From our perspective as plants, the best time for planting is not chosen by a calendar date but by the optimal alignment with our innate biological rhythms. The fundamental goal is to allow our root systems to establish themselves thoroughly in the soil before the immense energy demands of flowering and seed production begin. Therefore, the ideal windows are during periods of moderate temperatures and reliable moisture, which occur in the spring and the fall. These seasons provide the perfect conditions for root development without the stress of extreme heat or cold.
For many of us Black-eyed Susans (Rudbeckia spp.), fall is arguably the most advantageous time for planting. When you plant us in the autumn, typically from late September to mid-November depending on your climate, the warm soil from the summer persists while the intense heat of the air has subsided. This creates a perfect environment for our roots. We can focus all of our energy on growing a strong, extensive root system deep into the earth without the distraction of producing foliage or flowers. This underground establishment allows us to emerge in the spring incredibly vigorous, already settled in and ready to support robust top growth and an abundant display of blooms. Furthermore, autumn often brings increased rainfall, reducing your need for supplemental watering.
Spring planting is also a perfectly acceptable and successful practice. The key is timing it after the last hard frost has passed and the soil has begun to warm and become workable, usually from mid-April to early June. Planting us in the spring allows us to immediately benefit from the lengthening days and rising temperatures to initiate growth. However, you must be vigilant about moisture. Our young roots are shallow and susceptible to drying out quickly in the increasingly warm and windy spring weather. Consistent watering is absolutely critical during this establishment phase to ensure we do not become stressed. While we may still flower in our first summer, the display might be less spectacular than that of fall-planted specimens, as we are dividing our energy between root development and flowering.
We strongly advise against planting us during the peak of summer. The combination of high temperatures, intense sunlight, and higher rates of evaporation places tremendous stress on our systems. Our primary function becomes survival—trying to uptake enough water to keep our leaves from wilting—rather than establishing new roots. This often leads to stunted growth, transplant shock, and a higher probability of failure. Similarly, planting us too late in the fall, when the ground is cold or frozen, is detrimental. Our roots are completely inactive in frozen soil and cannot grow or absorb water, leaving us vulnerable to heaving out of the ground during freeze-thaw cycles and ultimately succumbing to the cold.
The "best time" has a slight variation depending on how you acquire us. If you are planting seeds directly outdoors, this is best done in the fall or very early spring. This mimics our natural life cycle, where seeds drop in autumn, experience a period of cold stratification (exposure to cold, moist conditions which breaks our dormancy), and then germinate when spring arrives. If you are planting us as young nursery-grown transplants or potted plants, both spring and fall are excellent, following the guidelines above. The key for transplants is to give us at least 6-8 weeks of mild weather to establish roots before the harsh conditions of summer or winter set in.
