Late spring marks a turning point in the garden. Tomatoes swell, beans race upward and borders burst into lush abundance. Then you brush against a leaf and encounter a cloud of tiny white insects – whiteflies have arrived.
These tiny sap-sucking pests shelter beneath leaves of tomatoes, cucumbers, courgettes and other summer vegetables, multiplying rapidly in warm weather. As the RHS notes: "Glasshouse whitefly is a common sap-feeding insect, mainly of house-plants and greenhouse plants. They excrete a sticky substance (honeydew) on foliage, which allows the growth of sooty moulds."
The good news? French marigolds. Their strong scent repels whiteflies naturally, which is why gardeners have relied on them for generations.
What makes French marigolds effective against whiteflies?
Whiteflies are guided by the scent cues plants release. Strongly scented companion plants can interfere with those signals, making it harder for pests to home in on their target. French marigolds disrupt this with their pungent scent, masking the signals whiteflies rely on to find their prey. The closer they sit to vulnerable plants, the stronger the effect.
Researchers at Newcastle University identified limonene, released by marigolds, as the main component responsible for keeping tomato whiteflies at bay. Since limonene repels whiteflies without killing them, using marigolds is a eco-friendly way to ward them off.
Why are French marigolds good for gardens?
Beyond whitefly control, French marigolds flower from late spring into autumn, asking little more than sunshine, regular watering and occasional deadheading. They're excellent for pollinators too, drawing in bees and hoverflies throughout the season. They grow compact and neat, fitting happily in raised beds, borders or containers.
Where do you plant French marigolds for best results?
Practical strategies include:
- Tuck marigolds densely around area to protect, such a tomato plants, positioning one plant between every two or three plants with additional plants around the bed perimeter.
- Line greenhouse entrances with marigolds, the scent stops pests in their tracks before they reach indoor crops.
- Use pots and containers for flexibility, positioning them strategically as pest activity changes throughout the season.
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