How to Grow Kohlrabi & Harvest It Before It's Woody
Learn how to grow crisp, tender kohlrabi from seed step-by-step guide covers planting, pests & the number one secret to harvest before it gets woody!
Kohlrabi is the quirky, alien-looking standout of the garden. But for every gardener who praises its crisp, juicy, and mild flavor, there’s another who has been burned by a bulb that was tough, fibrous, and woody. The difference between the two? It's all about timing.
This guide is built to do one thing: help you grow and harvest perfectly crisp, tender kohlrabi every single time. We're going to bypass the common mistakes and focus on the pro-level techniques that guarantee a delicious harvest. Forget what you think you know-this is the definitive guide to mastering this unique and rewarding crop.
{getToc} $title={Table of Contents} $count={Boolean} $expanded={Boolean}What Is Kohlrabi? (It's Not a Root!)
Let's clear this up first. Despite its appearance and "rabi" name (German for turnip), kohlrabi is not a root vegetable. It’s a proud member of the Brassica oleracea family, making it a close cousin to broccoli, cabbage, and kale.
The "bulb" you eat is actually the plant's swollen, fleshy stem that grows entirely above the ground. This distinction is crucial. Because it's a stem, it's designed to become tough and fibrous to support the plant as it gets older. Your job as a gardener is to harvest it while it's still young, tender, and juvenile.
The Number One Secret to Success: Kohlrabi is a Cool-Season Crop
You cannot ignore this fact. Kohlrabi, like its cabbage cousins, despises the heat of summer. High temperatures will cause two major problems:
- Bolting: The plant will panic and "bolt"-sending up a flower stalk to produce seeds before it dies. This turns the stem bulb hopelessly woody.
- Woodiness: Even if it doesn't bolt, heat stress slows growth and creates a fibrous, tough texture.
This means you have two primary windows for growing: spring and fall. Your goal is to get the plant to mature before the summer heat or after it has broken in the fall.
Popular Kohlrabi Varieties to Try
While there are many varieties, they generally fall into two categories. The flavor is nearly identical; the main difference is color and, in some cases, days to maturity.
- White (or Green) Vienna: A classic, pale green heirloom. Fast-maturing (around 55 days) and a reliable producer.
- Purple Vienna: A gorgeous, deep purple variety that adds visual pop to the garden. It can take slightly longer to mature (around 60 days).
- Winner (Hybrid): A common green hybrid known for its vigor and resistance to splitting.
- Kossak (Hybrid): A larger variety that can grow to 8-10 inches and reportedly stay tender, but for beginners, it's best to stick to harvesting small.
Tools & Materials You'll Need
Before you start, gather your supplies. This is a straightforward project, and having everything ready makes the process smooth. Your setup should look like the tools image below.
- Kohlrabi seeds or young transplants
- High-quality compost or well-rotted manure
- All-purpose, balanced organic fertilizer
- A garden trowel
- A watering can or hose with a gentle spray nozzle
- Garden markers or stakes
- Mulch (straw, shredded leaves, or pine bark)
- (Optional but Recommended) Floating row cover and hoops
SAFETY FIRST: Garden Prep Safety
All garden projects require basic awareness. This one is simple, but don't get complacent.
[SAFETY FIRST WARNING]: Always wear gloves when working with compost, manure, and garden soil. Soil can contain bacteria, and gloves protect your hands from cuts and irritation. If you are amending soil with a power tiller, wear sturdy, closed-toe boots and eye protection.
How to Grow Kohlrabi: A Step-by-Step Guide
Follow these steps for a foolproof harvest. The most important part of this entire process is Step 1 (Timing) and Step 4 (Thinning). Do not skip them.
Step 1: When to Plant (The Two-Season Strategy)
You have two distinct planting windows. Pick the one that works for your climate.
- For a Spring Harvest: Plant kohlrabi as soon as the soil can be worked. This is typically 2-3 weeks before your last expected frost date. The goal is to get the bulbs to mature before daytime temperatures consistently top 75°F (24°C).
- For a Fall Harvest (The Easiest Method): This is the superior method for most gardeners. Plant seeds 6-8 weeks before your first expected fall frost date. The kohlrabi will grow during the cooling days of late summer and mature in the crisp, cool autumn air. A light frost actually improves its flavor, making it sweeter.
Pro Tip: For a continuous supply, practice succession planting. For your fall crop, sow a new small batch of seeds every 1-2 weeks over a 4-week period. This staggers your harvest so you aren't forced to eat 20 kohlrabi at once.
Step 2: Choose and Prepare Your Planting Site
Kohlrabi is not a fussy plant, but it does have three requirements:
- Full Sun: Choose a spot that gets at least 6 hours of direct sunlight per day.
- Rich Soil: Kohlrabi is a moderate feeder. Prepare your bed by amending the top 6 inches of soil with 2-3 inches of high-quality compost or well-rotted manure.
- Good Drainage: Like its cabbage cousins, it doesn't like "wet feet." If you have heavy clay soil, grow in a raised bed or amend heavily with compost to improve tilth.
Before planting, work in a balanced, all-purpose organic fertilizer according to the package directions.
Step 3: Planting Seeds vs. Transplants
Kohlrabi is exceptionally easy to grow directly from seed, which is the recommended method.
- Direct Sowing (Recommended): Plant seeds 1/4 to 1/2 inch deep. Space them about 2-3 inches apart in rows that are 12-18 inches apart. Water gently but thoroughly, and keep the soil evenly moist until germination, which usually takes 7-10 days.
- Using Transplants: If you're starting with transplants (either home-grown or from a nursery), "harden them off" for a week by gradually exposing them to outdoor conditions. Plant them at the same depth they were in their container, spacing them 6-8 inches apart.
Step 4: Thinning Seedlings (This Is a Critical Step)
This is the step that separates beginner gardeners from pros. It feels wrong, but you must do it. Kohlrabi needs space for the stem to swell. If overcrowded, you will get tiny, useless bulbs or just a tangle of leaves.
Once your seedlings are 2-3 inches tall, you need to thin them. Your goal is to have one single, strong kohlrabi plant every 6-8 inches.
Look for the strongest, most vigorous seedlings and leave them. For the others, do not pull them out. This can disturb the roots of the seedling you want to keep. Instead, take a pair of small scissors (as shown in the image) and snip the unwanted seedlings off at the soil line.
Step 5: Watering and Mulching
Consistent moisture is key to a tender, non-woody bulb. Soil that swings from bone-dry to waterlogged will cause the bulbs to split or become tough.
- Watering: Aim for 1 to 1.5 inches of water per week, either from rain or irrigation. The soil should be consistently moist, but not soaking wet.
- Mulching: Once the plants are established, apply a 2-3 inch layer of organic mulch (like straw, shredded leaves, or pine fines). This is a game-changer. Mulch retains soil moisture, suppresses weeds, and keeps the soil cool, all ofF which kohlrabi loves.
Step 6: Fertilizing Your Kohlrabi
If you started with rich, compost-amended soil, you may not need additional fertilizer. However, if your soil is average, you can give your plants a boost about 3-4 weeks after planting. Use a balanced liquid fertilizer (like fish emulsion) or side-dress with a granular organic vegetable food, watering it in well.
Common Kohlrabi Pests & Problems (And How to Stop Them)
As a brassica, kohlrabi is a target for the same pests that plague your broccoli and cabbage. Here’s how to fight back.
Pests: Cabbage Loopers & Flea Beetles
- Cabbage Loopers (Small Green Worms): These are the larvae of a small white or gray moth. They chew large, ragged holes in the leaves. The best organic defense is to inspect your plants daily and hand-pick them. You can also use Bt (Bacillus thuringiensis), a safe, organic-approved spray that only affects caterpillars.
- Flea Beetles: These tiny black or bronze beetles chew hundreds of "shotholes" in the leaves. They are most damaging to young seedlings.
The number one solution for both of these pests is mechanical, not chemical. Cover your kohlrabi with a floating row cover immediately after planting. This lightweight fabric lets in sun, air, and water, but physically blocks the moths and beetles from ever laying their eggs. This is the single best way to ensure a beautiful, damage-free crop.
[Budget-Saver Tip]: A single roll of floating row cover is one of the best investments you can make in an organic garden. It will last you multiple seasons and can be used to protect kohlrabi, broccoli, kale, cauliflower, and even sensitive seedlings from frost.
Problems: Splitting, Bolting, and Woodiness
- Splitting: The bulb has a large crack. This is almost always caused by inconsistent watering (a long dry spell followed by a sudden, heavy rain or watering). Prevention is key: use mulch and water consistently.
- Bolting: The plant sends up a flower stalk. This is caused by heat. You planted too late in spring, or it's a sign to harvest immediately before the bulb gets woody.
- Woodiness: The texture is tough and fibrous. This is not a disease. It's a human error. You waited too long to harvest.
How to Harvest Kohlrabi (The "No-Woody-Bulb" Method)
This is the most important section of this guide. Read it, and you will never eat woody kohlrabi again.
The Critical Mistake: Waiting Too Long
The number one mistake gardeners make is treating kohlrabi like a storage turnip. They wait for it to get "big." This is wrong. Kohlrabi is meant to be harvested when it is young, small, and tender.
[Data-Backed Insight]: According to the University of Minnesota Extension, most kohlrabi varieties are "best when 2-3 inches in diameter." [Link to authoritative source like UMN Extension] Waiting for them to get to softball size is a recipe for a woody, fibrous disappointment.
The "Tennis Ball" Rule
This is the only visual cue you need. Forget the days-to-maturity on the seed packet. Go by size.
- Golf Ball Size: Edible, super tender, but small.
- Tennis Ball Size (2-3 inches): This is the PERFECT size. This is the absolute peak of flavor, sweetness, and crispness. Harvest it. Now.
- Baseball Size (or larger): You're too late. The outer layers will be tough, and the interior will likely be fibrous.
Your goal is to harvest at the "tennis ball" stage, as shown in the verification image. Don't be greedy! A small, tender kohlrabi is infinitely better than a large, woody one.
How to Cut and Store Your Harvest
Harvesting is simple. You don't need to pull the whole plant up.
- Take a sharp knife or pair of garden shears.
- Slide the knife under the bulb and cut the stem about 1/2 inch below the bulb, separating it from the main root.
- The root can be left in the ground to decompose, or you can pull it up and compost it.
To store, trim off the leaves immediately (they suck moisture from the bulb). You can store the unwashed bulbs in a plastic bag in the crisper drawer of your refrigerator for several weeks.
Don't Forget the Leaves!
Wait! Don't compost those leaves. Kohlrabi leaves are 100% edible and absolutely delicious. They taste (and cook) just like collard greens or kale. Wash them, chop them, and sauté them with a little garlic and olive oil for a fantastic, zero-waste side dish.
{getCard} $type={post} $title={How to Grow Cabbage at Home}FAQ About Growing Kohlrabi Until Harvest Time
How long does kohlrabi take to grow?
Most varieties mature quickly, typically between 45 and 60 days from seeding. Always check your seed packet, but use the "tennis ball" size rule as your primary harvest indicator.
Can you grow kohlrabi in containers or pots?
Yes, kohlrabi is an excellent container plant. Choose a pot that is at least 12 inches deep and 12 inches wide. Use a high-quality potting mix and be sure the pot has good drainage holes. You will likely need to water and fertilize more frequently than in-ground plants.
What part of kohlrabi do you eat?
You eat the swollen, round stem bulb. It's delicious raw (peeled and sliced in salads or slaw) or cooked (roasted, steamed, or puréed in soups). You can also eat the leaves, which are cooked like kale or collard greens.
Why is my kohlrabi woody and tough?
This is the most common complaint, and it has two causes. Cause 1 (Most Likely): You harvested it too late. Once the bulb gets larger than a tennis ball, it begins to turn fibrous. Cause 2: The plant was stressed by heat or lack of water. Always grow kohlrabi in cool weather and keep the soil consistently moist.
What is good kohlrabi companion planting?
Kohlrabi pairs well with beets, celery, cucumbers, and onions. Bush beans are also a great companion as they fix nitrogen in the soil. Avoid planting it near pole beans or tomatoes.
Why are my kohlrabi plants all leaves and no bulb?
This is almost always a spacing issue. If the plants are too crowded, they will compete for light and nutrients, and the stems will not swell. You MUST thin your seedlings to 6-8 inches apart to give them room to form bulbs.
