The Deep Winter Sleep
We’ve had some great frosts this year. I haven’t looked at the official records but it feels like it’s more than normal. I’m not complaining, I love the feel of the sun on my back on those crisp clear days. That said, when I’m at the farm and we’ve had a decent frost I look out at the bare, frozen paddock and wonder how anything could survive down there? The farm looks completely dead. The rows of quiet, dark dirt are empty. The brilliant pinks and deep reds of our spring harvest feel like a lifetime away.
The reality however is quite different. That biting cold isn’t hurting the peonies, it’s exactly what the peonies need. And without a hard winter chill, our spring wouldn’t have any flowers at all.
What Actually Happens Down in the Dirt?
Peonies originally evolved in temperate zones where winters are harsh. Like many plants that evolved in temperate zones, peonies “hibernate” to survive the freezing winters. As the autumn days shorten and the ground temperature drops, the peony moves into a phase called endodormancy. Endodormancy is essentially a deep, hormone-controlled winter sleep. It pulls all its energy down into the root and puts itself into lockdown.
This hibernation has two main jobs:
- A Heavy Shield Against the Cold: It stops the plant from active growth in deep winter so the freezing weather doesn’t kill off soft new tissue.
- Beating the “False Spring”: It keeps the plant from waking up too early. If we get a random warm week in August, the internal lock prevents the tuber from throwing up shoots that would just get zapped by the next late frost.
To wake up properly, the plant has to tick off a specific number of “chilling units.” Interestingly, the plant tracks low temperatures above freezing to count these units. The actual freezing nights don’t count toward the waking clock, but they are vital for building cold hardiness—the physical strength the root needs to survive the deep freeze.
Having received sufficient chilling units the peony then switches to ecodormancy. In ecodormancy the peony tracks the lengthening of the day and rising temperature to work out when it is safe to begin to grow.
Why Nelson Winters Mean We Have to Pick Wisely
Here’s the catch: if a peony doesn’t get enough cold hours, it stays sluggish. You get sub-optimal growth—short stems, fewer flowers, or “bud blast,” where the flower bud forms but dies before it can even open.
Different varieties need different amounts of cold. Some require a quick 400 hours, while others need up to 1,500 hours of chilling. Because our Nelson/Tasman climate is relatively mild compared to the deep south, we have to be smart about what we plant in our soil. We need varieties that get the job done with a lower chilling requirement.
Our Varietal Report Card:
- The Absolute Best Performers: All our Corals and the deep red Red Charm thrive beautifully in our winter conditions.
- Good, Reliable Growers: Festiva Maxima, Bridal Gown, and Chippewa handle our climate well.
- The Mistakes We Learned From: In hindsight, we have some varieties that struggle with our climate particularly Sarah Bernhardt, Dinner Plate, or Duchesse de Nemours.
It’s not just about the winter cold, either. It’s the spring transition. Varieties like Sarah Bernhardt need a long, slow, cool spring to develop their massive heads. Around here, our spring can flash hot very quickly. That rapid shift from winter chill to hot spring days can muck around with the plant’s system, leading to short stems and lost buds. There are some things we can do to help. For example, including Boron and Calcium in our foliar sprays strengthens the developing stems and handles that sudden heat shock.
Working With the Climate, Not Against It
Out on the farm, we don’t just leave it all to chance. We use a few practical, down-to-earth management techniques to make sure the tubers get every bit of cold they need:
- No / Limited Winter Mulching: While some gardeners love to blanket their beds, we leave our soil bare through autumn and winter. We want the ground to get the maximum amount of cooling on those crisp Nelson nights.
- Shallow Planting: We plant our tubers shallowly. It’s always colder right near the surface than it is buried deep in the earth.
- Reflective Mulches: If the sun starts beating down too early in the spring, we can apply reflective covers to keep the soil temperature down and give the flowers a few more precious days to grow tall.
So, the next time you see the frost thick on the grass, don’t feel sorry for the garden. Think of it as our farm’s kitchen working in reverse—patience, time, and cold soil are quietly mixing the ingredients for the heavy, fragrant blooms that will fill our Nelson home come November.
It takes a hard winter to make a luxury spring.