If you are planting (or have already planted) radish 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 radish seeds take to germinate? Radish seeds take 3 to 6 days to germinate. Radish seeds germinate faster with optimal soil temperature, humidity, and air circulation.
You can see how soil temperature affects seed germination with this app I made!
Of course, you can germinate radish seeds indoors and transplant outside later, but it is difficult to do so, and so it is preferable to germinate radish seeds directly in the soil outdoors.
Let’s take a closer look at some of the factors that affect how long radish seeds take to germinate. We’ll also see how we can optimize these factors to encourage faster seed germination.
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How Long Do Radish Seeds Take To Germinate?
Generally, radish seeds will germinate within a week of planting (as long as the soil temperature is not too cold or too hot – more on this later).
According to the University of Michigan Extension, radish seeds can germinate in as little as 3 days under optimal conditions. On the other hand, the University of Minnesota Extension suggests that radishes may take up to 10 days to germinate.
It will all depend on various 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.
Soil Temperature
***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 radish seed germination is 40 degrees Fahrenheit (4.4 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 radish seeds from sprouting at a time when they will be unable to survive.
The maximum temperature for radish seed germination is 95 degrees Fahrenheit (35 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 radish seed germination is between 65 degrees Fahrenheit (18.3 degrees Celsius) and 85 degrees Fahrenheit (29.4 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 radish seeds.
A cloche can be made from a plastic water bottle, and will keep seeds or seedlings warmer than the surrounding air, especially on sunny days.
A cloche can be made from a plastic water bottle to trap heat and moisture in a small area to help seeds germinate faster.
For more information, check out the table below, and check out this article from the University of California on ideal seed germination temperatures.
| Seed Temp | Temp (degrees F) | Temp (degrees C) |
|---|---|---|
| Min | 40 | 4.4 |
| Ideal | 65 to 85 | 18 to 29 |
| Max | 95 | 35 |
maximum temperatures for
radish seed germination.
Humidity
Humidity is another important factor to consider when germinating radish 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.
Air Circulation
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.
Radishes are grown for the roots, just like carrots. You might even consider adding sand to the soil to loosen it up for growing radishes.
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How Do I Make My Radish Seeds Germinate Faster?
If you want to make your radish seeds germinate faster, there are several important actions you can take.
First, protect your seeds from extreme heat and cold. As mentioned earlier, temperature is one of the most important factors that affect seed germination.
You can find your frost dates (spring and fall) on the Farmer’s Almanac website.
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. Just be extra careful when transplanting the seedlings outdoors!
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 radish seeds do not need light to germinate. If you start radish seeds indoors, give the seedlings bright overhead lights after germination.
For more information, check out this article on seeds and seedlings from the Penn State University Extension.
Fifth, make sure to plant your radish seeds according to the proper depth and spacing. Radish seeds should be planted at a depth of 0.5 to 1 inch (1.3 to 2.5 centimeters). If planting in rows, put 12 per foot (1 inch or 2.5 centimeters apart).
When the plants grow to about a week old, thin them so that they are 2 inches (5 centimeters) apart, meaning 6 plants per foot, to prevent competition between plants.
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 Radish Seeds Be Soaked Before Planting?
You can soak your radish seeds before planting to encourage faster germination. Put them in clean water and let them sit for up to 24 hours before planting.
However, this is not required – as long as the growing medium is moist and warm, the radish seeds should germinate well.
Can You Germinate Radish Seeds In A Paper Towel?
Yes, you can germinate radish seeds in a paper towel. The paper towel holds moisture and allows the seeds to breathe, serving as an alternative growing medium.
To germinate radish seeds on a paper towel, wet the paper towel until it is damp (not soaking wet). Then, lay out the radish 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!
Germinating radish seeds in a paper towel may be helpful if you live in an area with a short growing season.
Why Are My Radish Seeds Not Germinating?
There are a couple of possible reasons that your radish seeds are not germinating.
Your Radish 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.
Radish seeds tend to last about 4 years, 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 radish seeds are not germinating has to do with soil conditions.
If the soil is too cold, then your radish seeds might not sprout right away (whether you are growing indoors or outdoors). They may sprout when conditions improve and the soil warms up.
As mentioned above, the Old Farmer’s Almanac suggests planting radish seeds 6 weeks before the last spring frost.
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.
How Big Should Radish Seedlings Be Before Transplanting Outdoors?
Generally, radish seeds should be planted directly in the soil outdoors. If this is not possible, then transplant them outdoors when they have two sets of leaves.
For more information, check out this article on vegetable gardening from the University of New Hampshire Extension.
Conclusion
Now, you have a good idea of how long it takes radish 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.
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~Jonathon