The Saint Martin Dahlia offers a captivating display for any garden space, making it a popular choice for both seasoned and new gardeners. Its striking blooms and adaptable nature provide vibrant color from mid-summer until the first frost.
Understanding the Saint Martin Dahlia
The Saint Martin Dahlia is a decorative dahlia, often described as having a waterlily-type form. Its flowers are approximately 4 inches (10 cm) in diameter, showcasing a beautiful bicolored pattern. Newly opened blooms feature deep cherry-pink veins and tips, which gradually lighten to a snow-white base as they mature. This creates a dynamic range of shades on a single plant, from white with reddish-pink tips to white with splashes of deep rose or purple edges.
The plant reaches a height of 24 to 36 inches (60-90 cm) and has a spread of about 20 to 24 inches (50-60 cm). It develops an upright, bushy, clump-forming habit with dark green, toothed, pinnate leaves on strong, upright stems.
Growing Saint Martin Dahlias
Choosing the Right Spot and Preparing Soil
Saint Martin Dahlias thrive in full sunlight, ideally at least four hours per day. They prefer well-drained, fertile, and humus-rich soil, as soggy conditions can lead to tuber rot. Before planting, amend the soil by digging down 8 to 12 inches and incorporating compost or well-rotted manure to improve its structure and nutrient content.
Planting Your Tubers
Plant Saint Martin Dahlia tubers outdoors after the last frost has passed and the soil temperature has warmed to at least 60°F (15°C). Tubers should be planted 2 to 4 inches deep, with the “eye” facing upwards, and spaced 1 to 3 feet apart. For container planting, use a well-drained potting mix and position the tuber so the crown is about one inch below the soil surface. Growth begins within 14 to 20 days after planting.
Watering Needs
Dahlias require consistent moisture, especially during dry periods and blooming. After planting, avoid watering tubers until sprouts emerge to prevent rot. Once foliage appears, gradually increase watering to keep soil moist but not waterlogged. Deep watering, 8 to 10 inches into the soil, is more effective than shallow watering. Adjust frequency based on climate, increasing during hot, dry periods.
Feeding Your Plants
Fertilizing Saint Martin Dahlias supports robust growth and abundant flowering. About 30 days post-planting, begin a monthly schedule with a water-soluble, organic fertilizer. Choose a low-nitrogen formula high in phosphorus and potassium (e.g., 5-10-10 or 2-15-15), as too much nitrogen promotes foliage over flowers. Container plants may need more frequent fertilization, every two to three weeks, due to nutrient leaching.
Staking and Deadheading for Best Blooms
Tall dahlia varieties, including Saint Martin, benefit from staking to support heavy blooms and prevent falling. Insert stakes at planting time to avoid damaging tubers. As the plant grows, tie stems to the stake every 12 to 18 inches. Deadheading, or removing spent flowers, encourages more blooms and maintains tidiness. Snip faded blooms above the first set of healthy leaves or buds.
Common Challenges and Winter Care
Addressing Pests and Diseases
Saint Martin Dahlias are susceptible to common garden pests like slugs, aphids, and earwigs, particularly during early growth. Keeping the garden clean deters pests. Adequate air circulation also prevents fungal diseases like powdery mildew. If issues arise, apply general organic pest control methods.
Preparing for Winter and Storing Tubers
In colder climates (USDA Zones 3-7), Saint Martin Dahlia tubers must be lifted and stored indoors for winter protection. After the first hard frost blackens foliage, cut stems back to 2 to 6 inches above ground. Carefully dig up tubers, avoiding damage, and dry them for a few days in a frost-free location away from direct sunlight.
Once dry, gently remove excess soil and store clumps in a ventilated container filled with slightly moistened peat moss, sand, vermiculite, or dry compost. Store in a cool, dry, dark, frost-free area (40-50°F / 5-10°C). Periodically check tubers throughout winter, misting lightly if shriveled or removing any signs of rot.