The Webster Viridarium
With their stunning and long lasting blooms, Dahlias are a stunning addition to any garden. The middle of May is prime planting time for dahlias, as the last frost has passed (typically early May in Webster), and soil temperatures are above 60°F—perfect for these tender perennials.
1. Planting
- Timing: Plant now (mid-May) to ensure blooms by late summer (July–September). Dahlias need warm soil (60°F+), and nighttime temps should stay above 50°F, which they are in Webster this time of year.
- Starting: Use tubers (not seeds) for faster results. Look for firm tubers with visible “eyes” (growth points).
- Soil: Dahlias need well-drained, loamy soil (pH 6.5–7.0). Webster’s clay-heavy soil benefits from mixing in compost and sand or perlite. Dig a hole 6–8 inches deep, lay the tuber horizontally with the eye facing up, and cover with 2 inches of soil. As the sprout grows, gradually fill the hole.
- Spacing: Space tubers 1–2 ft apart (1 ft for dwarfs, 2 ft for larger varieties). Plant 1–2 tubers to avoid overcrowding.
2. Watering and Feeding
- Watering: Keep soil consistently moist but not soggy—about 1 inch per week. Water at the base to avoid wetting leaves, reducing powdery mildew risk (common in Webster’s humid summers). Once established, dahlias are somewhat drought-tolerant but don’t let them dry out completely.
- Mulching: Add 2 inches of straw or shredded bark mulch to retain moisture and keep soil cool. Keep mulch away from stems to prevent rot.
- Fertilizing:
- At planting: Mix in a low-nitrogen fertilizer (e.g., 5-10-10) to promote blooms over foliage.
- Monthly: Side-dress with a balanced fertilizer (e.g., 10-10-10) or compost tea until blooming starts (July). Too much nitrogen causes leafy growth at the expense of flowers.
3. Support and Pruning
- Staking: Most dahlias (except dwarfs) need support, as stems can snap in summer storms. Install a 4–6 ft stake or cage at planting time. Tie stems loosely with garden twine as they grow.
- Pinching: When plants reach 12–18 inches tall (around June), pinch the top growth above the fourth set of leaves. This encourages bushier growth and more blooms.
- Deadheading: Remove spent flowers weekly to promote continuous blooming through September. Cut back to the nearest set of leaves.
4. Pest and Disease Management
- Slugs: Slugs love tender dahlia shoots. Use your grapefruit traps near dahlias, and add a ring of diatomaceous earth around the base. Hand-pick at dusk if needed.
- Other Pests: Watch for aphids (spray with insecticidal soap) and spider mites (increase humidity, use neem oil). Japanese beetles may appear in July—hand-pick or use row covers.
- Diseases: Powdery mildew thrives in humid conditions. Ensure good air circulation (don’t overcrowd), and apply a sulfur-based fungicide if needed. Avoid overhead watering.
5. Overwintering in Webster
- Frost Timing: Dahlias are tender and won’t survive Webster’s winter (lows to -10°F). First frost hits ~October 5–15.
- Digging Tubers: After frost blackens foliage, cut stems to 4 inches, dig up tubers, and brush off soil (don’t wash). Dry them for 1–2 days in a garage or shed.
- Storage: Store tubers in a box with peat moss, vermiculite, or sawdust at 40–50°F (e.g., a cool basement). Check monthly for rot; mist lightly if they shrivel. Replant next May.
6. Local Tips
- Weather: May is rainy (3–4 inches average). Ensure good drainage to prevent tuber rot. July–August heat (80–85°F) will boost growth if you keep soil moist.
- Community: Cornell Cooperative Extension of Monroe County (585-461-1000) can provide soil testing to optimize your dahlia bed.
Quick Timeline
- May 14: Plant tubers, stake, water well.
- June: Pinch tops, fertilize, monitor slugs.
- July–September: Deadhead, water, enjoy blooms.
- October: Dig and store tubers after frost.
