8 Companion Plants for Brussels Sprouts: Stop Aphids, Block Worms, Boost Your Fall Harvest
Discover 8 research-backed companion plants for Brussels sprouts that repel diamondback moths, trap aphids, and recruit pest-eating wasps — plus which plants to avoid.
Brussels sprouts share a problem with every other brassica in your garden: they wear a target on their leaves from the moment transplants go in the ground. Flea beetles riddle seedlings with holes in early summer. Diamondback moths and imported cabbageworms chew through outer leaves from midsummer onward. Then fall arrives, and colonies of pale grey aphids wedge themselves into the forming sprouts where you can’t reach them. For complete growing instructions from soil prep to harvest, see the Brussels Sprouts Growing Guide.
Chemical sprays reach some of these pests, but they also kill the beneficial insects that would have done the job for free. A better approach is to build a mixed bed that confuses pest insects before they land and floods your plot with natural predators once they do. The catch is that not all companion plant advice holds up — and some popular recommendations have almost no research behind them.
This guide covers 8 companion plants that either have documented research support or strong mechanistic reasoning, plus a clear explanation of what each one actually does, how close to plant it, and what to skip.
Why Aromatic Companions Work: The VOC Mechanism
Pest insects like cabbage moths and aphids locate host plants largely by smell. They detect the specific volatile organic compounds (VOCs) that Brussels sprouts and other brassicas emit — glucosinolates and isothiocyanates that signal “brassica here, land and feed.” Dense plantings of strongly aromatic companions dilute or mask those signals, making it harder for flying pests to identify and commit to your sprouts.
Research published in Insects (PMC5746795) identified the specific compounds responsible: terpenoids including α-pinene and camphor from rosemary-family herbs show aphid-repelling action, while the sulfur compounds concentrated in alliums (garlic and onion) show particularly strong masking effects against multiple aphid species. The same review confirmed that intercropped aromatic plants delay winged aphid arrival and reduce peak-period abundance in several vegetable crops.
One honest caveat: under field conditions, VOC concentrations shift with wind, temperature, and irrigation. The masking effect is real but partial — it reduces pest pressure, it doesn’t eliminate it. Pair aromatic companions with a physical barrier like row cover during the highest-risk germination window, and treat companion planting as one layer in your pest management, not the whole system.
Thyme
Thyme is the most research-backed companion for Brussels sprouts. A greenhouse study cited by the University of Minnesota Extension found that sage and thyme specifically reduced diamondback moth populations on Brussels sprouts — one of the most destructive caterpillar pests of the brassica family. Earlier field work (Dove 1986, cited in a SARE project report) found fewer diamondback moths on Brussels sprouts intercropped with malting barley, sage, or thyme, establishing the pattern across multiple experimental settings.
The mechanism works two ways. Thyme’s terpenoids (thymol and carvacrol) actively confuse pest host-finding. And when thyme flowers — which it does readily in midsummer heat — its tiny blooms are landing platforms for parasitic wasps that target caterpillar eggs and larvae.
Plant creeping thyme (Thymus serpyllum) or common thyme (Thymus vulgaris) as a low border row or edge along the front of your Brussels sprout bed. Thyme’s ground-hugging habit fills the understory without shading your taller sprout plants. Allow flowering rather than shearing heavily — the bloom period is when thyme earns its keep. Space plants 12 inches apart and water in well at transplanting; once established, thyme is drought-tolerant and requires little attention.
Sage
Sage works from the same research base as thyme — it’s the other herb that UMN Extension specifically names as effective against diamondback moths in Brussels sprouts. Where thyme spreads low, sage grows upright to 18–24 inches, which lets it intercept flying pests at a different height in the canopy. The two herbs together create overlapping scent zones that are more disruptive to pest orientation than either plant alone.
Common sage (Salvia officinalis) is the most available variety, though any ornamental culinary sage works. Plant sage 18 inches from Brussels sprout stems to avoid competition for water — sage roots spread wide and the plant resents being crowded from above. In zones 4–8, sage is perennial and will return each year, giving you an established companion planting that requires no replanting. Clip back woody growth in early spring rather than fall to protect the crown from winter dieback.
Nasturtium
Nasturtium is the classic brassica trap crop, and with Brussels sprouts it works as advertised — aphids prefer the plant’s soft, peppery foliage over the waxy leaves of your sprouts. Caterpillars, including cabbage loopers and imported cabbageworm, are also drawn to it. University of Minnesota Extension lists nasturtium as one of the plant combinations that reduced cabbage looper and imported cabbageworm damage in companion-plant trials on brassica crops.
There’s a spacing rule that most companion planting guides skip: plant nasturtiums at least 18–24 inches away from your Brussels sprouts, ideally as a perimeter row around the outside of the main bed rather than woven through it. When aphid populations build on nasturtiums during warm weather, the colony can overflow onto adjacent plants. At 18–24 inches, you have a buffer. If you plant nasturtiums too close, you risk drawing aphids directly onto your sprouts rather than away from them. Check nasturtium plants weekly once aphid colonies establish; remove heavily infested stems rather than waiting for the population to disperse.
Trailing and climbing nasturtiums both work; dwarf bush varieties (like ‘Jewel Mix’) are easier to manage in a tight vegetable plot.
Sweet Alyssum
Sweet alyssum is the companion plant that professional vegetable growers use when they want to recruit natural pest control rather than repel pests by scent. A study at Stahlbush Island Farm in Oregon (conducted by Colley and Luna and reported by USDA ARS) found that parasitism of cabbage aphids by parasitic wasps nearly doubled in plots where sweet alyssum grew alongside brassicas compared to pure brassica stands. The reason is straightforward: adult parasitic wasps and hoverflies need nectar and pollen to sustain themselves, and sweet alyssum provides both in quantity through a long bloom season.
The honest caveat is that actual aphid population counts in the Oregon study showed no statistically significant difference, partly because cabbage aphids on brassicas wedge themselves into flower crevices where neither wasps nor spray reaches them easily. Alyssum works better for lettuce than Brussels sprouts, per USDA ARS researcher Dr. Brennan. Still, it’s free pest management infrastructure — cheap seed (~$3 a packet), minimal care, and 90+ days of continuous bloom that supports the entire predatory insect community in your garden, not just the ones targeting your sprouts.
Sow sweet alyssum directly in gaps between sprout transplants or in a 6-inch border strip along bed edges. It self-seeds readily in zones 5 and warmer, so one planting can sustain itself across multiple seasons.
Onions and Garlic
The sulfur compounds in alliums are among the most documented pest-masking agents in the companion planting literature. Research compiled in PMC5746795 found that allium sulfur compounds (present at up to 94% concentration in garlic) suppress aphid activity in intercropped systems, with garlic intercropped with tobacco showing delayed arrival of winged aphids and reduced abundance during peak pressure periods. Onion and garlic are also the companions most commonly cited alongside brassicas in university extension planting guides for their broad-spectrum masking effect against aphids, cabbage moths, and carrot flies.
For practical placement: plant garlic in fall for an established crop the following summer — mature garlic bulbs emit VOCs continuously as roots absorb soil water. Spring-planted onion sets work too, though the scent output builds more gradually as bulbs develop. Plant one allium for every two to three Brussels sprout plants, positioned along the row rather than scattered randomly — a continuous scent line is more disruptive to pest navigation than isolated plants. Avoid planting alliums next to any legumes in the same bed, as sulfur compounds can disrupt Rhizobium bacteria that beans and peas rely on for nitrogen fixation.
Dill
Dill is most useful when you let it flower. The flat-topped yellow umbels attract several species of parasitic wasps, including Braconid and Ichneumon wasps that parasitize cabbageworm and cabbage looper larvae. Before it flowers, dill provides minimal pest management benefit beyond slight VOC masking. This is a detail that most companion planting guides miss: dill as a seedling or vegetative plant is not the same as dill in full flower.
One plant management note: dill is allelopathic to some crops in its immediate root zone when it matures and drops seed. Keep dill at least 24 inches from Brussels sprout stems and harvest seed heads before they scatter if you don’t want dill spreading through the bed. Allow two or three plants to remain in flower continuously through summer by staggering sowings 3 weeks apart — this sustains the beneficial insect recruitment effect through the peak caterpillar season. Dill and brassicas share the same pest complex, so dill may also attract diamondback moths; treat it as a recruitment plant for predators rather than a pest repellent.
Crimson Clover
UC Agriculture and Natural Resources recommends crimson clover specifically as a living mulch companion for cole crops including Brussels sprouts. As a living mulch, it does several things at once: the dense low growth suppresses weeds without competing with the deeper-rooted sprouts, clover roots fix atmospheric nitrogen for later release through decomposition, and the blooms support beneficial insects including ground beetles that prey on soil pests like cabbage maggot larvae.
Plant crimson clover between Brussels sprout rows at transplanting time, seeding it at 1–2 inches apart and tamping lightly. It establishes quickly in cool weather and tolerates light shade from taller sprout plants as they grow. Mow or cut the clover back to 3 inches if it starts to shade lower sprout leaves; leaving the clippings in place returns nitrogen to the soil. In zones 6 and colder, crimson clover is an annual — reseed it each spring. In zones 7+, it may overwinter and reseed itself.
Beets
Beets share Brussels sprouts’ preference for cool weather, fertile soil, and consistent moisture, which makes them practical companions even without a documented pest management benefit. Their deep taproot loosens subsoil without disturbing the shallower, more fibrous root system of Brussels sprouts. Beet greens also provide ground-level shading that reduces moisture evaporation from the soil surface in summer heat — a real benefit in warm zones where Brussels sprouts can suffer during long stretches of high temperatures.
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→ View My Garden CalendarFrom a timing standpoint: sow beets at the same time you transplant Brussels sprout starts, or 3–4 weeks before. Beets mature in 50–70 days, meaning you can harvest the beet roots well before Brussels sprouts reach full size in fall. This makes beet a logical gap-filler that exits the bed on its own schedule and improves soil structure in the process. Space beets 4–6 inches apart in the rows between sprouts.
The Marigold Question
Marigolds appear on almost every Brussels sprouts companion planting list, so they deserve a direct answer: University of Minnesota Extension states explicitly that “there is little research to support” marigolds repelling flea beetles from brassicas. Marigolds do have documented benefits in other contexts — French marigolds (Tagetes patula) planted densely for 2+ months before a susceptible crop can reduce root-knot nematode populations in that soil zone — but this requires pre-planting as a cover crop, not simply tucking a few marigolds alongside your Brussels sprouts.
You can grow marigolds near your brassicas; they won’t cause harm and they do attract some beneficial insects. Just don’t rely on them as your primary pest management strategy for flea beetles or caterpillars. If flea beetle pressure is your main concern, arugula and mustard planted as trap crops (drawn from the same UMN research) show better evidence for pulling flea beetles away from your sprouts.
Plants to Avoid
A few plants consistently undermine Brussels sprouts and should be kept out of the same bed.
Other brassicas — cabbage, cauliflower, broccoli, kale, and kohlrabi attract the same pest complex as Brussels sprouts. Planting them together concentrates rather than disperses pest pressure, and any disease like clubroot or black rot that establishes in one plant spreads immediately to the others. Keep all Brassicaceae family members separated by at least 6 feet, or better yet, plan rotations across different beds.
Fennel is allelopathic to most vegetables, including brassicas. Its root exudates suppress neighboring plant growth, and Brussels sprouts planted within 3 feet of established fennel show stunted development. Keep fennel in its own isolated pot or bed corner, well away from the vegetable garden.
Strawberries are commonly cited as poor companions for Brussels sprouts, and several extension sources confirm the pairing underperforms. Both are heavy feeders in the surface soil zone, and strawberries harbor slugs — a significant pest of young Brussels sprout seedlings. The combination also creates harvesting and pruning conflicts as the plants mature.
Pole beans can be planted near Brussels sprouts, but avoid tall varieties that shade the sprout plants significantly. Bush beans are safer. Note that if you do plant any beans in the same bed, keep allium companions well away from the legume roots — garlic and onion’s sulfur compounds can inhibit the Rhizobium bacteria that legumes depend on for nitrogen fixation.
Setting Up Your Companion Planting Layout
The research from Illinois Extension makes an important point that most companion planting guides overlook: effectiveness depends on crop density, spacing ratio, and relative planting times — not just which species you choose. A single sage plant at the end of a 20-foot Brussels sprout row contributes almost nothing. The same plant repeated every 18–24 inches along the row creates a functional scent barrier.
| Companion | Primary Benefit | Spacing From Sprouts | Best Position |
|---|---|---|---|
| Thyme | Diamondback moth repellent | 12 inches | Front border row |
| Sage | Diamondback moth repellent | 18 inches | End-of-row anchors |
| Nasturtium | Aphid/caterpillar trap crop | 18–24 inches | Perimeter, outside bed |
| Sweet Alyssum | Parasitic wasp recruitment | 6–12 inches | Gaps between plants |
| Onion/Garlic | Sulfur VOC masking | 8–12 inches | Along rows, 1 per 2-3 sprouts |
| Dill (flowering) | Parasitic wasp recruitment | 24 inches | Back of bed, allow to flower |
| Crimson Clover | Living mulch, N fixation | Between rows | Fill row gaps at transplant time |
| Beets | Soil structure, gap fill | 6–8 inches | Between sprout plants in rows |
You don’t need all eight. A practical starter combination: thyme as a front border, a perimeter row of nasturtiums 20 inches out, and sweet alyssum tucked in the gaps between sprout transplants. Add garlic if flea beetles or aphids are consistent problems in your garden. That four-plant system covers the three main pest management mechanisms — scent masking, trap cropping, and parasitoid recruitment — without requiring a complex planting layout.
Timing matters as much as species selection. Establish thyme and sage before or at the same time as Brussels sprout transplants — companions that go in 4–6 weeks after the main crop miss the early season pest window. Sweet alyssum can be direct-seeded around transplants on the same day. Nasturtiums should be established and actively growing, with flower buds forming, before cabbage moth pressure peaks in midsummer.
For more context on vegetable companion planting principles, see our complete companion planting guide for vegetables. For timing your Brussels sprouts planting and your companion sowings relative to your last frost date, the year-round planting guide has zone-by-zone calendars. And for full growing guidance — from transplanting to staking to topping — see the Brussels sprouts growing guide.
Key Takeaways
- Thyme and sage are the only companion plants with documented evidence specifically reducing diamondback moth populations on Brussels sprouts.
- Plant nasturtiums 18–24 inches away from sprouts as a perimeter trap crop — not woven through the main bed — to prevent aphid overflow.
- Sweet alyssum recruits parasitic wasps that target cabbageworm eggs and aphids; sow it in gaps between sprout transplants at planting time.
- Marigolds are widely recommended but lack research support for flea beetle control on brassicas; use arugula or mustard as trap crops instead if flea beetles are your target.
- Keep fennel, other brassicas, strawberries, and pole beans away from Brussels sprouts.
- Timing and density matter as much as species choice — a single companion plant in a row has minimal effect; repeat it every 18–24 inches for a functional scent or recruitment barrier.
Sources
- University of Minnesota Extension. Companion Planting in Home Gardens. Cites Riesselman 2006 (Iowa study) and greenhouse results for sage/thyme on Brussels sprouts.
- USDA Agricultural Research Service. Flower Power: Attracting Natural Enemies of Pests to Your Field and Garden. Reports Colley-Luna OSU alyssum-brassica parasitism data.
- Ben-Issa R, Gomez L, Gautier H. Companion Plants for Aphid Pest Management. Insects. 2017;8(4):112. PMC5746795. VOC masking mechanisms and specific compounds.
- Sustainable Agriculture Research & Education (SARE). Final Report GW11-005. Cites Dove 1986 on barley/sage/thyme intercrops with Brussels sprouts.
- UC Agriculture and Natural Resources. Better Together: The New Science of Companion Planting. Crimson clover as living mulch with cole crops.
- University of Minnesota Extension. Growing Brussels Sprouts in Home Gardens. Key pests and spacing guidance.
- Illinois Extension. Companion Planting: Combining Plants for a Healthy, Well-Balanced Garden. 2025. Density and timing caveats.
