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How to map your garden's sun exposure

Morning shadeThey sell fancy gadgets to map the sun patterns in your yard, but it's not too tough to simply jot down shade outlines on a map a few times a day.  I opted to measure at 10:15 am, 1:30 pm, and 4:30 pm to get a good overview of the peak sun hours.  (Well, to be honest, I forgot I'd planned to make a sun map or I would have drafted an earlier morning map as well, and by supper-time, I wanted to be done with the project.)

My goal was to figure out which parts of the yard count as full sun, partial sun, or full shade around the summer solstice.  When gardeners talk about full sun, they mean an area that receives at least 6 hours of direct sunlight during the peak sun period (when you'd want to be wearing sunscreen): between about 10 or 11 am and 4 or 5 pm.  Partial shade/partial sun generally refers to 3 to 6 hours of sun, with less of an emphasis on getting that sun during peak hours.  (In fact, some partial shade plants Early afternoon shade mapmight burn to a crisp in bright afternoon sun.)  Full shade generally means that an area only gets light dappled through trees, perhaps with a couple of hours of direct sunlight.

When naming the type of sun in your garden, though, you also have to take your distance from the equator into account.  There's a reason that growers in equatorial areas came up with the concept of forest gardening and placed vegetables under their trees --- scorching sun in Mexico might be so extreme that "full sun" plants would prefer quite a bit of shade during the early afternoon.  On the other hand, if you live in Alaska, I'm not so sure that an hour of sun around noon would even count as half an hour of full sun.

Finally, there are more complex issues to consider.  Plants prone to fungal diseases (like tomatoes) really should get hit with sun early in the morning to dry off their leaves.  Late afternoon sunMeanwhile, I'm considering planting a peach or two in an area with only afternoon sun to slow the trees down in the spring so their flowers don't get nipped by frost.  And partial shade can be handy for eking spring crops out in the summer heat, especially if the vegetables are only bearing leaves.  (Leafy vegetables, in general, need less sun than vegetables who will be asked to produce fruit.)

If you have a graphics program that allows layering and transparency (I use the free program GIMP), it's simple to merge all of your day's maps together and decide which parts of your yard get what kind of sun.  As you can see from the composite image below, our clearing in the forest gets full sun only in the very center, with the east end shaded by trees in the morning and the west end shaded in the afternoon.  The powerline cut provides a bit more Sun map of the gardenof a full sun zone, and the spot behind the barn where we recently felled some trees to dry up the barn wall has a little pocket of full sun as well.

Of course, the patterns change dramatically throughout the year, so I'll make another map at the winter solstice, if I remember.  (Maybe at the equinoxes too.)  I know from the melting pattern of snow that the sunniest winter areas are quite different from the sunniest summer areas, with most of the warmth being concentrated in the mule garden.  (There's a big hill on the south side of our core homestead, so when the sun dips lower in the winter sky, it doesn't reach the southern parts of the yard much.  On the other hand, leaves are off the trees during the winter, so the forest giants edging our core area block less light.)

Hopefully getting a better handle on sun and shade patterns will help me fill in the gaps in our homestead most efficiently.  Already, I'm eying that area behind the barn for some kind of plant, and am realizing that the coop for the poor broilers is in the sun all day long.  Aren't maps fun?



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I would be very interested to see the winter maps if you ever draw them up. I plan to map out the sun/shade patterns on our land every season, too. It would be fun to do it every month even and then compare it to Google Earth's sun/shade approximation!
Comment by mitsy Mon Jun 25 16:07:57 2012

Mitsy --- I definitely recommend the mapping project. It's lots of fun and helps you notice shade patterns better than you'd see just looking on a map.

I admit to being a bit dubious that Google Earth could figure out our highly complex shade pattern, unless I went to a lot of trouble measuring the height of and adding in the trees encircling our core area. But who knows! I haven't actually played that much with Google Earth.

Comment by anna Mon Jun 25 19:27:55 2012

I have never thought of making a sun exposure map- what a great idea! I will get to work on my own right away. Well, after a few things... Maybe tomorrow.. :)

Comment by Eric in Japan Mon Jun 25 20:11:55 2012
Eric --- I hope you'll post your sun map on your blog! I'd love to see it.
Comment by anna Tue Jun 26 07:57:31 2012
Anna, I recently made a solar chronometer for less than $5. Just take the solar cell out of a solar pathway light from the dollar store and wire it to the battery terminals of an old or cheap analog clock. In bright sun the clock will run, but in shade it stops. If you set the clock to 12 and sit it in the yard, it tallies your hours and minutes of full sun. Of course unless you make multiplies, this really only works for one spot at a time, but it is set-it-and-forget-it.
Comment by Josh Tue Jun 26 07:58:44 2012
Josh --- I read about a system like that online and instantly wanted to make one! We'll have to keep our eyes open for a cheap analog clock. (We have lots of solar yard lights because Mark just thinks they'll be useful.... :-) )
Comment by anna Tue Jun 26 16:48:41 2012