From our perspective as plants, our flowering is primarily governed by photoperiodism—our physiological reaction to the relative length of daylight and darkness. We are "short-day" plants, meaning we initiate our flower buds as the nights grow longer in late summer and early autumn. Planting at the correct time is crucial to ensure we have a sufficiently established root system and vegetative growth to support this energy-intensive blooming process. If planted too late, we may not have the resources to produce robust flowers or survive the coming winter.
Our paramount concern is root establishment. For perennial varieties, our survival through winter depends on a strong, healthy root system that can anchor us and access water and nutrients. This process takes time. We require weeks of moderate soil temperatures to grow our roots outward into the surrounding soil. If planted too close to the first hard frost, the ground becomes too cold for our root cells to function, halting growth and leaving us vulnerable to heaving from the freeze-thaw cycle, which can expose and damage our delicate roots.
While your USDA Hardiness Zone indicates the average minimum winter temperature we can expect to survive, the planting time is more directly linked to the soil temperature in the months leading up to winter.
For zones 5-7: The ideal window is in the spring, after the last frost date when the soil has warmed. This gives us the entire growing season to establish ourselves. Early autumn (at least 6 weeks before your first expected hard frost) is a secondary option, but spring is vastly preferred for perennial types as it reduces winter stress.
For zones 8-9: You can successfully plant us in either spring or early fall. The milder winters and longer growing seasons mean the soil stays warm enough for our roots to establish well into the autumn months.
For zones 10 and above: Your climate presents a different challenge: heat. The best time to plant us is in the cooler months of late fall or even early winter, allowing us to establish roots without the extreme stress of summer heat before we begin our bloom cycle.
It is important to distinguish between hardy perennial garden mums and the potted "florist mums" often sold in full bloom at garden centers in the fall. We, the florist mums, are typically bred for a single, spectacular show and have not been selected for winter hardiness. For us, planting in the fall is perfectly acceptable for a brilliant annual display, as the goal is not our long-term survival but immediate aesthetic impact before the first killing frost.
To thrive after planting, we require your help. Please ensure we are situated in a location with well-draining soil; our roots abhor sitting in water, which leads to rot. Provide us with consistent moisture, especially in the first critical weeks, and place us where we will receive at least six hours of full sun daily. This sunlight is the energy that fuels our growth and, ultimately, our flowering process once the shorter days of autumn arrive.
