encourage germination. This can speed up germination and also increase germination rate (the percentage of seeds that sprout).
For more information, check out this article on seeds and seedlings from the Penn State University Extension.
Should Lettuce Seeds Be Soaked Before Planting?
You can soak your lettuce seeds before planting to encourage faster germination. Put them in clean water and let them sit for a day or so before planting.
However, this is not required – as long as the growing medium is moist and warm, the lettuce seeds should germinate well.
Can You Germinate Lettuce Seeds In A Paper Towel?
Yes, you can germinate lettuce seeds in a paper towel. The paper towel holds moisture and allows the seeds to breathe, serving as an alternative growing medium.
To germinate lettuce seeds on a paper towel, wet the paper towel until it is damp (not soaking wet). Then, lay out the lettuce seeds so that they are separated (not touching).
Be sure to keep the paper towel and seeds in a warm place, to encourage faster germination and higher germination rates.
The only drawback of this method is that you will need to transplant the sprouted seeds into soil by hand, since they will soon need nutrients from the soil to grow and establish stronger roots. Be gentle when handling the tiny sprouted seedlings!
It is preferable to sow lettuce seeds directly into the soil outside, since they do not always transplant well. However, germinating lettuce seeds in a paper towel may be helpful if you live in an area with a short growing season.
Why Are My Lettuce Seeds Not Germinating?
There are a couple of possible reasons that your lettuce seeds are not germinating.
Your Lettuces Seeds Are Too Old
One common reason for a lack of germination is that the seeds you are using are too old. In that case, the germination rate may be low, or even zero.
Lettuce seeds tend to last about 1 year, and germination rates will naturally decrease with each passing year. For more information, check out my article on how long seeds last.
Your Soil Is Too Cold Or Too Dry
Another reason your lettuce seeds are not germinating has to do with soil conditions.
If the soil is too cold, then your lettuce seeds might not sprout right away (whether you are growing indoors or outdoors). They may sprout when conditions improve and the soil warms up.
However, you might not want to wait that long, and you might not want to risk killing your seeds. In that case, start the seeds indoors, and use a heat lamp or heat mat to keep the soil warm enough so that the seeds can germinate. Just be very careful when transplanting to avoid damaging the roots.
Finally, remember that if the soil is too dry, then seeds will not germinate, and they may even die before you have a chance to correct the problem. Keep the soil moist, and consider using a humidity dome to help maintain the proper moisture levels in the soil and air.
If you have trouble with dry soil, check out my article on how to treat dry soil.
How Big Should Lettuce Seedlings Be Before Transplanting Outdoors?
If lettuce seeds are started indoors, they should be planted 4 to 6 weeks before the last spring frost date. To find out the last frost date in your location, check out this frost date calculator from the Old Farmer’s Almanac.
The lettuce should be watered thoroughly when you transplant them. Usually, you should aim to transplant lettuce seedlings outdoors after the last frost date, although lettuce that has been hardened can survive down to 20 degrees Fahrenheit (-6 degrees Celsius).
For more information, check out this article on lettuce from the Old Farmer’s Almanac.
By now, you have a good idea of how long it takes lettuce seeds to germinate. You also know about the factors that affect time to germination, how to optimize for faster germination, and how to troubleshoot a lack of germination.
I hope you found this article helpful – if so, please share it with someone who can use the information. If you have any questions about lettuce seed germination, please leave a comment below.