You bought four broccoli starts at the garden center, dug them into the bed, and three weeks later the leaves look like green lace. Cabbage worms. Then the cabbage you put in the same bed last year just refused to head up. Then your tomato neighbour suggested moving the brassicas next to your tomatoes for "structure," and your gut says no. Your gut is right.
This is the working companion planting guide for broccoli and the whole Brassicaceae family. You will get the herbs and flowers that actually reduce cabbage moth pressure, the cool-season vegetables that share a bed with broccoli without competing for nutrients, the four pairings to avoid, and the rotation rule that prevents clubroot from wrecking the bed in year three. If you have come from our companion planting chart, this is the brassica-specific deep dive.
The Brassicaceae family is bigger than most home gardeners realise, and that matters because every member shares the same pest list and the same disease cycle. If you plant broccoli, then plant kale in the same square next year, the soil treats them as the same crop. UC IPM groups them all under "cole crops" for pest management purposes.
| Brassica | Days to harvest | Spacing | Heat tolerance |
| Broccoli | 60 to 80 | 18 to 24 in | Cool to mild |
| Cabbage | 70 to 100 | 18 in | Cool |
| Cauliflower | 60 to 90 | 18 to 24 in | Cool |
| Kale | 50 to 75 | 12 to 18 in | Cool to cold |
| Brussels sprouts | 90 to 120 | 24 in | Cold |
| Kohlrabi | 50 to 70 | 6 to 9 in | Cool |
| Radish | 22 to 40 | 2 to 4 in | Cool |
| Turnip | 45 to 70 | 4 to 6 in | Cool |
| Bok choy | 45 to 60 | 6 to 12 in | Cool |
| Collards | 60 to 85 | 12 to 18 in | Wide range |
Sources: UMN Extension companion planting, Cornell Cooperative Extension family rotation.
All of them are heavy nitrogen feeders. All of them are cool-season crops that bolt or stress out above 75 degrees F (24 C). All of them attract the same three or four primary pests. Plan companions for one and you plan them for the whole family.
Companion planting only earns its place when it solves a specific problem. With brassicas, the problem is a small group of pest insects that can defoliate a planting before you notice. Knowing which ones you are up against tells you which companions to plant.
Imported cabbageworm (Pieris rapae). The familiar white butterfly hovering over your bed. Lincoln University Cooperative Extension documents that each female lays 300 to 400 eggs over 2 to 3 weeks, with 3 to 5 generations per year in much of the US. Larvae chew large irregular holes in leaves and can hollow out broccoli heads from the inside.
Cabbage looper (Trichoplusia ni). The bigger looping caterpillar with the inchworm gait. Koppert Biological Systems notes the larvae cause irregular holes, with later instars feeding extensively on foliage.
Diamondback moth (Plutella xylostella). The smallest and most globally damaging of the three. UC IPM warns that "diamondback moth infestations are most serious when they damage the crowns or growing points of young plants or Brussels sprouts." UGA IPM records 4 to 8 generations per year in warm regions.
Cabbage root maggot (Delia radicum). Below ground. Utah State University Extension documents that adults emerge in early May and "mated females lay eggs in the soil at the base of host plants. Small maggots hatch in 4 to 10 days and immediately burrow into the roots." Direct seedling kill in young transplants.
Key Takeaway
Companion planting for brassicas is mostly a pest management strategy. The four primary pests are cabbage white butterfly, cabbage looper, diamondback moth, and cabbage root maggot. Get the companion plants right and you reduce pressure from all four without spray. Get them wrong and you spend the season on damage control.
Two mechanisms do most of the work: volatile masking (strong-scented herbs hide the brassica scent that moths use to find host plants) and natural-enemy attraction (flowering herbs feed parasitoid wasps and hoverflies whose larvae kill the cabbage worms). A 2023 peer-reviewed review in PMC found that aromatic and medicinal companion plants reliably suppress pest insects through both mechanisms. A separate 2022 review in the Journal of Economic Entomology concluded that "most studies demonstrate clear benefits of intercropping for weed, pathogen, insect pest control, relative yield, and gross profitability."
Dill, chamomile and yarrow at the edges
Flat flower clusters feed parasitoid wasps (Cotesia rubecula, Diadegma insulare) that lay eggs in cabbage worms and diamondback moth larvae. The wasps are tiny, harmless to humans, and devastating to the caterpillars. Plant a 12 inch strip at the perimeter or in every fourth square of the bed.
Thyme, sage, rosemary, mint and oregano interspersed
Aromatic herbs mask the brassica volatile signature how to use mint near brassicas without invasion that the cabbage white butterfly uses to locate egg-laying sites. Tuck one square per 4 of broccoli. Use mint in a pot sunk into the bed to control its spread.
Onion, garlic, leek and chive rows
Sulfur volatiles disrupt host-finding by cabbage moths and aphids. UMN Extension recommends interplanting alliums with brassicas as a primary pest deterrent.
Nasturtium as perimeter trap crop
Cabbage whites and aphids preferentially land and lay on nasturtium foliage rather than your broccoli. UGA Cooperative Extension trap-cropping guidance validates this approach. Accept that the nasturtium will look chewed up. That is the entire job.
White clover or low groundcover as living mulch
The Finch and Collier "appropriate / inappropriate landing" mechanism: cabbage moths drop to investigate bare soil and abandon sites that look green from below. Undersown clover gives the bed a continuous green carpet and significantly reduces egg-laying.
Lettuce, spinach, beet, swiss chard, radish in the gaps
Cool-season companions with non-overlapping nutrient and light needs. They mature before broccoli reaches full size and clear the space. Radish doubles as a fast-cycle trap for flea beetles.
Why This Works: Volatiles, Wasps, and the View from a Moth's Eye
Cabbage moths find your broccoli by smell. The bed releases a distinctive brassica volatile signature that a hungry female reads as "lay eggs here." Aromatic herbs flood the same airspace with thyme, sage, dill and chamomile, scrambling the scent. Meanwhile, the dill and chamomile flowers feed parasitoid wasps that hunt the caterpillars the moths have already laid. And the white clover groundcover under the broccoli changes what the bed looks like from above. None of these companions kills a single moth directly. They simply break the chain that lets the moth find your plant, lay her eggs, and have her larvae survive long enough to chew.
| Avoid | Why |
| Tomato | Both are heavy nitrogen feeders. Tomato wants warm soil (60 F+); broccoli wants cool (50 to 65 F). Season overlap is poor and they compete for the same nutrients. Farmer's Almanac and UMN Extension both flag the pair. |
| Strawberry | Shared verticillium wilt pathway. Avoid co-planting; rotate at least 3 years apart. Cornell Cooperative Extension. |
| Pole bean, climbing bean | Rhizobia conflict with brassica root chemistry. Bush beans are fine; pole beans tend to suppress brassica vigour at close range. |
| Pepper, eggplant | Different temperature window, competing nutrient needs. Plant in a separate bed. |
| Fennel | Allelopathic to most vegetables. Plant in its own container at least 10 feet away. |
| Other brassicas in the same square next year | Clubroot (Plasmodiophora brassicae) and black rot survive in soil for years. Rotate 3 to 4 years minimum. Penn State Extension. |
Sources: Penn State Extension family rotation, UMN Extension companion planting, Cornell Cooperative Extension.
Common Mistake to Avoid
Do not replant broccoli (or any brassica) in the same square or bed within 3 years. Clubroot fungus survives in the soil for 7 to 10 years once established, and the spores build to damaging levels with every consecutive brassica crop. Rotate brassicas to a different bed each year and follow them with a legume (bean, pea) or a member of an unrelated family (carrot, allium).
A practical companion-planted broccoli bed at 4 by 8 ft (32 sq ft total). For a deeper walk-through of the underlying spacing math and bed orientation, see our companion planting layout planner. For raised-bed specific patterns, see companion planting for raised beds.
Row 1 (north edge): 4 broccoli plants spaced 18 inches apart (1 plant per square in 4 of the 8 squares; the alternate squares get garlic or onions).
Row 2: 4 cabbage or cauliflower plants in the same pattern. If you want kale, slot it into the alternate squares with chive or shallot.
Row 3: 2 squares dill (4 plants per square), 2 squares chamomile (4 per square), 2 squares lettuce (4 per square), 2 squares spinach (9 per square).
Row 4 (south edge): 2 squares radish (16 per square, fast cycle), 2 squares beetroot (9 per square), 2 squares onion sets (16 per square), 2 squares carrots (16 per square).
Corners and perimeter: French marigold and nasturtium at all four corners; nasturtium also trailing the south edge. Optional white clover broadcast as living mulch.
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Send Me the ChartThe single mistake that ends a productive brassica bed faster than anything else is replanting brassicas in the same soil year after year. Clubroot (Plasmodiophora brassicae) and black rot build up with every consecutive brassica crop. Both can persist in the soil for a decade once established. Skip rotation and your broccoli will eventually stop heading regardless of how perfect your companions are.
The fix is a 3 to 4 year rotation, recommended by Penn State Extension and Cornell Cooperative Extension. A working four-bed rotation cycles brassicas, legumes (peas, beans), root crops (carrot, beet, parsnip), and a fallow or cover-crop year. The legume year leaves nitrogen in the soil that the brassica year needs.
Onions, garlic, leeks, and chives reduce cabbage moth pressure through sulfur volatiles. Dill, chamomile, thyme, sage, rosemary, and mint mask brassica scent and attract parasitoid wasps. Nasturtium acts as a trap crop for cabbage whites and aphids. Lettuce, spinach, beet, swiss chard, and radish share the bed without competing. Bush beans or peas fix nitrogen for the heavy-feeder broccoli. White clover undersown gives the bed a green groundcover that suppresses cabbage moth egg-laying.
Tomatoes (different temperature window, shared heavy-feeder competition), strawberries (shared verticillium wilt), pole or climbing beans (rhizosphere conflict at close range), peppers and eggplants (different season), fennel (allelopathic to most vegetables), and other brassicas in the same bed within 3 years (clubroot and black rot soil buildup).
Yes, in the same season. They are the same plant family, so they share companion needs and tolerate each other well in the current year. The catch is rotation: do not plant any brassica (broccoli, cabbage, cauliflower, kale, Brussels sprouts, kohlrabi, radish, turnip) in the same square next year. The 3 to 4 year rotation applies to the whole family combined, not to each crop individually.
No. Tomatoes are warm-season crops (soil temperature 60 F or above) while broccoli is cool-season (50 to 65 F). The growing windows barely overlap, and both are heavy nitrogen feeders that compete for the same root zone nutrients. Plant them in separate beds, ideally in different rotation years.
UMN Extension and most home-garden guides recommend 18 to 24 inches between plants and 24 to 36 inches between rows. In a square foot gardening layout, one broccoli plant per 1 sq ft section is the standard density. Tight spacing reduces airflow and increases fungal disease pressure; wider spacing wastes bed space.
Marigolds primarily suppress soil-borne plant-parasitic nematodes (documented by LSU AgCenter), not cabbage worms directly. For cabbage worms, the more effective companion is a combination of nasturtium (trap crop), dill or chamomile (parasitoid wasp feeders), and aromatic herbs (volatile masking). Marigolds still belong at the corners of the bed because they pull in pollinators and beneficial predators.
White clover is the best-studied option. It fixes nitrogen for the heavy-feeder broccoli, gives the bed a continuous green ground cover that disrupts cabbage moth egg-laying (Finch and Collier appropriate-inappropriate landing theory), and tolerates light foot traffic. Sow it 2 to 3 weeks after the broccoli transplants establish.
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