Prairie View

Tuesday, November 22, 2022

Gardening: Persephone Period

I'm experimenting with a new blogging format.  That is, instead of trying to pull together various threads of content in coherent essays or substantive paragraphs, I will write about one detail at a time.  For this I will adopt titles similar to what Facebook calls hashtags.  Here the titles might often consist of two words, a general category and a specific topic in that category.  On FB, hashtags appear with a pound sign in front of a subject (#oftenarunononelikethis).  I've never done it, but I think that makes possible a search for content on that particular subject. Since we are at the beginning of the Persephone Period where I live, this will be the topic of today's post. It's a subtopic of gardening.   

Persephone Period (per-SEF-uh-nee) refers to the time of year when daytime consists of fewer than ten hours of light.  I will use the term in abbreviated form at times.  At our latitude, this period extends from November 21 to January 21.  It's easy to remember this if you note that it starts a month before the winter solstice and extends to a month afterward.  The duration of this period varies, based on how far from the equator a location is, but it always centers on the winter solstice, and extends an equal distance on either side of that.  We are at approximately 38 degrees North Latitude.  Every location at this latitude in the northern hemisphere will have the same Persephone Period.  Places north of here have a longer Persephone Period and places south of here have a shorter one.

This period of limited daylight coincides with the slowest plant growth of any time of year, even for plants that are cold tolerant enough to stay alive through the winter.  Photosynthesis depends on sunlight, and, not only does sunlight not last very long at this time of year, it enters the atmosphere at such a low angle that even at high noon it's "weak." This happens because the sunlight is passing through a lot of the density of the atmosphere instead of mostly the vacuum of space as happens at high noon on the summer solstice.  

In practical terms, reckoning with Persephone means that gardeners are able to think beyond first frost dates--usually thought of as the end of the growing season.  For fall crops, conventional wisdom says that everything should be ready to harvest before the average date of the first killing frost.  If you plant cold-hardy crops, however, they will be able to survive and even grow beyond the first killing frost.  In other words, they have varying levels of cold tolerance beyond a minimum temperature of 32 degrees, and can continue to grow for about another month under typical fall conditions. For crops like this, Persephone can be considered the end of the growing season.  In our area, this means we can add a month to our growing season for cool season crops.  

This year was not a typical year for us.  Unseasonably cold weather arrived before the middle of November and hung on for several weeks.  Nighttime temps went down to 15 degrees--colder than almost all cool season garden crops typically tolerate.  I covered what I could in the garden, but I haven't had the courage to uncover everything to examine how things fared.  Sometimes our relatively mild fall weather continues into December.  

One more tidbit I picked up recently relates to how cold hardy plants deal with cold weather in relation to their growth cycle.  If plants are the heading-followed-by-flowering type (think cabbage, cauliflower, and broccoli), productivity will occur under one of several cold weather scenarios.  1.  They will be planted early enough to produce a harvest before intolerably cold  weather arrives.  2.  They will  grow to maturity before Persephone, but will survive outdoors throughout the winter, perhaps with some protection like mulch or row covers.  3.  They will be so small at the beginning of Persephone that they have not begun to form a head.  They will survive through the winter and then start growing after Persephone and produce an early harvest in late winter or early spring.  

It's likely to result in a lack of productivity if  heading has started before Persephone.  In that case, the plants will likely bolt to seed almost as soon as growth starts again after Perspehone.  

I found another nuance of growth timing from reading.  It's related to another part of the plant growth equation, soil temperature.  Soil temperature usually has a lag time of about three weeks in relation to the Persephone Period.  In other words, soil temperature can actually still accommodate some plant growth for three weeks after Persephone starts, and it will likely not warm to suitable temperatures again till three weeks after Persephone ends.  What this means is that the growing season can possibly be stretched two notches after the average killing frost date.  The first stretch lasts till Persephone begins and the second stretch lasts another three weeks.  

Persephone was a character from Greek mythology.  Because part of her story involved Persephone being banished for a period of time each year, the garden guru, Eliot Coleman, used her name to identify the sun's "going away (or banishment)" period.

 I used the NOAA (National Oceanic And Atmospheric) weather site to find our latitude location, although I'm sure that many other sources would have this information as well.  Information on Persephone Periods is available on the Johnny's Selected Seeds website.  I don't remember how I found when we have our Persephone Period, but I'll leave that to you to figure out for your location.  Google is your friend for answering questions like this.  Do leave a comment or shoot me an email though if you'd like for me to help you with this.  

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