Certain plants growing together - companion planting - can be of mutual benefit and help one other to thrive. It’s a technique that’s been around for years and is certainly worth a try if you have any interest in avoiding the use of chemicals in the garden.

How do companion plants work?

Companion plants attract beneficial insects and keep pests at bay by acting as a decoy or emitting chemicals that repel the pest. They provide nutrients to the soil, protection from the wind and sun, and support.

Beneficial insects

Bees are of enormous help with pollination. They love flowers where they can get to the nectar easily, so single rather than double-flowered blooms are the best. Remember that bees can reverse, though, as you’ll know if you’ve ever seen one backing out of a foxglove!

Dahlia merckii. Grow dahlias

Dahlia merckii. © Marktee1 and reused under https://creativecommons.org/licenses/by-sa/3.0/

Ladybirds are great in the garden because they eat large quantities of plant pests such as aphids – greenfly, whitefly and blackfly are examples - and mites.

Keeping pests at bay

As well as attracting lots of good predatory insects, certain plants may emit chemicals which confuse and keep pests away. Lavender is good for this.

Lavender is good for you. Companion

Lavender in full bloom in Somerset. Sarah Buchanan

Plant the strong-smelling French marigold (tagetes) between your tomatoes to keep aphids at bay.

Garlic under the roses will repel aphids.

Pink rose and fan trellis. Companion plants

Pink rose and fan trellis. © Tony Buser and licensed for reuse under CC BY-SA 2.0

Nasturtiums will help to keep fruit trees aphid-free. They are also attractive to butterflies looking for somewhere to lay their eggs. These then hatch into caterpillars which start to eat the nasturtiums – leaving your cabbages alone.

Make sure companion plants are planted at the same time as your fruit and vegetables to prevent pests from getting a foothold.

Providing nutrients in the soil

The pea family is particularly generous in providing (or ‘fixing’) nitrogen in the soil. Peas, beans, lupins and sweet peas take nitrogen from the air and store it in their roots.

Three sisters protect and support one another

Planting the three sisters – sweetcorn, beans and squash - together is a Native American technique.

Sister Corn provides the support for the climbing beans to scramble up. Sister Bean provides nitrogen in the soil, as I’ve just mentioned, and helps to stabilise the sweetcorn in the wind. Finally, Sister Squash provides a mulch over the soil to keep moisture in and weeds away.

Sweetcorn, runner or French climbing beans, and squash can all be sown inside in pots now, ready for planting out in the warmer and more reliable days at the end of May.

Two sisters will also work well together, depending on your likes and your garden. Some people are tempted to use sunflowers in place of sweet corn but this works less well. That's because sunflowers use a lot of nitrogen from the soil, and also can be toxic to other plants.

Three Sisters method of companion planting, Asheville, North Carolina. Companion plants

An example of the Three Sisters method of companion planting, Asheville, North Carolina. © Perry Quan and reused under https://creativecommons.org/licenses/by-sa/2.0/

Give it a go! If you don’t like using chemicals in the garden, companion planting is a good path to explore.