Kohlrabi Planting Guide: Crisp Above-Soil Stems

Plant Kohlrabi Right From The Start

Plant kohlrabi in cool weather, sowing seed ¼–½ inch deep and thinning plants to 4–6 inches apart for standard fresh harvests. Space rows 12–18 inches apart so leaves can expand without crowding the above-soil globe. The crisp round portion is a swollen stem, not a root, so keep the crown and developing bulb visible; do not hill soil or pack mulch over it. Direct-seed 2–4 weeks before the last spring frost or 8–10 weeks before the first fall frost. Set transplants at the same depth they grew in the tray once they have 3–4 true leaves. Keep soil evenly moist, about 1 inch of water per week, and harvest most varieties when stems reach 2–3 inches wide.

That sequence—shallow seed, cool timing, open spacing, steady moisture, exposed crown, and young harvest—prevents many woody, cracked, or misshapen kohlrabi crops.

Quick Planting Checklist

• Choose a cool window: plant for spring or fall while temperatures are mild; fall crops often produce the sweetest stems.
• Prepare fertile soil: loosen the bed 8–10 inches deep and mix in finished compost before sowing or transplanting.
• Sow shallowly: cover seed with only ¼–½ inch of soil and keep the surface damp until seedlings emerge.
• Thin early: leave 4–6 inches between standard plants, or 8–10 inches for large storage varieties.
• Protect the globe: place mulch around the root zone while keeping the swelling stem uncovered.
• Harvest young: cut stems at soil level when most are 2–3 inches across unless the variety is bred for larger storage size.

Understand The Above-Soil Stem

What Part Of Kohlrabi Are You Growing?

Kohlrabi is a cool-season Brassica oleracea crop grown for an enlarged stem that forms above the soil surface. This is the practical difference between kohlrabi and root crops such as turnips, beets, or radishes. The roots anchor and feed the plant below ground, while the edible globe expands at the crown.

If soil piles against the globe, it can encourage blemishes, trapped moisture, distortion, and uneven color. During weeding or cultivation, brush loose soil away from the crown instead of hilling it. For market growers, this detail improves appearance as well as eating quality.

Kohlrabi belongs to the same brassica group as cabbage, broccoli, kale, and cauliflower, so rotate it away from recent brassica beds when pest or disease pressure has been high. A 2–4 year rotation helps reduce problems such as clubroot, black rot, and cabbage root maggots. For broader rotation planning, see The Rike guide to brassica crop rotation.

Time Spring And Fall Plantings

Kohlrabi grows best when days are cool and growth is steady. Heat, drought, and crowding slow the plant down, which can make stems fibrous before they reach useful size. Spring crops are valuable for early harvests, but fall crops often produce smoother texture because stems size as nights cool. The University of Minnesota Extension, University of Wisconsin-Madison Extension, and University of Illinois Extension all emphasize cool-season timing, shallow planting, and harvesting before stems become oversized.

Many kohlrabi varieties mature in about 45–60 days from seeding, though weather and cultivar choice change the harvest window. Storage types need more space and time than standard fresh-market types. For succession timing across lettuces, greens, brassicas, and roots, use The Rike cool-season vegetable garden planning guide.

Prepare Soil And Choose The Site

Choose full sun for the most uniform stems. In regions with hot late-spring weather, light afternoon shade can reduce stress, but dense shade delays stem enlargement. Kohlrabi needs soil that drains well yet holds enough moisture to prevent stop-and-start growth.

Target a soil pH near 6.0–7.5. The Michigan State University Extension recommends a pH range of 6.0–7.5 for kohlrabi, while the University of Minnesota Extension recommends fertile, well-drained soil and consistent moisture for good quality. A soil test is the best guide for lime, phosphorus, potassium, and micronutrient adjustments.

• Mineral soil beds: incorporate 1–2 inches of mature compost and rake a fine seedbed for shallow sowing.
• Raised beds: use a friable mix that drains quickly but does not dry out between waterings.
• No-till beds: open a narrow planting furrow through residue and keep mulch off the crown.
• Containers: choose a deep potting mix with drainage holes and enough compost to buffer moisture swings.

If your bed needs organic matter before planting, review The Rike guide to using compost in vegetable gardens.

Set Depth, Spacing, And Stand Density

Sow kohlrabi seed ¼–½ inch deep. Shallow placement allows fast emergence, but the surface must stay damp until seedlings are established. In field rows, sow lightly and thin promptly; waiting too long creates stretched plants and inconsistent stem size.

For transplants, set seedlings at the same depth they grew in the tray. Do not bury the stem up to the leaves as you might with tomatoes. Firm the soil around the root ball, water immediately, and leave the crown exposed. For tray timing and hardening-off habits, see The Rike seed starting guide.

Water, Feed, And Mulch Correctly

The difference between crisp kohlrabi and woody kohlrabi is usually growth rate. Drought, heat stress, low fertility, or overcrowding can slow development and toughen the stem. Provide about 1 inch of water per week from rainfall or irrigation, increasing frequency in sandy soil, raised beds, and containers.

Compost supports soil structure and slow-release fertility, while a moderate nitrogen side-dress can help when stems begin to swell. Use local soil-test recommendations for exact nutrient rates. Too much late nitrogen can produce lush tops and weaker storage quality, so feed early enough to support steady growth without forcing excessive leaves.

Mulch is useful for moisture control, weed suppression, and soil temperature moderation. Place straw, leaf mold, or biodegradable mulch around the plant base, but keep it away from the swelling stem. If rain or cultivation splashes soil onto the globe, gently clear it.

Prevent Pests And Disease Early

Kohlrabi attracts many of the same pests as cabbage and kale. Prevention is easier than correction, especially for organic gardens and wholesale growers supplying clean bunched produce. Install floating row cover immediately after seeding or transplanting, sealing the edges to block flea beetles, cabbageworm moths, and cabbage root maggot flies. Vent or remove covers if heat builds up. The UC IPM cole crop guidance supports regular monitoring for cole crop pests, and extension row-cover guidance commonly recommends exclusion barriers before insects arrive.

• Flea beetles: watch for tiny shot holes on seedlings and protect young stands before damage spreads.
• Cabbageworms and loopers: inspect leaf undersides for eggs, chewing, and green frass.
• Cabbage root maggots: prevent fly access with row cover and rotate away from infested brassica beds.
• Aphids: reduce lush nitrogen-heavy growth and encourage beneficial insects.
• Clubroot: manage with long rotations, sanitation, drainage, and pH correction where appropriate.
• Black rot: use clean seed, avoid overhead irrigation when possible, and remove infected residue.

For physical pest exclusion in small beds, see The Rike guide to floating row covers.

Harvest And Handle For Crisp Quality

Harvest most fresh-market kohlrabi when stems are 2–3 inches across. The University of Wisconsin-Madison Extension notes that kohlrabi is best harvested while young and tender, and the University of Illinois Extension recommends harvesting when bulbs are about 2–3 inches in diameter. Cut at soil level with a clean knife, trim roots, and remove damaged leaves. Young leaves are edible and can be cooked like kale, but bulky tops draw moisture from stems during storage.

Cool harvested kohlrabi quickly. Cold, humid storage helps preserve crispness, while dehydration leads to rubbery texture. For market channels, decide whether the crop will be sold with leaves, trimmed tops, or as stem-only units so grading and packing stay consistent.

Large storage cultivars can be held longer than tender baby types, but they still need steady growth before harvest. Separate lots by variety and harvest date so older stems do not get mixed into premium fresh packs.

Match Kohlrabi To Your Growing Situation

Small Homestead Gardens

Plant short succession rows every 10–14 days during cool weather instead of one large block. This keeps kitchen harvests tender and reduces waste from oversized stems.

Wholesale Seedling Production

Use 128-cell or 72-cell trays, maintain strong light, and ship seedlings before roots circle heavily. Label trays with “plant at tray soil level” so customers do not bury the developing stem.

Containers And Patio Kits

Provide at least 1–2 gallons of potting mix per plant and consistent water. A 10–12 inch pot suits one standard kohlrabi, while larger planters can hold several plants if spacing is maintained.

Fall Storage And Farmstand Sales

Select varieties bred for larger stems without rapid woodiness. Give them wider spacing and enough time to size before hard freezes.

Regenerative And Low-Input Beds

Plant after a composted cover crop or after legumes that leave residual nitrogen. Rotate afterward into alliums, legumes, or fruiting crops to reduce brassica pest carryover. For layout help, use The Rike vegetable garden planner.

Avoid Common Kohlrabi Mistakes

Mistake: Burying The Bulb

The round harvestable portion is a swollen stem and should remain above soil. Burying it can cause blemishes, misshaping, and moisture damage.

Mistake: Waiting For Giant Standard Stems

Most common varieties taste best at 2–3 inches wide. Oversized stems may turn fibrous, especially after heat or drought stress.

Mistake: Treating Kohlrabi As A Summer Crop

Kohlrabi tolerates light frost better than sustained heat. In warm climates, shift production to fall, winter, or very early spring.

Mistake: Thinning Too Late

Crowded seedlings compete before stress is obvious. Thin as soon as plants are large enough to handle.

Safety: Use Compost Correctly

Use finished compost instead of raw manure near harvest. Commercial growers should follow local food-safety rules for soil amendments, tools, wash water, and packing surfaces.

Myth: Purple Kohlrabi Tastes Completely Different

Purple skin adds color, but variety, water, temperature, and harvest size usually matter more for flavor than skin color.

Kohlrabi Planting FAQ

How Deep Should Kohlrabi Be Planted?

Sow seed ¼–½ inch deep. Set transplants at tray depth with the crown and developing stem above the soil.

Does Kohlrabi Grow Above Or Below Ground?

The edible swollen stem grows above ground. The roots stay below the soil, which is why kohlrabi should not be hilled like a root crop.

When Is The Best Time To Plant Kohlrabi?

In many temperate areas, plant in early spring and again in late summer. For fall crops, count back 8–10 weeks from the first expected frost.

Why Is My Kohlrabi Woody?

Woodiness usually comes from late harvest, drought, heat, poor fertility, or crowding. Harvest standard varieties at 2–3 inches wide for the crispest stems.

Can Kohlrabi Be Grown In Pots?

Yes. Use a container with drainage, allow 1–2 gallons of potting mix per plant, keep the crown exposed, and water consistently.

Sources

• University of Minnesota Extension: Growing kohlrabi
• University of Wisconsin-Madison Extension: Kohlrabi
• University of Illinois Extension: Kohlrabi
• Michigan State University Extension: How to grow kohlrabi
• UC IPM: Cole crops pest management guidance

Shop Sustainable Essentials

Support cool-season kohlrabi planting with practical supplies that help keep stems evenly watered, well spaced, protected from pests, and grown with lower-waste habits.

• Shop The Rike home and garden collection for sustainable gardening basics.
• Explore gardening essentials for seed starting, composting, containers, and bed preparation.
• Browse organic seeds for cool-season vegetable succession planting.