Marigolds (\(Tagetes\) species) and strawberries (\(Fragaria\) \(\times\) \(ananassa\)) are indeed excellent companions in the garden, forming a beneficial relationship known as companion planting. This practice involves growing different plants together to enhance growth, provide natural pest control, or improve soil health for one or both species. The pairing of these two plants is often cited for its potential to improve the overall vigor and productivity of the strawberry patch. This positive association is primarily due to the marigold’s unique ability to influence the soil environment and attract beneficial insects. The effectiveness of this pairing depends on understanding the specific biological mechanisms at play and implementing proper planting techniques.
The Science Behind Marigold Pest Control
Marigolds are widely recognized for their ability to suppress plant-parasitic nematodes, which are microscopic roundworms that attack plant roots. This defense mechanism is an example of allelopathy, where a plant releases chemical compounds that affect the growth of other organisms. The key compound responsible for this action is alpha-terthienyl, a naturally occurring substance exuded from the marigold roots into the surrounding soil. This chemical acts as a nematicide, creating oxidative stress within the nematode’s body and ultimately leading to their mortality. The most significant effect is seen on root-knot nematodes (\(Meloidogyne\) species) and lesion nematodes (\(Pratylenchus\) species).
For maximum nematode suppression, the marigolds must be grown densely for a full season, often as a cover crop, and then tilled into the soil to release the highest concentration of the compound. When marigolds are intercropped, or planted directly alongside strawberries, the impact on soil nematodes is generally less pronounced than a full-season cover crop rotation. However, the continuous presence of the living marigold roots still provides a measurable suppressive effect on nematode populations in the immediate root zone. This ongoing release of alpha-terthienyl contributes to a healthier soil environment, particularly beneficial in perennial plantings like strawberry beds.
Specific Benefits for Strawberry Health
Nematode Control
The primary advantage of planting marigolds near strawberries is the control of root-knot nematodes, which can cause significant damage to the strawberry root system. Nematode feeding leads to the formation of galls and lesions on the roots, disrupting the plant’s ability to absorb water and nutrients. This results in stunted growth, wilting, and reduced fruit yield in strawberry plants. By reducing the nematode population, marigolds help the strawberry plants develop a more robust and efficient root structure, leading to improved plant health and fruit production. The pairing offers a non-chemical form of pest management, supporting a more sustainable gardening approach.
Above-Ground Benefits
Marigolds also provide secondary benefits above ground by attracting a variety of beneficial insects with their bright, open flowers. Pollinators such as bees are drawn to the blooms, which can simultaneously improve the pollination rate and subsequent fruit set of the nearby strawberry flowers. Additionally, the flowers attract predatory insects like hoverflies and ladybugs. These beneficial insects are natural predators of common strawberry pests, including aphids and thrips. The strong scent emitted by the marigold foliage is also believed to repel certain herbivorous insects and even larger garden nuisances like rabbits.
Essential Planting and Care Guidelines
Variety Selection and Density
To maximize the benefits of this companion planting, selecting the correct variety of marigold is important. French Marigolds (\(Tagetes\) \(patula\)) are generally considered the most effective type for nematode control, often outperforming the larger African Marigolds (\(Tagetes\) \(erecta\)). Specific cultivars bred for high nematicidal properties, such as ‘Nemagold’ or other dense-rooting French varieties, are the best choice. For nematode suppression, the marigolds need to be planted with a high density, spaced about seven inches apart, to ensure a sufficient concentration of alpha-terthienyl is released into the soil. While intercropping provides some benefit, the most significant nematode control is achieved by using marigolds as a full cover crop rotation before the strawberries are established.
Growing Conditions and Maintenance
Both strawberries and marigolds require full sun exposure, meaning at least six hours of direct sunlight daily, and thrive in well-drained soil. Marigolds should be planted early in the season, soon after the last frost, to allow their root systems time to develop and begin releasing their defensive compounds. Consistent, moderate watering is necessary for both plants, as waterlogged conditions can promote fungal issues. When interplanting, ensure the marigolds do not become so large that they shade out the lower-growing strawberry plants, which would negatively affect fruit production. Choosing dwarf varieties of marigolds can help manage this competition for light and space, and regularly removing spent flowers will encourage continuous blooming.