It is frustrating to carefully plant your tomato seeds, only to find that they fail to sprout (germinate) after 14 days or more. I did some digging to unearth all of the possible reasons that your tomato seeds might fail to germinate, and I want to share what I found with you.
So, why are your tomato seeds not sprouting? Tomato seeds will fail to sprout if temperatures are too cold (below 50 degrees Fahrenheit). Tomato seeds will also fail to germinate if they dry out. Tomato seeds that are more than 3 years old may germinate poorly, or not at all. Tomatoes can take a couple of weeks (14 days) to germinate at cooler soil temperatures (below 60 degrees Fahrenheit), so be patient.
Of course, patience alone may not be enough if conditions are not right for tomato seed germination. Luckily, there are some steps you can take to ensure that you get a higher germination rate and faster germination for your tomato seeds.
Let’s start with a little more detail on why your tomato seeds may fail to germinate and how to fix it. Then we’ll get into ways to help your tomato plants to grow better once they do germinate.
Why Are My Tomato Seeds Not Sprouting
Tomato seeds will not sprout if they are too cold (or too hot), too dry, or too old. Two of the most important factors for seed germination are soil temperature and soil moisture.
If the soil is too cold (or too hot), then none of the other factors will matter, so we’ll begin with temperature.
Soil Temperature Is Too Low (Or Too High)
Tomatoes are a warm weather crop, so they do not grow well in cool soil. They need consistently warm soil, free from any danger of frost, in order to germinate properly.
If the soil temperature is below 50 degrees Fahrenheit (10 degrees Celsius), then your tomato seeds will completely fail to germinate. There is nothing you can do about this – it is Mother Nature’s decision, not mine!
Even with slightly warmer soil temperatures in the 50s Fahrenheit (10 to 15 degrees Celsius), it can take several weeks for tomato seeds to germinate. I would suggest one of two things: more patience, or more heat for your tomato seeds!
The ideal temperature range for tomato seed germination is 65 to 85 degrees Fahrenheit (18.3 to 29.4 degrees Celsius). In this temperature range, tomato seeds can germinate in 6 to 8 days (assuming also that the soil is moist enough during this time).
If you need to warm up the soil for tomato seeds, there are a couple of ways to do it. The first way is to use a seedling heat mat.
A heat mat uses electricity to generate heat, and it warms up a container of soil placed on top of it. You can achieve a similar effect by putting the container on top of a running refrigerator (which also gives off heat).
Another way to warm up the soil for tomato seeds is to cover the soil with plastic and put it in sunlight (for example, a sunny windowsill). One option to cover the soil is to use a cloche, which is a cover that protects seeds and plants from cold.
You can cut out the bottom of a plastic bottle to make a cloche. You can also remove the cap and use the opening on top of the bottle as a vent to cool things down if the soil gets too warm.
Another option is to use a sheet of clear plastic wrap to cover the soil in a tray of seeds. Just be sure to keep an eye on them – you don’t want the soil to get too hot!
At the other extreme, tomato seeds will fail to germinate if soil temperatures are too high above 95 degrees Fahrenheit (35 degrees Celsius).
If you live in a colder climate, you probably won’t have to worry about this in the late winter or early spring when you start tomato seeds indoors (but you never know!)
Soil Dried Out
Dry soil is another reason that tomato seeds will fail to germinate. Seeds need to absorb enough moisture through their coating before they will break dormancy and begin to sprout.
Dormancy is the period of time when a seed does not sprout. The purpose of dormancy is to protect the seed from sprouting when it is too cold or too dry for the young plant to survive.
Warmer soil temperatures and increased moisture levels tell seeds that spring has arrived. When starting tomato seeds indoors in late winter or early spring, you will need to give them enough moisture to convince them that it is time to germinate.
The key is to keep the soil evenly watered and consistently moist to encourage tomato seed germination. If you let the soil dry out too much after you start the germination process, the seeds will die.
Keep in mind that it is also possible to over water your seeds during the germination phase. You don’t want so much water that you wash away the tomato seeds, or the soil covering the seeds.
A spray bottle is a good way to keep the soil moist enough without over watering. It is much easier to control the amount of water you add to soil when using a spray bottle.
It is also much easier to add even moisture across the top of the soil with a spray bottle than with a watering can.
Seeds Are Buried Too Deep
Even with proper soil temperature and moisture, it is possible that your tomato seeds are buried too deep for proper germination. If the seeds are buried too deep, they won’t be able to break through the soil to reach the surface and get sunlight.
Tomato seeds should be planted at a depth of about a quarter inch, or 0.25 inches (0.63 centimeters). However, it can be tricky to dig very small and shallow holes, plant small tomato seeds in them, and cover them up.
Here is an easier alternative. Put some soil in a container (or in separate cells). Then, lay out the tomato seeds where you want them.
Finally, sprinkle some soil over the seeds so that there is about 0.25 inches of soil covering the seeds. You can press down the soil lightly, but don’t pack it down hard. You want to leave space in the soil for air and water.
After planting your seeds at the proper depth, spray some water on top to keep the soil moist. Then, warm up the soil up to the right temperature and wait for the seeds to sprout!
Seeds Are Too Old
Seeds do not last forever, and tomato seeds are no exception. Over time, the germination rate of tomato seeds will decrease, until almost none of them will sprout (no matter how perfect the temperature and moisture levels!)
The germination rate is the percentage of seeds that sprout (germinate) and have a chance to grow into tomato plants. For example, a germination rate of 90% means that if we plant 100 tomato seeds, we would expect 90 of them to germinate (90 out of 100, or 90/100, equals 90 percent).
As time passes, the germination rate of seeds starts to decrease, and eventually approaches zero. Tomato seeds tend to last about 3 years. After that, their germination rate drops quickly.
Some seeds, like spinach and lettuce, last only 1 year before they need to be replaced. To learn more about how long seeds will last, you can read my article about it here.
Seeds Were Stored Improperly
If you stored your tomato seeds improperly, then you might see a low germination rate (or no sprouting at all!) This is more likely if you saved seeds from last year’s plants without taking the proper steps to preserve them.
The following seed storage problems can lead to a poor germination rate:
- High temperatures – the seeds can be damaged if they get too hot. For example, if they are left out in the sun in late summer heat.
- Low temperatures – the seeds can also be damaged by extreme cold. For example, if you stored seeds in the freezer without drying them properly.
- High Moisture or Humidity – the seeds can be damaged by mold growth. For example, if they are stored in a paper packet in a damp part of your house (basement/cellar).
Why to Start Your Tomato Seeds Indoors
Starting tomato seeds indoors helps you to avoid many of the problems that lead to poor germination. Starting seeds indoors lets you control soil temperature and moisture.
You also avoid most of the risk of a late spring frost that will kill young plants. You can use this tool from the Old Farmer’s Almanac to find the frost dates in your location.
Staring seeds indoors also protects your seeds from scavengers who might dig them up. In addition, your young sprouted seedlings will be safe from cutworms and other pests that can damage them.
Starting seeds indoors is very important if you live in a cold climate with a short growing season. By starting seeds indoors, you will be able to get a head start on the growing season. Your tomato plants will then have enough time to grow and produce a harvest before the first frost in the fall.
How to Help Tomato Seeds to Germinate Faster
Now that you know the most important factors that affect seed germination, it’s time to look at some tricks to get your seeds to germinate faster and better.
Soak the Seeds
Soaking your tomato seeds before planting can give them the moisture boost they need to break dormancy. This will help them to sprout faster.
However, you should not soak tomato seeds for more than 1 or 2 days. Otherwise, they will start to rot. (This is a case where more is not better!)
Use Newer, Younger Seeds
New seeds will have a higher germination rate than old seeds. So, be sure to buy new seeds from a trusted seed company. If using saved seeds, plant them within a year or two of when you harvested them.
If you tend to forget things, be sure to label your seed packets with the month and year that you bought or saved them. Keep all of yours seeds together in the same place.
That way, you will know when you need to order more seeds (and how much to buy). You might even be able to get free shipping if you order online and buy enough seeds at the same time.
Use Proper Seed Spacing and Depth
Don’t plant your seeds too deep (or too shallow), or you will run into germination problems. Remember, 0.25 inches (0.63 centimeters) is the proper soil depth.
If the seeds are too deep, it might be difficult to keep the soil around them wet enough with a spray bottle. The seeds also might not be able to break through so much soil to reach the light.
If you plant your seeds too close together, the roots might get tangled after the seedlings start to grow. This will make it very difficult to transplant them later without damaging the roots!
Use a Humidity Dome
A humidity dome helps to maintain consistent moisture in the air around your soil and seeds. You can make your own, or you can buy one ready-made. You can learn more about humidity domes here.
Water Your Seeds Properly (Keep the Soil Moist)
As mentioned before, soil moisture is one of the most important factors in seed germination, aside from temperature. You should check the soil frequently and spray with water as often as necessary to keep it moist.
A humidity dome (mentioned above) will help to maintain moisture in the air and soil, but it is no substitute for careful attention from you. Tomato seeds should germinate in about a week with proper soil temperature and moisture, so you won’t have to obsess over them for long!
How to Help Your Tomatoes Grow Better After Germination
Even if your tomato seeds sprout well, it will still take some effort to care for them and get a bountiful harvest of tomatoes. Here are a few ways to ensure a good tomato harvest.
Give Them Plenty of Light
Tomato seeds do not need light to germinate, but seedlings do need light to continue growing after they sprout. Grow lights (and perhaps a timer) can help with this if the days are still short, or if you are starting your tomato seeds in the basement.
Established plants also need plenty of sunlight for optimal growth. Give them full sunlight (at least 8 hours of sunlight per day) for best results.
This means that you will need to choose the right location to transplant the tomato plants after starting the seeds indoors. Pay attention to trees and buildings (sheds, garages, etc.) that might shade your plants later in the season.
Enrich Your Garden Soil
This is something to do before the growing season starts. The best way to enrich your garden soil is to add compost or manure. This has two major benefits.
First, it restores nutrients that your plants used for last year’s growth. Second, it replaces organic material in the soil.
Organic material helps soil to stay moist in dry weather and drain well in wet weather. Organic material also encourages the growth of beneficial soil organisms, such as earthworms and bacteria.
You can also add fertilizer and other additives, such as lime or Epsom salt, to your garden to supplement nutrients that your plants need to grow.
However, make sure to get a soil test before you add anything to your soil. You don’t want to end up with an excessive amount of any nutrient. For example, too much nitrogen prevents flowering, while too much magnesium prevents plants from absorbing calcium.
For more information, check out my article on how to do a soil test for your garden.
Adjust Soil pH
Tomato plants (and all other plants) grow best if the soil pH is within the proper range. The ideal pH range varies by plant, but most will do well between 6.0 and 6.8 (slightly acidic to neutral).
A soil test will tell you the pH of your soil. If the pH is too low (acidic), you can add lime (calcium carbonate) to raise it. If the pH is too high (basic or alkaline), you can add sulfur to lower it.
Now you know have a much better idea of why your tomato seeds failed to sprout, and what you can do to fix the problem. You also know some ways to make your tomato seeds germinate a little faster in the future.
You might also be interested in reading about when you can direct sow tomato seeds – and when you might be better off starting seeds indoors.
I hope you found this article helpful – if so, please share it with someone who will find the information useful. It’s time to get back to the garden and help your tomato seeds to sprout!