Growing Dahlia FAQs

In short, no! In Georgia, the ground rarely freezes, so your dahlias can stay in the ground through the winter.

Winter Care Tips:

• Mulch: After cutting back the stalks, cover the tubers with 4-6 inches of mulch, such as pine straw, to protect them from temperature fluctuations.
• Protect the Stalks: Place a cap of tin foil secured with a rubber band over the cut stalks to prevent water from entering. This will help avoid crown rot, which can damage the eyes that will sprout next year’s growth.
• Dividing Tubers: To maintain healthy flowers and a manageable mass of tubers, divide your dahlias every 2-3 years. This helps keep the plants strong and the tubers from overcrowding.

Dahlia Growing Tips for Optimal Health

• Sunlight: Dahlias thrive with 6+ hours of sunlight daily, but 10-12 hours is ideal. Late afternoon shade is acceptable.
• Soil pH: Aim for a pH between 6.2 and 6.8, with 6.5 being optimal for healthy growth.​​​​​​​
• Planting Depth: Dig your planting bed 12-18 inches deep to ensure good drainage, as dahlias require well-drained soil.​​​​​​​
• Soil Enrichment: Dahlias are heavy feeders, so add plenty of leaf mold compost, Black Kow, or other organic humus to enrich the soil.​​​​​​​
• Improving Georgia Clay: If possible, replace Georgia clay with a better quality soil or mix it with organic amendments to improve texture and drainage.​​​​​​​
• Raised Beds: If using raised beds, make them 10-12 inches high with 2-inch boards and fill with a high-quality garden soil mix for optimal results.

Planting Your Dahlia Tubers

For optimal growth, plant your dahlia tubers around the same time you plant tomatoes, when the soil temperature reaches about 70°F. This typically happens after May 1st in most areas.

Planting Instructions:

• Digging the Hole: Create a planting hole 3-6 inches deep. Place the tuber in the hole with the growing tip facing upward.
• Planting Depth: Avoid planting the tuber too deep, as cooler soil temperatures may cause it to rot. Planting too shallow could expose the growing tip to the sun, risking sunburn or freezing during a harsh winter.​​​​​​​
• Staking: Place a 5-7 foot stake next to the eye end of the tuber to support the plant as it grows.​​​​​​​
• Spacing: Space your tubers 18-24 inches apart, with rows 24-36 inches apart to allow for proper air circulation.​​​​​​​
• Watering: Do not water immediately unless the soil is extremely dry. Let the natural moisture help the tuber settle in.

Fertilizing Your Dahlias for Optimal Growth

• Initial Fertilization: Start by applying OSMOCOTE 14-14-14 (about a tablespoon and a half or a small handful per plant) to the soil. Work it in gently to a depth of about 1 inch. This balanced fertilizer will help support early growth.
• Mid-Season Care: Around August 1st, switch to a different fertilizer as Osmocote’s effects begin to fade. Many growers opt for Miracle-Gro Rose or Tomato Food to keep the plants well-fed through the late summer.​​​​​​​
• Managing Nitrogen: By early September, start reducing high-nitrogen fertilizers, unless the area has been receiving inadequate rainfall. Excess nitrogen late in the season can cause the tubers to shrivel as they mature in the ground.​​​​​​​
• Long-Term Soil Management: After growing dahlias in the same location for several years, phosphorous can build up in the soil, potentially locking up other essential nutrients. To avoid this, experienced growers often switch to Calcium Nitrate 15.5-0-0 (which includes 19% calcium for improved blooming) or UREA (46-0-0). These fertilizers, applied 3-4 times a year, are gentle on plants and won’t burn them. Avoid ammonium nitrate, as it can scorch your plants.​​​​​​​
• Foliar Feeding for Stronger Stems: During the blooming period, apply Potassium Nitrate (found on eBay) every couple of weeks. This helps strengthen stems and supports overall plant health.

The Importance of Mulching Dahlias in the South

Mulching is crucial for growing dahlias in the South. Originating from the cooler mountain climates of Mexico and Guatemala, dahlias are not naturally suited for the hot, humid conditions we experience here.

• Root Needs: Dahlia feeder roots grow just 1 inch beneath the soil and can spread up to 2 feet in all directions. Keeping these roots cool is essential for healthy growth.
• Heat Protection: To combat the Southern heat, start with heat-tolerant dahlia varieties, and then apply at least 2 inches of mulch around your plants. Choose a mulch that allows water to pass through while keeping the soil cool, especially during the summer heat.​​​​​​​
• Timing: Be sure to mulch by July 1st to give your plants the protection they need to thrive through the hot months.

Watering Your Dahlias

Dahlias require consistent moisture but do not like soggy soil, so proper drainage is essential.

• Watering Frequency: Water your dahlias once a week or twice if the soil is dry. Be sure to water deeply to encourage strong root growth.
• Avoid Wet Foliage: Water the base of the plant, not the foliage, to prevent mildew and fungal issues.​​​​​​​
• Prevent Overwatering: Over-watering can lead to stem or root rot, so always ensure the soil is well-drained before watering again.

Pinching and Debudding Dahlias for More Flowers

To encourage a compact, bushy plant with more blooms, pinch out the central growing tip when the plant is about 12 inches tall and has at least 3-4 sets of leaves. This process, known as stopping, encourages the plant to grow multiple side shoots rather than just one tall stalk.

• Stopping: Pinching out the center growth tip helps the plant focus energy on lateral branches, resulting in a fuller, more productive plant.
• Debudding: Each lateral stem will develop three buds. To increase the size of the flowers, you can debuddle by pinching off the two side buds, leaving only the central bud to grow. This will allow the remaining bloom to become larger and more impressive.

This technique is effective for dahlias of sizes BB (4-6 inches), B (6-8 inches), A (8-10 inches), and AA (over 10 inches).

Protecting Your Dahlias from Pests and Diseases

Dahlias are prone to insect infestations and leaf diseases, especially in hot and humid climates. To ensure your dahlias thrive, it’s essential to spray them weekly with the appropriate treatments.

• General Pest Control: Most products you use for other plants will work just as well for dahlias. Regular spraying helps prevent pest damage and ensures healthy growth.
• Two-Spotted Spider Mites: These mites can become a problem as the weather heats up. Use a miticide to keep them under control. The most effective (but costly) option is AVID, available in pint-sized containers at southernag.com. For a more affordable, organic alternative, try Organicide Three-in-One, which works effectively and is available at Home Depot or online.​​​​​​​
• Powdery Mildew: This fungal issue often appears by late July. JMS Stylet Oil is the top product for curing and preventing powdery mildew. It treats infected leaves and protects unaffected ones. Visit Stylet-oil.com for more details. Alternatively, Neem Oil is an organic option that suffocates mildew spores. Start applying around early August and continue as needed.​​​​​​​
• Cucumber Beetles & Bud Worms: Late-season pests like cucumber beetles can damage blooms, and bud worms may infest your flowers. Mavrik is the best option for controlling these pests without discoloring your blooms (when used at a 50% concentration). Sevin is another option, though it may cause some discoloration.

Protecting Your Dahlias from Deer, Voles, and Chipmunks

Dahlias are a favorite snack for deer, voles, and chipmunks, so it’s essential to take steps to protect your plants.

Deer and Chipmunk Protection:

• Repellex: This product uses hot pepper tablets that deer and chipmunks find unappealing. While it’s a bit costly, it’s highly effective. Simply place one tablet per foot of growth. For new plantings, crumble two tablets per plant into the planting hole and water them in to activate the pepper. Once the animals taste the pepper, they tend to stay away.
• Liquid Fence: This organic deterrent, made from rotten eggs and garlic, effectively keeps deer and rabbits at bay. It’s safe for plants and works best when reapplied after rain.

Vole and Chipmunk Protection:

• Plant in Pots or Wire Baskets: To protect your tubers from voles and chipmunks, plant your dahlias in one-gallon pots or wire baskets buried below the soil surface. The plants will grow as if the pot isn’t there, and the barriers will keep pests away. Just be sure not to cut the bottom or drill holes in the sides.​​​​​​​
• Bondie Mole Max: This product is effective for repelling moles and voles. If voles remain a persistent issue, trapping may be necessary.

Storing Dahlias: Tubers Left in the Ground

Leaving Tubers in the Ground:

If you choose to leave your tubers in the ground over winter, mulch them with 4-6 inches of material. In early April, dig them up to divide, allow them to dry for 24-36 hours, then replant once the soil warms up.

Storing Tubers:

For short-term storage of freshly cut tubers, place them in plastic grocery bags. Ensure each division has at least one tuber and an eye.

Winter Storage of Tubers (Optional):

If you prefer to dig and store your tubers each winter, follow these steps:

1. Wait until two weeks after a hard frost: Leave the tubers in the ground after the frost has killed the tops, as this allows them to cure and harden.
2. Dig and wash: Gently wash the tubers with a hose, avoiding direct sunlight or concrete, and let them dry in a cool area.​​​​​​​
3. Store and Dry: Place the tubers in plastic grocery bags and store in a cool garage or basement. Check them regularly for rot (about once a month).​​​​​​​
4. Dividing Tubers: If you want to divide your tubers right away (easiest to do now), ensure each division has a piece of the crown (where the eyes are). Allow the cut tubers to air-dry for 24-36 hours before re-storing them in the bags.

Storage Tips:

• Regularly check your stored tubers for any rot, as neglecting to check can lead to loss of the entire batch.
• While other methods exist, this approach has proven to be the simplest and most reliable for winter storage, with minimal risk of rotting or shriveling.