What is the most important factor that limits growth of vegetables in winter? While cold temperatures are important, I would make a case that the shorter winter days are even more important. Temperatures can be altered with cold frames and row covers, but we are at the mercy of day length. Plant growth slows to a crawl, and in some crop types stops completely in winter, even when temperatures are mild, because most plants require at least 10 hours of daylight for active growth.
Winter garden master, Eliot Coleman calls this period of winter the “Persephone Days,” after the Nature Goddess whose annual return to Hades in winter caused the earth to become barren.
Knowing when the Persephone Days begin will help you plan for a green and productive winter garden. I also find this information helpful in knowing when the best time to start my cool season spring plants.
Successful winter gardening is getting a head start. This means knowing when to time plantings so that they will begin to reach maturity when the Persephone Period begins. What you don't want to do is what most of us do as beginners- wait to plant until the Persephone period is underway. While in theory this makes sense, broken down it will not get you a lot of food for the winter. You will get a nice jump in early spring, but if your goal is winter veggies, you need mature plants before the Persephone Period starts.
Depending on where you are in the country, the days during winter where there will be LESS than 10 hours of sunlight start in mid-November and end about the first week of February. If you want specific times, you can look up your location on the United States Naval Observatory website for planning. I am happy to stick with these rough dates because it gives me enough to work with.
The secret to bountiful winter crops is to work around these dates. Since most seedlings need 60 to 90 days from planting to harvest, you can get a head start by planting fall and winter vegetable seedlings between mid-August and mid-September. The seedlings will take advantage of the daylight and warmth to reach maturity by mid-November. As the days shorten and growth comes to a virtual standstill, then it becomes simply a matter of protecting plants from the elements so that they can be harvested as needed.
When the Persephone Period ends in late winter is very helpful too. Most zones can begin re-sowing greens and root crops as needed to fill holes or start new rows, and peas and fava beans can be sown quite early with frost protection. I find it extremely satisfying to start seeing the new growth begin again about the end of January. There’s nothing like winter greens to cure the winter blues!
I hope this helps clear up some confusion about winter gardening!
Written by Sow True Seed's Education Director, Angie Lavezzo.