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a photo of a ladybug on garden soil by owlcreek.ca

Natural Pest Control Through Companion Planting

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This is part 6 of 8 in the series Companion Planting

Every gardener knows the frustration of seeing precious seedlings demolished by pests, underscoring just how essential pest control is in maintaining a healthy garden. In Alberta’s Zone 3, where the growing season is already limited, safeguarding your plants from insects and diseases can make the difference between a bumper harvest and a disappointing yield. While pesticides might offer a quick fix, they can have negative impacts on soil health, beneficial organisms, and even pollinators. Instead, companion planting provides an organic, sustainable strategy for keeping pests under control by leveraging nature’s own checks and balances. By selecting the right plant partnerships and encouraging beneficial insects, you create a garden ecosystem where harmony—not havoc—prevails.


an image of ladybugs attacking aphids in a garden by owlcreek.ca made in DALL-ECommon Zone 3 Garden Pests

Zone 3 gardeners regularly contend with a handful of notorious pests that thrive in cooler climates. Cabbage moths, for example, lay their eggs on brassicas such as cabbage, kale, and broccoli. The small green caterpillars that emerge can skeletonize leaves in a matter of days, leaving behind ragged plants and substantially reduced yields. Aphids are another widespread nuisance—tiny, sap-sucking insects that cluster on the undersides of leaves and can stunt growth or transmit plant viruses. They flourish in mild weather and multiply quickly, so a few aphids can turn into a full-blown infestation almost overnight.

Another formidable intruder is the squash vine borer, which primarily attacks squash, zucchini, and pumpkins. The adult borer is a clearwing moth that lays eggs at the base of the plant’s stems. Once the eggs hatch, larvae tunnel into the stem, cutting off water and nutrient flow and often causing the plant to wilt rapidly. Early warning signs include small holes near the base of the stem and a sawdust-like residue (frass). Covering young plants with row covers, using resistant varieties, and practicing regular crop rotation are effective ways to mitigate vine borer damage.

Other common Zone 3 pests include flea beetles, which pepper leaves with tiny holes, giving them a “shotgun” appearance, and cutworms, which often lurk in the soil and cut through the stems of seedlings at ground level. Knowing how to spot early signs of infestation—such as yellowing or curling leaves for aphids, frass for cabbage moth larvae, or sudden wilting for vine borers—can help you act quickly. The sooner you address pests, the easier they are to control without resorting to chemicals. By recognizing these symptoms and understanding which insects are likely to appear, you can plan your companion planting strategy to deter them from the start.


Key Companion Plants for Pest Control

One of the most effective ways to discourage pests is to plant crops they dislike or find confusing. Marigolds are a prime example: they’re best known for repelling nematodes in the soil, but their scent and chemical secretions are also believed to deter aphids and whiteflies. Planting marigolds in and around your vegetable rows introduces a protective barrier and adds a burst of color, attracting pollinators while pushing pests away. Another protective companion is nasturtiums, which serve as an excellent “trap crop.” Aphids and flea beetles seem to love nasturtiums even more than they love your vegetables, so the pests congregate on these sacrificial plants, leaving your main crops relatively unscathed. Nasturtiums’ bright, edible blooms also add a decorative touch to the garden.

Meanwhile, members of the allium family—garlic, onions, and chives—are remarkable multitaskers. They exude strong sulfur compounds that repel a wide range of insects, from aphids to Japanese beetles, while also adding flavor to your harvest basket. Placing garlic or onions near susceptible crops like lettuce, tomatoes, or cabbage can make those vegetables less appealing to pests that rely on scent to locate their meals. Plus, alliums are fairly easy to grow in Zone 3, performing well in raised beds and coming back year after year if you allow a few bulbs to reseed.


Beneficial Insects & How to Attract Them

an image of ladybugs attacking aphids in a garden by owlcreek.ca made in DALL-ECompanion planting isn’t just about repelling unwanted bugs; it’s also about welcoming beneficial insects that help keep pest populations under control. Ladybugs, for instance, are voracious predators of aphids, devouring hundreds of them per day. Lacewings target small, soft-bodied insects such as thrips and mealybugs, while parasitic wasps lay their eggs inside caterpillars or aphids, effectively neutralizing these threats. To attract these valuable garden allies, you’ll want to provide them with sources of nectar, pollen, and shelter.

Flowers and herbs rich in nectar—like dill, fennel, cosmos, and sweet alyssum—offer a buffet for adult beneficial insects. Even allowing a few of your culinary herbs (basil, cilantro, oregano) to bloom can make your garden more appealing to pollinators and natural predators alike. Creating small “wild” patches of native flowers or ground covers also gives these insects a place to hide and breed. The idea is to cultivate a balanced ecosystem where beneficials are present in sufficient numbers to keep pests in check, long before those pests can become an overwhelming problem.


Organic Pest Control Methods

Sometimes, even with the right companion plants, you may need a bit of extra intervention. Manual removal is a tried-and-true approach for dealing with pests like cabbage caterpillars: simply inspect the undersides of leaves regularly, pick off any eggs or larvae, and dispose of them. A quick spray of water can dislodge aphids from leaves, reducing their numbers significantly in just a few days. Homemade sprays, such as a dilute solution of mild dish soap or a garlic-and-chili mixture, can also help deter insects without causing harm to pollinators and other wildlife.

In more severe cases, biological controls—like introducing ladybugs or parasitic nematodes—can be highly effective. Parasitic nematodes target soil-dwelling pests such as cutworms, while ladybugs can be purchased and released directly in the garden. While these methods cost more upfront, they are significantly safer than broad-spectrum pesticides, which often kill beneficial insects along with the pests. The key is to avoid chemicals that disrupt the garden’s natural balance. By working with companion planting and natural controls, you encourage a thriving biosphere that’s resilient enough to handle minor pest pressures on its own.


Natural pest control through companion planting requires patience, experimentation, and a commitment to nurturing biodiversity. When you focus on encouraging beneficial insects, interplanting pest-deterrent species, and avoiding harsh chemicals, you create a garden that harmonizes with nature rather than struggling against it. The result is a healthier, more balanced space where plants, insects, and even soil microbes work together—making the most of Zone 3’s short growing season while still delivering a generous and sustainable harvest.

Amy
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