Marigolds were one of the first plants I grew from seed as a child. While my floral palette has expanded quite a bit since then, there are still plenty of reasons to grow marigolds in the garden!
For example, even if you’re not a vegetable gardener yourself, I’m willing to bet you’ve walked past a neighborhood bed or two with rows of marigolds tucked between tomatoes, cucumbers, and a host of other crops. This is because many gardeners consider marigolds to be an effective companion plant for pest control and other benefits.
In this article, I’ll explore the science behind growing these brightly colored summer flowers, and share some of the very best companion plants for marigolds.
What Is Companion Planting?
Companion planting is a way of growing different plants together in the same garden bed. The idea behind companion planting is that certain plants can benefit each other when grown together. This can happen in a number of ways:
- Some plants emit substances that deter pests. For example, marigolds are known to release chemicals that control nematodes (microscopic roundworms that live in the soil).
- Many plants attract pollinators and predatory insects. The pollinators are crucial for many fruit and vegetable crops and the predatory insects feed on aphids and other pests.
- Certain plants, especially legumes (like beans and peas), have a symbiotic relationship with bacteria in the soil that allows them to “fix” nitrogen. These plants replenish the soil over time.
- Larger plants can provide physical support for climbing plants or shade for those that don’t do well in direct sunlight. A classic example of this is the ‘Three Sisters’ garden. In this setup, corn provides a structure for pole beans to climb.
Real Benefits of Growing Marigolds
Marigolds are easily one of the most utilized companion plants out there, especially when it comes to vegetable gardens. Some gardeners plant marigolds because they think they deter insect pests. Others use these flowers to keep rabbits and other foragers away from their crops.
While companion planting as a practice is at least several centuries old, we’ve only just started to research the science (or lack thereof) behind it. And, unsurprisingly, marigolds have been the subject of many studies.
I think it’s very important to separate fact from fiction when talking about companion plants and other types of gardening. So here are the most common claims about marigolds and what the available science tells us.
Claim: Planting marigolds will keep rabbits, deer, and other wildlife away from my vegetables.
Verdict: Most experts agree that marigolds are no less appetizing to wildlife than other plants in the garden. The only real benefit of planting marigolds around your vegetable crops is that the rabbits might opt to graze on the flowers instead of your cabbages.
Claim: Marigolds release a special odor that pest insects will avoid at all costs.
Verdict: Though prevalent in many gardening spheres, researchers have been unable to prove this claim. However, marigolds do attract beneficial predatory insects (e.g., parasitic wasps, hoverflies, and ladybugs) that can help keep local pest populations under control.
Claim: The roots of marigolds release a toxic chemical that kills bad things in the soil.
Verdict: Research has shown that marigolds do produce an allelopathic compound called alpha-terthienyl. This biochemical prevents certain insects, fungi, and pathogens from thriving in the soil around the marigolds.
Claim: Growing marigolds will kill off harmful nematodes in your garden.
Verdict: According to the University of Florida, alpha-terthienyl inhibits the hatching of nematode eggs. Root lesion nematodes (Pratylenchus spp.) and root-knot nematodes (Meloidogyne spp.) are the most heavily affected. Marigolds will not, however, kill off mature nematodes within the soil.
Best Companion Plants for Marigolds
Marigolds are sun-loving flowers that prefer well-drained soil and moderate moisture. They aren’t particularly picky about soil fertility but will benefit from organic matter. When considering companion plants, choose ones that thrive under similar conditions.
Since marigolds can grow to different heights depending on the variety, consider the size and growth habits of potential companions to ensure good use of space and the overall aesthetics of your garden.
Vegetables
Tomatoes: Marigolds may control nematodes that attack tomato plants. They also attract predatory insects that feed on common tomato pests. You can also use marigolds as a trap crop around tomatoes to deter aphids.
Peppers: Like tomatoes, pepper plants will benefit from marigolds’ natural allelopathic properties and the presence of predatory insects that are drawn to the bright flowers.
Potatoes: Marigolds supposedly deter Colorado potato beetles (Leptinotarsa decemlineata) and other crop-damaging pests. Planting marigolds may bring in more beneficial insects like ladybugs and predatory stink bugs as well.
Cucumbers: Grow marigolds in your vegetable garden to distract aphids and thrips from nearby cucumber plants. Parasitic wasps, which help control cucumber beetle populations, may also be drawn to the marigold flowers.
Squash: Good pollination is often one of the biggest obstacles for home gardeners trying to grow squash. Planting marigolds and other vibrant flowers nearby is a great way to boost your garden’s pollinator activity.
Carrots: Routinely growing marigolds in your veggie patch during the off-season could decrease the number of nematodes in the soil that attack carrots. I recommend starting the marigolds early in the season and then replacing alternating rows with carrots after about 2 months.
Lettuce: If slugs often do a number on your yearly lettuce harvest, try planting marigolds close by. Slugs love marigolds and may opt to munch on the flowers instead if they’re easier to access!
Herbs
Basil: Basil and marigolds are great neighbors since they both enjoy full sun and well-draining soil. Marigolds may distract slugs that would otherwise feed on the basil. I like to combine these two plants in ornamental containers (you can still harvest the basil as needed!).
Rosemary: Rosemary is a tough perennial herb that loves the summer heat. Interplanting rosemary and marigolds might help repel some common garden pests. The contrasting foliage is also aesthetically pleasing.
Sage: Marigolds are some of the best flowering companions for sage because they easily tolerate harsh sun and poor soils. Letting your sage go to flower is a good way to draw in additional pollinators and beneficial insects.
Thyme: Interplant this low-growing perennial with marigolds to create an interesting border around other vegetables and herbs. When it comes to companion planting, Thyme is extremely aromatic and some gardeners believe the scent deters unwanted bugs. In addition, it is tolerant of a variety of growing conditions.
Dill: Dill is an excellent culinary herb to grow if your goal is to reduce pest populations in the garden! Its flowers attract a wide range of predatory insects, including lacewings and hoverflies. The foliage is also a vital food source for black swallowtail caterpillars.
Flowering Ornamentals
Nasturtiums: As one of the most popular trap crops in existence, nasturtiums pair well with marigolds for a number of reasons. Planting the two together is a wonderful way to deter aphids while adding some diverse texture to the garden.
Petunias: Though petunias have few benefits as companion plants (aside from attracting pollinators), I find them to be great marigold partners for aesthetic reasons. These annuals come in an extremely wide variety of colors and patterns for every garden design.
Salvia: Salvia plants look great grown alongside marigolds and other cottage-style flowers. They’re also very attractive to pollinators like bees and hummingbirds.
Zinnias: Zinnias, like marigolds, are bright and showy. The daisy-like flowers come in almost any color you can think of. While double and semi-double zinnias are very attractive, single blooms tend to be best for local pollinators.
Sunflowers: Companion planting sunflowers means they can tower above marigolds, adding height and contrast to your garden. They’re also great for attracting beneficial insects and birds. Just be careful not to completely shade out your marigolds.
Roses: Marigolds can help draw aphids and other pests away from rose bushes. If you’re looking for an annual to plant around your roses, I highly recommend some type of marigold.
Worst Companions for Marigolds
Marigolds are very versatile and hardy, and will happily coexist with most common garden plants. Of course, not all plants will see a benefit from growing next to marigolds. But no harm will come from planting them together anyway.
While there is no definitive list of poor marigold companions, you can rule out most ill-suited companions just by looking at their cultural needs. For instance, hydrangeas may not be the best companions for marigolds, as hydrangeas prefer cool, moist soil and may overshadow the marigolds, blocking access to sunlight.
Also, note that marigolds’ allelopathic properties might affect nearby plants just as they do microorganisms in the soil. So I don’t recommend planting marigolds in the same garden bed as delicate seedlings. Established plants shouldn’t be affected by nearby marigolds.
Are Marigolds Really Effective Against Nematodes?
Yes and no. Marigolds can certainly benefit your garden by suppressing harmful nematodes in the soil. However, the research indicates that marigolds are most effective as a cover crop and that you need to keep growing marigolds year after year to maintain the benefits.
Remember that marigolds prevent the next generation of nematodes from hatching. They don’t do anything to the mature worms. If you interplant marigolds at the same time as the rest of your garden, the nematodes will just avoid the marigolds and target other plants instead.
It’s also important to note that not all nematodes are bad. The vast majority of nematodes are actually extremely beneficial to the garden ecosystem!
If that wasn’t enough, not all types of marigolds target lesion and root-knot nematodes equally. For example: according to Louisiana State University, ‘Tangerine’ French marigolds are more effective against root-knot nematodes than other tested varieties.
Effective control often requires taking a soil sample, determining which nematode species are present, and then planting a specific marigold variety that will suppress them.
For the best results, you need to grow marigolds in your vegetable garden for at least 2 months prior to the season starting. This practice could help suppress nematode populations, so there are fewer present in the soil when it’s finally time to plant your vegetable crops. But it’s much easier said than done!
Citations
- University of Florida Effect of Marigolds on Nematodes
- Louisiana State University ‘Tangerine’ French marigolds for nematodes
Ben's horticultural interest grew when graduating from Hertfordshire University in 1997. Having contributed to numerous publications including Better Homes & Gardens, Garden Design Magazine, and The English Garden. He is also the author of Propagating Houseplants Made Easy.
