Companion planting is the growing of different plant species close together, for expected benefits in productivity – and it’s easier than you think.
It is hardly surprising that companion planting can seem to be a rather mysterious art. Many books and articles throw around statements such as “carrots love onions!” with little explanation or evidence, and in fact the expected benefits of companion planting come in many different ways.
Our guest blog this month on Companion Planting is from Naomi Distill, a very knowledgeable gardener and the inspiration behind Incredible Edible St Albans, a project of FoodSmiles St Albans and a past winner of Environmental Champion in the St Albans Mayor’s Pride Awards.
Every garden is an eco-system – with more organisms than we know – affecting it…
Benefits of Companion Planting
- Pest control
- using plants which repel pests by smell
- using plants which attract predatory insects to eat pests
- by trap-cropping (using alternative plants as decoys to attract pests away from the main crop)
- by disrupting the odds of a pest successfully landing on its desired host plant
- Increased pollination (using plants that attract extra pollinators)
- Maximising use of space or time (e.g. catch-cropping by planting fast-growing extra crop between a slower-growing main crop, or growing plants with different root depths together to make the most of root space)
- Maximising efficiency by grouping plants with similar needs
- Exploitation of another plant’s physical properties (e.g. one that shades, supports or protects another, or one that provides groundcover to reduce weeds and evaporation)
- Effects from chemical secretions released into the soil by roots
- Adding nutrition to the garden (i.e. nitrogen-fixing plants or those with very deep roots can accumulate nutrition and make it available to other plants).
Companion planting is an inexact science
Though beginners often get started with companion planting using a long list of ‘rules’ that simply pair plants together – or forbid pairing them – these rules fail to take into account the complex relationships found in a garden, and can make veg-plot planning feel like doing an impossible jigsaw! But companion planting is an extremely inexact science.
Every garden is an ecosystem, with more organisms than we know affecting it: feeding from it, fighting for survival in it, and putting inputs into it. Soil life below the surface is even more complex, and the unique mineral make-up of your soil has its effects too, and then there’s the microclimate of your garden to consider. No two plots are the same – and no two years are the same.
Learning the Hard Way: Mistakes and Myths
The first year this trial of companion planting worked a dream; not an aphid in sight and the lettuces seemed better than ever. The second year however, there were soon aphids all over the lettuce – and the coriander too! Its repellent power could obviously not be relied upon.
As I looked round the allotment at all the other plants nearby, I quickly realised there were, of course, other factors in play when you tried companion planting. Perhaps something else nearby attracted the aphids? Or a shortage of other food plants elsewhere brought them? Maybe those lettuces were particularly attractive? Could there have been higher numbers of the pest this year? The possibilities were endless.
“Little did I know that horseradish plants are thugs, with deep roots, and very hard to remove!’
Horseradish and Potatoes – yes or no?
Another memorable lesson of trying out companion planting was realising how foolish it had been to plant horseradish throughout my potato patch. I had read that horseradish repels potato-munching eelworms and wireworms. Little did I know then that horseradish plants are thugs, with deep roots, and very hard to remove! How anyone can make that pairing work is a mystery to me!
Onions with carrots? Sage with brassica?
Two pairings often quoted in companion planting books are onions with carrots (to repel carrot fly), and sage with brassicas (to repel white butterflies). However, in truth it seems that you need far more of the repellent plant than the intended crop in order for the rules to work well. Companion planting here means several rows of onions per row of carrots, and many sage plants per brassica plant. It might just work out if you don’t eat very many carrots, but who can use that much sage?
Green Beans and nitrogen
Another common companion planting suggestion is that beans should be grown close to crops that would benefit from the extra nitrogen fixed by their roots, however this is not supported by science (see this article, or this). Though the bean roots may gather nitrogen early on in life, most of it is used by the plant for the formation of flowers, pods and seeds, and only a negligible amount remains or goes into the soil.
An Easier Method: Companion Planting- the four rules
So I’d like to propose a different approach to companion planting, focusing on biodiversity and natural design. This method means including as many useful plants in the garden as possible, in any layout. Our Incredible Edible gardens use this approach and I have used it in my allotment and garden for years, and there are only four rules:
1. Right plant, right place
Plant the sun-loving crops in the sunny spot, the shade-tolerant ones in the shade, the damp-loving ones in the wet corner. Keep the tall ones out of the worst of the wind, if possible. Under the trees in the Incredible Edible gardens we have adopted a forest gardening approach. We choose low-maintenance edibles that happily grow under trees in the wild.
2. Mix things up
Minimise traditional rows, and interplant with abandon! Add flowers and herbs to your veg patch and veggies to your flowerbeds. When a pest settles on a new plant, don’t let it find a whole tasty row all laid out and waiting! Make it harder for them. This intermingling approach makes crop rotation much less important, which is a help in any small plot where rotation can be tricky.
3. Common sense first!
Let common sense and your own observations rule. Use trial and error to find what works best in your own garden and your own microclimate. Think logically about the relationships between your plants, and the physical shade and shelter they provide. If you’re not sure how big a plant will get or how long it will live, look it up! But don’t overthink it. With gardening you always get another chance next year.
4. Maximise plant diversity
Employ plenty of great all-round companion plants to increase diversity: those listed below will enrich your garden, whatever plant you grow them next to. The more biodiverse your garden is, the more easily it will find a healthy natural balance. It will give you better crops, with fewer problems. Animal diversity helps too, so keep your garden free of pesticides, and welcome wildlife by providing plenty of habitat.
Eight best companion plants to use in your garden
Eight Best Companion Plants To Use In Your Garden
Edible Alliums
Garlic, chives and onions repel a variety of pests – including the four legged kind. They also attract pollinators with their flowers. Their roots accumulate antifungal sulphur in the topsoil which can benefit nearby plants. They are a great companion for virtually anything!
Calendula (pot marigold)
This is a brilliant plant for a veg plot, as it attracts a wide variety of insects including aphid-munching hoverflies. It is edible and medicinal, flowers from early till late and often overwinters (cut back the dead bits and it’ll often reshoot from near the ground). It is always happy among veggies and easily self-seeds to save you a job next year.
French marigold
Another powerhouse in the garden; repelling pests, attracting beneficial insects, and releasing secretions in the soil which keep nasty nematodes away.
Nasturtiums
As well as attracting pollinators, these are an excellent ‘trap’ crop, attracting blackfly and cabbage butterflies to lay their eggs away from your main crops. Once they’re infested though, don’t let the pests breed in your garden! It’s better to dispose of the infested parts right away.
Flowering herbs: mint, oregano, marjoram, thyme, dill, fennel, lovage, lavender, hyssop, camomile
Herbs are a worthy addition to your garden for their culinary benefits alone. But they also attract a huge variety of insects, many repel pestilence, and some (especially camomile and parsley) are said to improve the health and flavour of nearby plants in more subtle ways through the soil too. Note that lovage and fennel are larger plants than most here. Give each a good space to itself and note that they can get very tall. In fact, their height will attract insects from even further afield!
Comfrey or stinging nettles
Though you’ll want to give these a corner of the garden to themselves (there is no digging comfrey out once it’s in!) they can provide a really useful service in the garden by bringing extra nutrition up from the depths of the soil with their deep roots. Harvest this nutrition by cutting the leaves a few times a year and adding them to your compost heap, or scattering them on veg beds and leaving them to decompose. You can also leave them rotting in water to make a (smelly!) concentrated liquid plant feed. Comfrey attracts bees too, and stinging nettles are an important food plant for certain butterflies.
Clover
Experiments showed that growing clover under brassicas consistently reduced the success of cabbage moths looking for a host plant, thus bringing a protective effect. What’s more, the clover offers bee-attracting flowers, and anytime it gets too much you can dig areas of it into the soil (preferably in spring before flowering) for a nitrogen-boosting effect.
Nectar-rich annual flowers (e.g. sunflowers, borage, cosmos, cornflowers, zinnias, scabious, echium)
A few favourite annual flowers such as these will fill gaps in the garden and spread insect-attracting colour anywhere; your local pollinators and predators will thank you! Many will self-seed too (stop deadheading by late October to allow this) and give you a new round of flowers for free next year.
So put the rulebooks away, focus on increasing the diversity in your garden, and always let common sense rule!
Local Food Gardening Events: find out more
Come and grow with us! Volunteer at the Incredible Edible gardens on the second and fourth Sundays of each month. Email Incredible Edible here to join the mailing list or find out more about Incredible Edible St Albans
See more about FoodSmiles here
Find out about Sustainable St Albans Open Food Garden summer programme
If you live in Sopwell ward, you can try some food gardening at the Grow Community Sopwell Community Garden
SustFest22 Gardening Events
During SustFest22 (15-31 May) there are loads of gardening events to look out for.
The programme comes out on 14th April, on social media and the Sustainable St Albans website. Here are just a few events, to whet your appetite!
- Grow Community Sopwell Community Garden Open Day including Seed & Seedling Swap, 15th May, 10:30am-12:30pm
- ‘Adopt a plant for your pollinators’ at Greenwood URC, May 17th and 19th, 2:30-3:30pm
- Visit the CDAH Community Garden on Hixberry Lane, 19th May, drop in 10:30-2pm
- ‘How to grow Asians herbs and spices’ with HAWA, also 19th May, 12-2pm, at the CDA community garden on Hixberry Lane
- ‘Gods Green House’ plant sale and eco garden tour, at St Paul’s Church Blandford Road, 21 May, 10:30-12:30pm
- ‘Come and Grow’ at Incredible Edibles, Russell Avenue, 22nd May 1-4pm
- ‘How we built an eco garden for next to nothing’, at Marshalswick Baptist Free Church, 24th May, 2-3pm
- FoodSmiles open day, Hammonds End Farm, 25th May, 1:30-4pm
- Grand Opening of the George Street Canteen Wildlife Garden, 29 May, 11-3pm