Make companion planting work
Some gardeners swear by it; others say it doesn’t work. Here’s how to decide what to plant together, writes
Ireally want to believe in companion planting. There’s something appealingly mystical and witchy about thinking that your nasturtiums will protect your lettuces from pests, that your tomatoes love your carrots or that they’ll have a far superior flavour if they’re planted beside basil.
But science has debunked many of the ideas around companion planting, which, it has to be said, vary wildly. It’s not all horticultural woo-woo though. Some plants are definitely better off with certain companions as opposed to others or none at all – diversity is always better than a monoculture.
Fortunately, working out which plants to put together needn’t be as complicated as deciding the seating plan for a wedding.
Basically, companion planting means choosing plants that complement each other, act as a deterrent for pests or diseases, enhance soil and don’t occupy the same space as their neighbours.
Friends give each other space
Plants all need room to grow but some need more space than others. Where possible, group similar-sized crops together.
Lettuces, spinach, strawberries, bok choy, capsicums, chillies, leeks and onions make nice, compact neighbours.
Plants such as pumpkins, tomatoes and sweetcorn spread themselves out or grow tall.
There are some exceptions though. Lettuces can dry out in the heat of summer, turning bitter, so planting them at the base of corn or tomato plants provides them with some welcome shade. Native Americans have planted the ‘‘three sisters’’ – beans, corn and squash – together for centuries. The beans don’t need staking because they grow up corn stems (wait till the corn is tall and strong before sowing the beans) and the squash grows at the base of these plants, its big, wide leaves mulching the soil and suppressing weeds. The beans add nitrogen to the soil which the other plants can use.
Similar interests
Plants have different soil requirements so it pays to group different edible crops together according to their needs.
Leafy crops such as lettuces and brassicas are nitrogen hungry and will benefit from nitrogen-rich fertilisers and foliar feeds.
Fruiting crops, such as tomatoes and capsicums, will put their energy into growing lush foliage instead of fruit if the soil is too rich – once they develop flowers they do better with a potassium-rich fertiliser.
Cucurbits such as melons and cucumbers are heavy feeders and like a rich soil, whereas carrots and beetroot need a finely tilthed soil or they will fork and split.
As a general guide, grow beans, peas and brassicas together, placing climbing beans at the back of a bed so they don’t shade the brassicas.
Plant herbs and heat-loving solanaceae such as tomatoes, eggplants, chillies and capsicums together. Potatoes are also solanaceae but these should be grown with your other root crops.
Grow cucurbits (melons, zucchini, pumpkins and cucumbers) and corn in a group and pop lettuces into any gaps.
Plant corn in blocks rather than rows, as it is wind pollinated.
Sow pumpkins direct on the northfacing edge of your bed so they can wander off, soaking up sun and saving you planting space.
Grow root crops and edible alliums together. Garlic and shallots are planted in winter. Sow carrots direct in spring and summer in fine soil. Plant spuds in trenches at least 20 centimetres deep.
Sow radishes on top of spuds or carrots to mark the rows. Slowmaturing onions and leeks can be interplanted with spring onions. Plant ku¯ mara here, too.
Rotate these plant groups to different beds every year to prevent a build-up of pest and diseases in the soil and to ensure you don’t strip the soil of one thing.
Attract good and bad attention
Growing flowers among your crops doesn’t just pretty up your vege patch.
Bright blooms scream ‘‘Come and get me!’’ to beneficial bugs, such as ladybugs, honeybees and hover flies, which act as pollinating and/or pestcontrol agents on your flowers and their next-door-neighbour edible crops.
For maximum pest control and pollination, aim for a ratio of 40 per cent flowers to 60 per cent edibles in your vege patch and go for mass plantings about 1 metre in diameter of at least three or four different types of flowers such as alyssum, borage, buckwheat and phacelia.
Providing a strong visual is especially important for honeybees as most of them spend their entire lives foraging from one type of plant, so provide them with an all-you-can-eat location. Some flowering plants act as catch crops (kind of like a decoy), distracting bad bugs and keeping them off your edibles. Cleome spinosa is an excellent vege-patch companion as it is adored by sap-sucking green vege bugs. It’s striking too, growing up to 1.5m tall, with pretty white, pale pink or magenta flowers. It has prickly stems though so don’t plant it by a path or it will catch you.
The poster child of beneficial flowering plants to plant beside your edibles is the frilly headed, pungentsmelling tagetes marigold. This is partially due to its reputation for killing nematodes (microscopic worms that attack plant roots) as tagetes roots contain a chemical that acts as a nematocide.
However studies have shown that for tagetes to be effective as a nematode deterrent for your edibles, the tagetes plants need to have been growing for at least four months before planting your edible crops, then dug into the soil or removed before planting your edibles in exactly the same spot.
If this sounds like too much work, marigolds (calendula and tagetes) also attract beneficial bugs, so they’re still worth growing, as is any flowering plant that provides food for pollinators in your vege garden, as ultimately this means you’ll end up with more food too.