Ah, late February. Punxsutawney Phil (only a 45-minute drive away from the farm) predicted six more weeks of winter, and it sure seems like he was right. This month saw a brief respite from the deep freeze of January, but we’re right back in the middle of another very cold stretch, with lows in the single digits and highs in the low 20s. We’re still a far cry from the warm, sunny days of spring.
Or are we? As a farmer, a major lesson I’ve learned to take note of is that the main driver of plant growth has much less to do with the temperature than with the angle of the earth towards the sun. It may seem like we’re still in the doldrums of winter, but in fact the earth is rapidly bringing sunlight back to the northern hemisphere as we speak.
The Solar Cycle
I could tell right away that this mid-February cycle of cold temperatures was much different than the one in January. The clues lay in the patterns of snowmelt the afternoon after we received a couple inches of snow. Whereas in January, the snow would barely melt on the limbs of trees even in the afternoon sun, this sunny day melted large swaths of the ground. Despite the air temperature staying 22, the sun felt warm and strong.
I took a look at a chart showing the number of hours of sunlight per day in our region, and we’re very quickly coming up on 11 hours of sunlight per day. That may not seem like much, but it’s similar in terms of sunlight to mid-October, hardly a frozen time of year.
Not only that, but the amount of sunlight is accelerating at full speed. The earth’s tilt toward the sun follows a sort of parabolic curve, meaning that the amount of sunlight day by day is relatively constant around the summer and winter solstice, but changes dramatically day to day around the spring and fall equinox. We’re approaching the spring equinox in around a month, and that means that we’re gaining 2-3 minutes of sunlight every day.
As the chart shows, the change in sunlight across the year has everything to do with latitude. We are almost directly on the 40th parallel here, and that means that our sunlight ranges from a mere 9 hours and 15 minutes in winter to a whopping 15 hours in mid-June. This swing is even more pronounced as you go north. The northern US, Canada, and much of Europe are well north of here and experience even longer days in summer and shorter days in winter. Likewise, sunlight around the equator remains fairly constant year-round.
What Does This All Mean?
Okay blah blah blah sunlight is getting stronger every day, who cares? To my point above, growing plants has everything to do with sunlight. Much work has been done to understand how vegetables specifically respond to different amounts of sunlight. There is a rough consensus that when the amount of daily sunlight drops below 10 hours, most plants no longer have enough photosynthesis power to keep growing.
As a farmer, I’m thinking about how to extend the growing season to have fresh food available as often as possible. We start to dip below that 10-hour threshold in mid-November here at the farm, which means that if I want to harvest things past that date, my plants need to be mostly mature before then. This dictates when I start those very late-season crops like lettuce, kale, and spinach.
When do we start to get back above 10 hours of sunlight? Well, right about now in early-mid February! Not only am I able to feel the strength of the sun on my face even in the cold weather, but I can see the plants that have been sitting still in my high tunnels begin to stir and grow again.
In a way, this time of year is the very first sign of spring. While most others might think more about forsythia blooms or mowing the lawn, farmers are delighting in the simple fact that the earth is tilting back toward the sun. From here until June, the trend of growth will accelerate until the amount of life on the farm is exploding each and every day.
Cheers to the sun! Stay warm.