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The Truth About 'Companion Planting'

Q: I am a brand new gardener and want to plant small, raised bed, vegetable gardens. Are there certain vegetables to plant together? Vegetables that shouldn't be planted together? Flowers that should be planted to help with growth or pest control? I want my first experience to be bountiful, and any tips or suggestions would be greatly appreciated. I also want my garden to be organic; what products do you recommend? Thanks,

    ---Sandy in Maggie Valley, NC; around 3500 feet up in the mountains
A. Wow; we knew North Carolina was a beautiful state, filled with interesting places—but a valley two-thirds of a mile above sea level is really something!

Anyway, you're already on the path to organic success with those small raised beds. Keeping each bed small and raised allows you to garden without ever stepping on the loose, rich soil within; and that lack of compaction keeps plants very happy and healthy. (See this Previous Question of the Week for lots of details on building raised beds.)

Feeding that soil—instead of the plants—with organic matter (i.e., compost) is the other necessity. So your first 'product' should probably be a nice load of compost trucked up into your valley to get you started.

Then you'll want several composters to begin making your own Black Gold. And maybe a compost tea brewer if you want to get fancy. What you'll need beyond that depends on what you'll be growing and what kinds of nasty creatures appear to stop you. But I'd suggest having some row covers handy in the beginning. These spun polyester fabric 'blankets' can protect a large number of crops from a large number of pests. And they'll extend the season for things like salad greens a good month in both directions.

And, ah, yes: 'Companion planting'; a topic laced with more folklore, hopefulness, bad information and just plain hype than just about any other in the gardening world. It's said to have begun just as the world was going from BC to AD, when the oft-quoted Pliny the Elder wrote that the (highly toxic) plant rue was a "very friendly" companion to figs. And there we were, off and running to 'Roses love Garlic'.

The most basic truths in companion planting lie squarely in common sense. Growing a mid to late summer run of lettuce behind sweet corn, for instance, fulfills two conditions of good neighborly-ness. Both crops are nitrogen hungry, so a bed rich in composted horse or poultry manure would serve them both well. And because it would be shaded by the tall corn, the otherwise heat-hating lettuce could be started much earlier than usual—in mid-summer, as opposed to very late summer. Pull out the corn stalks after the weather cools down, and your lettuce now has the full sun it craves in late summer and fall. Good companions, indeed!

And one huge and well-proven aspect of companion planting we've been trying to hammer home for many years is using plants to attract beneficial insects to the garden.

Garlic, in reality, would make a pretty lousy companion for roses. It would disrupt the rose roots when you planted the cloves in the fall. It would disrupt those roots mightily when you harvested the full-sized garlic bulbs in June. The tall garlic plants would greatly reduce the air circulation those disease-prone posies crave. Etc., etc…. And it doesn't attract any beneficial.

Ah, but the herb tansy would make an excellent rose companion! Aphids are a notorious pest of roses, and tansy attracted more aphid-eating ladybugs and lacewings to its pretty yellow flowers than any other plant in a large-scale study. Tansy may even be the best all-around companion; in a study performed at the Rodale Institute Research Center in Pennsylvania back in the 90s, inter-planting tansy with potatoes reduced the numbers of those nasty Colorado potato beetles by 60 to an astonishing 100%!

Other excellent beneficial insect-attracting companions in the Rodale study included the "White Sensation" variety of cosmos, and many herbs. Caraway, dill and fennel were the biggest herbal attractors; let some of those go to flower in the middle of your garden and lots of helpful bugs will arrive to imperil your pests.

And just plain having different companions—that is, mixing up your garden instead of planting in small mono-cultures—can be highly effective at keeping pests at bay. Many studies have shown that having a single plant of something in each bed as opposed to having all of them grouped together greatly reduces the incidence of pests and disease.

And finally, some other specific companions also have proof in their puddings. Here's a nice little list of companions shown to have been effective in at least one scientific study, compiled by garden writer Robert Kourik in his classic 1984 book, "Designing and Maintaining Your Edible Landscape". Just be warned that some of these ideal companions are weeds.

  • Dandelions grown near tomatoes provided protective against fusarium, a nasty wilt that strikes tomatoes grown in the same soil year after year. The dandelion roots were found to produce an acid that essentially 'starved' the disease of iron, a nutrient necessary for it to do its dirty work.

  • Broccoli grown near cucumbers repelled striped cuke beetles.

  • Tomatoes were shown to keep flea beetles away from collard greens. (Collards?! Who cares? If only it had worked for eggplant, the crop flea beetles bother the most!)

  • Tomatoes were also shown to reduce the number of diamondback moth caterpillars on nearby cabbages.

  • Growing onions near carrots kept the larvae of the notorious carrot rust fly from making those nasty tunnels in the carrots underground.

  • And pigweed and ragweed (a-choo! ) kept leaf miners away from bell pepper plants. Now, I would never plant HIGHLY allergenic ragweed deliberately. But beautiful and nutritious amaranth—one of the late Bob Rodale's favorite plants—is a form of pigweed. So maybe the striking Elephant's Head amaranth I have growing throughout my garden explains my absolute lack of leaf miner problems. Other experts have explained that the best way to control leaf miners is to attract the beneficial insects that go into the leaf to prey on them; so I'm assuming that plants in the pig weed family attract the correct good bugs. (If you try this, be sure and keep the amaranth under control; I haven't planted any since my first batch was seeded 20 years ago and I've had a nice crop come up every season since!)

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