Companion planting has a reputation for being either magic or nonsense, depending on who you ask. The truth is somewhere in the middle. Some combinations have solid evidence behind them. Others are passed down from gardener to gardener without much scrutiny. After nine seasons of growing at Green Roots Collective, here is what we have actually observed.

The three sisters: corn, beans, squash

This is one of the most documented companion planting systems, developed by Indigenous farmers in North America over centuries. Sweetcorn provides a structure for climbing beans. Beans fix nitrogen in the soil, feeding the corn and squash. Squash leaves shade the ground, reducing moisture loss and suppressing weeds. It works, but it needs space. On a 4x2m raised bed, it is tight. On a 4x4m ground plot, it is worth trying.

Basil and tomatoes

The claim is that basil repels aphids and whitefly from tomatoes. The evidence is mixed. What we have observed at Green Roots Collective is that basil planted at the base of tomato plants does not obviously reduce pest pressure, but it does make harvesting more pleasant and the two crops have compatible water needs. Grow them together if you like both. Do not expect the basil to do the pest management for you.

Nasturtiums as a trap crop

This one we do believe in. Nasturtiums attract blackfly strongly enough that they draw aphids away from beans and other crops. Plant them at the edges of your bed, let the blackfly colonise them, and then cut the affected stems and compost them. It is not a complete solution, but it reduces the pressure on your main crops noticeably. We plant nasturtiums along the south edge of the communal beds every year.

What does not work as advertised

Planting marigolds to deter all pests is probably the most overstated claim in companion planting. French marigolds do produce a root exudate that suppresses certain soil nematodes, but they do not repel slugs, aphids, or most of the things that actually trouble a small vegetable bed. They are cheerful and they attract pollinators, which is reason enough to grow them. Just do not rely on them as pest control.

Companion planting is worth experimenting with, but treat it as one tool among many rather than a system that replaces observation and intervention. The best pest management is still checking your plants regularly and acting early.