If you are planning on growing radishes in your garden this year, you might be wondering how big they will get. That way, you can plan the number of plants and the amount of space you will need for your crop of radishes.
So, how big do radishes get? Radish plants grow 4 to 14 inches (10.2 to 35.6 centimeters) tall, 3 to 14 inches (7.6 to 35.6 centimeters) wide, and produce roots that are 1 to 4 inches (2.5 to 10.2 centimeters) in diameter. Some tall radish varieties, such as Daikon, can have roots as long as 8 to 14 inches (20.3 to 35.6 centimeters)!
Of course, the quality of your radishes (if you get any at all!) depends on the care that you give your plants. Let’s take a closer look at radishes, including size, growing conditions, and time to maturity.
How Big Do Radishes Get?
Radish greens (the stalks and leaves) can grow to a height of 4 to 14 inches (10.2 to 35.6 centimeters) above the soil, with a width of 3 to 14 inches (7.6 to 35.6 centimeters).
The roots of many small, round radish varieties may only be 1 to 2 inches (2.5 to 5.1 centimeters) in diameter. Some larger round radishes can grow to 3 or 4 inches (7.6 to 10.2 centimeters) in diameter.
However, you will want to harvest your radishes before they grow too large. Otherwise, you will get radishes with a bitter flavor.
The tallest radish varieties, such as Daikon, are longer and thinner, and can get into the range of 8 to 14 inches (20.3 to 35.6 centimeters).
How Long Does It Take Radishes to Grow?
Some radishes can grow to maturity in as little as 20 days! However, most radishes will take 20 to 40 days to mature.
However, there are certain varieties, such as Daikon radishes, that can take up to 60 or 70 days to mature.
According to Michigan State University, radish seeds will germinate in 3 to 10 days, assuming proper moisture and ideal soil temperature of 65 to 85 degrees Fahrenheit (18.3 to 29.4 degrees Celsius).
How Do You Know When to Pick Radishes?
For most radish varieties, you can harvest them when the roots are 1 inch (2.5 centimeters) in diameter at the surface of the soil.
For more information, check out this article on radishes from the Old Farmer’s Almanac.
Keep an eye on your radishes, since they mature and grow very quickly! Check on them daily when they get close to maturity (look at the seed packet to get an idea of the days to maturity).
Why Are My Radishes So Small?
Radishes will grow small if you provide too much nitrogen in the soil or give the plant too much shade.
In both cases, the radish plant will grow large leaves at the expense of the root. Avoid adding too much nitrogen or planting radishes in the shade of trees and other tall crops in your garden.
What Do Radishes Look Like?
Radishes are roots that grow in the ground. Some are small and round, while others are longer and more similar in shape to carrots.
Radishes can be red, purple, white, or black on the outside. Radishes are usually white on the inside, although some have purple or red color inside.
Radishes send up stalks with leaves on them (greens). These greens can be used in salads, but you will want to harvest when they are young and tender for this purpose.
Otherwise, you can boil or steam radish greens, similar to how you would use spinach or beet greens.
Are Radishes Hard to Grow?
Radishes like full sun, so make sure you do not plant them in the shade of trees or other crops in your garden. Otherwise, you will get radish plants with large leaves and small roots.
Like carrots, radishes are grown mainly for the roots, which need loose, sandy soil to grow without obstruction.
There are many other factors that affect radish growth, including temperature, watering, fertilizing, and spacing. Let’s start with temperature.
Temperature for Radishes
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. This is why it is suggested that you start radish seeds indoors to avoid cold soil temperatures in early spring.
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. So, don’t wait too long to plant your radish seeds and transplant your established plants outside!
The Old Farmer’s Almanac suggests sowing radish seeds directly into the soil outdoors, 4 to 6 weeks before the last spring frost date.
You can start seeds indoors if the growing season is short where you live. However, remember that it is easy to disturb the roots of radishes when transplanting them outside.
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 to retain warmth and humidity in the soil for seeds or seedlings as they grow.
For more information, check out the table below, and check out this article from the University of California on ideal seed germination temperatures.
|Ideal||65 to 85||18.3 to 29.4|
Watering for Radishes
Radishes need plenty of water, and they need even moisture levels to develop properly. Periods of dry soil followed by too much water will cause radishes to split or develop a bitter flavor.
Putting mulch on top of your soil will help to retain moisture, especially during periods of hot, dry weather. If you find that you have a problem with dry soil, check out my article on how to treat dry soil.
On the other hand, over watering your radish plants (or any plants for that matter) can lead to root rot and eventual death. The best way to decide when to water is to feel the soil with your fingers.
If the soil feels dry 2 or 3 inches below the surface, then go ahead and water. For more information, check out my article on over watering your plants.
Try to water early in the morning, rather than at night, to allow water to soak into the soil. Avoid getting the leaves wet to prevent rot, mold, and diseases.
Fertilizing for Radishes
According to Burpee, you should avoid adding too much nitrogen to your soil when growing radishes. Otherwise, you will get lots of green growth (stalks and leaves) but small roots.
For more information, check out my article on over fertilizing your plants.
Adding compost to your soil before planting is a good way to improve drainage for clay soil, improve water retention for sandy soil, and add nutrients to your garden.
For more information, check out my article on making compost.
Spacing for Radishes
Sow radish seeds directly into the garden, at a depth of 0.25 to 0.5 inches (0.6 to 1.3 centimeters).
For more information, check out this article on radishes from the University of Illinois Extension.
Thin the radish plants to 1 inch (2.5 centimeters) apart for spring varieties, and 2 to 4 inches (5.1 to 10.2 centimeters) apart for winter varieties. Do your thinning when the radishes are a week old (or when they have two sets of true leaves).
For more information, check out my article on thinning seedlings.
You can plant radishes in the spring (May) to get a first crop, and also get a fall crop by planting in late summer (August).
Now you have a much better idea of how big radishes get, in terms of both the root below ground and the stalks above ground. You also know a bit more about the care that is necessary to ensure a healthy crop of radishes in this year’s garden.
You might also want to read my article on fall planting for cool weather crops.
I hope you found this article helpful – if so, please share it with someone else who can use the information. If you have any questions or advice about radishes, please leave a comment below.