What is the Persephone Period? What it Means for Winter Growing

When people ask me when I plant winter-harvested crops like carrots and kale, they’re often shocked to learn I put these seeds in the ground in late summer or early fall. And that makes sense! It’s easy to assume people plant these cold-hardy crops in late fall and harvest them a few months later in winter.

However, plant growth slows as days become shorter. And once daylight drops below ten hours, a time known as the Persephone period, plant growth practically stops. Never heard of this period before? No worries!

I’ll share details about this part of the year and explain why understanding it is important for successful winter growing. 

The Long Answer

We know the Persephone period relates to daylight and impacts plant growth, but how exactly should you consider it when planning your winter garden? I’ll share some more details about this gardening term and cover how you can use it to plant winter crops at the correct time.

History

Halfway through the year, the Earth has rotated halfway around the sun. Now, the southern hemisphere tilts towards the sun, and the northern hemisphere faces away, leading to a change in seasons.

But we don’t just snap our fingers and watch the longest day of the year transform into the shortest. Instead, we see a gradual shift in day length and a change in seasons. And this change brings the first ten-hour day, otherwise known as the start of the Persephone period.

While this period has always existed, Maine vegetable farmer and winter-growing pioneer Eliot Coleman coined the term, which people continue to use today. But he didn’t come up with the myth of Persephone. No, that was the ancient Greeks.

Persephone was the daughter of Demeter and Zeus and the goddess of vegetation. According to the legend, Persephone was out in a field picking flowers when the Earth suddenly opened up. Hades, the king of the underworld, appeared out of the crack and abducted Persephone. When Demeter learned of her daughter’s abduction, she became distraught and forced plants to stop growing as a form of protest. Eventually, people became hungry, and Zeus forced Hades to return Persephone. When the goddess returned to the surface, plant growth resumed.

This myth gave the darkest part of the year its name.

How to Determine

The start of the Persephone period varies depending on your longitude. You can look up a day-length calendar to determine when the first ten-hour day will occur.

Where I live in East Tennessee, day length drops to ten hours on November 26. Days continue to decrease until the winter solstice on December 21. After the solstice, days increase until they return to ten hours on January 16. That means the Persephone period in my area occurs from November 26 until January 16.

The Role of Light in Plant Growth

While many people think that cold prevents us from growing plants in winter, light also plays a big role. Sure, a frost will zap cold-sensitive plants, but even if the weather remains above freezing, plants will still experience decreased growth. And that’s all because of decreased light!

To help clarify the importance of light, let’s look at the example of growing winter greens like spinach and kale in a protected structure like a high tunnel. Even if this tunnel is heated and remains above 50°, winter plants will experience stagnant growth. If you plant kale seeds in December, they will grow only an inch or so over the next month. But if you plant these seeds in September, they’ll experience multiple inches of new growth.

While the warmer temperatures slightly impact the difference in growth, light is the major factor! This makes sense when you consider plants receive about three hours more light in mid-September than in mid-December.

Some people think this slowed growth is bad, but it’s a natural plant process. Low light leads many perennial plants to experience slowed photosynthesis and respiration, which leads to decreased growth. Cold temperatures also limit enzyme function and kill above-ground plant tissue. These plants enter dormancy to survive both low light and cold temperatures and then regrow the following spring.

Planting Winter-Harvested Crops

Fortunately, you can grow many crops throughout the winter. Cold-tolerant veggies like spinach, kale, and carrots can survive frosts, and flowers like violets beautify porches and gardens even after the snow falls.

But even though these plants are cold-tolerant, it doesn’t mean they’ll grow with little light! Like all plants, they won’t experience much growth once the light drops below ten hours. And they’ll experience decreased growth as light fades leading up to the first ten-hour day.

A good rule of thumb is to plant winter-harvested crops so they’re 100% mature when the Persephone period starts. Since they won’t grow much afterward, you can leave them in the ground and harvest them throughout the winter (assuming you protect them from the cold).

Some crops that can hold well throughout the winter include carrots, kale, spinach, beets, parsnips, lettuce, and leeks. But remember that these cold-tolerant crops are still susceptible to damage from frigid temperatures! If you live in a cold climate, you may need to use cold frames, high tunnels, or row covers to protect the crops from damaging frosts.

Determining when to plant involves more than looking at the start of the period and the days to maturity on your seed packet. Remember, plant growth will slow as daylight slows. So, when should you plant crops if you want to harvest them during the winter?

Let’s look at ‘Vivian’ romaine lettuce as an example.

The seed packet states that it takes 50 days for the lettuce to grow from a seedling into a dense romaine head. However, this number assumes that the lettuce is growing in full light. If the lettuce grows in the fading light of fall, you must account for slower plant growth. 

A good rule of thumb is to increase the plant’s expected days to maturity by 40% in the fall. That means that although ‘Vivian’ will take 50 days to mature in spring, it will take 70 days to mature when you plant it in fall.

With this information in mind, let’s determine when I would want to plant ‘Vivian’ if I want it to be mature for winter harvest. First, we have to determine the start of the Persephone period. As I mentioned above, this occurs on November 26 where I live. Next, we’ll count back 70 days to reach September 17. That means I’ll want to get my ‘Vivian’ transplants in the ground by September 17 if I want them to mature by the time growth stops.

Planting Overwintered Crops

If you want to plant crops in the fall and harvest them the following spring, they don’t have to be fully mature by the time the Persephone period starts. Although the plants will experience stalled growth during winter, they’ll resume growth once the winter solstice passes and days grow longer than ten hours.

That means spring-harvested crops only need to be 25-75% mature by the start of increased darkness. When winter arrives, the more mature the crops are, the earlier they’ll mature in spring.

However, you should note that some crops are more susceptible to cold damage if they’re more mature. For example, garlic overwinters best when the shoots are only a few inches long. If the plants have put on a foot of growth, cold is more likely to damage them.

Some crops that overwinter well include onions, garlic, carrots, lettuce, and arugula. Just make sure to protect them from cold temperatures and drying winds.

Succession Planting for Fall and Winter Harvests

Since decreased daylight slows plant growth, succession planting in fall looks different than succession planting in summer. If I want to harvest radishes every week in late spring and summer, I plant a new round of radish seeds each week.

But if I want to harvest radishes each week in late fall, I’ll plant a new round of seeds every few days in mid-fall. Seeds planted two months before the Persephone period experience noticeably different growth rates even when planted a few days apart.