There’s a lot of misinformation and confusion when it comes to companion planting. That’s because it is so hard to test theories. No season is the same as another and no garden is like any other. That makes it hard to tell if it was the pairing of two plants that gave you desirable results or if it was something else entirely.
That doesn’t mean companion planting does not work. It just means that you will need to test things out for yourself. One of the companion planting tenants that has shown... some success is interplanting different vegetables to thwart insect pests. Like humans, insects have their preferred foods. Very often they find these foods by scent. You can make it harder for them to locate the buffet by mixing in plants that will confuse their sense of smell, such as planting onions between cabbages. This means you won’t be able to plant in tidy rows and large blocks of a single vegetable, but it doesn’t take a lot to have an effect.
Even if you don't have great success at deterring pests, a bonus effect is that, some of these plants will attract the beneficial insects we want in the garden. This is another type of companion planting that is proving to have great use for gardeners.
Plants with pungent scents are among the most successful insect deterrents. Do your own study and test some of these near any vegetables you have reoccurring problems with and see if it makes a difference. Even if they aren’t as effective as you might hope, you will still have lots of herbs for seasoning.
Carrots Love Tomatoes, by Louise Riotte, Storey Publishing, 1998
Great Garden Companions, by Sally Jean Cunningham, Rodale Press, 1998
Rodale’s Successful Organic Gardening Companion Planting, Rodale Press, 1994
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Basil repels: Asparagus beetle, tomato hornworm. It’s the scent that deters the insects, so gently crushing the leaves as you walk by improves its effectiveness.
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Borage repels:Tomato hornworm. It also attracts beneficial insects and pollinators. Allow it to self-sow.
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Calendula repels: Asparagus beetle. It also attracts beneficial insects, so use throughout your garden.
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Chives repel: Aphids, Japanese beetles. This plant also tends to spread quickly, if you allow it to go to seed.
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Dill repels: Cabbage moths. Dill is also a good plant for attracting beneficial insects and is a host plant for black swallowtail butterflies.
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Garlic repels: Aphids, cabbage moths, Japanese beetles. Planting garlic under roses to repel Japanese beetles is a classic companion planting technique.
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Horseradish repels: Colorado potato beetle. Unfortunately its hard to plant a perennial with a crop like potatoes, that needs to be dug every season but it should have some effect if grown in the general vicinity.Continue to 9 of 19 below.
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Hyssop repels: Cabbage moths. A good companion for all sorts of cole crops.
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Mint repels: Aphids, cabbage moths, ants. You can just lay sprigs of mint among the plants you want to protect, so that the mint plant does not spread and take over the garden, but needs to be replaced often.
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Onions repel: Aphids, carrot rust flies, flea beetles. The combination of carrots and onions has done well in testing. To foil flea beetles on my eggplants, you can try tossing onion peelings around them, although the actual onion plants work better.
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Oregano repels: Cabbage moths. Oregano can be difficult to interplant, because it is a spreading perennial.Continue to 13 of 19 below.
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Parsley repels: Asparagus beetles. As with basil, you’ll need to gently crush the leaves to release the scent.
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Radish repels: Cucumber beetles. For this you will need to seed 3 or 4 radishes in each hill and leave them there to mature.
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Rosemary repels: Cabbage moths, carrot rust flies, Mexican bean beetles. Although rosemary is not hardy in all zones, you can usually find small plants inexpensively at the start of the season and you can always bring them indoors for the winter, as houseplants.
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Sage repels: Cabbage moths and carrot rust flies. Sage is a perennial plant and can be hard to intercrop, but is still useful along the border.Continue to 17 of 19 below.
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Savory repels: Mexican bean beetles. Summer savory works best and is easier to interplant, because it is generally grown as an annual.
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Thyme repels: Cabbage moths. Most thymes are low growing and double as ground covers in the garden.
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Wormwood repels: Flea beetles. It also seems to deter mice.