A Companion Planting Chart That Grades Every Pairing by Evidence
A companion planting chart that grades every vegetable, herb, and flower pairing by how well the evidence supports it, with corrected marigold, basil, and carrot rows.
Companion planting works best as a garden-planning method, not a magic list of plants that “like” one another. The useful question is not simply whether basil belongs beside a tomato. It is whether the two plants can share the available light, water, root space, airflow, and harvest window—and whether the claimed benefit is strong enough to justify the space. University of Minnesota Extension notes that some pairings have a clear mechanism while others rest on observation and are not equally reliable (University of Minnesota Extension).
Roughly a quarter of common pairing claims have some experimental support; the rest are tradition, observation, or folklore. WSU Extension EM128E (Chalker-Scott 2023) makes that split explicit, warning that popular charts are usually unsupported (WSU Extension EM128E). This page grades each of the 14 rows below so you can tell which pairings earn bed space and which are just folklore.
What companion planting can and cannot do
Companion planting means growing different species near one another for a plausible benefit: staggered harvests, physical support, shade on the soil, habitat for beneficial insects, or disruption of a pest’s ability to find a host. The most dependable benefits are often geometric. Radishes mature before a pepper canopy closes. A trellis lets beans grow upward while lettuce occupies the lower space. Flowers provide nectar and visual diversity. Those are real outcomes even when a claim that one plant “repels all insects” is not.
What companion planting cannot do is cure blight, replace a barrier, or make an overcrowded bed healthy. No companion fixes poor spacing, bad drainage, or skipped rotation. Treat companions as one part of a plan that also includes scouting, barriers, and crop rotation.
How to read the evidence tiers
- Tier 1 — Documented mechanism. Research or well-established practice supports a specific mechanism (nitrogen fixation, physical support, documented pest disruption under defined conditions).
- Tier 2 — Plausible but mixed or density-dependent. The mechanism is sound in principle, but results vary with plant density, timing, or cultivar; evidence is partial or contradictory.
- Tier 3 — Folklore or unsupported. No credible research supports the claimed benefit; the pairing may still work as ordinary diversity or timing, but not for the reason usually given.
Vegetable companion planting chart
| Main crop | Useful companions | Evidence tier | Why the pairing can work | Watch out for |
|---|---|---|---|---|
| Tomato | Basil, calendula, carrots, lettuce, parsley | Tier 2–3 | Diversity and temporary understory; no pest or flavour benefit proven for basil/tomato (Bomford 2004) | Shade, shared disease, crowding |
| Pepper | Basil, carrot, onion, marigold | Tier 2–3 | Similar warm-season timing; marigold benefit is as a cover crop, not an interplant | Do not let flowers block airflow |
| Eggplant | Beans, basil, marigold, thyme | Tier 3 | Low companions and insect habitat only | Eggplant still needs full sun |
| Potato | Bush beans, horseradish, peas, radish | Tier 2 | Different canopy timing and root zones; nitrogen from legumes | Keep away from tomato beds |
| Bean | Cucumber, corn, radish, squash | Tier 1–2 | Three Sisters structure and nitrogen fixation documented | Separate from onions and garlic |
| Pea | Carrot, radish, spinach, cucumber | Tier 2 | Cool-season overlap and trellis use | Peas dislike hot weather |
| Corn | Bean, cucumber, melon, squash | Tier 1–2 | Support and space stacking; block planting needed | Plant corn in a block for pollination |
| Cucumber | Bean, dill, radish, nasturtium | Tier 2 | Trellis, flowers, early radish harvest | Vines can smother neighbors |
| Squash | Corn, bean, dill, nasturtium | Tier 2 | Ground cover and pollinator draw | Give each plant several square feet |
| Brassica | Dill, onion, thyme, beet, lettuce | Tier 2 | Aromatic disruption is density-dependent (Finch et al. 2003) | Shared caterpillars still need scouting |
| Carrot | Chive, leek, onion, radish, rosemary | Tier 2 (carrot/onion) / Tier 3 (others) | Carrot/onion effect is real but density-dependent; not shown for chive, leek, or rosemary | Do not use woody herbs as shade |
| Beet | Bush bean, cabbage, lettuce, onion | Tier 3 | Compact roots and leafy canopy only | Avoid dense wet foliage |
| Lettuce | Carrot, cucumber, radish, strawberry | Tier 2 | Cool, quick crop under taller plants | Pull before heat and shade stress |
| Onion | Beet, carrot, lettuce, brassica | Tier 2 | Slow upright roots with low companions | Keep away from beans and peas |
Correcting three popular rows
Marigold. French marigold (Tagetes patula) is widely sold as a tomato companion, but WSU EM128E notes it harms beneficial insects as well as pests and works better as a cover crop or rotation element than as an interplant (WSU Extension EM128E). Plant marigolds in a separate block or use them in rotation, not tucked between every tomato.
Basil with tomato. No research supports the claim that basil improves tomato flavour or repels tomato pests; Bomford (2004) found no such effect. Grow basil beside tomatoes if you want both crops and the spacing works, not because it is a “companion.”
Carrot and onion. The carrot/onion pairing has real, documented effects, but they are density-dependent: the aromatic disruption shows up at sufficient plant density and is not demonstrated for chive, leek, or rosemary despite their being close relatives. Treat carrot/chive/leek/rosemary claims as Tier 3.
How to use the chart without overcrowding
Plant companions close enough to share a bed, not so close that their leaves touch from the moment they are planted. A practical starting point is the same spacing you would use for either crop, with flowers and herbs tucked along edges. The more vigorous plant gets its full mature spacing first; the companion fills the remaining, temporary space.
Match light, roots, water, and maturity
Put tall crops on the north side of the bed in the Northern Hemisphere so they do not shade shorter neighbors. Pair crops with similar water needs. Keep a drought-tolerant rosemary plant away from a cucumber that needs consistently moist soil. Use maturity dates as a design tool: plant quick greens between slow tomatoes, then harvest before shade and humidity increase. RHS guidance on companion planting stresses that geometry and timing usually matter more than alleged chemical friendships (RHS).
Reliable pairings by crop
Tomatoes, peppers, eggplant, and potatoes
Tomatoes, peppers, and eggplant are all nightshades. Basil, parsley, calendula, and low lettuce can occupy nearby space, but the most important rule is airflow. Avoid turning one plant into a wall of foliage around another. Stake tomatoes early and plant companions on the sunny side where they will not disappear under the canopy.
Potatoes also belong to the nightshade family, so keep them in a separate block from tomatoes when possible. Separation does not guarantee disease prevention, but it makes scouting and rotation easier and reduces the chance that one dense canopy becomes a shared disease environment. WVU Extension and Penn State Master Gardener guidance both frame companion planting as spacing and rotation help rather than pest control (WVU Extension, Penn State Master Gardener).
Beans, peas, corn, cucumbers, and squash
Beans and corn can be paired when the corn is planted in a block strong enough to support the beans and the site is fertile enough for both. Cucumber can climb a trellis near bush beans, while radishes or dill occupy the edge. Squash needs more ground than most charts admit; its vines are not a filler plant for a small square.
Beans and peas should be kept away from onions, garlic, and other alliums when space allows. The practical reason is competition and the possibility of stunting in tight mixed beds, not a universal chemical rule. If a small garden forces the pair together, increase distance, observe growth, and rotate the block next season.
Brassicas, carrots, beets, onions, and greens
Brassicas benefit from a diverse bed with dill, thyme, onions, beets, or lettuce, but no companion makes cabbage whiteflies or caterpillars disappear. Use row cover while plants are small, inspect leaf undersides, and remove pests early.
Carrots and radishes are a classic timing partnership: radishes mark the row and mature quickly while carrots take longer. Once the radishes are harvested, the carrots have more room. Onions, beets, and lettuce are useful low plants around a taller crop as long as watering remains compatible.
Herbs and flowers as companions
Herbs are valuable companions when you grow them for harvest, scent, flowers, or structure—not because a single sprig guarantees pest control. Dill, fennel, cilantro, and parsley can feed beneficial insects when they flower, but fennel can spread and may compete with nearby vegetables. Grow aggressive herbs in containers or a defined edge.
Pollinator strips and beneficial insects
Calendula, alyssum, borage, dill, and marigold can provide nectar or habitat. Plant them in a short strip or small cluster so insects can find the resource, and put the strip at the bed edge where it will not shade vegetables. Continuous diversity generally gives you more ecological value than one decorative flower at each corner. A trap crop such as nasturtium only helps if you inspect it: if aphids or caterpillars build up, remove the worst leaves or plants before the pest population moves inward.
Pairings to separate or avoid
Avoid fennel near most vegetables when possible; it is a poor neighbor for a mixed food bed and can be difficult to contain. Keep tomatoes and potatoes in separate blocks or at least at opposite ends of the plot because they share diseases and make rotation more difficult.
Separate beans and peas from onions and garlic if you have space. Do not put corn beside tomatoes in a small bed where both become tall, heavy feeders. Keep two vigorous climbers off the same small trellis, and never pair a sprawling zucchini with a delicate seedling and pretend the seedling will receive enough light.
A simple 4-by-8-foot companion layout
Start with the north edge. Put two trellised cucumbers or a row of peas there, leaving the spacing required by the variety. Place tomatoes or peppers in the next band, with basil or calendula on the sunny side. Use the front half for lettuce, radishes, beets, and bush beans that can be harvested early.
Leave a path or stepping stones outside the bed so you never compact the soil to reach the center. Mark when radishes should be pulled. If the cucumber vines run across the lettuce, guide them upward rather than allowing “companion” foliage to become a blanket. For a layout-first companion plan, see companion planting vegetable garden layout.
Crop rotation matters more than a perfect pairing
Companion charts can distract from the larger disease-management rule: do not plant the same crop family in the same soil year after year. Rotate nightshades, brassicas, legumes, and cucurbits through different beds. A tomato beside basil is still a nightshade block if tomatoes return to that soil every season.
Keep a simple map with the family, not just the crop name. Next year, move the nightshade block and use the old space for a different family. This reduces repeated exposure to crop-specific pests and lets you improve the soil without chasing a new pairing every weekend. For the broader evidence question, see does companion planting actually work.
Conclusion: a shortlist worth the space
The pairings worth the space are the ones with a mechanism: Three Sisters (corn, beans, squash), carrot/radish timing, onion/carrot at sufficient density, and edge flowers for beneficial insects. Everything else is diversity and timing, which still has value but should not be sold as pest control. Marigolds belong in rotation or separate blocks, not between every tomato; basil is a crop, not a tomato protector.
Use the chart to decide who shares space, then let light, water, airflow, mature size, and weekly scouting make the final call. For crop-specific pairings, see companion plants for tomatoes, marigold companion plants, basil companion plants, carrot companion plants, and onion companion plants. That is more reliable—and more productive—than treating any pairing as a guarantee.
Related guides
- Companion planting vegetable garden layout — spacing-first bed plans.
- Does companion planting actually work? — the evidence behind the claims.
- Herb companion plants — herb-specific pairings.
- Companion plants for tomatoes — crop-specific detail.
- Marigold companion plants — marigold evidence and uses.
- Is companion planting worth it? — cost/benefit framing.
