To explain seasonal changes, the ancient Greeks told the story of Persephone, goddess of the Spring, who was abducted by Hades and taken to the underworld. Her mother Demeter, goddess of Agriculture, was filled with grief and neglected the earth, creating a famine. Zeus interceded with Hades and negotiated Persephone's return. However, since she had eaten four pomegranate seeds, she has to stay in the underworld for four months each year. During that time Demeter mourns her daughter's absence, causing the earth to enter a period of dormancy when nothing grows until Persephone's return.
This mythological story serves as an allegory for the seasonal changes we see in nature, particularly the transition between growth and dormancy in plants. Today you may still hear the time of winter dormancy referred to as the Persephone Period. In his book The Winter Harvest Handbook, Eliot Coleman describes the Persephone Period as the time of year which begins when daylight falls below 10 hours per day and ends when it rises back above 10 hours. Because most plants need more than 10 hours of daily sunlight for growth, we can use this concept as a guideline to help us know when to plant and harvest as we transition into the winter months.
To find out the local dates of the Persephone Period in Contra Costa, we used the tool developed by the Naval Observatory. This year the Persephone period in Contra Costa starts on November 20 and runs through January 22. Between those dates our gardens will be largely dormant. Plant growth slows down or in some species halts completely as the plants seek to conserve energy for the chilly months ahead.
The secret to healthier plants and larger harvests is to work around these dates. For your winter garden, time the planting of cold-hardy vegetables (leafy greens like kale, spinach and Swiss chard, or root vegetables like carrots, turnips and parsnips) to give them ample time to establish before the temperatures get too low. If you plan to grow from seedlings, knowing the dates of the Persephone Period will help you decide when to sow. A rule of thumb is to seed your plants so they are about 75% mature by the time you enter the Persephone Period, which means starting your seedlings between mid-August and mid-September. This timing will allow them to take advantage of the daylight and warmth to reach maturity by mid-November.
This year it may be too late for you to use the Persephone Period to plan your winter garden. But you can still use the end of the Persephone Period in late January to remind you it's time to plant seeds as your garden begins to return to life.
Help Desk of the UC Master Gardeners of Contra Costa County (RDH)