Dahlia Tubers: A Step-by-Step Guide to Planting and Care

Where To Plant Dahlia Tubers

Choosing the right location to plant dahlia tubers is essential for promoting their lush growth and abundant blooms.

Sunlight: Plant dahlia tubers in a location with at least 6 hours of direct sunlight daily, especially morning sun to help prevent mildew.

Soil: Choose well-drained soil, as tubers can rot in waterlogged conditions. Slightly sandy soil or soil amended with compost works best. Dahlias prefer slightly acidic to neutral soil (pH 6.5-7.0). Test your soil if unsure and amend as needed.

Borders and Backdrops: Dahlias are ideal for adding height and structure to flower beds. Plant taller varieties, like Dinner Plate dahlias, at the back of borders to create a dramatic backdrop. Their large blooms make excellent companions for perennials and shrubs with contrasting foliage, such as ornamental grasses or silver-leaved plants, adding layers of texture and color.

Mixed Borders: Combine dahlias with other flowering plants like coneflowers (echinacea), black-eyed Susans (rudbeckia), and sage (salvia) for a vibrant, multi-season display. Medium-height dahlias work well in the middle of borders, creating a focal point that draws the eye inward. Their blooms blend beautifully with pastel and bold colors, allowing for creative garden color schemes.

Raised Beds: In clay-heavy soils, plant dahlias in raised beds or mounds to improve drainage and prevent tuber rot.

Cottage or Cutting Gardens: Dahlias are a staple in cottage gardens and cutting gardens, where their continuous blooms from midsummer to fall add an abundance of color. Plant them among other classic flowers like zinnia, sunflower (helianthus), and cosmos. Their bright flowers provide endless cutting options for indoor arrangements, making them practical and ornamental.

Garden Pathways and Walkways: For a charming garden pathway, plant compact dahlias along walkways to create a vibrant edging that guides visitors through the space. Use a mix of colors and textures to give a dynamic and inviting look.

In Pots and Containers: Dahlias in pots add a warm welcome to entrances, patios, and balconies. Choose dwarf or medium-sized dahlias, which are well-suited for containers, and arrange them near doorways or seating areas for bursts of color and visual interest. Place pots in groups with other annuals or perennials for a layered look.

Protection from Wind: For taller varieties, choose a sheltered location or use stakes to prevent bending or breaking under heavy blooms.

How to Plant Dahlia Tubers

Planting dahlia tubers properly sets the foundation for strong, healthy growth and abundant blooms. Follow these steps to give your dahlias the best start:

Prepare the Soil: Loosen the soil to a depth of 12-15 inches (30-37 cm), mixing in compost to enrich it. Aim for a slightly acidic to neutral pH (6.0-7.5), which supports nutrient absorption.

Dig the Planting Hole: For each tuber, dig a hole 4-6 inches (10-15 cm) deep. Place the tuber horizontally with the “eye” or growing point facing upward. Avoid watering right after planting, as excess moisture can lead to rot.

Space Appropriately: Optimal spacing for dahlias is essential for healthy growth, providing adequate air circulation, minimizing disease risk, and allowing each plant to reach its full potential:

• Large Dahlias (like Dinner Plate varieties): Space 24-36 inches (60-90 cm) apart. These dahlias can grow up to 4-6 feet tall with large blooms, so they need ample room to expand and for good air circulation.

• Medium Dahlias: Space 18-24 inches (45-60 cm) apart. This spacing works well for medium-sized varieties, allowing sufficient room for growth without crowding.

• Compact or Dwarf Dahlias: Space 12-18 inches (30-45 cm) apart. Smaller varieties are perfect for borders, containers, or smaller garden spaces, and this spacing supports airflow while maximizing display impact.

Staking for Support: For taller varieties, place a stake in the ground near the tuber at planting time. As the plant grows, tie the stems to the stake to support heavy blooms and prevent bending.

Watering and Mulching: Once shoots appear, water moderately to keep soil moist, not soggy. Mulching around the plants can help retain moisture and suppress weeds.

Digging Dahlia Tubers

Timing: Wait until the first frost blackens the foliage before digging up tubers. This ensures they’ve had time to mature fully in the soil.

Preparing the Plants: Cut dahlia stems down to about 4 inches (10 cm) above ground, which makes it easier to handle the clump and prevents rot from entering the tubers.

Removing Weak Plants: Remove and discard any weak or virus-infected plants to prevent the spread of disease to healthy tubers.

Digging Technique:

• Dig around each plant about 12 inches (30 cm) from the main stem to avoid damaging the tubers.
• Loosen the soil on all sides with a garden fork, then lift the entire clump gently to avoid breaking the delicate necks of the tubers.

Handling After Digging:

• Turn the clumps upside down to let any water drain from the stems.
• Allow clumps to sit for a couple of hours in a shaded area to firm up the tubers before washing off the soil.

Cleaning: Use a garden hose to wash away excess soil, which can harbor microorganisms. This also makes it easier to inspect for any damage or signs of disease before storage.

Dividing Dahlia Tubers

Optimal Timing: Dividing is usually done in fall when tubers are freshly dug. This makes it easier to see the “eyes” and ensures tubers aren’t overly hardened.

Tools and Sterilization: Use sterilized cutting tools, and sterilize them between cuts to avoid spreading viruses. A solution of 1 part bleach to 10 parts water is effective.

Identifying the Eyes:

• Each division needs a piece of the crown with an “eye,” which is where new shoots will emerge.
• Eyes are usually more visible if you cut the stems a few days before digging, as this encourages eye development.

Dividing Process:

• Carefully separate individual tubers within the clump, ensuring each piece has an eye.
• Discard the “mother root” (the oldest tuber) as it often lacks feeder roots and will not produce strong plants.

Inspecting and Treating:

• Remove any damaged or brown areas, as these may indicate rot.
• Apply fungicide powder or sulfur dust to cut ends to reduce the risk of rot during storage.

Labeling: Mark each division with the variety name and other identifying details. Use indelible markers or labels to avoid losing track of each tuber’s identity.

Storing Dahlia Tubers

Drying: Let tubers dry for 1-2 days in a shaded area with good air circulation before storage to prevent moisture buildup that could lead to rot.

Storage Mediums:

• Use materials like coarse vermiculite, wood shavings, or slightly moistened sand to maintain a balanced moisture level.
• Avoid peat moss, as it can either dry tubers out or promote rot if too moist.

Containers:

• Place tubers in ventilated plastic bags, paper bags, or storage boxes, layering them with your chosen medium.
• Ensure containers are airtight but allow some air circulation if in a humid area.

Temperature Control:

• Store tubers in a cool, dark location around 40-50°F (4-10°C). This prevents freezing and reduces premature sprouting.
• Some growers use insulated garages or unheated basements, while others may use unused refrigerators.

Regular Inspections:

• Check tubers monthly for any signs of rot and discard affected tubers to prevent spread.
• If a tuber starts to shrivel, add a small amount of moisture to the storage medium to maintain tuber health.

Preparing for Spring: Move tubers to a warmer spot in early spring to encourage the eyes to sprout, signaling that they’re ready for replanting.

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Frequently Asked Questions

What month do you plant dahlia tubers?

Plant dahlia tubers in spring after the last frost has passed and the soil has warmed to about 60°F (15°C). This is typically around April to May, depending on your region and climate.

Do dahlias come back each year?

Dahlias can come back each year in mild climates (USDA zones 8-11), where the ground doesn’t freeze. In colder areas, they can be treated as annuals or dug up, stored, and replanted the following spring.

Do you have to dig up dahlia tubers every year?

In colder climates (zones 7 and below), it’s recommended to dig up and store tubers each year before the first frost, as freezing temperatures can kill them. In warmer zones, tubers can often stay in the ground year-round.

What is the difference between dahlia bulbs and tubers?

Dahlias grow from tubers, not true bulbs. Tubers store nutrients and have multiple “eyes” from which new shoots can grow, while bulbs typically have a single growth point and layered scales.

Should I soak dahlia tubers before planting in the ground?

Soaking dahlia tubers is optional. If tubers look dry, you can soak them for an hour to help rehydrate, but avoid soaking too long as this can lead to rot. In most cases, planting directly into moist soil works well.

What not to plant with dahlias?

Avoid planting dahlias with heavy feeders like large shrubs or other tall, dense plants that compete for light and nutrients. Avoid plants prone to similar pests or diseases, as well as groundcovers that may hinder airflow and increase disease risk.

Should you deadhead dahlias?

Yes, deadheading spent blooms encourages more blooms to develop, prolonging the flowering period and keeping plants looking tidy. Regular deadheading directs energy to new flowers rather than seed production.