Calculating Your Garden’s Persephone Days

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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.

These Asian greens were sown October 28th, and almost two months later (December 21st) are only baby-sized. Persephone Days slow growth, but don't stop it entirely -- which is good, since these will be a source of winter salads.

These Asian greens were sown October 28th, and almost two months later (December 21st) are only baby-sized. Persephone Days slow growth, but don’t stop it entirely — which is good, since these will be a source of winter salads.

 

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 you stop and consider that this is a four-month supply of fresh vegetables that will hold in the garden through winter, you understand why so much is planted.

When you stop and consider that this is a four-month supply of fresh vegetables that will hold in the garden through winter, you understand why so much is planted. (Photo November 2nd, 2014).

 

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.

Day Length Table

 

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.

Daylight Hours Explorer
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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16 Comments

  1. Texan

    December 21, 2014 at 6:45 pm

    This was very interesting, I think I will have to go to the site with the graph! I am as you say more graphically inclined :O) The photos of your garden all grown and full WOW! Beautfiul and yummy!

  2. Sandy Sparacino

    December 21, 2014 at 6:58 pm

    Ok that was so cool I did both sites and printed off my daylight graph and then my table chart!

  3. kayleigh

    December 22, 2014 at 2:46 am

    I tried the first option and I couldn’t understand or make it work. I live in Canada. It’s a bit frustrating! I like the idea and would love to have a copy for future reference!

  4. newbiegardengirl

    December 22, 2014 at 7:51 pm

    Are those the only crops you sow when your Persephone Days end? What about peas…root veggies (beets, carrots)? And when you say ‘under low tunnels’ are you referring to those covered with cloth, not plastic?

    • Cathy

      December 31, 2014 at 8:03 pm

      Root veggies don’t have time to develop when planted that late. I use both cloth and plastic-covered low tunnels, but don’t put any plastic covers on until temperatures are predictably in the teens and lower at night. Happy gardening!

  5. Jess

    December 22, 2014 at 9:49 pm

    It’s already been said, but this was a great read!! I played with both charts as well. Science is fun…gardening’s even better!

    • Cathy

      December 31, 2014 at 8:01 pm

      Glad you enjoyed it!

  6. Peggy

    December 23, 2014 at 10:09 pm

    Liked it so much I wish I had written it but I did tweet it!

    • Cathy

      December 31, 2014 at 8:00 pm

      Thank you, Peggy!

  7. Sheri K

    December 30, 2014 at 8:33 pm

    Thanks for sharing this info. My gardening site was fun to analyze – Persephone days start on my birthday (close enough for me to use that date) and end on Valentine’s day. Both easy to remember! Yay.

    • Cathy

      December 31, 2014 at 8:00 pm

      Nice! Thanks for coming by!

  8. Cliff Hawley

    January 23, 2015 at 9:14 am

    Great to see my Persephone Days are just ending. I guess this means some of my stuff that got in a little late will start taking off. I’m looking forward to purple sprouting broccoli this spring.

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  10. Laurie B

    July 25, 2015 at 9:42 am

    You didn’t really define what a Persephone day IS… You said yours starts around Nov 22, so based on the charts posted I can only assume that means whenever the amount of daylight drops below 10 hours? That would put then end of them around Jan 20th?

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