Companion Plants for Dahlias in Containers | Good and Bad

Dahlias (Dahlia pinnata) are flowering perennials that add a splash of color to any garden from summer into fall. There are thousands of varieties of dahlia, all of which boast unique petal shapes and colorations. Their eye-catching appearance makes them ideal for garden centerpieces, but they also look great mixed with other plants. 

Dahlias can be grown in the ground but will also thrive in containers if given the correct conditions. Although they require little maintenance, the health and aesthetic appeal of dahlias in containers can be greatly improved through companion planting. 

Looking for the perfect partner for your dahlia can be somewhat of a challenge as not every species will make a great companion. Luckily for you, I have provided lots of useful information to help you find the right companions for your dahlias.

What is Companion Planting

Companion planting is the practice of growing different species of plants close together so that they will provide benefits to one another. 

This is a traditional method that was first used by Native American tribes around 10,000 years ago. It’s still widely implemented today because of the huge variety of benefits that can be achieved from companion planting. 

This method of pairing plants is an entirely natural and organic practice that can be achieved without the use of harsh chemicals. Instead, it relies on the natural characteristics of plants and places complementary species together. 

One of the oldest and most popular examples of companion planting is known as “The Three Sisters” method and is used to grow beans, sweetcorn, and squash. It was found that these three sister plants grew better as part of a symbiotic planting, instead of individually. 

As part of the legume family, beans are known as nitrogen fixers. They take nitrogen from the air and convert it to a fixed form in the soil, which the sweetcorn and squash can take up and use to help their growth.

The sturdy, upright nature of sweetcorn means it acts as a natural support structure for the beans to climb up. the squashes shade the soil with their large leaves, which help to retain moisture in the soil and reduce evaporation. The dense canopy also helps to suppress weeds, which would compete with the crops for water and nutrients. 

Companion Planting Benefits

Companion planting has a huge variety of benefits mainly because it is an organic technique that brings positive effects not only on the plant but also on the wider ecosystem. For example:

Increases Pollination: Growing a diverse range of plants in one area mimics a natural environment that is beneficial to wildlife. Combining plants that are highly attractive to pollinators with those that are not so appealing, will help bring pollinators into your garden.

The majority of the world’s food crops are pollinated by animals, namely bees, highlighting how important they are to sustain the human race. Insect diversity increases pollination, leading to a higher product yield. 

Eco-Friendly: Companion planting removes the need to use any harsh chemicals on your plants, which is better for the environment and our health. Having a variety of plants in a concentrated area also saves space and water. This is because the less bare soil there is, the less evaporation will occur. 

Reduces Pests: Rather than using chemical-based pesticides, companion planting capitalizes on the natural, pest-repelling properties of certain plants. Some plants such as mint and garlic, are heavily fragranced which deters pests. The scent can also be used to mask the smell of any plants you wish to protect from pests. 

Other plants are attractive to predator insects and can be grown to entice them and prey on pests to keep their populations down. This is known as biological pest control. 

Improves Soil Health: Plants from the “Fabaceae” family, commonly known as the legume, pea, or bean family, are nitrogen fixers. This means they absorb nitrogen from the air and convert it to a fixed form in the soil. 

Nitrogen is an essential nutrient for plant growth. Crops neighboring legumes can readily use the nitrogen they put into the soil, helping them to grow strong and healthy. 

Additionally, plants with deep roots, such as parsnips, can help to break up compact soil. This makes it more porous and well-draining, which the majority of plants favor as it recused the likelihood of waterlogging. 

Provides Shelter: Large plants can be grown among smaller ones in order to protect them from strong winds and provide shade from the harsh sun. 

Provides Support: Tall, sturdy plants like sweetcorn can be grown as a “living fence” upon which climbing species can grab onto and grow up.

Suppress Weeds: A high density of plants reduces the amount of bare soil, leaving less room for weeds to grow. This will benefit your plants as they won’t be in competition with weeds for water and nutrients. 

Considerations when Choosing Companion Plants

Prior to purchasing your companion plants, you need to consider a few different factors. Even if some plants look aesthetically pleasing when placed together, they may be incompatible.  

Growing conditions definitely need to be taken into consideration. For example, a plant that thrives in dry, hot climates would not grow well with a plant that requires damp, cool climates. Similarly, an acid-loving plant should not be planted with an alkaline-loving plant, as the health of one or both of them would be compromised. 

Growth rates are another factor to think about. A fast-growing, invasive herb like mint would make a terrible companion for a slower-growing herb such as oregano. Mint would “steal” the space, water, and nutrients meant for the oregano. 

You should also avoid growing plants that are susceptible to the same pests and diseases together. This will increase the likelihood of pest infestation and disease transfer. 

What occurs below the surface is also important. Growing deep-rooted plants like asparagus alongside shallow-rooted plants like cabbage is a good use of soil space. This way, the roots won’t be in competition for space, water, or nutrients. 

Aesthetic appeal is important to many gardeners and especially to ornamental ones. Think about the blooming season of the plants and whether they are evergreen or deciduous. For example, planting early and late-blooming perennials near each other will maximize the time flowers are on show. 

Best Companion Plants for Dahlias

There is a huge variety of companion plants for dahlias in containers. Herbs are a popular choice for providing scent and repelling pests that are attracted to dahlias. Flowering perennials will add even more color to your container and can either contrast or complement your dahlias. 

Dahlias are easy-to-grow perennials that are hardy in zones 8 to 10. They bloom from summer right into the fall, boasting their unique petals that can be white, yellow, orange, red, pink, or purple. 

Ideally, dahlias should be grown in full sun with rich, moist-well draining soil that has a pH between 6.5 and 7.0. Whilst some species can reach more than 6 feet in height, others are much shorter and ideal for growing in containers, indoors or outdoors. 

The overall health, growth, and blooms of dahlias can be improved through companion planting, and here below are some examples of excellent companion plants for dahlias: 

Snapdragon: These perennials have similar sun, soil, and pH requirements to dahlias, making them a great pairing plant. Their upright stature and distinctive blossoms provide an excellent backdrop for dahlias. They also attract a variety of pollinators. 

Cosmos: The spikey foliage of the cosmos makes a contrasting, textured background for your dahlias. They thrive in full sun and grow best in soil conditions that are similar to dahlias. 

Rosemary: The needle-like green foliage provides an aesthetic contrast to dahlias. The fragrance released by rosemary is a natural insect repellent too and will serve to deter pests not only from your dahlias but also from strongly scented lemon trees too. 

Sneezewood: Their red, daisy-like flowers bloom at the same time as dahlias and complement one another. Sneezewood can be planted with dahlias that are a similar height, to create a full display. 

Bee Balm: This plant will flourish alongside dahlias in a pot with rich, moist soil. Their strong aroma attracts a variety of pollinators such as butterflies and bees. During the summer months, the leaves of bee balm provide shade to the dahlia’s roots. 

Lantana: Very attractive to pollinators due to their vibrant colors, lantana makes a great companion plant to dahlias. It’s hardy and drought tolerant and its evergreen foliage helps retain moisture in the soil. 

Thyme: A perennial herb that provides both aesthetic and practical benefits. Thyme is a low-growing plant so its roots will not be in competition with the dahlias. Its strong fragrance repels pests and encourages pollinators. 

Nasturtium: The colorful blooms of this plant work well with dahlias and are completely edible. Nasturtium attracts aphids so can be planted as a trap crop around dahlias. They also attract beneficial pollinators like butterflies. 

Cilantro: The white flowers of this plant sit below dahlias, creating a carpet-like effect. Cilantro also naturally repels aphids, a common dahlia pest. This herb is a popular accompaniment to many dishes. 

Sweet Alyssum: When planted in pots alongside dahlias, sweet alyssum cascades over the edges. It acts as a soft, filler plant and makes the vibrant dahlias stand out. 

Fountain Grass: An ornamental grass that provides a unique contrast to the bright flowers of dahlias. Its long and feathery foliage adds height and texture to your dahlia container. 

Dahlias and Fountain Grass Companion Plants
Dahlias and fountain grass make excellent companion plants

Tulip: Blooming between spring and summer, tulips flower before dahlias meaning your container will be filled with color for longer. 

Worst Companion Plants for Dahlias

Of course, there are lots of bad companion plants that can impose negative effects on the health of your dahlias.

Below is a list of plants that you should avoid planting near dahlias:

Vining Plants: Climbing plants grow relatively fast and may grasp onto the dahlia stems which can damage them. This damage is intensified if the climbing vine has thorns. Lightweight dahlias will be unable to support the weight of a climbing plant.

Shallow-Rooted Plants: Dahlias have thin, fragile, and shallow roots. Growing plants with shallow roots near dahlias will put them in competition with one another for water and nutrients. 

Vegetables: Most vegetables are heavy feeders and will likely take up large amounts of water and nutrients from the soil, depriving the dahlias of them. This can stunt the growth and development of your dahlias. 

Thick Ground Cover Plants: Although it may look aesthetic, thick ground cover plants retain a lot of moisture in the soil, which is accentuated in a container. Heavily saturated soil can lead to the dahlias getting root rot. 

Citations

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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.