Introduction
There is nothing quite like the excitement of seeing the first dahlia buds begin to swell in mid-summer. As these garden superstars prepare to take center stage with their dinnerplate-sized blooms and intricate geometric petals, the right supporting cast makes all the difference. At Longfield Gardens, we believe that while dahlias are spectacular on their own, they truly shine when paired with companions that highlight their colors and provide interest while the tubers are still waking up.
In this guide, we will explore the best annuals, perennials, and herbs to plant alongside your dahlias to create a lush, multi-layered landscape. Whether you are looking to deter pests, fill in gaps at the base of tall stalks, or create breathtaking floral arrangements, choosing the right neighbors is the key to a rewarding season. Understanding a few basics about sun and soil will help you design a garden that thrives from early summer through the first frost.
The Secret to Great Dahlia Companions
Before picking out specific plants, it is helpful to understand what a dahlia needs from its neighbors. Dahlias are "heavy feeders," which simply means they require a lot of nutrients and water to produce those massive, colorful flowers. Because of this, their best companions are plants that play well with others without being overly aggressive or "resource hungry."
The most successful pairings follow the "right plant, right place" rule. Dahlias need at least six to eight hours of direct sunlight and soil that drains well—meaning the water moves through it easily rather than sitting in puddles. When we choose companions, we look for plants that enjoy these same sunny, well-drained conditions.
Spacing is the other quiet winner in a mixed dahlia bed. Most dahlias grow into substantial plants, often reaching three to five feet in height and two feet in width. Giving them enough "breathing room" prevents issues like powdery mildew by allowing air to circulate between the leaves. Your companion plants should be tucked in around the base or set slightly forward in the border to ensure every plant has the space it needs to breathe.
Key Takeaway: Choose companions that share the dahlia's love for full sun and well-drained soil, but ensure they aren't so aggressive that they steal all the nutrients from your tubers.
Annuals for Texture and Color Contrast
Annuals are perhaps the most popular choice for dahlia companions. Because they grow and bloom in a single season, their lifecycle perfectly mirrors that of the dahlia. They provide instant gratification and can be easily swapped out each year as you experiment with new color palettes.
Airy Fillers: Cosmos and Verbena Bonariensis
Dahlias often have heavy, dense foliage and solid, bold blooms. To balance this, we love using "airy" plants that add a sense of movement.
- Cosmos: With their feathery, fern-like leaves and delicate daisy-shaped flowers, cosmos act like a soft cloud around the structured stems of dahlias. They fill the gaps between plants without creating a wall of heavy greenery.
- Verbena bonariensis: This plant is a favorite in our trial gardens. It features tall, wiry stems topped with clusters of tiny purple flowers. Because the stems are so thin, you can plant them right in front of your dahlias; they create a "see-through" effect that adds depth to the garden without hiding the main attraction.
Ground Covers: Sweet Alyssum and Nasturtiums
The bottom foot of a dahlia plant can sometimes look a bit bare or "leggy" as the season progresses. Low-growing annuals act as a living mulch, keeping the soil cool and hiding the bases of the stalks.
- Sweet Alyssum: This is a fantastic "spiller" for the front of the bed. It forms a low carpet of tiny, honey-scented white or purple flowers. It is excellent for attracting pollinators and covers the soil beautifully.
- Nasturtiums: These are dual-purpose companions. Their round, shield-like leaves provide a lovely texture contrast, and their bright orange or red flowers are cheerful. Many gardeners use them as a "trap crop," as they tend to attract aphids away from the dahlias.
Sophisticated Spikes: Snapdragons and Cleome
To create a professional-looking garden bed, you want to vary the shapes of your flowers. Since dahlias are usually round or star-shaped, adding vertical spikes creates visual excitement.
- Snapdragons: These bloom early and often provide a pop of color while the dahlias are still just green mounds of leaves. They come in almost every color imaginable, making it easy to coordinate with your favorite dahlia varieties.
- Cleome (Spider Flower): For taller dahlia varieties like 'Thomas Edison' or 'Emory Paul', cleome is a wonderful backdrop. Its tall stalks and unique, whiskered blooms provide a mid-to-back-of-the-border interest that matches the dahlia’s grand scale.
Perennials for Seasonal Succession
Perennials are the backbone of the garden, returning year after year. When pairing perennials with dahlias, the goal is often "succession planting"—choosing plants that bloom at different times so the garden is never without a focal point.
Early Season Stars: Peonies and Oriental Lilies
Dahlias take their time to get started. Usually planted in late spring, they don't hit their stride until mid-to-late summer.
- Peonies: These bloom in late spring and early summer. By the time the peony flowers fade, the dahlia foliage is growing tall enough to hide the spent peony leaves. It’s a perfect hand-off of the "blooming baton."
- Oriental Lilies: Lilies often bloom in mid-summer, just as the first dahlias are beginning to open. The fragrance of the lilies compensates for the fact that most dahlias are unscented.
Late Season Partners: Salvia and Phlox
- Salvia: Many varieties of perennial salvia, such as 'May Night', produce upright spikes of deep blue or purple. This vertical form provides a stunning contrast to the mounded shape of a dahlia. Butterflies and hummingbirds also love salvia, bringing even more life to your garden.
- Tall Garden Phlox: Phlox offers large, fragrant flower heads in shades of pink, white, and purple. They bloom during the height of dahlia season, creating a lush, cottage-garden look that feels full and romantic.
Ornamental Grasses for Softness
We often suggest incorporating ornamental grasses like Pennisetum (Fountain Grass) or Panicum (Switchgrass). The fine texture of the grass blades and the soft, bottle-brush seed heads in late summer provide a neutral "breathing space" between vibrant dahlia colors. This prevents the garden from looking too busy or overwhelming.
What to do next:
- Identify the "empty" windows in your garden's bloom schedule.
- Choose 1-2 perennials that bloom during those quiet times.
- Plant them at least 18-24 inches away from where you plan to put your dahlia tubers to avoid root competition.
Functional Companions: Herbs and Pest Deterrents
Gardening is about more than just looks; it’s also about creating a healthy ecosystem. Some of the best plants to go with dahlias are those that help keep the "bad bugs" away or attract "good bugs" that do the work for you.
Herbs as Natural Protectors
- Artemisia: This silvery foliage plant is more than just pretty. Its scent is known to be unappealing to slugs and snails, which are the primary enemies of young dahlia shoots. Planting a border of Artemisia 'Powis Castle' or 'Silver Mound' around your dahlia patch can create a protective barrier.
- Cilantro and Anise: When these herbs are allowed to go to flower (bolting), they produce flat, umbrella-like clusters of tiny blossoms. These flowers are a magnet for predatory wasps and hoverflies, which are natural enemies of aphids—a common dahlia pest.
- Basil: Not only does basil smell wonderful, but it also thrives in the same hot, sunny conditions that dahlias love. It fills in the mid-layer of the garden with lush green or deep purple leaves.
Attracting Pollinators
While many modern dahlias are so full of petals that bees struggle to find the nectar, planting "open" flowers nearby ensures your garden remains a haven for pollinators. Single-flowered dahlias (like the 'Happy Single' series) are great for this, but you can also supplement with:
- Agastache (Hyssop): This perennial is a hummingbird favorite. Its licorice-scented leaves and spiked flowers are a great addition to any sunny bed.
- Zinnias: Like dahlias, zinnias come in a wide array of colors and are very easy to grow from seed. They are absolute magnets for butterflies, especially the large Monarchs and Swallowtails that visit in late summer.
Designing by Color and Height
One of the most enjoyable parts of gardening is playing with color. Because we offer dahlias in everything from soft pastels to moody dark bicolors, the pairing possibilities are endless.
The Romantic Pastel Garden
If you love the creamy, blush tones of 'Cafe au Lait' or the soft pink of 'Lucky Number', pair them with silver and white companions.
- Dusty Miller: Its silver, velvety leaves act as a neutral "ribbon" that makes pastel colors pop.
- White Sweet Alyssum: This creates a clean, bright border that feels fresh and classic.
- Silver Sage: Large, fuzzy silver leaves provide a dramatic texture contrast to the smooth green dahlia foliage.
The "Hot" Tropical Border
For a high-energy garden featuring fiery reds, oranges, and yellows (like the cactus-flowered 'Vwu' or 'Color Spectacle'), look for bold companions.
- Canna Lilies: With their massive leaves and tropical blooms, cannas match the dahlia's "bigger is better" energy.
- Crocosmia: These produce arching wands of bright red or orange flowers that look like flickering flames among the dahlia leaves.
- Dark-Leaved Plants: Plants with burgundy or "black" foliage, such as certain varieties of Heuchera or dark-leaved Coleus, make bright red and orange flowers look even more intense.
Managing the Height
Always place your tallest dahlias in the back of the border or in the center of a circular island bed. Use mid-height companions (like Phlox or Zinnias) to bridge the gap between the tall stalks and the ground. Finally, finish with low-growing "spillers" at the very edge. This "stair-step" approach ensures that every plant gets the sun it needs and nothing is hidden from view.
Practical Tips for Planting Success
To get the most out of your dahlia combinations, timing and technique are just as important as the plants you choose.
Start with Warm Soil
A common mistake is planting companions too early while the soil is still cold. Dahlias are tropical plants at heart and won't start growing vigorously until the soil temperature reaches about 60°F. Wait until the danger of frost has passed before planting your annual companions or moving your dahlias into the ground.
Water Deeply, Not Constantly
Dahlias and their companions prefer a deep soaking once or twice a week rather than a light sprinkle every day. This encourages the roots to grow deep into the soil, making the plants more resilient during hot spells. If you are growing in containers, you will need to water more frequently, as pots dry out much faster than the ground.
Mulching for Moisture
Once your dahlias and companions are established, a layer of organic mulch (like shredded bark or compost) helps keep the soil moist and suppresses weeds. Just be sure to keep the mulch a few inches away from the dahlia stems to prevent rot. For additional guidance, see this guide to mulching dahlias.
Key Takeaway: Success comes from matching the timing of your planting to your local weather and ensuring all plants have enough space and deep water to thrive during the heat of summer.
Plants to Avoid Growing with Dahlias
While dahlias are generally easy-going, there are a few types of plants that do not make good neighbors.
- Shade Lovers: Plants like Hostas, Bleeding Hearts, or Ferns require cool, shady spots. Since dahlias need full sun, these plants would likely scorch or wilt if planted in the same bed.
- Bog Plants: Plants that like "wet feet," such as certain Irises or Marsh Marigolds, are a poor match. Dahlia tubers are prone to rotting if the soil stays soggy for too long.
- Invasive Spreaders: Avoid plants that spread aggressively through underground runners (like some types of mint or invasive bamboo). These will quickly wrap around the dahlia tubers and compete for nutrients, making it difficult to dig up your dahlias at the end of the season if you live in a cold climate.
- Desert Plants: Cacti and succulents prefer very dry, lean soil. The rich, frequently watered soil that dahlias love would likely cause these plants to rot.
Creating the Perfect Cutting Garden
Many gardeners grow dahlias specifically for bouquets. If this is your goal, your "companion plants" might actually be "filler flowers" for your vases. Longfield Gardens also offers plants for cutting gardens.
- Eucalyptus: For a modern look, the silvery-blue foliage of eucalyptus provides a stunning backdrop for dahlia blooms in a vase.
- Ammi majus (False Queen Anne's Lace): This provides a delicate, lace-like texture that makes a heavy dahlia bloom look even more elegant.
- Statice: Known for its "paper-like" flowers, statice adds long-lasting color and structure to arrangements.
- Bupleurum: This is a florist's secret weapon. It produces yellowish-green clusters that act as a neutral filler, making the colors of your dahlias appear more vibrant.
When growing a cutting garden, we often recommend planting in rows. This makes it easier to access the plants for deadheading (removing spent blooms) and harvesting. At Longfield Gardens, we suggest harvesting your dahlias in the cool of the morning for the longest vase life. Unlike roses or lilies, dahlias will not open much after they are cut, so wait until they are almost fully open before snipping.
Conclusion
Choosing what plants go with dahlias is one of the most creative parts of gardening. By focusing on plants that share the same sun and soil requirements while offering a contrast in shape and texture, you can transform a simple flower bed into a professional-looking landscape. Remember to:
- Use low-growing annuals like Sweet Alyssum to cover the base of the plants.
- Incorporate "airy" companions like Cosmos to add movement.
- Include herbs like Artemisia to help with natural pest management.
- Plan for "bloom windows" using perennials like Peonies for early-season color.
At Longfield Gardens, we are here to help you every step of the way, from choosing the perfect tubers to providing the advice you need to see them flourish. Gardening is a journey of discovery, and every season offers a new chance to try a different combination.
Final Thought: Start with the basics of sun, soil, and space, and then let your personal style lead the way. There is no "wrong" color combination if it brings you joy!
FAQ
What are the best low-growing plants to hide dahlia stalks?
Sweet Alyssum and low-growing Nasturtiums are excellent choices. They create a "living mulch" that keeps the soil cool and covers the bare lower stems of the dahlias without competing for sunlight.
Can I plant dahlias and lavender together?
Yes, as long as the lavender is planted on the sunnier, drier edge of the bed. While both love sun, lavender prefers slightly drier soil than dahlias, so place the lavender where it won't get hit by the frequent, heavy watering that dahlias require.
Which plants help keep pests away from dahlias?
Artemisia is great for deterring slugs and snails, while flowering herbs like Cilantro and Anise attract beneficial insects that eat aphids. Nasturtiums can also be used as a "trap crop" to draw aphids away from your prized dahlia blooms.
Should I plant companions at the same time as my dahlia tubers?
It is best to wait until the dahlia tubers have sprouted and are a few inches tall. This prevents you from accidentally digging into your tubers while planting companions and ensures the young dahlias aren't shaded out by faster-growing annuals during their first few weeks of growth. For more guidance, see this dahlia planting guide.
