How to Grow Kohlrabi: Complete Beginner's Guide

Understanding the quirks of how to grow kohlrabi is the first step. I remember giving a neighbor a fist-sized bulb of kohlrabi vegetable and he thought it was a UFO. This fast-growing brassica, with both crunchy stems perfect for slaws and tender greens excellent for stir-fries, astonishes novice gardeners with its directional bounty. Timing is everything. If planted too late, the heat of summer will cause the bulb to become woody.

Space the seedlings 6 inches apart because having them too close together will stunt growth. I learned this the hard way in my first crop when I paid no attention to spacing and ended up with bulbs the size of marbles. Kohlrabi is fond of rich soil with something like compost added to it. Water it deeply, but don't over-saturate the roots. Regular moisture will help prevent bitterness from developing.

Harvest when the bulbs reach a width of 2-3 inches. Harvesting can be accomplished by twisting at the base or you can use a sharp knife. They will keep for weeks in the refrigerator, and should not be washed before storage. Unsightly leaves can be used to make pesto, while you can freeze any extra to add to soups in the winter months. Kohlrabi fits so easily into the garden, or in pots, for growing.

To prepare for kohlrabi, attention should be paid specifically to soil texture. For instance, heavy clay soils are mitigated by mixing into the soil 2 parts coarse sand to 1 part compost, which helps reduce the risk of waterlogging. Meanwhile, sandy soils should benefit from 3 inches of compost applied to the soil surface before planting. Before planting, you can also get a soil test kit to measure the soil pH. The goal is to have the soil pH between 6.0 - 7.5. If the soil pH is too acidic, then apply 5 pounds of lime per 100 square feet. Soil that is too alkaline can be amended with sulfur. I learned all of this after losing a crop one season to soil pH that had not been tested!

Sow seeds to a depth of 1/4 inch (6 mm) in rows that are 12 inches apart. For transplants, dig a hole that is the same depth as the starter pot - about 4 inches (10 cm). Direct sowing works best in early spring when the soil temperature is about 45°F (7°C). For transplants, the advantage is that they can get a 3-week jump on flower development simply because they started to grow under grow lights for a few weeks indoors. I generally prefer to sow seeds directly, rather than using transplants, to help avoid disturbing the roots of the plant, but I use transplants in the fall crops to escape the summer heat.

Successful gardening relies on timing. For spring crops, direct sow 2-4 weeks before your last reported frost. If you'd like to plant transplants for fall harvests, you'll want to transplant 6 weeks before the first frost. Stagger any transplant plantings every 10 days for a continuous yield. Also, be sure to mulch your seedlings in straw to retain moisture and suppress weeds, but be careful not to suffocate the stems.

Source: commons.wikimedia.org

Kohlrabi Seeds

• Germination: 5-10 days at 18-24°C (65-75°F)
• Sowing rate: 3 seeds per 10 cm (4 in) interval
• Thinning: Keep strongest seedling at 2 true leaves

Source: stockcake.com

Seedling Trowel

• Transplant depth: Match nursery soil level
• Spacing: 30 cm (12 in) rows for airflow
• Watering: 500 ml (17 oz) per plant after transplanting

Source: commons.wikimedia.org

Soil pH Meter

• Calibration: Required before first use with buffer solution
• Depth: Insert probe 15 cm (6 in) into moist soil
• Timing: Test morning/evening for stable readings

Source: www.rawpixel.com

Seed Spacer Template

• Material: Durable plastic with 10 cm (4 in) markers
• Usage: Press into soil to create uniform holes
• Benefits: Prevents overcrowding in rows

Source: commons.wikimedia.org

Compost Sieve

• Mesh size: 0.6 cm (0.25 in) for fine texture
• Application: Remove twigs before amending soil
• Storage: Hang vertically to save space

Source: www.culturallandscapesinc.com

Mulch Layer

• Materials: Straw/grass clippings 5-7.5 cm (2-3 in) thick
• Timing: Apply after second set of true leaves
• Warning: Keep 2.5 cm (1 in) from stems

Source: commons.wikimedia.org

Frost Blanket

• Material: Lightweight polypropylene with UV treatment
• Installation: Secure edges with soil or rocks
• Ventilation: Remove daily above 10°C (50°F)

Source: stockcake.com

Soil Thermometer

• Ideal range: 18-24°C (65-75°F) for germination
• Depth: Measure at 5 cm (2 in) depth
• Timing: Check 3 days before planting

Source: animalia.bio

Dibbler Tool

• Spacing: Creates 4 cm (1.5 in) deep holes
• Material: Hardwood with depth markings
• Use: Perfect for transplanting seedlings

Source: www.pexels.com

Seedling Trays

• Cell size: 5x5 cm (2x2 in) for root development
• Drainage: Requires 2 holes per cell
• Sterilization: Soak in vinegar solution between uses

Source: commons.wikimedia.org

Hori-Hori Knife

• Uses: Weeding, transplanting, and bulb harvesting
• Blade: 18 cm (7 in) with depth measurements
• Care: Wipe clean after each use

Source: commons.wikimedia.org

Watering Can

• Capacity: 5 liters (1.3 gallons) for easy handling
• Nozzle: Adjustable rose for gentle showers
• Material: Galvanized steel for durability

Grasping how to grow kohlrabi starts with selecting what variety works best for you. Early White Vienna matures fairly quickly, in just 55 days, great for impatient gardeners! The Giant Kossak takes 80 days but will store for months. I have had great luck with staggered plantings of either variety to extend harvests of both from spring until frost. The purple types, such as the Kolibri Hybrid, provide visual punch but need a little extra protection from frost compared to the green varieties that are hardier.

A key differentiator between winners and winter casualties is cold tolerance. Purple kohlrabi can endure short dips to 25°F (-4°C) with a strong hardening off-stage. The green variation can withstand somewhat lower temperatures, but because their tops are less firm, they tend to rot faster in the soil as the days go by in cold, wet soil after harvest. My trials for Zone 6 revealed that the Grand Duke green types performed better in terms of over-wintering under straw, than the purple varieties.

Ensure the appropriate bulb size for your growing environment. Compact types like Quickstar have an 8-inch container spacing, while Kossak will want about 18-inch spacing for its sprawling habit. I use the large types for raised beds and smaller varieties are typically lumped between flowers. I've unsuccessfully grown oversized bulbs in cramped quarter-sized spaces which split and caused me years of headaches.

Details of flavor are important. Purple kohlrabi tends to taste sweeter when eaten raw, while green kohlrabi is better when roasted. Superschmelz is best if the kohlrabi grows to a size of around 10 inches in diameter as it will stay tender. I have served both kinds of kohlrabi at dinner parties and dinner guests have never guessed they are the same species of vegetable. It is best to try different varieties before deciding to plant a large amount.

Source: commons.wikimedia.org

Early White Vienna

• Maturity: 55 days at 15°C (60°F)
• Yield: 700-900 g (1.5-2 lbs) per plant
• Special trait: Bolt-resistant in spring

Source: commons.wikimedia.org

Kolibri Hybrid

• Cold hardiness: Survives -6°C (21°F)
• Skin color: Deep purple with white flesh
• Culinary use: Vibrant raw salads

Source: commons.wikimedia.org

Kossak Hybrid

• Storage: 4 months at 2°C (36°F)
• Texture: Stays crisp when large
• Cooking: Ideal for stews and roasts

Source: commons.wikimedia.org

Grand Duke

• Speed: Ready in 50 days
• Space-saving: 15 cm (6 in) spacing
• Taste: Mild flavor for kids

Source: commons.wikimedia.org

Superschmelz

• Disease resistance: Immune to clubroot
• Size: 15-18 cm (6-7 in) without woodiness
• Versatility: Raw or cooked

Finding the right water application methods plays a significant role in kohlrabi's growing success. For example, drip irrigation applies water directly to the soil for root uptake, eliminating leaf wetting and lowering the chances of mildew. Overhead sprinklers provide quick cooling during heat waves, but they also create disease problems if the crop plus soils are wet. I learned the hard way when I lost a crop to leaf rot, then switched to soaker hoses which leave kohlrabi bulbs fat and disease-free.

Bulb firmness is determined by soil moisture. Check the soil weekly, 3 inches down should feel damp. Crunchy bulbs mean drought stress and split skins mean inconsistent watering. One of my poorest harvests was during a vacation when the ambient temperature increased and my neighbor forgot to turn the hose on. Consistency never waivers.

Detect pests early. Flea beetles will pockmark leaves with tiny holes. Cabbage loopers will skeletonize the entire foliage overnight. Slugs leave slimy trails. I check the undersides of affected plants during the early morning when pests are feeding. You can also use yellow sticky traps for winged insects that land in your garden. If life gets out of control, mix up a 1:10 solution of neem oil as a spray to smother unknown larvae without harming bees.

The best defense against pests organically is prevention. Row covers are effective against moths that would lay their eggs in brassicas. Planting dill as a companion plant attracts beneficial wasps. I had an aphid infestation on my purple kohlrabi; I released ladybugs in the late evening and in the morning they cleared all of the aphids. Chemical pesticides remain in the soil longer and I would rather lose some leaves.

Source: commons.wikimedia.org

Neem Oil Concentrate

• Mixing ratio: 15 ml/liter (2 tbsp/gallon)
• Application: Spray undersides of leaves
• Timing: Evening applications avoid sun damage

Source: commons.wikimedia.org

BT Spray

• Effective against: Caterpillars only
• Reapplication: After heavy rain
• Safety: Harmless to bees and ladybugs

Source: commons.wikimedia.org

Copper Tape

• Slug barrier: 5 cm (2 in) width
• Installation: Wrap around container rims
• Maintenance: Clean oxidation monthly

Source: commons.wikimedia.org

Soil Moisture Meter

• Depth range: 30 cm (12 in) capability
• Calibration: Test in water first
• Battery: 9V lasts 2 growing seasons

Source: commons.wikimedia.org

Row Cover Fabric

• Weight: 17 g/m² (0.5 oz/yd²) for pest exclusion
• Installation: Secure edges with soil
• Ventilation: Remove when temps exceed 27°C (80°F)

When to time your kohlrabi harvest can make a difference in flavor. Spring bulbs will taste best when they are harvested at approximately 2-3 inches wide, and anything larger will be firmer and more at risk for woodiness. Fall crops can be larger, growing to 4 inches in diameter, as long as they are growing in cooler temperatures. I left a spring bulb too long and lost all the crispness to a fibrous disappointment. Fall varieties will be sweeter with the frost but watch out for hard freezes which will damage The cell structure.

Look out for visual signs. For spring bulbs, the smooth and taut skin should not show cracks at harvest time. For fall varieties, deeper color should appear after a light frost. I usually check by pushing in my thumbnail gently. Spring bulbs should hold their shape, while fall varieties give in slightly. Always harvest in the mornings to help preserve moisture.

Cut the foliage down to approximately 1-2 inches above the bulb. Keeping the stems will slow down the depletion of water from the bulb through the foliage. I learned this the hard way when I stored some leafy bulbs and they took only a few days to shrivel up. Unwashed bulbs can be refrigerated in perforated bags. If you are storing in a root cellar, you can layer the bulbs in slightly damp sand. My grandma would use this method and keep them until New Year's.

Frost alters sugars. When the night is around 28°F (-2°C) you will see an increase in sweetness, but you will need to pick those. If there is a potential for frost before maturity, use row covers. I always do a taste test of my fall harvest after coming through a frost, the crunch with caramelization is worth the extra attention. Cold-tolerant varieties like Kossak handle fallen temperatures very well.

Source: commons.wikimedia.org

Stainless Harvest Knife

• Blade length: 15 cm (6 in) serrated edge
• Handle: Non-slip grip for wet conditions
• Care: Sharpen weekly during peak harvest

Source: commons.wikimedia.org

Root Digging Fork

• Tines: 4 rounded prongs @ 5 cm (2 in) spacing
• Leverage: 60 cm (24 in) handle length
• Use: Loosen soil without piercing bulbs

Source: itoldya420.getarchive.net

Harvest Basket

• Capacity: 10 kg (22 lbs) weight limit
• Ventilation: 2.5 cm (1 in) mesh sides
• Padding: Line with damp burlap

Source: stockcake.com

Pruning Shears

• Cut capacity: 2 cm (0.75 in) stems
• Safety: Spring-loaded automatic open
• Sterilization: Dip in vinegar solution

Source: commons.wikimedia.org

Curing Rack

• Dimensions: 60x90 cm (24x36 in)
• Spacing: 5 cm (2 in) between slats
• Location: Shaded, well-ventilated area

The preservation of kohlrabi freshness requires some thought and an approach. Keeping the kohlrabi in the refrigerator, where the bulbs remain intact and crispy for up to three weeks at 36°F (2°C) and 95% humidity, means wrapping the bulbs in damp towels and placing them in perforated plastic bags. If you have space in a root cellar or shed, kohlrabi can be kept even longer by layering the bulbs in a sand-filled crate at 40°F (4°C). My standing stock in a cellar can last until March before it shrivels!

The key to freezing something is accuracy. Blanch the cubes that are one inch thick for three minutes, and then shock them in ice water. The blanching will help move some excess moisture from the product. You will want to dry them before placing them in vacuum seal bags. The smaller (1-inch) pieces (plum or even smaller) break down or turn mushy. The Kossak Hybrid freezes particularly well as it is denser, making it more tolerant to temperature fluctuations.

Fermenting reveals the sour potential of ingredients. To ferment, for instance, wash and shred bulbs with carrots, then pack them into jars with a 3% brine solution, and weigh down the vegetables so that they are slightly submerged beneath the solution. Remember to 'burp' the jars daily for 7 days. My kimchi recipe, which uses gochugaru and ginger, became a quintessential winter recipe for immune-boosting probiotic foods during the flu season.

Select varieties based on their intended use. Early White Vienna is delicious raw in salads but loses its crispness after 2 weeks in the cold. Giant Kossak meets 4 months of storage in cellars. I roast long-storage varieties with some rosemary, with the caramelization masking any changes in texture due to being long-holding.

Source: commons.wikimedia.org

Mandoline Slicer

• Blade options: 1-5 mm thickness settings
• Safety: Cut-resistant glove included
• Cleaning: Dishwasher-safe components

Source: commons.wikimedia.org

Fermentation Crock

• Capacity: 5-liter (1.3-gallon) stoneware
• Weight system: Water channel + clay weights
• Seal: Grooved lid for CO₂ escape

Source: www.flickr.com

Vacuum Sealer

• Bag size: 20 cm (8 in) wide rolls
• Presets: Dry/Moist food modes
• Maintenance: Monthly oiling of suction channel

Source: commons.wikimedia.org

Dehydrator Trays

• Material: BPA-free plastic mesh
• Spacing: 2.5 cm (1 in) between trays
• Cleaning: Soak in baking soda solution

Source: stockcake.com

Root Cellar Racks

• Slat spacing: 5 cm (2 in) airflow gaps
• Load capacity: 25 kg (55 lbs) per shelf
• Treatment: Food-safe mineral oil finish

The kohlrabi variety choice plays a critical role in the entire growing process. For the impatient grower, the Early White Vienna variety, which harvests in only 55 days, will be very appealing; meanwhile, the Kossak variety takes a while to grow, but it produces substantial kohlrabi for winter storage. Through some trial and error, I have learned that misunderstanding the time to harvest a variety of kohlrabi often leads to cracked bulbs and disappointed expectations. It is always best to pair the cultivar with your climate and growing calendar.

Organic methods are worth their weight in gold, year after year. A well-timed application of neem oil, for example, will control flea beetles while causing no collateral damage. Cabbage worms, meanwhile, can be diverted from the fall crop by companion-planting nasturtiums. In addition to mitigating pest issues, methods like these are also building the health of the soil, which is an advantage of organic methods over the eons of lifeless dirt chemicals left behind.

Bulb size has a direct effect on your plate. Golf ball-sized kohlrabi provides crunch for fresh slaws, fist size is better when roasted. My kitchen tests of oversized Kossak bulbs show that they bake down silky when roasted, a lesson in how "flaws" become features with creativity. The timing of the harvest is your flavor dial.

As a way to create a sustained harvest, stagger your plantings every 10 days. I interplant Grand Duke, a fast-maturing crop, in between slower crops. This practice helps finish off space in the garden and keep variety in dinner menus. Each year, try one new gardening practice. For example, last year I tried companion planting garlic with kohlrabi and had huge, pest-free garlic bulbs and plump cloves. Curiosity equals mastery!