There are plenty of articles about companion planting and other ways you can make pest and plant behavior work for you instead of against you. Here are some tactics I've used to make growing season more rewarding while keeping my blood pressure -- and my garden center bills -- down.
Good Bugs vs. Bad Bugs - The Epic Battle of Good vs. Evil
Some plants attract beneficial insects, while others discourage destructive insects. With a little forethought, you can make these behaviors work for you by being smart about your garden design. This is one of the basic ideas behind companion planting. These days, CP is often considered an organic gardening solution, but even if you use pesticides occasionally, the neighborly approach (as in good neighbors make a great first line defense against pests) can still help you grow healthier, happier plants.
Hey, think of it as a free layer of protection. All you have to do is change the seating chart a little. For example: I like planting rue near my rose bushes because it attracts lady bugs, which in turn devour encroaching aphids. I also try to plant sage near broccoli and kale because it repels white cabbage moths. Gardeners have come up with lots of CP matchups that work for different applications. More on this in a minute.
Sneaky but Legal
There are also other ways to beat the bugs at their own game:
Lures - If you love squash but hate squash bugs, plant bright yellow flowers away from your vegetable patch. Squash bugs are attracted to yellow (because squash flowers are typically yellow) and will be lured away from your planted squash. You can then use insecticide on the non-edible flowers to keep squash bugs under better control. (Another option is to use yellow fabric or even Mylar ribbon attached to a nearby fence or tree as a lure.)
You can also use commercially available traps that rely on natural pheromones to lure a variety of bugs into small containers from which they are unable to escape. (Although this seems like an organized and efficient solution, remember, any overflow pests that don't make it into the trap will be free to roam around your garden.)
Parasites - Microscopic worms collectively called "beneficial nematodes" are available that will kill the early developmental stages of bugs like flea beetles, squash bugs, bagworms, Japanese beetles and others. You spray a water mixture containing the worms on your lawn and soil once or twice a year to keep pest populations down. The spray is colorless, odorless and won't hurt honey bees or most other beneficial insects.
Protective Reinforcements - Another option is to purchase a live community of beneficial bugs like praying mantis or lady bugs to protect your property. Think of them as insect mercenaries guarding your borders. Yes, some do fly away, but others take up residence and do their duty just fine.
Repellents - If you have Japanese beetle problems, say, you can always kill a few beetles, make a "tea" of bug bits and water and leave it in a bucket. The smell will discourage new beetles from staking a claim to your rose bushes. This olfactory tactic can work for other types of bugs, too.
The Example of the Three Sisters
Companion planting also works in ways unrelated to pest control. It can use a plant's native habit, color or chemical makeup to produce "cooperative" success in the garden. For example, planting a climber like beans near a tall, stable plant like corn produces a support structure for the bean without your having to put down a pole or add a trellis. This is one of the benefits of the "three sisters" approach to farming, a classic Native American example of the dynamic power of companion planting.
You've probably heard it referred to before: The three sisters are three plants that help one another through the growing season: corn, climbing beans and squash. The corn provides the "pole" for the beans; the beans add nitrogen to the soil to help sustain the corn and squash; and the squash offers natural mulch and protection from moisture loss through evaporation, all while keeping weeds to a minimum by blanketing the soil with a dense, shady canopy of large leaves. Elegant. Simple. Effective.
You can find examples of three sisters gardens here: Three Sisters
As promised above, here are some popular examples of plants (often herbs with vegetables) that grow well together:
- Asparagus with parsley or dill
- Beans with beets, lovage, corn, rosemary, larkspur or radishes
- Beets with garlic
- Cabbage with thyme, dill, chamomile, onion or mint
- Carrots with peas, radishes or tomatoes
- Celery with chives or rosemary
- Corn with beans, squash, potatoes or cucumbers
- Eggplant with thyme, mint, catnip or garlic
- Grapes with hyssop
- Leeks with carrots
- Lettuce with cucumbers or strawberries
- Melon with pigweed or summer savory
- Okra with chervil
- Peas with garlic or mint
- Peppers with carrots or bee balm
- Potatoes with cilantro
- Pumpkins with oregano
- Raspberries with garlic
- Squash with tansy
- Strawberries with sage, thyme and borage
- Tomatoes with basil or bee balm
- Turnips with peppermint or sage
- Watermelon with nasturtium (Works with other melons, too.)
Okay, a list of good plant pairings is helpful, but it doesn't give you much wiggle room. Many of these pairings use one plant's pest repellent ability to protect the other plant from insects that would otherwise consider it a banquet.
If some plants naturally repel certain insects, then placing those plants where you have, or figure you might have, a specific insect problem should help keep pest populations down, whether they're next to historically compatible companions or not.
If you've struggled with whitefly in the past, knowing a variety of plants whitefly avoids will help you choose a winner -- but with a little more flexibility. In this case, nasturtium, French marigold and basil do a good job of repelling whitefly, so if you want a flowering plant, choose French marigold or nasturtium. If you want an edible plant, then basil is your best bet.
What follows is a list of insects - and one pesky mammal - together with the plants they really don't like being around. These pairings probably won't do the same bug prevention job as a strong pesticide, though. If they could, pesticides would be obsolete. They will help control pest populations somewhat successfully without a lot of chemicals.
You can also grow these plants in bulk and use them to prepare homemade bug sprays (or noxious smoothies). Homemade sprays can be quite effective, but they need to be reapplied often.
Oh, and don't expect one puny specimen to hold back the horde. You don't need a one to one ratio necessarily, but make sure your pest control plants have strong representation in the garden. It's also a good idea to place them next to vulnerable plants as well as around the perimeter of the garden and in locations where there's good air flow (so their fragrances will travel a respectable distance).
Pests and the Plants they Love to Hate
For the most part, I haven't included the scientific names for the plants or insects, but absent any notation, you can assume I'm referring to the most common variety your likely to find in your garden or at your local nursery. Related plant cultivars may work as deterrents, but keep in mind it's a trial and error proposition.
- Ants - catnip, peppermint, tansy
- Aphids - chives, rue, pyrethum, mustard, dill, mint, nasturtium, coriander (cilantro), garlic
- Asparagus beetles - calendula (pot marigold), basil, tomato plant, petunia, parsley
- Bean beetles - santolina (a particularly effective artemisia), nasturtium, summer savory, rosemary, marigold
- Black flies - garlic
- Borers - garlic, onion
- Cabbage looper - artemisias, eucalyptus, dill, hyssop, garlic
- Cabbage moths - mint, celery, nasturtium, chamomile, sage, hyssop, artemisias (like wormwood), thyme, oregano
- Cabbage worms - thyme
- Carrot fly - sage, rosemary, onion, leek
- Caterpillars (various) - garlic, bay laurel
- Cockroaches - feverfew, tansy
- Codling moths - artemisias
- Corn earworms - thyme, geranium, cosmos
- Cucumber beetles - marigold, oregano, rue radish
- Cutworms - onion
- Earwigs - wormwood
- Flea beetles - catnip, catmint (different but related to catnip), mint, rue, artemisias, sage
- Fleas - pennyroyal, yarrow, rue, lavender, sage
- Flies - basil, pennyroyal, mint, tansy, rue, wormwood, lavender
- Gnats - pennyroyal, lemon balm
- Hornworms (Tomato hornworms) - basil, petunia, marigold, dill, borage
- Japanese beetles - rue, garlic, geranium
- Leaf hoppers - pyrethum (chrysanthemum cinerariifolium)
- Mice - mint, wormwood, tansy
- Mites - dill, chives, pyrethum, onion
- Mosquitoes (or their larvae) - basil, pennyroyal, yarrow, lemongrass, geranium, tansy, lavender, lemon balm, rosemary
- Moths (various) - lavender, mugwort, rosemary, santolina, coriander (cilantro), wormwood, sweet woodruff, tansy, rosemary
- Nematodes - chives, dahlias, French marigold (There are destructive nematodes around and chives repels the good with the bad.)
- Potato beetles (Leptinotarsa decemlineata) - nasturtiums, coriander (cilantro)
- Potato bugs (Stenopelmatus spp.) - horseradish
- Pumpkin beetles (various) - nasturtiums
- Slugs - sage, onions, fennel, rosemary, wormwood
- Snails - sage, onions, fennel, wormwood, rosemary
- Spider mites - coriander (cilantro), garlic, dill
- Squash beetles - nasturtium, catnip,
- Squash bugs - peppermint, dill, tansy, nasturtium
- Sticks (Phasmatodea) - sage
- Termites - catnip
- Whitefly - nasturtiums, French marigold, basil
Not all plant pairings are copacetic. Next time we'll discuss "lousy neighbors." You know, those folks that just never seem to get along. I wouldn't want you to accidentally create a plant feud.
Have a great weekend.
Cornell University Cooperative Extension. "Companion Planting." 1999
Painter, Tammie. "Plants that Repel Insects." Mother Earth Living. 2010 http://www.motherearthliving.com/gardening/fresh-clips-herbs-to-repel-insects.aspx#axzz2WsGdw7rr>
Home Grown Texas. "Herbs That Repel Bugs." 2003. http://www.homegrowntexas.com/issues/NovDec03/
Alabama Cooperative Extension. "Companion Plants." Undated. http://www.aces.edu/counties/Limestone/MastGard/companions.htm
Photo 1 - Tomato Hornworm By George Bredehoft (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons http://upload.wikimedia.org/wikipedia/commons/5/54/Tomato_Hornworm_in_hand.jpg http://commons.wikimedia.org/wiki/File%3ATomato_Hornworm_in_hand.jpg
Photo 2 - Aphids By Alvesgaspar (Own work (own photo)) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons http://upload.wikimedia.org/wikipedia/commons/5/51/Aphids_September_2008-1.jpg http://commons.wikimedia.org/wiki/File%3AAphids_September_2008-1.jpg
Photo 3 - Squash Bug By Noel Feans [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons http://upload.wikimedia.org/wikipedia/commons/4/40/Coreus_marginatus_-_Squash_Bug.jpg http://commons.wikimedia.org/wiki/File%3ACoreus_marginatus_-_Squash_Bug.jpg