Coreopsis, commonly known as Tickseed, is a popular choice for gardeners due to its cheerful, daisy-like blooms and low-maintenance nature. These flowers can be annual or perennial, thriving across a wide range of growing zones. Gardeners frequently ask whether the seeds require cold conditioning, or stratification, to successfully sprout. The need for stratification depends on the specific variety being grown.
Understanding Coreopsis Seed Dormancy
The need for cold stratification in Coreopsis is not universal, but depends heavily on the seed lineage. Many popular, commercially available cultivars have been selectively bred to bypass the requirement for a cold period entirely. These non-dormant seeds germinate easily with just moisture and warmth.
Seeds collected from native species or older varieties frequently exhibit physiological dormancy, a natural mechanism that prevents premature sprouting. This dormancy ensures the seed only germinates after surviving a winter. For these seeds, exposure to cold, moist conditions is necessary to break down internal germination inhibitors. Without this chilling period, the germination rate for certain native varieties, such as Coreopsis lanceolata, can be significantly lower or fail completely.
Step-by-Step Cold Stratification Methods
For Coreopsis seeds that require a chilling period, simulating winter conditions is a straightforward process. The goal of cold stratification is to keep the seeds consistently moist and cold, ideally within 35–40°F (2–4°C). The treatment duration is typically between 30 and 60 days, depending on the species.
Indoor Stratification
One popular indoor method is the “baggie method,” where seeds are mixed with a sterile, moisture-retaining medium like fine sand, vermiculite, or a damp paper towel. This mixture is sealed and placed in the refrigerator’s crisper drawer for the specified duration. The medium must be damp, not soaking wet, to prevent the seeds from molding or rotting.
Winter Sowing
Alternatively, gardeners can utilize the outdoor “winter sowing” technique, which uses the natural environment for stratification. Seeds are planted in containers with drainage holes, covered, and left outdoors in a protected spot to experience natural temperature fluctuations. This method provides the required cold and moisture while protecting the seeds from wildlife.
Standard Indoor and Direct Sowing Techniques
Whether using stratified or non-dormant seeds, the planting process must account for Coreopsis’s specific germination needs.
Indoor Sowing
For indoor starting, sow seeds six to eight weeks before the final expected frost date. Use a sterile seed-starting mix in trays, scattering the seeds across the surface. Coreopsis seeds require light to trigger germination, so they should be barely covered or simply pressed firmly onto the surface. Maintain a soil temperature between 65–75°F (18–24°C) and keep the medium lightly moist for successful sprouting. Seedlings can be grown under bright grow lights or on a sunny windowsill until ready for transplanting.
Direct Sowing
Direct sowing outdoors offers a simpler approach, either in late fall for natural stratification or in early spring after the last hard frost. Prepare the soil by lightly raking the surface to create a fine seedbed. Press the seeds onto the soil surface, ensuring good seed-to-soil contact without burying them deeply.
Essential Care After Sprouting
Once Coreopsis seeds have germinated, the seedlings require careful management to ensure healthy growth before moving outdoors. Seedlings must be thinned once they develop their first true leaves, spacing them about two inches apart or reducing them to one per cell. This practice eliminates competition for resources, promoting stronger individual plants.
Adequate light is primary; indoor seedlings need 14–16 hours of intense light daily, typically achieved with supplemental grow lights. Soil moisture should be consistently maintained, keeping the medium damp but never waterlogged to prevent fungal diseases. Water deeply and allow the top layer of soil to dry slightly between waterings once the plants are established.
Before transplanting, the young plants must undergo a gradual process called hardening off. Over seven to ten days, expose the seedlings to increasing amounts of direct sunlight, wind, and lower temperatures. Begin with one to two hours in a shaded area, slowly increasing the time outdoors until they can tolerate a full day outside.