Calculating Your Garden’s Persephone Days
What’s the most important factor that limits growth of vegetables in winter? You’d be right if you said colder temperatures, but shorter winter days are a close second. Plant growth slows down dramatically in winter, even when temperatures are mild, because most plants require at least 10 hours of daylight for active growth. Winter gardening guru, Eliot Coleman (see below), describes this time period as the “Persephone Days,” after the vegetation goddess whose annual return to Hades in winter caused the earth to become barren. But even though plant growth may slow dramatically in winter, your garden doesn’t have to be empty.
Knowing when the Persephone Days begin will help you plan for for a green and productive winter garden. The key to gardening in winter is getting a head start — time plantings so that they will begin to reach maturity when the Persephone Days begin (see Note below). Since that’s around November 22nd at my latitude, I complete the bulk of my planting between mid-August to mid-September, since most crops take around 60 to 90 days to mature. After the Persephone Days kick in, it’s simply a matter of protecting plants from the elements so that I can harvest them as needed (I call my low tunnels “living refrigerators” for that reason).
When do the Persephone Days begin in your part of the world? Here are two easy ways to find out. The United States Naval Observatory provides an online tool that produces a Duration of Daylight Table for any location in the world. Here’s an example for my garden.
For those of you that are more graphically-inclined and know your latitude, the University of Nebraska-Lincoln has a nifty tool that allows you to explore a graph of your location’s yearly day length.
Knowing when your Persephone Days end is helpful, too. I begin sowing cool-weather crops like fava beans, mache, spinach, and lettuce in my low tunnels around February 1st, which is soon after the Persephone Days end for me. And it’s fun to watch how growth of the over-wintered crops suddenly speeds up again. Winter greens are a great cure for the winter blues!
Additional Winter Gardening Resources:
These books are in my personal library, and I highly recommend them (these affiliate links cost nothing extra to you, but generate advertising fees that help me support this blog):
And more from me:
For more information about vegetables that you could be growing this winter, check out my Winter Vegetable Planting Guide, and guide to 10 Vegetables More Cold-Hardy Than Kale. And for more winter gardening resources from me, including how to build an inexpensive low tunnel, click the winter gardening tab above.
Note: Some folks will tell you to do an additional calculation for your planting dates for fall harvest — adding 14 days to account for the “fall effect” of cooler temperatures and shorter days, plus an additional 14 days if you’re planting transplants (to account for transplant shock). This calculation is great for fall harvests, when you might not be using low tunnels to protect plants into winter — it insures that you’ll be able to harvest before deep freezes arrive. For winter harvests, this additional calculation isn’t necessary, as even though plant growth slows, it doesn’t stop completely, so vegetables will continue maturing through March. My only exception to this rule are brassicas like cauliflower, broccoli, and some of the less-cold-tolerant cabbages; since these can’t survive my Kentucky winters, even under low tunnels, I plant these for fall harvest and use the 14-day addition to maturity.
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