Companion plants are different plants that give you a better crop when they’re grown together. Some companion plants aren’t really edible, and if you only have a small growing space then it’s a good idea to look for ones that are good to eat, or at least pretty to look at if you have a potager or cottage style kitchen garden.
The main thing to learn from the principles of companion planting is this: monoculture is not that productive, especially when you grow rows and rows of the same thing. Your crops will be more susceptible to pests and diseases, and er, it’s boring. Variety is a good thing in your kitchen garden and in your diet.
Much of what is written about companion planting is wildly unscientific, and can’t be reproduced in experiments, so I’m not going to point you in the direction of overly-complicated plans and tables that might not be that much use in real life. However, there is definitely something in at least some of it, and it’s worth experimenting with it from time to time.
Companion plants seem to work in different ways. For example, they may be:
- Releasing protective chemicals into the soil
- Adding nutrients to the soil
- Releasing pest repellent fragrances into the air
- Mechanically breaking up soil to help other nearby roots
- Providing ground cover
- Disguising appearance to confuse pests
- Attracting pollinators
- Attracting or sheltering other beneficial insects (such as predators of pests)
- Attracting pests away from the main crop
Some traditionally-described ‘companion’ plants like radishes may also simply be filling convenient gaps, rather than doing anything special, which really makes them intercropping plants rather than companions.
Herbs might be more than just tasty plants
Conveniently, many herbs are supposed to be good companion plants for fruit and vegetables, as well as adding flavour and complexity to your meals. Rosemary, chives and thyme all attract bees and other pollinators with their flowers, which can help nearby plants get pollinated too – handy if you’re growing squashes, courgettes, peppers, tomatoes and so on.
There’s also a theory that aromatic herbs give off fragrances that scare off pests, including ants and aphids. I’m not so sure about this, as I’ve seen chives and basil done in by these very same pests. It might be true that chives and other alliums confuse some pests that hunt by smell, perhaps in the case of carrot root fly. I’ve also tried growing savory amongst broad beans to prevent blackfly and haven’t seen a jot of difference.
There is some fairly good evidence to suggest that growing basil close to tomatoes can moderately increase their yield, and I do put in a couple of basil seedlings with my toms when I’m growing them in pots for this reason. Also, even if this turns out to be mumbo jumbo, the proximity is very convenient for me – if I’m making tomato salad, soup or sauce then chances are I’ll be putting basil into it too, so it’s handy to pick them both at the same time.
Some plants may act as a disguise for your crops. For example, pigeons and cabbage whites are both allegedly attracted by the bluey-green of most brassica leaves, so having other bluey-green plants nearby might serve to confuse them. That might include leeks, or clover – which could also act as ground cover or ‘living mulch’ to retain moisture, keep weeds out and add nitrogen and organic matter to the soil, all of which help brassicas too. Shame clover isn’t a crop for humans to eat as well.
On the subject of disguise, it’s also possible that coriander sown amongst carrots is another way to confuse the dreaded carrot root fly, as it looks similar to the carrot tops.
The ‘trap’ crop that I know most about is nasturtiums. They do seem to be quite efficient at drawing aphids and caterpillars away from other nearby plants. Most gardeners leave it at that, but as aphids reproduce so quickly I sometimes take the opportunity to squish a few so they don’t get out of hand. In addition, these plants have edible flowers and baby leaves, and there are different varieties that can give you attractive ground cover, or trailing blooms. Nasturtium seeds are also very easy to collect and store in the late autumn, so you can sow and grow them again for free the following year.
Some notes about marigolds
Marigolds are regularly mentioned as companion plants. There is definitely some reasonably good evidence to suggest that marigolds are healthy companions, as both French and African marigolds secrete compounds from their roots that keep harmful soil nematodes away. French / tagetes marigolds are also claimed to give off a fragrance from their leaves and flowers that scares off whitefly and other nasties, and they are often ‘prescribed’ for tomatoes for this reason.
The catch with marigolds is that it takes them 4 to 6 weeks after planting to start making their root compounds, so if you wish to grow them as a companion plant, start them off early and plant them out as soon as you dare. If you keep dead-heading them, they will also make new blooms throughout the summer. As a bonus, the flowers are edible and can be added to salads.
To get the most benefit from marigolds, it looks like they need to be dug into the soil at the end of the growing season, where they will provide help to plants the following year as well. If you’re growing them, you might as well dot a few of them all round the plot. It’s also easy to collect and save their seeds at the end of the growing season.
There are loads of different types of French marigold available, and some are very ornamental and lovely to look at. If your garden’s small there are dwarf types to try, and if they get a bit too big during the summer they can be cut back as well. As I have a cottage-style garden which aims to be pretty as well as productive, I put one or two marigolds in my hanging baskets and window boxes as well, to keep the colour scheme going around the whole area.
Three sisters companion planting
The ‘three sisters’ are North American plants – maize, climbing beans and squashes – that traditionally provided staple foods to the indigenous people. In theory, they can be planted together to their mutual benefit, although you may need a fair amount of room to do this successfully in the UK.
The three sisters companion planting is supposed to work like this: the tall sweetcorn provides a framework for the beans to climb up, the beans fix nitrogen into the surrounding soil to improve it, and the squash flops around below and keeps water in the soil / crowds out weeds / scares bugs away with its prickly stems and leaves.
I must confess that I have never seen this trio work that well in a small, compact British garden, because the beans never seem to thrive for whatever reason. I’d hazard a guess that growing them too closely together causes excessive competition for nutrients and water. Plus you need a critical mass of maize planted in a block to ensure successful pollination, and that’s not always achievable in a small space.
However, growing squash / courgettes / pumpkins (without the beans) around the base of sweetcorn does seem to work pretty well at conserving water and suppressing weeds, so it’s an option for medium-sized plots. If you’ve succeeded in growing the three sisters productively together in Great Britain, I’d love to hear from you.
Plants that don’t get along
It’s also worth remembering that some plants are the opposite of companions – they just don’t seem to get along for whatever reason. This could be:
- Competition for nutrients or space
- Carrying pests or diseases
- Releasing unhelpful chemicals into the soil
For example, it’s traditionally said that tomatoes and potatoes simply don’t like each other. This is a bit unlikely, as they’re from the same family, but they are perhaps going to compete for similar nutrients, and potato blight is the same thing as tomato blight so this disease can spread more easily if they’re all grown together.
Mints are often described as good companion plants for most edible plants, but they have such invasive roots that they can essentially strangle most things. Not very companionable behaviour as far as I can see! They have some great culinary uses though, so there’s no harm in growing them in raised or sunken pots to keep them under control.
The one thing I’ve definitely seen with my own eyes is legumes (peas and beans) not getting along with alliums (leeks, onions, chives, garlic). The closer the legumes are, the smaller the pea or bean plants will be, and the fewer pods they’ll produce. While I’m not exactly sure why this is, my theory is that the allium roots may have an antibacterial action, and legumes use friendly bacteria in the nodules on their roots to fix nitrogen – bacteria which perhaps can’t work in the proximity of alliums.
Other ‘not getting along’ theories may simply be related to overcrowding, overshadowing, or wicking away of water, so that’s likely to be more mechanical than magical, and not that specific to individual types of plant.
Anyway, there we have it. Companion planting is having a resurgence, and while a little of it has been scientifically shown to work, there are also plenty of grey areas where it’s rumour and hearsay. It looks like the best thing to do is to avoid monoculture in general, and try a few experiments here and there to see what works for you.
Have you seen any real life companion plants? Have you ever experimented with growing them?