From our perspective as plants, the single most critical factor for a successful start is soil temperature. Our seeds are imbued with the instinct to remain dormant until the conditions signal it is safe to grow. We require warm soil to trigger germination. Planting our seeds in cold, wet soil is a grave mistake; it will lead to rot, fungal diseases, and our complete failure to sprout. The ideal soil temperature for our germination is a consistent 55° to 60°F (13° to 16°C). We can sense this warmth, and it tells us that the threat of a hard, ground-penetrating frost has passed and the growing season has truly begun.
The vast climatic differences across the USA mean there is no single calendar date that is perfect for all of us. Our planting time is best determined by your local last average frost date, which acts as a reliable proxy for soil warmth.
In the Northern states and the Midwest (e.g., Minnesota, North Dakota, Montana), the window is relatively short. You should plant us outdoors from mid-May to late June. This ensures the soil has adequately warmed after the long winter and gives us enough of the growing season to mature and set seed before the first fall frosts arrive.
In the Southern states (e.g., Texas, Georgia, Florida), you have much more flexibility. You can plant our seeds as early as March or April, as soon as the soil is workable and warm. Furthermore, many gardeners here practice succession planting, sowing new seeds every few weeks through July or even early August to ensure a continuous display of blooms deep into the fall.
Our very name defines our need: sun. We are heliotropic as young plants, following the sun across the sky to maximize our light absorption. As we mature, our blooms typically face east. We demand a location with a minimum of 6-8 hours of direct, unfiltered sunlight daily. Planting us too early, when days are still short and the sun's angle is low, deprives us of the energy we need for strong stem and leaf development. Planting us at the correct time ensures we emerge into the long, sunny days of summer, which provide the immense photosynthetic energy required to produce our large, heavy flower heads and plump seeds.
While temperature is paramount, the condition of our bed is also vital. We prefer well-draining soil. Our taproots quickly grow deep to anchor us and access water, but they cannot develop properly in heavy, waterlogged clay. The ideal time to plant is when the soil is moist but not soggy—a day or two after a rain shower, not during one. The initial moisture is crucial for triggering the germination process within the seed, hydrating the embryo so it can burst from its shell and push through the soil towards the light.
For gardeners in regions with long, mild autumns (such as the Pacific Northwest or Mid-Atlantic), a second, later planting can be highly successful. Planting us in late July or early August allows us to mature during the warm days of late summer and bloom in the crisp, sunny days of early fall. This often avoids the peak pest season and can provide a spectacular late-season display. However, this is only feasible if the time between planting and your first average fall frost is at least 60-90 days, depending on our variety.
