What is companion planting?
Companion planting is an organic method of maintaining a natural balance in your garden by growing plants together that are mutually beneficial. Planted together, certain plant combinations can aid pollination, prevent disease and keep pest numbers down. Most companion plants are strongly scented and can confuse pests looking for their host plant, some have antibacterial or anti-fungal properties, while others attract beneficial insects, such as ladybirds and lacewings, which prey on aphids. Most companion planting occurs in the vegetable patch, but some ornamental plants, such as roses, can also benefit from particular plants growing nearby.
What are the benefits of companion planting?
Companion planting can help your plants to grow better and with fewer pests and diseases. Ultimately this benefits the gardener as this means less work for higher crop yields.
Plant combinations to avoid
There are some obvious plant combinations to avoid, for example you should avoid planting tall plants next to shorter plants, as they will block light and prevent them from growing well. Growing thirsty plants next to drought-tolerant plants is also not advised, as one plant will either be getting too much water, or too little.
Some plants appear to have what's known as allelopathic properties. This means that the plants release chemicals that inhibit growth of other plants. One of the most commonly known plants thought to be allelopathic is the walnut tree – it's commonly advised not to grow plants close to walnuts as they won't thrive. However, this theory has been disputed in horticultural circles and it's not known for certain how allelopathic walnut trees really are.
There's no science to confirm or deny allelopathic properties in plants, and much more research needs to be done but, anecdotally, the following plants are thought to not grow well together:
- Garlic and onions with beans and peas
- Mint or onions with asparagus
- Cucumbers, squashes, radishes, sunflowers or tomatoes with potatoes
- Cabbages or other brassicas with strawberries
- Brassicas and potatoes with tomatoes
Browse our list of the best companion plant combinations, below.
Mint and brassicas
The strongly scented leaves of mint confuse flea beetles and can deter them from laying eggs on the leaves of brassicas such as cabbage, broccoli, radish and cauliflower. However, it's best to grow mint in a pot, or it could smother your crop.
Marigolds and tomatoes
Carrots and leeks
Strongly scented crops can work wonders on the vegetable patch. Alliums such as onions, garlic and leeks are often paired with root crops like carrots and parsnips. This combination seems particularly effective – the smell of carrots can deter leek moth from leeks, but the small of leeks can deter carrot fly from carrots. If you don't have room for leeks, try garlic chives (Allium tuberosum) as an alternative.
Lavender with carrots and leeks
Lavender attracts a range of pollinators, including bees, butterflies and hoverflies, so planting it close to crops such as tomatoes and beans could increase numbers of pollinators to your patch. However, its strong scent can also deter insect pests – plant with carrots and leeks for the best results.
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Wormwood and beans
Wormwood, Artemisia absinthium, is a strongly scented herb that can deter aphids such as blackfly, from broad beans and other bean crops. What's more, its yellow flowers attract hoverflies, lacewings and ladybirds, which prey on aphids.
Calendula and beans
The marigold, Calendula officinalis, can lure aphids away from beans, and makes a great companion plant for runner beans and French beans. It also attracts beneficial insects, including ladybirds, lacewings and hoverflies, which prey on aphids.
Sage and brassicas
Sage, Salvia officinalis, is strongly scented and will confuse pests of brassicas, such as flea beetle, if planted alongside them. What's more, its blue flowers attract bees and hoverflies, which also pollinate crops.
Borage and strawberries
Borage is an attractive plant with hairy leaves that have a slight cucumber flavour. If planted near strawberries, borage is said to improve their flavour. What's more, borage flowers are a magnet for pollinators, such as bees, butterflies and hoverflies, which pollinate crops.
Thyme and roses
Another strongly scented herb, thyme is an excellent companion plant as it can confuse pests by masking the scent of the pest's host plant. Thyme makes a good companion plant for roses, as its strong scent deters blackfly.
Calendula and courgettes
Calendula is extremely attractive to pollinators, and can therefore increase pollination of some vegetable crops. Underplanting courgettes with calendula can be extremely useful, especially in dull weather, when courgette flowers may be overlooked by pollinators.
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