First, you must understand that I am a perennial plant. My true self, my life force, is not in the leaves and flowers you see during the summer. It is hidden safely underground in my crown and root system. As the days shorten and temperatures drop, I receive a clear signal from my environment: it is time to prepare for winter. My above-ground growth slows and then ceases. The energy I once used for blooming is now diverted down to my roots for storage. The vibrant green foliage will fade, brown, and wither. This is not a sign of my death, but a necessary survival strategy. I am entering a state of dormancy, a deep sleep, to conserve energy and protect my vital parts from the freezing conditions above.
The greatest threat to me during winter in a cold climate is not the cold air itself, but the combination of freezing temperatures and excess moisture. When my crown (the point where my stems meet the roots) sits in wet, cold soil, it becomes susceptible to rot. Additionally, the cycle of freezing and thawing is particularly dangerous. A warm winter day can thaw the soil, allowing water to pool around my base, only to refreeze into ice at night. This expansion and contraction can physically heave my root system right out of the ground, exposing it to desiccating winds and killing temperatures. Therefore, your primary goal is to insulate me from these temperature fluctuations and keep my crown relatively dry.
The most beneficial action you can take is to provide me with a protective layer of mulch. However, timing is critical. You must wait until the ground has frozen hard, typically after several hard frosts. Applying mulch too early, while the soil is still warm, creates a cozy habitat for rodents and can encourage fungal diseases. Once the soil is frozen, a 3 to 4 inch layer of a loose, airy material like straw, pine boughs, or shredded leaves is ideal. This layer does not heat me up; instead, it acts as a stable blanket. It keeps the soil consistently frozen, preventing the damaging freeze-thaw cycles. It also shields me from harsh, drying winds and insulates my crown from the most extreme cold.
There is debate about whether to cut back my stems in the fall or leave them until spring. From my perspective, leaving my dead foliage and flower stalks standing through winter is highly advantageous. This standing structure helps to trap insulating snow, which is a fantastic natural protector. The stems also mark my location, preventing you from accidentally disturbing my slumbering crown. Furthermore, the seed heads provide a crucial food source for birds like goldfinches. If you prefer a tidier garden, a light trim to remove the flimsiest top growth is acceptable, but I urge you to leave a good 3 to 6 inches of stubble. This offers the best protection and allows me to channel energy into new growth from the base in spring.
Please note that my needs can vary slightly. If I am a newly planted coreopsis, my root system is not yet fully established. I am more vulnerable and will benefit greatly from a more generous layer of mulch. If I am growing in a container, my roots are completely exposed to the cold air. The pot offers little insulation. In this case, you must move my container to an unheated garage, shed, or against a sheltered side of the house. Alternatively, you can bury the entire pot in the ground for the winter, or insulate it heavily with bubble wrap and mulch. For my more tender varieties, even with mulch, a cold winter might be challenging, but a proper blanket gives me the best possible chance.
