Use Trap Crops to Protect Your Most-valued Garden Plants
If you are trying to go pesticide-free in the garden, consider a version of companion planting that has one plant “sacrifice” itself for its more valuable neighbor. These heroic varieties are known as trap plants or trap crops, and they work by attracting a specific pest that might otherwise attack a more valuable plant nearby.
Tomatoes
We all know that marigolds are adept at killing nematodes, the root-borne pest that loves tomato plants. But the nematodes don’t hurt the marigolds; these flowers do just fine alongside your Whopper and Big Yummy tomato plants. What are some plants that can deter a pest from reaching your tomatoes — by sacrificing themselves for the cause?
Tomato hornworms can be a big problem for your plants, so you might want to surround your tomatoes with dill plants. The hornworms will attack the dill instead, staying clear (for the most part) of the tomatoes. Similarly, aphids are a huge pest. Interplant your tomatoes with okra to minimize this problem. You may not get as big an okra harvest, but your tomatoes will be all the healthier.
Roses
What’s the biggest scourge of roses in most American gardens? Let’s all say it together: Japanese beetles! (If you aren’t sure what a Japanese beetle looks like, go check your rose foliage. That glittering, metallic, multicolored beauty of a bug is the culprit.)
The only plant Japanese beetles seem to like better than roses is four-o’clock flowers, which is why many gardeners ring their rose garden (or even interplant it) with this easy-grow, fragrant annual. If you’re thinking, “But I love my four-o’clock flowers, too!” here’s a solution: go out in the garden in early morning and simply strip the sleeping Japanese beetles off the four-o’clock flowers. Wear gloves and dunk them right into a pail of soapy water. You can probably save your four-o’clock this way. But if you’re more ruthless (or less fond of four-o’clocks), wait until the plant is teeming with Japanese beetles, then uproot it and dunk the whole thing in soapy water. Repeat every few days with remaining plants, all season long or until the problem stops.
Another annual, even more beloved than four-o’clock, that is also great for luring Japanese beetles away from roses and onto its own foliage is zinnia (If you thought uprooting a blooming four-o’clock was hard… ) The funny thing about zinnia, though, is that it’s such a good attractor of pollinators and “good bugs” that you’ll want it everywhere in the garden anyway. Plant it freely and consider a little damaged foliage a small price to pay for its wondrous beauty and pest-fighting ability.
Finally, scented geraniums (pelargonium) are a great lure for Japanese beetles. On four-o’clock, they attack the leaves, but on scented geraniums they like the flowers which are toxic to them! I think this is a decent compromise when it comes to pest control, because most of us grow scented geraniums for the fragrance more than the flowers. If we can pick off the Japanese beetles, fair trade
Cabbage, Broccoli, and Other Brassicas
Flea beetles look a bit like fleas, and they certainly hop like them — from leaf to leaf, munching away. They love Brassica crops and can do a lot of damage very quickly. So, plant radishes and nasturtiums in between your Brassicas to attract flea beetles in the vicinity.
Nasturtium, it should be added, is also a magnet for aphids. Plant it everywhere in the vegetable garden. It won’t look so terrific as the season goes on, but your veggie plants sure will.
Another common pest is the cabbage worm, which can be protected by collards nearby. Fewer collard greens, more cabbage — a good tradeoff for many of us.
Lettuce and Other Ground Crops
Slugs and snails make a feast out of anything they can crawl to, and they prefer to stay on the ground, nibbling at soil level. But if given a choice, they will abandon the tender arugula and butterhead lettuce in favor of . . . chervil, also known as French parsley. Chervil is your best friend for trapping these slimy pests. Plant it liberally. Is Chervil too expensive to use as a trap crop? Its cousin parsley works well too, and is an inexpensive seed.
Strawberry
Also known as tarnish bugs, lygus bugs can really do damage to your strawberries and other fruit plants. Tempt them away from these edibles with mustard plants. Like zinnia, mustard attracts both good and bad bugs. Let it flower (it’s beautiful) and go to seed in your vegetable, herb, and flower gardens.
Squash
Few things are as frustrating to a new gardener as not being able to grow squash (“It’s so easy!” everyone tells you; “I had more than I knew what to do with last summer!” etc., etc.). The culprit is usually squash bugs, and they will NOT go away easily.
A beautiful and easy (yeah, you’ve heard that before!) solution is to grow Millet among your squash. This ornamental grass, actually a grain, is the preferred food of the squash bug. Be diligent about going out early and stripping the bugs off the plants and into soapy water, though. They are persistent little devils.
Cucumber
Amaranth is lovely, and it really stands up to cucumber beetles. You know a pest is common when it’s named for the plant it attacks. Cucumber beetle can really take hold, so fend it off with amaranth. This works particularly well in fall, when you have adequate time to start Amaranth in the warm weather and then surround your fall cuke plants with it.
Sunflower
Sunflower is such a magnet for stink bugs that it is used as a trap plant in commercial crops. But at home, we want the Sunflowers. So, what’s even more tempting for these destructive little bugs? Millet and vetch can lure it away! These two plants are also good soil builders, so you have a win-win.
To Trap Crop or Not to Trap Crop?
You have probably already thought of the argument against trap cropping: by growing plants that a particular pest loves, are we running the risk of attracting more of that pest into the garden?
Probably so. My advice is not to trap crop until you have identified a problem with a particular pest. The first year you grow tomatoes or roses, watch and see what jumps all over them. You may find that you (and your favorite plants) have a high tolerance for holey leaves and damaged foliage. But if the damage is severe, the following year you may want to think about growing a trap crop.
Timing the Trap Crop
Ideally, you want your trap crop to be a little more mature than the plant it’s protecting. If your Roses start blooming in late spring, it would be terrific if the four o’clocks, zinnias, and/or scented geraniums were already going strong by this time, so the Japanese beetles were never even tempted to wander over to the rose. That’s not always possible, but try to start trap crops early, and always set out extras, in case you lose one or more to pests.
The Economics of Trap Cropping
Commercial growers use trap crops not only to save on pesticides, but because the trap plants are usually much cheaper than the crops they are protecting. You can buy a pack of 50 zinnia seeds for just a few dollars, but a rose bush can cost you $25+. Especially if you are growing food for the family, you can save a lot of money, and keep your garden organic or at least pesticide-free, by growing inexpensive trap plants from seed. Give it a try with a problem plant or two this season and tell us how it works for you.
