Does companion planting in containers work?

Companion planting is a technique where different plants are grown near each other for mutual benefit. It is reputed to enhance growth, deter pests, and improve pollination among plants. For example, marigolds are often planted amongst vegetables to repel aphids. There is a lot of anecdotal evidence that this works in the ground, and some scientific evidence to back it up. 

But does it work in containers? The short answer is that, yes, it can sometimes. But it's important to be aware that things are not as clear cut when choosing how to use companion planting in containers at your home, because:-

1. In containers, plants have access to less water, food and root space than in the ground. This results in more intense competition for resources between plants. It is quite common for one plant to struggle and the other to take over. This means that planting different plants together in the same container doesn't always work as well as in the ground. It also means that companion planting strategies are more likely to work in larger containers. 
2. The best known companion combinations were developed in a part of the world where the climate and conditions suit that combination. However, the same combination may not work as well in the balcony or patio in the town and climate where you live.

Examples of Well Known Companion Combinations 

The Three Sisters

One of the most famous companion plantings is the Three Sisters: growing squash, climbing beans and sweetcorn together. The corn provides height and structure, the beans climb up the corn and the squash leaves shade the soil, helping to prevent the growth of weeds. It’s a brilliant way of growing, developed by Native American Indians hundreds of years ago - and is extremely effective when grown in the ground in the American climate.

However, due to limited space in a pot, it is much harder to get all the plants to grow well, particularly in the UK climate.

It’s still a fun one to try - I love how the beans climb the sweetcorn… Just don’t expect a bumper harvest. Here is my attempt back when I lived in London. The foliage grew OK - but apart from a few beans, I didn't get much to eat from it. Others I've spoken to have had similar experiences.

My attempt at growing the Three Sisters in a pot outside my London flat. 

Tomatoes and Basil

As an example of how climate influences the choice of which companion combinations will work, consider tomatoes and basil. In warmer parts of the world where basil grows well outside this is potentially a great combo for containers - as basil is reputed to repel some pests like aphids and also helps shade the soil. Also, basil and tomatoes are both excellent choices for container gardens. But, where I live in the north England, it's simply too cold to grow basil outside for most of the year so this combination is not an option. 

Applying the Principles of Companion Planting more Broadly

As well as looking for specific combinations that will grow well in the same container, another approach is apply the general principles of companion planting across different containers to achieve similar benefits. This is the way I apply the idea of companion planting to my container garden. 

For example, you can:-

• Grow a wide diversity of plants. Many pests find their host plants by sight. By growing more variety you make it harder for them to find those plants they most like to eat. It also reduces the risk that you will lose a lot of plants in one go, because many pests are quite plant specific.
• Add in some strong smelling plants like garlic, chives, rosemary and sage. Some pests use smell to find their preferred plants, so this can help to confuse them. 
• Grow flowers to support pollinating insects. Great choices for the container garden include things like borage, dill, pot marigold and herbs like chives, sage and rosemary.

In other words, plants do not have to be grown in the same container to achieve many of the benefits of companion planting.

My front yard: by growing a wide diversity of plants contributes to a healthy garden. 

Is companion planting the best strategy to reduce pests?

Over the years, I’ve seen a number of articles that convey the impression that companion planting is the solution to pest problems in the container garden. I think this is misleading. Companion planting is just one way to help prevent pests. More broadly, the principle of diversity and growing different plants is also highly recommended for overall garden health. However, other things like good watering, and using a high quality, microbial active potting will usually do more to reduce overall pest problems.

Your Turn - which plant combinations do work well in the same container? 

For companion planting to be relevant to container gardening, we need to learn more about which combinations work best in containers. 

If you’ve tried any combinations that have worked well in your containers, I’d love to hear from you in the comments.

Hopefully over time we can develop a list of companion combinations that are well suited to container gardeners.