Kohlrabi is the sprinter of the cabbage family — seed to harvest in 45 to 60 days, sometimes 40 from transplants. That speed is exactly what makes it such a useful companion crop: it slips into gaps between slower vegetables, grabs a harvest, and is gone before anyone starts competing. The catch is that it still carries full brassica pest baggage, so the neighbors you choose matter more than its easygoing reputation suggests.
The strong pairings: beets, lettuce, spinach, onions, chard, and aromatic herbs like sage, dill, and thyme. West Virginia University Extension's companion planting tables list these as friends of the cabbage family — kohlrabi included — with the practical rule of keeping friends within 2 to 3 rows and foes at least that far away.
The interesting evidence isn't about scent-repelling folklore, though. A 2006 study in the Journal of Sustainable Agriculture (Guvenc and Yildirim) found that cabbage-based intercropping systems increased total yield, productivity, and profitability compared with monoculture — the gains came from packing compatible growth habits into the same space, which is precisely the game kohlrabi plays best. Mississippi State Extension's honest review of companion planting lands in the same place: the reliable benefits are space efficiency, soil cover, and beneficial-insect habitat, not magic pairings.
What you'll find below:
Key Takeaway
Kohlrabi's best companion strategy is temporal: pair it with cool-season crops on its own schedule (lettuce, beets, onions), tuck it into gaps other crops haven't filled yet, and harvest at 2-3 in. (5-7.5 cm) before the bulb turns woody.
Kohlrabi is a cool-season crop, and that shapes everything. University of Minnesota Extension recommends direct seeding from mid-April to early May, then again in July for fall harvests, and Utah State's guidance targets growth below about 75 F (24 C). The companions that thrive in exactly that window: lettuce, spinach, beets, chard, peas, and early onions.
Lettuce and spinach are the classic in-row partners — shallow roots, quick harvests, and they shade the soil around kohlrabi's swollen stem. Beets pull from a deeper root zone and, like kohlrabi, come out of the bed by early summer. Onions and other alliums line the bed edges, adding the same scent-disruption service they provide our other brassicas — see the pattern in our cabbage companion guide.
Herbs earn a spot too: a clump of dill or sage at each bed end feeds hoverflies and parasitic wasps that hunt cabbageworm eggs. Keep the herb clumps modest — they're insect habitat, not hedges.
Why This Works: Niches in Time
Permaculture design usually talks about stacking plants in space — canopy, shrub, ground cover. Kohlrabi demonstrates the other axis: stacking in time. A 45-day crop occupies a niche that exists between a bed's major acts, the way spring ephemerals flower and finish before the forest canopy closes. The Guvenc intercropping study measured what forests already know: systems layered in time and space out-yield single crops on the same ground.
This is kohlrabi's signature move: it fills gaps other crops leave behind. Because it matures in six to eight weeks, you can slot it into three distinct windows across the season.
Spring opener (April-May)
Sow 1-2 weeks before your last frost, per Utah State Extension. Kohlrabi matures alongside lettuce and spinach and vacates the bed just as tomato-transplant season peaks.
Summer gap-filler
Anywhere a spring crop finishes — garlic, peas, early potatoes — a kohlrabi transplant turns the empty square into a 40-day harvest instead of a weed patch.
Fall relay (July sowing)
UMN's July window sets up an October harvest. Utah State notes fall kohlrabi holds fine 2-3 weeks past the first frost, and cool finishing weather makes the sweetest bulbs.
Respect the rotation
UMN Extension's one hard rule: don't plant kohlrabi where broccoli, cabbage, or other brassicas grew within the past 4 years. Pest and disease carryover is the fast crop's slow enemy.
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Send Me the ChartThe extension "foe" list for the cabbage family: fennel, strawberries, pole beans, and tomatoes. Fennel is the clearest case — it's allelopathic, releasing compounds that suppress most vegetables, so it belongs in its own corner entirely. Pole beans climb into the light and their vigorous roots compete hard; strawberries fight for the same shallow root zone.
The tomato claim deserves honesty. The popular version says kohlrabi and tomatoes "stunt each other," but no controlled study demonstrates a specific antagonism. What's real: both are hungry crops, and their comfort zones barely overlap — kohlrabi wants under 75 F (24 C) while tomatoes are just warming up. Most reported "stunting" is probably seasonal mismatch and nutrient competition, not chemical warfare. Practically, the advice stands — separate beds — but the mechanism is scheduling, not poison. It's also worth avoiding a solid block of brassicas for pest reasons; our broccoli and brassicas guide and Brussels sprouts companion guide show how to break up the family.
| Neighbor | Verdict | Evidence |
| Lettuce, spinach, beets, chard | Plant together | Shared cool-season window, complementary roots (WVU) |
| Onions, garlic | Plant together | Edge rows, pest scent disruption (WVU) |
| Dill, sage, thyme | Small clumps nearby | Beneficial insect habitat (MSState) |
| Tomatoes | Separate beds | Seasonal mismatch + nutrient competition; "stunting" is folklore |
| Pole beans, strawberries | Keep 2-3 rows away | Extension foe lists (WVU) |
| Fennel | Isolate entirely | Documented allelopathy |
Sources: WVU Extension Companion Planting, Mississippi State Extension: Companion Planting Myth or Truth
Kohlrabi's most dangerous fortnight is right after emergence. The Pacific Northwest Insect Management Handbook warns flea beetles can destroy a new brassica planting within 24 hours at the cotyledon stage, while plants with 3-5 true leaves usually shrug off the damage. Penn State Extension's cole crop guidance puts a number on it: act at one beetle per transplant (or five per ten) during that cotyledon window.
The fix is cheap and physical: floating row cover installed at seeding, before beetles arrive, edges sealed with soil. Pull it once plants pass the 5-leaf stage. PNW data adds a useful scouting shortcut — infestations concentrate within 200 ft (60 m) of field borders, so check bed edges first. Later-season caterpillars (cabbageworm, looper, diamondback moth) still visit per Illinois Extension's kohlrabi profile, but a fast, well-fed kohlrabi usually outruns them to harvest.
Common Mistake to Avoid
Letting bulbs "get a little bigger" past 3 in. (7.5 cm) is the classic kohlrabi error. Utah State and Minnesota Extension both warn that oversized bulbs turn woody and fibrous. Harvest on time — that's also what frees the space for whatever relay crop is waiting.
One soil note before the FAQ: K-State's Butler County Extension pegs kohlrabi's sweet spot at pH 6-7 with about 1-2 lb of balanced fertilizer per 100 sq ft (0.5-1 kg per 9 sq m) worked into the top of the bed. If your brassicas keep sulking, test before you blame the companions — our soil pH guide covers the how.
Key Takeaway
Give kohlrabi row cover for its first two weeks, cool-season neighbors, and an on-time harvest, and it repays you faster than any other brassica — then hands the bed to the next crop.
Keep kohlrabi away from fennel (allelopathic to most vegetables), pole beans, strawberries, and tomatoes, per West Virginia University Extension's companion tables. Also avoid planting it where any brassica grew in the past four years — Minnesota Extension's rotation rule — because the family shares pests and soilborne diseases. The full friend-and-foe logic for every crop is in our companion planting chart.
Utah State Extension recommends 6 in. (15 cm) between plants with rows 12 in. (30 cm) apart. That tight spacing is part of why kohlrabi intercrops so well — a single 12 in. band between lettuce rows holds a full planting. Sow seeds about 1/2 in. (1.3 cm) deep and thin early; crowded seedlings make small, slow bulbs, which defeats the whole point of growing the fastest brassica.
Cut the stem just below the swollen bulb with a sharp knife when the bulb reaches 2-3 in. (5-7.5 cm) across — roughly tennis-ball size at the upper end. Don't pull; the root system is surprisingly stubborn and you'll disturb the neighbors you interplanted. Both the bulb and the young leaves are edible. Harvest promptly: bulbs left past 3 in. turn woody and bitter, per Utah State and Minnesota Extension.
One bulb per plant — kohlrabi is a single-harvest crop, unlike broccoli's side shoots. The productivity comes from speed and density instead: at 6 in. (15 cm) spacing, a 4 ft (1.2 m) row yields eight bulbs in under two months, and you can run two or three successions a season in the same footprint. Giant storage varieties like Kossak grow far larger without going woody, but they need more room and time.
Not meaningfully. Once you cut the swollen stem, the plant may push a few small leaf shoots from the stump, but it won't form a second bulb. Pull the stump, drop it in the compost, and use the vacated space for the next relay — that's the permaculture way to think about a fast crop: the harvest isn't the end of the bed's season, just a scene change.
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