8 Perfect Cosmos Companion Plants & 5 to Avoid

As a dedicated urban gardener, my journey into the world of gardening started in my childhood, surrounded by the beauty of greenery. My passion lies in transforming my small backyard into a vibrant oasis, focusing on the sustainable practices of companion planting. Today, I’m excited to share my insights on cosmos companion plants, highlighting 8 perfect companions that will enhance the beauty and health of your cosmos, as well as 5 plants to avoid to keep your garden flourishing.

Best Cosmos Companion Plants

Marigolds

Marigolds are a gardener’s best friend when planted alongside cosmos. Their ability to repel pests and nematodes makes them invaluable. These vibrant flowers thrive in similar conditions as cosmos, requiring plenty of sunlight and well-draining soil.

• Planting Instructions:
  1. Plant marigolds in full sun, where they can bask alongside your cosmos.
  2. Space the seeds or seedlings 8-10 inches apart to allow for growth and airflow.
  3. Water regularly, ensuring the soil is moist but not waterlogged.

Explore more about these vibrant protectors in our detailed post on marigold companion plants – definition of beauty.

Basil

Basil not only enhances the flavor of your dishes but also the health of your cosmos. This aromatic herb repels mosquitoes and flies, providing a protective shield over your garden.

• Planting Instructions:
  1. Plant basil around your cosmos to create a living barrier against pests.
  2. Ensure both plants receive at least 6 hours of sunlight daily.
  3. Keep the soil moist, and mulch around the basil to retain moisture.

Dive deeper into the symbiotic relationship between basil and other plants by reading our article on basil companion plants – choosing the right companions.

Lavender

Lavender‘s soothing fragrance does more than just attract bees; it also wards off unwanted insects. Planting lavender near your cosmos can create a serene and protective environment for your garden.

• Planting Instructions:
  1. Choose a sunny spot for both your lavender and cosmos, ensuring they have room to breathe and grow.
  2. Water moderately, as lavender prefers drier conditions compared to cosmos.
  3. Trim the lavender back in early spring to encourage fresh growth and better airflow.

Learn about the benefits of planting lavender in your garden in our lavender companion plants post.

Zinnias

Zinnias and cosmos share a love for the sun and an ability to attract pollinators. This makes zinnias a colorful and beneficial companion for your cosmos.

• Planting Instructions:
  1. Sow zinnia seeds directly into the garden alongside your cosmos for a vibrant display.
  2. Space them at least 12 inches apart to give each plant ample room to flourish.
  3. Water regularly, especially during dry spells, to keep both plants happy.

For more information on zinnia companions, check out our insights on zinnia companion plants.

Sunflowers

Sunflowers stand tall and proud, offering more than just their striking appearance. They serve as natural trellises for climbing plants and can provide shade for cosmos during the hottest parts of the day, reducing stress on the plants.

• Planting Instructions:
  1. Plant sunflower seeds in a location that receives full sun, ideally on the north side of your cosmos, so they don’t cast too much shade.
  2. Space sunflowers about 18-24 inches apart to ensure adequate room for growth.
  3. Water deeply but infrequently to encourage strong root development.

For further insight into the companionship between sunflowers and other garden plants, check out our detailed guide on best 13 sunflower companion plants.

Nasturtiums

Nasturtiums are not only a beautiful ground cover but also a superhero in the garden, repelling a variety of pests that might otherwise target your cosmos. Their bright flowers attract beneficial pollinators, creating a more dynamic ecosystem around your cosmos.

• Planting Instructions:
  1. Sow nasturtium seeds directly into the soil around the base of your cosmos to create a living mulch.
  2. Keep the soil moist until the seeds germinate and the plants are well established.
  3. Nasturtiums prefer poorer soils, so avoid fertilizing heavily around these companions.

Discover more about nasturtium and its companion planting benefits by visiting our post on nasturtium companion plants.

Alyssum

Alyssum, with its delicate carpet of flowers, offers a striking contrast to the tall, airy cosmos. It attracts beneficial insects, including hoverflies and lacewings, which help control pest populations.

• Planting Instructions:
  1. Plant alyssum seeds or seedlings around the base of your cosmos for a beautiful, low-growing floral carpet.
  2. Alyssum prefers full sun to partial shade and will happily bloom throughout the season.
  3. Water regularly, allowing the soil to dry out slightly between watering sessions.

Engage with the tiny but mighty alyssum further by exploring our alyssum companion plants guide.

Chives

Chives bring more than just culinary delight; they also repel pests with their oniony scent, protecting your cosmos from unwanted invaders.

• Planting Instructions:
  1. Plant chives in close proximity to your cosmos to take advantage of their pest-repellent properties.
  2. Chives thrive in full sun and well-draining soil, conditions that cosmos also enjoy.
  3. Regular harvesting of chives promotes growth and prevents the plants from taking over the garden.

Learn about the symbiotic relationship between chives and other garden plants in our guide to chive companion plants.

Plants to Avoid Planting with Cosmos

Fennel

Fennel is notorious for being a poor neighbor in the garden due to its allelopathic properties, which can inhibit the growth of surrounding plants, including cosmos.

• Why to Avoid:
  1. Fennel’s root system releases substances that might stunt the growth of cosmos.
  2. It tends to attract specific pests that could potentially harm nearby plants.

Before planning your garden layout, consider our advice on fennel companion plants to avoid unwanted interactions.

Walnut Trees

The allelopathic chemicals in walnut trees, primarily juglone, can be toxic to cosmos, inhibiting their growth and potentially leading to their demise.

• Why to Avoid:
  1. Juglone can cause cosmos and other sensitive plants to wilt and die.
  2. The extensive root system of walnut trees competes for water and nutrients, further disadvantaging cosmos.

Mint

While mint is known for its vigorous growth and pest repellent qualities, it can quickly become invasive, outcompeting your cosmos for space and resources.

• Why to Avoid:
  1. Mint spreads rapidly through runners, which can overtake the root system of cosmos.
  2. Its aggressive growth habit requires frequent pruning to prevent it from overwhelming cosmos and other nearby plants.

Before adding mint to your garden, consider reading our comprehensive discussion on mint companion plants to understand its behavior in the garden.

Cabbage

Cabbage and other brassicas can attract pests that may also target cosmos, such as aphids and cabbage worms, making them less-than-ideal neighbors.

• Why to Avoid:
  1. The specific pests attracted by cabbage can easily migrate to your cosmos, causing damage.
  2. Both plants have different watering and nutritional needs, which can complicate garden management.

For gardeners interested in growing cabbage, our article on best and worst cabbage companion plants offers valuable insights on creating a harmonious vegetable garden.

Companion Planting Chart for Cosmos

Below is a concise table summarizing the good companions for cosmos, highlighting why they make great partners in your garden. This guide aims to provide a quick reference for planning your garden layout to ensure mutual benefits among your plants.

Good Companions	Why They’re Great Together
Marigolds	Deters pests with their scent, adds vibrant color, and promotes a healthy garden ecosystem.
Basil	Repels mosquitoes and flies with its aromatic leaves, enhancing the growth environment for cosmos.
Lavender	Attracts pollinators like bees and butterflies, while its scent deters pests, creating a protective barrier around cosmos.
Zinnias	Provides a habitat for beneficial pollinators, enhancing biodiversity and aiding in pollination.
Sunflowers	Acts as a natural trellis for climbing plants and offers shade, reducing stress on cosmos during peak sun hours.
Nasturtiums	Repels various pests with their peppery scent, while their bright blooms attract pollinators, enhancing the garden’s appeal and health.
Alyssum	Attracts beneficial insects that control pest populations, providing ground cover that enhances soil moisture retention around cosmos.
Chives	Emit a scent that repels pests, including aphids, and their purple flowers add an extra layer of beauty to the garden, creating a symbiotic relationship with cosmos by deterring unwanted visitors and attracting pollinators.

This table encapsulates the essence of companion planting, demonstrating how each plant can contribute to a thriving garden when paired with cosmos. The choice of companions can influence not only the health and yield of your cosmos but also the overall biodiversity and beauty of your garden space. Remember, the principles of companion planting extend beyond just aesthetics, fostering an environment where plants support each other’s growth and resilience against pests and diseases.