If you are planning to grow kohlrabi in your garden this year, you might be wondering how big the plants and fruit will get. That way, you can plan the number of plants and the amount of space you will need for your crop of kohlrabi.
So, how big do kohlrabi get? Kohlrabi can grow 6 to 18 inches (15.2 to 45.7 centimeters) tall, 12 to 18 inches (30.5 to 45.7 centimeters) wide, and produce bulbs up to 6 inches (15.2 centimeters) in diameter.
Of course, the quality of your kohlrabi (if you get any at all!) depends on the care that you give your plants. Let’s take a closer look at kohlrabi, including size, growing conditions, and time to maturity.
How Big Do Kohlrabi Get?
A kohlrabi plant, including the stalks, can grow up to 18 inches (45.7 centimeters) tall, with a width of up to 18 inches (45.7 centimeters).
The bulb on a kohlrabi plant can grow up to 6 inches (15.2 centimeters) in diameter for large varieties. This is a circumference of over 28 inches (71 centimeters)!
However, keep in mind that kohlrabi bulbs will become bitter and tough if they get too large. You should make plans to keep an eye on your kohlrabi, since they grow very quickly. Make sure to harvest your kohlrabi before they get too large and become bitter (more on this later).
How Long Does It Take Kohlrabi to Grow?
Kohlrabi can take between 40 and 60 days from the time you plant a seed to the time you get a mature plant with bulbs that are ready for harvest. Of course, the time to maturity depends on the variety. There are both green and purple kohlrabi plants available.
For more information, check out this article on kohlrabi from the University of Illinois Extension.
Kohlrabi seeds usually germinate in 7 to 10 days, assuming that soil temperatures are between 50 and 85 degrees Fahrenheit (10 to 30 degrees Celsius).
For more information, check out this article from West Coast Seeds on growing kohlrabi.
Does Kohlrabi Grow Above Ground?
Yes, kohlrabi grows above ground. The stem, which looks like a bulb, develops mostly above ground. This bulb is the part of a kohlrabi plant that is usually grown for eating.
There are also stalks that grow upwards from the stem of a kohlrabi plant. These stalks have leaves at the ends, and are sometimes also harvested for food when still young and tender.
Can Kohlrabi Get Too Big?
Yes, kohlrabi can get too big. When a kohlrabi bulb gets too big, the stem gets woody and tough, and the flavor becomes bitter. The stalks and leaves will also become tough and bitter as the kohlrabi plant gets older and larger.
To avoid tough kohlrabi bulbs and stalks, harvest the plant when the bulb is 2 to 3 inches (5.1 to 7.6 centimeters) in diameter. Cut the bulb from the base of the plant, and wash off the dirt.
You can eat the bulb raw or cook it like a turnip. If you use the foliage for salad greens, harvest some of them when the plant is still young, before the stalks and leaves get tough. That way, the remaining stalks and leaves will help the kohlrabi bulb to continue growing.
What Do Kohlrabi Look Like?
A kohlrabi plant has a round globe (the bulb) that grows mostly above the soil line. There are numerous shoots (stalks) with leaves at the ends that grow up from the bulb.
Kohlrabi stalks and their leaves look like kale. You can eat kohlrabi stalks and leaves raw in a salad, or you can steam or boil them like spinach. You can also use them as garnish for a dish, such as a stir-fry, just like you might with other microgreens.
Kohlrabi bulbs and stalks can be green or purple. The leaves of a kohlrabi plant are green.
Are Kohlrabi Hard to Grow?
Kohlrabi plants like at least 6 hours of full sun per day, and they prefer a soil pH between 6.0 (slightly acidic) to 7.5 (slightly basic).
If you are not sure about your soil pH, you should get a soil test to make sure you are in the correct range. For more information, check out my article on soil testing.
Kohlrabi can be difficult to grow in warmer regions, since it is a cool-weather crop. Also keep in mind that too much heat or water stress can cause kohlrabi bulbs to become bitter, even if the plant does grow well.
There are many other factors that affect kohlrabi growth, including temperature, watering, fertilizing, and spacing. Let’s start with temperature.
Temperature for Kohlrabi
Kohlrabi is a cool-season crop in the Brassica family (along with broccoli, cauliflower, cabbage, etc.). Kohlrabi seeds will germinate in soil temperatures as low as 45 degrees Fahrenheit (7.2 degrees Celsius).
For a spring crop, plant kohlrabi 4 weeks before the last spring frost. For a fall crop, plant kohlrabi 6 weeks before the first fall frost.
According to Bonnie plants, kohlrabi can survive frost, and a light frost can even enhance flavor of the plant. However, a hard freeze will kill kohlrabi.
To protect kohlrabi from late a spring freeze or early fall freeze, use cloches to cover young plants, or row covers for larger, more established plants.
A cloche can be made from a plastic water bottle. It can also be used to retain warmth and humidity in the soil for seeds or seedlings as they grow.
Watering for Kohlrabi
Kohlrabi needs even watering in well-drained soil to avoid cracking and splitting. Water stress can also lead to bitter flavor, so you may need to use mulch to keep the soil moist.
You may also need to water more often if you have sandy soil, which drains quickly.
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 kohlrabi 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. Watering deeply and infrequently encourages stronger root systems in plants.
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. Also, avoid getting the leaves wet to prevent rot, mold, and diseases.
For more information on watering, check out this article on kohlrabi from the University of Minnesota Extension.
Fertilizing for Kohlrabi
Before you do any fertilizing or planting, it is a good idea to add some compost to your soil. This will provide organic material and nutrients for your kohlrabi plants. It will also improve drainage in clay soil, and improve water retention in sandy soil.
The best part about compost is that you can make it from recycled kitchen scraps and yard waste. For more information, check out my article on how to make compost.
After adding compost to the soil, the University of Utah Extension suggests using 4 to 6 cups of a balanced fertilizer (such as 10-10-10) early in the kohlrabi plant’s growth, to encourage bulb and leaf growth.
Avoid excessive nitrogen, since this can burn plants. The same warning applies if you decide to use manure to help fertilize your garden. Make sure that the manure is fully decomposed before using it!
For more information, check out my article on over fertilizing your plants.
Spacing for Kohlrabi
Sow your kohlrabi seeds ¼ to ½ inch (0.6 to 1.3 centimeters) deep in the soil. When the seedlings have 3 or 4 true leaves, thin them so that the remaining plants are 4 to 6 inches (10.2 to 15.2 centimeters) apart, leaving 2 to 3 plants per foot. (You can use the seedlings you pulled up as microgreens in a stir-fry or other dish!)
For more information, check out my article on thinning seedlings.
Leave 12 to 18 inches (30.5 to 45.7 centimeters) between plant rows, to allow for easy watering, weeding, and harvesting of your kohlrabi.
Now you have a much better idea of how big kohlrabi will get, in terms of both the bulb and the plant itself. You also know a bit more about the care that is necessary to ensure a healthy crop of kohlrabi 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 kohlrabi, please leave a comment below.