Fall Garden: Planting By Length of Daylight

Several years ago, I blogged about what I had learned about soil temperature and plant growth (“What I’m Learning About Fall Gardening.”) For awhile, I tried to plant my fall garden after the soil temperature dropped below 80°F (26.6°C). But for some reason, taking the soil’s temperature everyday became extra chore that got lost in the huge pile of other things to do. The other day, I was reading Debby Riddle’s blog Riddle Family Farm, and she mentioned the Persephone season. I had completely forgotten about that. I shouldn’t have, because the concept is extremely useful for fall and winter gardeners.

The Persephone season is a concept that Eliot Coleman mentions in his books, The Winter Harvest Handbook and Four Season Harvest. The story of Persephone is a mythological explanation of why most plant life becomes dormant in winter. Technically known as solar winter, Eliot’s observation is that plant growth pretty much ceases when daylight is less than ten hours in length. For fall planting, the recommendation is to get cold tolerant crops planted so that they are fairly well established by the time solar winter begins. A good estimate of that is approximately 75% of their days to maturity.

According to TimeAndDate.com’s sunrise and sunset calculator for my location, 10-hour days begin November 30 for me. So, for example, if a seed packet lists 60 days to maturity, I’ll calculate 75% of 60.

60 x 0.75 = 45

So I count back 45 days from Nov. 30 and plant my seed before that date. In this case, before October 16th.

I’m not discounting soil temperature, but have to say that for me and my lifestyle, having a set date really helps. My cooperative extension says to plant fall crops in August, but it’s often so hot and dry in August, that planting just doesn’t feel right. And I know from experience that if I wait until late October, I’m not planting a fall garden, I’m getting an early start on the following year’s spring garden. Intuitively, September has always felt right, so working this out systematically has been very affirming.

This dovetails beautifully with my agrarian year. My winter months are December, January, and February, and I find it fascinating that solar winter for my location begins the last day of November. I love it when all the pieces fit so neatly together.