Painting trunks for sunburn and rodents

General Fruit Growing
#141

I have never tried. but for heat management white works best. but a verry light green will likely also be oky. And blends in better. it will protect a little less against heat. But likely is better than the darker bark colour. I also suspect that white paints protects a little against UV. And for that id expect no difference between the white and light green paints.

What color is a mirror?
We see the colour of an object because objects reflect a lot of light back. They also absorb some light. The light they absorb usualy gets changed to heat energy from the light energy. This is how an objects heats up from laying in the sunlight.

If we see an object as light blue, that means it reflects back a lot of light (thats why it’s a lighter not darker coloured blue) But it also means it proportionally sends back more blue light than other colours light. It absorbs the other colours proportionally more than the blue colour. And thus it looks blue to the human eye

How bright an objects apears to us depends on how much (and what colour) light it reflects back. Lighter objects reflect back more light. Darker ones absorb more. White sends back most visible light and the darkest black absorbs most visible light and thus sends back the least visible light.

There is more light than humans can see
You might wonder why i specified “visible light” in that last part. Thats because humans only see a verry limited amount of the light spectrum. For example we can’t see Ultraviolet or infrared light. You can look at the luminous efficiency function

If you look at the luminosity fungction. You can see non colour blind humans are most sensitive to 555nm light. Which we see as green or yellow green.
Our eyes are much less sensitive to red and blue light. So you need more blue or red light to see somting as bright, than you’d need green light to see somthing as bright.

You = lightbulb?!?
All objects with an temperature above absolute 0, give of light. colder objects infrared, warmer objects go to visible light. Thats why your skillet on the stove feels warm if you hold your hand next to it. it gives off enough light that your skin absorbs and turns into heat to feel it. Humans just can’t see it. However if someting gets hot enough it starts to look red, this is because at higher temperatures the light colour that the object emits changes, and than falls into the human vision range.
The surface of the sun is aprox 5800 degrees kelvin. And sends out a light spectrum matching that colour.

This is also how we rate the colour of lightbulbs. How hot the sun would have to be to emit that colour light. Lower kelvin bulb like 4000k are thus more yellow/orange/red. And higher kelvin bulbs like 6500k look more blue.

The old 3300K incandesent light bulbs actualy got to 3300K degree’s (~5000 farenheit)

back to us, we send out light. it’s just not visible because our eye’s can’t see infrared. But some animals can. And we thus look like a light source to those animals. We literaly glow in the dark!!!

If you scroll down on the luminous efficiency fungction wiki page. you can see how a small change in light perception can make some-one colour blind
most non primate mamels have the same vision as colour blind humans. And thus have a lower sensitivity to red light. You use this effect when looking at animals at night with a red light source. That way you don’t spook them using red light, they are “coulor blind” to the red light.

green+red makes yellow but green+red makes not yellow.
This is awesome to mess with peoples mind. Especialy fun experiment to do with young kids.

If you mix green and red light from for example Green and Red LED’s. You see a bright yellow.

However if your mixing green and red paints. you get a dull brown.

This is because with paint, the color is seen because the paint filters (absorbs) “all” colours light except the colour the paint is.

So green paint reflects Green light back
And absorbs Blue and Red light. (R- G+ B-) (could say that as R- G+ B- To signify it decreases Red(-) but increases Green (+) and decreases Blue(-)

Red paint reflects red light back,
And absorbs Blue and Green light (R+ G- B-)

Blue paint reflects back blue light.
And absorbs Green and Red (R- G- B+)

So green + red paint
(R- G+ B-) (green)
(R+ G- B-) (red)
makes
( B–) (brown)

You would almost expect to get black. Since all 3 colours are absorbd (Blue and red get absorbd by green paint. Blue and Green get absorbd by red paint)

However both Red and Green get also reflected. So you end up with a confusing mixture of black and yellow = roughly brown. (also the paints are not perfect)

Yellow = oposite blue?
This is why your printer does not use Blue Green and Red ink. But Magenta (purple) Cyan (blue/green) and Yellow.

Magenta reflects back Red and Blue. And absorbs only green. (R+ G- B+)
You could see magenta as “opposite Green”

Cyan Reflects back Green and Blue. And thus absorbs Red (R- G+ B+)
“opposite Red”

Yellow reflects back Red and Green. And thus absorbs Blue (R+ G+ B-)
“opposite Blue”

Mixing these gives “better results”

Mix yellow with megata.
(R+ G+ B-) (yellow)
(R+ G- B+) (magenta)
makes
(R++) (red)

see Color mixing - Wikipedia

Now back to some tree painting relevance.
Since our eye’s are so sensitive to green light. Light green paint apears lighten than it actually is. So a light blue or light red (pink) paint would likely reflect more light. However, the sun does not send out the same amount of each colour light. And a lot of what it sends out we can’t even see. Like infra red.
Practicly light colours stay cooler. And colours that reflect back more infrared can become even cooler.

Cool brown?!? Cold brown? how would you call a brown paint that stays cooler in sunlight?
There are also special paints that have pigments we can’t see. But reflect more infrared light. And thus heat up less in the sun.
https://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-14282015000300010

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#142

Oscar, this is interesting and very well written, amazingly so given English isn’t your original language (you are Dutch, right?), but what is astounding is that you composed all this, minus Wiki paragraphs, which, interesting as it is, far exceeds the scope of the question.

How do you find the time… and in spring?

#143

@ alan thanks :slight_smile: . I know it went a little off topic. sorry for that :sweat_smile: but still it had some relevance on the colour of paint and how it reduces heating. It’s also somthing to me at least thats fun/wonderful to learn :grin: and i have fun showing it to others :smiley:

Im not a native english speaker yes. Im Dutch.
How did i find the time? i diden’t, i could not finish it before… But it sometimes rains and there’s something going on worldwide that makes everyone spend a little more time inside right now :pensive:

To finish the light/paint colour story

yellow light/paint is not all the same.
Next to the combination of green and red light thats forms yellow. There is also pure yellow light.
You have different wavelengths for each colour. Yellow for example is ~ between 560-590 nm
red 635-700nm and green 520-560nm

Multiple ways to “make” yellow
So you can “make” yellow light 2 ways

  1. use “pure” yellow light of wavelengths between 560 and 590 nm.
  2. use a combination with no actual yellow light. But trick your eye’s into seeing yellow by using the right combination of red and green lights.

The same goes for paints and objects. Some paint’s/objects can seem yellow because the reflect red and green in the right amounts in the right light. And some seem yellow because they reflect the specific yellow wavelengths of “pure” yellow light.
Most of the time it’s a combination of the 2.

Faking it
A lot of our screens and printers work on the faking yellow with the right combination of red and green principle. This is why we only need 3 different coloured ink cratridges and not hundred (thousands).

But this “explains” why some objects/paint colours seem “off” when viewed under fluorescent or some LED lights.

And why the color yellow can look yellow under white or a combination of red and green light. But might look off when viewed under pure yellow light.

Changing the colour of “pure” light. Fake glow in the dark
An extreemly beatiful effect is when pigments absorb light of shorter wavelengths (for example blue 450nm) and re-emmit it with a longer wavelength. (for example green 550nm)

Since our eye’s are roughly 20 times more sensitive to green light around 550nm than to blue light around 450nm we see these pigments as if they where a light source. While actualy they only “shift” light thats already there to be more visible by us. They help us “see” whats already there

Some corals do this. and people use a lot of violet and blue light in their aquariums to give this “glowing” corals effect.

Short video showing of these fluorescent corals (you can mute sound if you don’t want to hear talking about corals/aquariums, just the pictures are amazingly beatiful)

Longer video showing you how different things (corals) look under light sources with different wavelengths of light (different lights side by side from 1:15 on)

see the light source slowly become more blue and how that changes the colours

amazing how they look. i can (and have) watched for hours.

Im sorry if this was to much off topic. Maybe i should move these posts to a seperate topic in the lounge? (how would i do that??)

4 Likes
#144

Wait, painting tree trunks is a thing? Should we just paint all our tree’s trunks, or what are the guidelines?

#145

Hi, @mamuang . My domestic lionhead rabbits savor bitter plants like dandelions and chickory, so there may be a different chemical that rabbits are sensing. Laura

#146

@Drew51 , you just gave me a great use for the hot, hot pepper that I’ll probably never use up. Thanks.

1 Like
#147

As the post title suggests it is for reducing sun and pest damage.
Some trees can be damaged by the sun in cold climates in the winter…the sun heats up the bark which causes it to expand or lose dormancy, then when the sun goes down it cools rapidly to the ambient temp which causes cell death. This ultimately leads to wounds on the tree and potential death of the tree.
painting the trunk white causes the sun to reflect and reduces the heat absorption by the trunk, thus preventing the thaw/freeze cycle that causes the damage.

1 Like
#148

  1. So this is only for winter? What month should I start painting the trunks of my trees? September/October?

  2. I know that my grapevine and pomegranate have lost some of their bark down at the base. Will that doom them down the line?

  3. How come if it’s so important, it’s not talked about much if at all. I’ve never encountered a YouTube video discussing it, and this is the first post I came across on this topic. You would thing something so important would be more talked about, at least on YouTube.

1 Like
#149

Yeah! :slightly_smiling_face: Glad to know I’m not missing anything.

So far as I know, painting trunks is customary in the fall (or every other fall). Snow reflects the sun in the early spring and can heat tree trunks above freezing. Extremely cold nights cause the trunks to freeze again, causing tissue damage, which looks like split bark. White paint reflects the snow-light and reduces the thawing and subsequent refreezing.

#150

I think it’s only important for some trees in some climates. Not like you need to rush out and paint every tree or vine you have :grin:

I only learned about it in my research over the years on pawpaws. If you spend much time at all reading about them, you’ll definitely hear about painting trunks.

#151

Kind of pricey but here is the OMRI listed solution to latex paint: Introducing new Eco-Orchard Paint! – milkpaint

It’s what I am now using.

3 Likes
#152

Santa Rosa, Elephant Heart and Satsuma plums as well as apricots seem like prime candidates here in S. NY to paint. They often suffer cambium damage sometimes dying as a result. Other times they can be stunted by it.

The only thing that stops me from doing it in my nursery is fear of how my customers will react to painted trees- that and the time.

2 Likes
#153

Before the summer heat arrives just a reminder some trees trunks readily sunburn.

#154

Blake…how has the eco-orchard milk paint worked for you? Are you planning to use it again this winter? I’ve been looking for some information on it, but the MSDS on their site has a link to the wrong product.

#155

It works well. However it also degrades faster than latex paint and lasts one season. However, latex paint only lasts about one season as well. They both work about the same in my experience, so it boils down to whether you are OK using latex paint or you want a more organic option. Either way most fruit trees benefit in multiple important ways from seasonal painting with white paint.

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#156

Just a related anecdote about reflectivity and heat adsorption . Some years back I got a used propane tank for the new greenhouse. It was painted silver. Propane guy checked it out and filled it, then a few weeks later on some hot, sunny days I noticed the release valve venting a bit of propane. I called the propane shop and they said paint your tank white. I did, and it solved the problem. The difference in reflectivity between pure white and silver (which is white with a bit of black mixed in) was dramatic.

As this relates to tree trunks, if you live in a very sunny area where sun scald is a potential problem, probably worthwhile to use white paint to be safest. Other light colors will work to an extent, but white really will do the best in keeping the heat out.

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#157

Welp, we’ll see how it works. 1/2 gallon interior latex, and about a pint of castor oil. I was going to do 2:1 but then I read the castor oil label which recommended something like 6 oz per gallon… I used maybe half of my quantity for 24 smallish fig trees, some single trunk some multi.

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#158

Painted about 1/2 my trees today. I lost so many trees to rabbits last winter that this was essential.

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#159

Painting the tree trunk doesn’t stop rabbits. I paint the tree trunk every year and the rabbit still chewed trunk every year.

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#160

Hmm, IV organics claims that rabbits are stopped by their paint. They claim that castor oil in their paint makes the bark inedible. I guess I’ll have to protect with chicken wire also.

1 Like