Rudbeckia Germination

Starting From Seed

• Coneflowers have germination rates of 80 percent under the right conditions. They require soil temperatures around 70 degrees Fahrenheit for germination, and seedlings can take anywhere from seven to 30 days to emerge. Gardeners should sow seeds 1/16 inch below the soil surface for best results. Although most rudbeckia seeds germinate best in the spring, planting dates can vary significantly by climate zone. Sow coneflowers in June or July in zone 7, May in zone 8, April in zone 9 and October in zones 10 and 11.

Direct Sowing in Gardens

• Coneflowers grow well when sown directly into flowerbeds or garden soil, although germination is sometimes problematic, and flowers may require up to two years to become fully established. Give seeds a head start by rolling them in a moist paper towel, placing them in a zipped plastic bag and refrigerating for six to eight weeks. This results in a higher germination rate for direct-sown coneflower seeds. Rudbeckia plants will frequently self-sow and spread in the garden once they are established, as long as conditions remain favorable for growth.

Germinating Indoors

• Start coneflower seeds indoors in early March, ensuring they receive at least 10 to 11 weeks of indoor growth before placing them outside in the garden. Soil-less potting mixes, typically composed of peat moss and vermiculite, are best for starting seeds indoors. These mixes are sterile, free of weed seeds, and have density and moisture retention characteristics ideal for the growth of tender seedlings. Avoid starting coneflower seeds in windowsills, since indoor levels of natural light are rarely sufficient for healthy plant growth. Fluorescent tubes hung 4 inches from the soil surface will provide Rudbeckia seedlings with adequate light.

Additional Cultural Considerations

• Plants of the Rudbeckia genus germinate best and grow most vigorously in full sunlight, spaced 18 to 24 inches apart. They are hardy in USDA hardiness zones 2 to 11 and tolerate a wide range of soils. Coneflowers thrive in clay, sand, loam and acidic conditions and are drought tolerant as well. They prefer well-draining soils and are unaffected by high salt levels found in some areas. They are resistant to most pests, although mildew, leaf spot and aphids are occasionally problematic.