Companion Planting Calculator
Which Crops Help Each Other, and Which Compete
Companion planting is traditional garden knowledge built up over generations of observed interactions — certain crop pairings seem to repel shared pests, fix nutrients for a neighbor, or share space efficiently, while other pairings compete for the same resources or attract the same problems. This calculator looks up a specific pair of crops and returns the traditional guidance for planting them near each other.
How the Lookup Works
Rather than a numeric formula, this tool checks the selected pair against a reference table of documented companion relationships and returns one of three ratings:
Well-Known Good Pairings
| Pairing | Reason |
|---|---|
| Corn + Beans + Squash | The traditional "Three Sisters" — beans fix nitrogen for corn, cornstalks act as a bean trellis, and squash leaves shade out weeds. |
| Tomato + Basil | Basil is said to repel aphids and hornworms and may improve tomato flavor and growth. |
| Carrot + Onion | Onion scent helps deter carrot fly; carrots return the favor against onion pests. |
| Tomato + Marigold | Marigolds help repel nematodes and several common garden pests. |
Pairings Worth Avoiding
| Pairing | Reason |
|---|---|
| Tomato + Potato | Both are nightshades that share susceptibility to early and late blight. |
| Tomato + Cabbage family | Heavy nutrient competition between tomatoes and brassicas (cabbage, broccoli, kale) can stunt both. |
| Beans + Onion | Onions can stunt bean growth and inhibit the beans' nitrogen fixation. |
| Carrot + Dill (mature) | Mature dill can stunt carrot growth and cross-attract shared pests. |
How to Use This Calculator
- Select the first plant from the dropdown.
- Select the second plant from the dropdown.
- Select Calculate to see whether the pair is a documented Good, Bad, or Neutral combination, along with the reasoning.
Related Calculations
Once you've settled on a compatible crop mix, work out how many of each will fit with the Plant Spacing Calculator, or plan your indoor sowing dates with the Seed Starting Date Calculator.