Companion Plants that Help Deter Mischievous Insects
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Interactions between plants and insects are mediated in part, through the exchange of chemical cues. Plants generate chemical compounds to attract beneficial insects and deter mischievous ones, and insects sense chemicals to locate and evaluate potential food sources.
Insects perceive plant chemicals through olfactory (sense of smell) and gustatory (sense of taste) receptors, with odors playing an especially important role in providing information.
Researchers understand that the overall odor of a habitat plays a role in allowing insects to identify resources. Additionally, the structure of vegetation (number and size of plants) influences the diffusion of odors. Given this, simply increasing the diversity of plant species in a habitat can help protect preferred plants from mischievous insects, as their efficiency in filtering odors is hindered in a complex background.
Further, researchers report that specific plants emit imposing odors that help mask the scent of others, influencing insect orientation. These plants, sometimes called “pest confusers”, release a variety of compounds that can confound mischievous insects, hindering their ability to find target plants. Although many strong-scented plants can perform this function, below are a few treasured examples.
Good native* pest confusers that also attract beneficial insects include:
- alliums, such as wild chives (Allium schoenoprasum), nodding onion ( cernuum), ramps (A. tricoccum), wild leak (A. burdickii), and meadow garlic (A. canadense), each additionally offering culinary options
- anise hyssops (Agastache spp.), such as yellow giant hyssop (Agastache nepetoides) and purple giant hyssop ( scrophularifolia); the equally lovely anise/blue giant hyssop (A. foeniculum) is native to north-central and northern North America
- bee balm/ bergamots (Monarda spp.), of which there are five native varieties, and the leaves of didyma, M. fistulosa, and M. punctata have been traditionally used to make a tasty tea with therapeutic properties
- goldenrod (Solidago spp.), with over 20 native varieties, the leaves and blossoms of several of which can be brewed into a delicate tea with therapeutic properties
- native mints, for example field mint (Mentha arvensis), Canada mint (Mentha canadensis), peppermint ( piperita) and mountain mints (Pycnanthemum spp.), all of which have been used in culinary applications or to make tea
- saturejas (Clinopodium spp.), such as limestone calamint ( arkansanum) and wild basil (C. vulgare), whose leaves can be used in place of basil (dried or fresh) in culinary applications or as a flavorsome tea
- wormwoods (Artemesia spp.), such as native biennial wormwood (Artemesia biennis), field sagewort ( campestris) and perennial white sagebrush (A. ludoviciana); for more detailed information on native and non-native wormwoods, please see below
- yarrow (Achillea millefolium), that further offers therapeutic properties
Good non-native pest confusers include:
- basil (Ocimum spp.)
- hyssop (Hyssopus officinalis)
- lavender (Lavendula spp.)
- marigolds (Tagetes spp.)
- oregano (Origanum spp.)
- tansy (Tanacetum vulgare)
- wormwood (Absinthium spp.); for more detailed information on native and non-native wormwoods, please see below
*Here, “native” refers to the east, north-central Midwest.
Wormwood species (Artemisia spp.) offer a variety of natural pest management options, deterring mischievous insects without harming beneficial ones. Different varieties of Artemisia species offer diverse advantages for varying scenarios, and the silvery-leaves of many varieties offer a special magic of their own*.
Most wormwood varieties do not require special soil amendments, and most perform best in well-draining soil and full sun. Wormwoods generally offer the best pest management benefits when planted 3-4 feet apart along orchard or food forest perimeters (for access to sun), or as pest barrier rows between fruit varieties.
Each of the native Artemisias, including biennial wormwood (Artemesia biennis), field sagewort (A. campestris) and white sagebrush (A. ludoviciana) have been shown to deter mischievous insects. White sagebrush (A. ludoviciana) specifically, is known to thrive in diverse climates (from Canada to Mexico) without special amendments or additional irrigation once established, and is known for her spreading rhizome system that makes her an effective, low-growing groundcover that supports beneficial ground beetles that hunt larvae and of cabbage worms, cutworms, corn earworms, and slugs). Once established, A. ludoviciana tends to thrive without care, but may warrant a trim of runners (or mowing) annually to prevent congestion around the bases of trees.
Although not native, common wormwood (Artemisia absinthium) is easy to establish in full sun and well-draining soil, and is considered a premier, perennial variety for deterring aphids, codling and oriental fruit moths, thrips, and spider mites. Happy common wormwood plants can grow up to 5-6 feet tall and 2-3 feet wide.
Another very nice option is mugwort (Artemesia vulgaris), native to temperate Europe and Asia and naturalized in North America Mugwort is an adaptable perennial growing 3-5 feet tall, tolerating drought one established and a bit of shade. Mugwort has deep tap roots and does not tend to compete much with fruit trees and shrubs with shallow roots (apple and cherry trees, elderberries, etc.), all the while deterring aphids, various moth species, plus scale insects. Mugwort does spread (self-seeding), but is not considered aggressive and can be controlled with root division.
Tarragon (Artemisia dracunculus), native to temperature Eurasia (and the wild form possibly to temperate North America), is dual-purpose, offering culinary benefits along with insect management, with aromatic compounds that confuse aphids, various moth species, plus scale insects (aphids and scale insects). The methyl chavicol and estragole compounds in tarragon are known to aromatically confuse pests near target plants (within 10-15 feet), with peak effectiveness during warm afternoons through evening. Harvest in late spring and mid-summer (allowing recovery prior to winter) the top 2/3 of the outer tarragon stems in the early morning hours, preserving her center growth.
For an annual option, sweet wormwood (Artemesia annua), native to Asia and naturalized in North America, is a fast-growing annual that can be planted in spring for optimal pest deterrence in midsummer. As an annual, it can be replanted (relocated) each year to target needed areas. It is primarily credited with helping to deter aphids, codling and oriental fruit moths, thrips and spider mites.
Another option is to create a spray from wormwood leaves. To do so, harvest leaves in the morning hours before flowering, and combine 1 cup of fresh leaves per half-gallon of water. Wormwood leaves can also be dehydrated or dried for storage, to create foliar teas/ sprays year-round.
*Silver in Nature is truly special, inspiring fresh perspectives and helping advance keen insight and increased sensitivity, along with higher awareness and perception. Interestingly, wormwood is also used therapeutically for ‘dislodging’ unhelpful things in bodies, so there is a special parallel there … For more information on this and other magical wonderments in Nature, see my book The Sacred Healing Alchemy of Flowers.