Fiann Ó Nualláin on plants and herbs that co-habit beautifully — and in binary and non-binary ways, too.

You could say that placing plants together — side by side and interacting — is the essence of gardening. 

We productive gardeners don’t necessarily think of the visual effect of the combinations, we have the criteria of crop rotation to think off.

But we can certainly think of putting combinations of plants together for their mutual benefit. 

That too is perhaps one of the oldest gardening traditions. In this article, I want to look at culinary herbs as companions so what we get is more harvest and the benefits of co-planting strategies.

The western tradition of companion planting can be traced back over 2,000 years to a Roman agriculturalist called Varro, who noted: “Large walnut trees close by, make the border of the farm sterile,” and so began some investigations into how plants react when side by side.

The Chinese had long established the co-planting of nitrogen-fixing plants with nitrogen-hungry plants and for thousands of years before St Brendan, the Vikings or the Europeans set foot in the Americas, the indigenous peoples had mastered the three sisters’ technique — co-planting beans, maize and squash.

Plants that work well together two-by-two and row-by-row

Maize as crop and as a support for the beans to climb and thrive, beans as a crop and as nitrogen fixing for the maize and squash, and the squash more productive and protected in the shelter of the other two.

Companion planting is knocked by its detractors as a pseudo-science or unsophisticated practice — very often by the same people who would institutionalise you for opting for a cup of chamomile tea over a foil packed, stock exchange-floated, chemical-heavy, side-effect- disclaimer sedative.

Meanwhile, the champions of companion planting are those who have availed of its benefits over many years and have witnessed first-hand its helpfulness in the garden.

So this is how it works for me and this is how you can make it work for you. In recent years I’ve seen many writers and pundits frame companion planting as a trick to attract or deter insects – as if that’s all it does.

Well, companion planting is far from being a one-trick pony, yes plants with certain fragrances can be utilised to attract beneficial insects or decoy harmful pests — more anon — but companion planting can also help the neighbouring crops to better absorb nutrients, share disease defence mechanisms and increase each others pollination. 

Many of us heretics also argue that certain combinations also improve the flavour of the cohabiting plants.

Plants that work well together two-by-two and row-by-row

One such flavour enhancer is basil (Ocimum basilicum) combine with tomatoes. 

Some suggest the volatile oils emitted from basil are absorbed by the nearby tomatoes and add to the flavour— just as the garlic aroma is used by organic rose growers to impart that scent to the rose plants and put off aphids who recognise the garlic aroma as a toxin.

Another reason may be that because the basil fragrance repels many of the insect pests of tomatoes, the less-stressed fruiter has more energy to build flavour molecules than defence or repair mechanisms, which can bitter up the plant and its yields.

Many plants under attack will purposely alter flavour to bitterness to deter the munching pest and many of the plant’s phytochemicals to fight diseases are bitter alkaloids too. 

So basil keeps things sweet. And I have found that the basil is less prone to some of its pests and diseases when grown with tomatoes.

It is one you have to treat as an annual herb when growing outside with tomatoes and there can be issues with cold spells and too much rain and even, not enough warmth to build up the volatile oils that work on the tomato pests, but under cover, in polytunnels or other, basil and tomatoes really work together — and they are excellent on the plate together too.

Chives (Allium schoenoprasum), are much hardier and so easy to grow. I use them as edging in some of my raised beds – it transfers around well so I can move it with crop rotations and allow it to protect and enhance my carrots.

That oniony fragrance deters many carrot pests — in particular it confuses the carrot root fly. Not just during the growing season, but when you are thinning or harvesting do pull a few chives too, to put that disruptor waft on the air and mask and disorientate odour positions. 

I find chives easier to grow amongst or beside carrots than onions or garlic. Chives have some of the antifungal and anti-insect qualities of garlic, so any glut makes for some great home tonics and natural pesticide.

Plants that work well together two-by-two and row-by-row

Parsley (Petroselinum crispum) is said to benefit from the company of asparagus or tomatoes and I knew a rose-grower who planted parsley at the base of his roses to increase fragrance. 

We generally harvest parsley in its first year as a foliage herb but letting it flower and go to seed is no big mistake — in fact when in flowers, it is one of the best companions at attracting hoverflies and predatory wasps that will rid you of many caterpillars and other garden pests.

Thyme (Thymus vulgaris and varieties) not only attracts pollinating bees, but also entices beneficial predator insects to keep any populations in check. It’s one I also use as an edger in raised beds. 

When those beds are host to cabbage crops then the thyme helps to deter cabbageworm and whitefly. When host to root crops, it benefits with a decrease in the nasty nematodes.

Sage (Salvia officinalis) deters cabbage moth and carrot fly and oregano (Origanum vulgare) is good with summer squash, potatoes, and tomatoes.

Dill attracts many pests so it can used to lure pests away from cauliflower and cabbage in the garden by planting in the vicinity, but not amongst.

A herb bed looks great and all the herbs pretty much have the same cultural requirements, so it makes sense to cluster them together in the same sunny free draining spot. But being a little more adventurous and turning them into companion plants can bring richer rewards.

Next week I will take a further look at combinations and explore what plants might reduce the risk of potato blights and what plant is a natural immune system booster for all your crops.


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