Jill Severn's Gardening Column

Astronomy for gardeners


Once, ages ago, I was a guest on a radio talk show in Vancouver, B. C., and a caller asked if he could grow tomatoes on his apartment balcony. I asked him what direction his balcony faced. He didn’t know. So I asked him whether it was sunny in the morning or the afternoon. He said he’d never noticed. On further questioning, he said he had not noticed, even when outdoors, where the sun came up or went down.

I gently suggested that he needed to do some observational research to find out whether his balcony was sunny enough for growing tomatoes.

His might have been an extreme case of celestial cluelessness, but it’s not an uncommon problem. For any gardener inclined to make New Year’s resolutions, a good one might be to make closer observation about where the sun lands on various parts of your garden at various times of the year.

For anyone who hasn’t paid attention, here are some basic solar facts: In the winter, the sun rises and sets low in the southern sky – a short trip, making for short days. After the winter solstice, the days lengthen as the sun moves further north, until it’s high in the sky – a longer trip from east to west, making for longer days. At its most northern point, we get the longest day of the year, aka the summer solstice, between June 20 and 22.

Then, as the sun slides southward again, the days become shorter.

The result is that what’s in the shade and what’s in the sun changes a lot over the course of a growing season. To make sense of what’s going on in our gardens, we need to track those changes.

For example, in my garden, there’s a 20-foot space between the south side of my house and the house next door. Right now, with the sun low in the southern sky, the sun stays below the roof of my neighbor’s house and keeps the area in total shade. It doesn’t get high enough in the sky to shine directly on the ground until spring.

Then by late summer, as the sun heads south again, the sharp line of shade creeps back across this narrow garden from south to north.

I have watched this for years, but I have never tracked the sun carefully enough to know the date on which that line of shade reaches the fence between my house and the neighbor’s in the spring. I’ve decided it would be helpful to know that because that’s where I plant sweet peas.  

So my New Year’s resolution is to identify the date when the sun reaches the fence so I can refine my sweet pea planting time and get it right every year instead of just two out of three. (I’m also thinking about sticking a thermometer in the soil to get a handle on the ideal temperature for sweet pea germination, but that’s another matter.)

I’m making my resolution in public so I’ll be embarrassed if I fail.

Maybe you live on an open prairie where the sun shines on your garden without obstacles such as trees or houses. If so, lucky you, your life is simpler. (Though you might miss shade-loving plants.) For the rest of us, paying close attention to changing sunlight and shade over the course of the growing season is essential to the refinement of our gardening skills.

Jill Severn writes from her home in Olympia, where she grows vegetables, flowers and a small flock of chickens. She loves conversation among gardeners. Start one by emailing her at  jill@theJOLTnews.com


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