Reading about climate change has made me aware of the importance of white arctic ice in reflecting sun and keeping our planet cool. The term albedo is often used in articles describing the thermodynamics of white ice reflecting sunlight and black earth absorbing heat: white reflects sunlight, black absorbs the sun’s energy.
We all implement the albedo phenomenon when we wear white on a hot summer day and stay off the asphalt. A visit to Guatemala some time ago showed me how people routinely use black water tanks to heat water for showers and surround summer gardens with white rocks. Living in New Mexico where we have over 300 days of sunshine per year, there are many ingenious strategies for using white materials to reflect sunshine where heat is a problem and using black materials when heat is desired: roof-tops, side-walks, and porches.
Today, I mixed an old can of white, indoor latex paint with 50% water and painted over the sun-scald on 20 fruittrees. Then took the thinned white paint and covered an over-exposed garden bed as shown in the picture. Another project this year involved hanging black curtains in a cold adobe building to absorb sunshine streaming into the building.
Inspired by the absorbing power of black and the reflecting power of white, I’m asking for Permies experiences: how have you strategically used black and white in your landscape?
I have fairly challenging light conditions on my 1/3 acre. The neighbor has tons of unkept Norway maples on my southern fence line, to the east are a pair of hundred year old sugar maples, also on a neighboring property. I have good sun to the west, which is also the front of the house, so I need to keep up appearances in my nascent permaculture garden. The north is shaded by the house.
However, I actually have had some decent plant growth on the north side of the property. There’s a fairly tall white picket fence that catches and reflects afternoon sun, and even a bit of morning sun, so it isn’t as full shade as one might expect. It’s not deliberately planned, but it’s working out.
Clay, shade, neighbor’s Norway maples.....we’ll work it out.
Hi Daniel and thanks for your reply.
Your post is very helpful to me. Originally, I thought that the white object would be cool and thus not reflect back any energy. But of course heat is only one form of energy. Your post caused me to look further. The fact that we see a particular color means that the object so "colored" is sending out wavelengths of that part of the white light spectrum: energy. When we see white, all the wavelengths are reflecting back. I'm no expert but it sure sounds like your plants might be thriving because they are receiving the all the visible wavelengths of light bouncing back off your white fence. In a hot climate like that in New Mexico, those full visible spectrum rays would help the plants grow without the radiant heat from a black surface frying them. Thank you for your observations and inspiring me to look more deeply into what is happening in the landscape.
Yep, you’re exactly right. White object reflect all, or mostly all, of the visible spectrum of light, so they do end up feeling cooler to the touch. In New Mexico, you’d most likely be using that to keep objects cooler. In my case in Pennsylvania, I’m capturing some small amount of light that would otherwise be lost to me.
It’s a great question. I was just reading that flat white paint reflects light most efficiently, at around 75-80%, whereas semi-gloss is less efficient, at closer to 50%. The page I found was about indoor growing, but I imagine the lessons still apply.
Hello and thanks for this link Daniel. Flat white paint at 75-85% reflective power vs aluminum foil (and mine would be wrinkled) at only 35%?! Now that's fascinating. In addition to growing healthier plants, I'll use that information while building my black (exterior) and white (interior) solaroven. Very useful.
Have a beautiful day Daniel.
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