Companion planting is not folklore — some of it is genuine pest deterrence and root-space efficiency, and some of it is repeated garden-forum myth. Here is what has consistent horticultural backing for the three crops most home gardeners grow first.
Tomatoes
- Good: basil (some evidence it deters thrips), marigolds (roots deter root-knot nematodes), carrots (shallow roots share space without competing).
- Avoid: brassicas like cabbage and broccoli, which compete heavily for the same nutrients and stunt tomato growth.
Peppers
- Good: onions and garlic (their scent can mask peppers from aphids), basil (similar sun and water needs, easy to interplant).
- Avoid: beans, which can be too aggressive a climber near young pepper plants and compete for the same soil nitrogen peppers need for fruiting.
Squash
- Good: corn and beans (the classic Three Sisters planting — corn provides a trellis, beans fix nitrogen, squash shades the soil and suppresses weeds).
- Avoid: potatoes, which compete for the same below-ground space and can encourage similar fungal issues.
The single highest-value pairing for most beginner gardens is still marigolds along the bed perimeter. They are inexpensive, reseed themselves, and provide a real, documented reduction in root-knot nematode populations around tomatoes and peppers.
