Dahlias (Dahlia pinnata) are perennial flowers that are native to Mexico meaning they flourish in warm, sunny climates. These plants are winter hardy in zones 8 to 11. Picking a favorite dahlia can be difficult as they come in a broad array of colors, shapes, and sizes.
Due to their diverse range, dahlias alone can make for a very striking display. However, they really shine when paired with complementary or contrasting companion plants.
From herbs to flowers to vegetables, choosing a companion plant from the vast array of options can be somewhat of a challenge. This is why I have compiled a list of species that make the best companion plants and why, as well as those you should steer clear of.
Companion Planting Explained
Companion planting is the practice of growing two or more different plant species together, with the aim they will provide benefits to one another. In this way, the overall growth and health of the plants will be improved in an organic way, without the need for harsh chemicals.
Native American tribes first practiced companion planting around 10,000 years ago to help improve their crop yield. Since then, companion planting has been widely adopted all over the world. Although it is commonly used for crop plants, it can also be implemented in your garden to aid aesthetic appeal.
One of the most famous examples of companion planting involves growing beans, sweetcorn, and squash together. This is known as the “Three Sisters” method. Each crop plant benefits another in a certain way which ultimately benefits the grower.
Beans belong to the legume family, all of which are nitrogen fixers. This means they take nitrogen from the air and converted it into a fixed form in the soil. Sweetcorn and squash can use this nitrogen to help them grow big and strong.
Sweetcorn grows tall and sturdy. It acts as a living, structural support upon which the beans can climb up. Squash plants grow low to the ground meaning they won’t be in competition with the beans and sweetcorn for sunlight.
Squashes have large, dense leaves which shade the soil, helping to retain moisture and suppress the growth of weeds.
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Companion Planting Benefits
There are a number of reasons why implementing companion planting in your backyard is a great idea. Although it was traditionally used to maximize crop yield, the concept is also highly effective for a number of ornamental plant species, including dahlias.
Here are some of the biggest benefits you can gain from companion planting:
Pest Control: A number of plants naturally deter common garden pests by releasing strong scents or potent chemicals. This eliminates the need to use chemical-based pesticides.
Other plants attract predator insects which will feast on the pest insects, keeping their numbers down. This is known as biological pest control.
Improves Soil Health: Beans, peas, and lentils, collectively known as legumes, belong to the “Fabaceae” family. These plants are nitrogen fixers which means they take nitrogen from the air and convert it into a fixed form in the ground. Nitrogen is an essential nutrient for plant growth. Surrounding species can capitalize on this nitrogen fixation to help them grow.
Additionally, deep-rooted plants can penetrate far into the soil which helps to break it up. Less compact soil means it will drain much better, helping to prevent waterlogging from occurring which will kill most plant species.
Improved Aesthetics: Commonly, companion planting for ornamental species is purely aesthetic. By mixing annuals and perennials together you can ensure your garden has a prolonged blooming period.
Moreover, evergreen, low-lying shrubs make a wonderful backdrop for vibrant flowers. You can also choose to create displays that are either complementary or contrasting.
Enhances Pollination: High pollinator diversity is obtained through having a diverse range of plants. Generally, pollinators are attracted to brightly colored and highly scented plants. Not only will these look stunning in your garden but also attract pollinators.
Reduces Competition: Unlike monocultures which see lots of the same species being grown in one area, companion planting is a form of polyculture. Different species require different amounts of nutrients, reducing competition for them. Additionally, the roots of different plants can uptake water and nutrients at varying depths.
What to Consider When Companion Planting
When deciding on companion plants for your dahlias, there are a few things you need to consider beforehand. Not every plant will make a great Dahlia companion.
Think about the conditions in which your plants will be grown. A plant that thrives in a hot and arid environment would not grow well with a plant that requires a cool and wet climate.
Soil type is another important factor. A plant that needs acidic soil should not be grown with a plant that needs alkaline soil The plant with the less favorable conditions simply will not thrive and potentially both could suffer.
With ornamental gardens, aesthetic appeal is very important. Think about the type of look you are trying to achieve. Do you want a display of flowers in similar hues or do you want to focus on plants that bring unique and clashing textures to your garden?
Plant seasonality is another factor to consider regarding aesthetic appeal. Growing early-blooming species with late bloomers will ensure you have flowers for most of the year.
Likewise, incorporating evergreens into your display will inject life into your garden during the fall and winter.
Individual plant characteristics are another determiner of whether plants will make good companions or not. Fast-growing plants may become invasive and engulf slow-growing species if planted next to them.
Growing plants with different root depths and lengths will reduce the competition for nutrients and water in the soil. If a plant needs lots of sunlight to grow, you should avoid planting it near a species that will cast lots of shade upon it.
Best Companion Plants for Dahlias
The best companions for dahlias will be those that thrive in similar conditions so choose plants that grow best in a warm, sunny but sheltered spot, and fertile, moist soil that is well-draining. Ideally, the soil should be neutral to slightly acidic.
Dahlias come in a variety of colors and petal patterns. Generally, they flower from summer through until the frosts hit in the fall. These tender perennials can grow anywhere from 1 foot to 6 feet. They boast a beautiful flower atop a leggy stem. As such, short and full plants can fill out the display and support the slender stems.
From my experience, I have found ideal dahlia companions are those that bloom early or repel insect pests. Below are some of the best companion plants for dahlias:
Aster: Dahlias and asters belong to the same family and require similar growing conditions. Just like dahlias, asters will also attract lots of pollinators to your garden and – as seen in the picture above – make for a fabulously colorful summer display in beds and borders.
Thyme: This perennial herb provides aesthetic and practical benefits. Thyme is low growing and will add some texture and density around the dahlia’s leggy stems. Thyme also gives off a strong scent, which to us smells wonderful but repels insects’ pests.
Globe Thistle: This ornamental perennial can be grown as a stand-alone centerpiece but also provides great contrast against dahlias. The thorny foliage of the globe thistle deters grazers such as deer and rabbits. Its purple blooms also attract many pollinators.
Marigolds: The unique scent of marigolds repels many insect pests. Marigolds grow low to the ground and act as great filler plants around tall dahlias. The fiery blooms of marigolds also look stunning against dahlia blooms.
Sweet Alyssum: The dense foliage and small, delicate flowers make sweet Alyssum ideal for ground cover around dahlias. It will help keep the soil moist and cool during the summer months. Sweet alyssum is also low-maintenance and drought-tolerant, meaning it won’t be in competition with your dahlia for water.
Rosemary: The needle-like foliage of rosemary provides great cover and texture among your dahlias. The fragrant scent of rosemary gives off also repels insect pests.
Fountain Grass: Instead of other flowers, why not incorporate ornamental grasses into your display to add interest and texture? Purple fountain grass boasts long, feathery blooms that last into the fall after dahlias have died. Their look contrasts wonderfully together.
Anise: This evergreen shrub will ensure life in your garden even when your dahlias have died back. Anise attracts a variety of beneficial insects, including predatory wasps. These wasps prey on insect pests like aphids that feast on dahlias.
Bee Balm: Like dahlias, bee balm also requires rich and moist soil. The strong scent given off by bee balm attracts a number of pollinators. The leaves of this plant also provide shade and help retain moisture in the soil during the summer months.
Cosmos: These hardy annuals tolerate a variety of soil conditions and have similar environmental requirements to dahlias. They make perfect pairing plants because they will not be in competition with one another for resources.
Cosmos foliage can also help to fill out the display.
Cilantro: This edible herb thrives in the same environmental conditions as dahlias. The thick foliage and white flowers make a great filler plant for dahlias. Cilantro acts as a natural pest control through its strong aroma and by attracting insect predators.
Nasturtium: The vibrant blooms of this plant complement dahlias. Nasturtium attracts aphids so can be planted as a trap crop around dahlias to help protect them. Nasturtium also attracts a number of pollinators.
Daylily: The large blooms of daylilies come in a variety of colors that can either contrast or complement your dahlias. Daylilies do not grow as tall as dahlias so look best when planted in front of them. they also add some structure to the leggy dahlia stems.
Worst Companion Plants for Dahlias
Although there are plenty of great companion plants for your dahlias, there are a handful of plants you should avoid. Below is a list of bad companion plants for dahlias:
Fruit and Vegetables: As well as beneficial insects, dahlias attract a lot of pests. This means any crop plants grown alongside them will be very vulnerable to pest infestations.
Grasses: Fast-spreading and thick ground cover plants like grasses can deprive the dahlias of water and nutrients. Over time they can choke out the dahlias.
Heavy Feeders: Dahlias are heavy feeders themselves so planting them with other heavy-feeding plants will mean they are in competition for nutrients and water. This can inhibit the growth and development of one or both plants. You can apply a fertilizer suited to dahlia, which can help in this situation.
Climbing Plants: Dahlia stems are long, thin, and fragile. Vining plants may try to climb up their stems, which can damage or even break them.
Citations
- Britannica Encyclopedia – Dahlia
- Harvard University – Legumes
- USDA – Three Sisters
