Author Topic: Sun Screen for the Root Zone  (Read 4508 times)

Treebeard55

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Sun Screen for the Root Zone
« on: August 04, 2012, 11:29 PM »
We all know that a dark-colored pot in full sun can get so hot that fine roots beside the inner pot wall are killed. I realized about a month ago that it's a good idea to consider the heat absorption of the soil mix, too.

I was checking my containers, assessing which ones might be too dark for the well-being of the resident tree's roots. My yamadori ponderosa is still in a wooden training box, so I started to pass it by. But then I really noticed the color of the mix. The mix is 60% scoria, and much of the scoria is a dark charcoal gray; some is almost black. Even the granules that aren't gray are rather dark in color.

I laid my hand on the surface of the mix and was surprised at how hot it was! Not too hot to touch, but hot enough that I don't think it was doing the tree's roots any good.

So I cut a little sun screen out of a roll of perforated vinyl. (The sun reflectors made for cars' windshields gave me the idea.) I made a little cut-out for the trunk, and a cut from one side to fit the cut-out in place. The vinyl has some stains, but seems to work very well. A bonus is that the reflected solar rays are sent back up into the branches from below.

A sun shield like this could be made with any material that: is waterproof; reflects light; and lets air thru. Even a small white-painted wooden lattice would do the trick.
 

John Kirby

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Re: Sun Screen for the Root Zone
« Reply #1 on: August 05, 2012, 12:33 AM »
Sphagnum moss woks as well.
 

Treebeard55

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Re: Sun Screen for the Root Zone
« Reply #2 on: August 05, 2012, 09:28 PM »
You're right, John; especially the lighter-colored sphag, which would reflect a little light.

I was out of sphag, had the vinyl handy, and am still a bit leery (probably too much so) of anything that might hold too much water for too long near the roots of a ponderosa!

Jerry Meislik just suggested, on another forum, that I record some of the temperatures in the mix, with and without the vinyl. I just might do that; tho I'll have to find my soil thermometer first ...
 

John Kirby

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Re: Sun Screen for the Root Zone
« Reply #3 on: August 06, 2012, 01:06 AM »
Be like the Japanese, only water when they are dry/somewhat dry. Let us know how your experiment goes.
 

Treebeard55

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Re: Sun Screen for the Root Zone
« Reply #4 on: August 06, 2012, 12:11 PM »
Be like the Japanese, only water when they are dry/somewhat dry...

That's good advice; my only problem there is that -- typically, anyway, and this year's atypical -- we get rain often enough that the tree doesn't always dry out between rains. When I can, I do wait until the mix is visibly dry -- or almost so -- about 1/4-inch down, before I water. (Gotta say I love the color change of Turface as it dries!)
 

Chrisl

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Re: Sun Screen for the Root Zone
« Reply #5 on: August 07, 2012, 10:57 AM »
You can try also putting like a 70% sunscreen around the pots.  Here from late afternoon till sunset the pots get hit directly from the sun and the root mass does warm up very much.  I also don't think it's healthy for the tree.
 

Treebeard55

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Re: Sun Screen for the Root Zone
« Reply #6 on: August 07, 2012, 03:30 PM »
Yeah, Chris, that can also help. In the case of my ponderosa, tho, the scoria is definitely darker than the wood of the training box. So it's the mix, rather than the container, that absorbs more radiant heat.
 

davestree

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Re: Sun Screen for the Root Zone
« Reply #7 on: August 07, 2012, 04:47 PM »
John are you saying that the Japanese don't shade the roots when it is hot ?  I have always thought this was a good idea.
 

John Kirby

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Re: Sun Screen for the Root Zone
« Reply #8 on: August 07, 2012, 07:06 PM »
Davestree, no, I do believe that some in very hot climates  do shade with towels, or straw, or styrofoam over containers. What I was referring to was the fact that if you are worried about the soil heating up, you can use mulch or sphagnum to maintain moisture. Then only water when the trees are drying. I have friends in Texas who do shade pots with towels on exceptionally hot days, some keep on water tables, or both.

In Southern California, the hot areas away from the coast, I would certainly consider shading pots, but frequently placing trees closer together can provide a good amount of shade.  I guess my question is, why do you think that you need to cool the pots? Are your root systems dying off? When you repot are there no new white roots?

Typically I will say "do anything that gets you out with your trees as much as possible.", maybe I am just being overly skeptical. I think the world of Steve and what he is doing in Indiana, but if he showed me 5 ponderosa pines that he had shaded for 4 or 5 years vs 5 that  he had not shaded, then I could evaluate effect of his procedure. But, to me the best thing he could do would be to get the trees out of turface and organic and get into an inorganic mix (turface and pumice, or something else...).
 

Treebeard55

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Re: Sun Screen for the Root Zone
« Reply #9 on: August 07, 2012, 08:42 PM »
... if he showed me 5 ponderosa pines that he had shaded for 4 or 5 years vs 5 that  he had not shaded, then I could evaluate effect of his procedure.


Maybe I'll have some more substantial data in a few years, John; it would be useful to know just how much difference a screen like this makes, and not just for ponderosas.

...But, to me the best thing he could do would be to get the trees out of turface and organic and get into an inorganic mix (turface and pumice, or something else...).

This tree is now in 10% organic, 30% Turface, and 60% scoria. It will probably be repotted next spring, and I'm seriously considering eliminating the organic component. I do want to do a little research on cation exchange capacity first: organic matter and colloidal clays are supposed to be best for that. Maybe the CEC of scoria-Turface will turn out to be OK.
 

Chrisl

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Re: Sun Screen for the Root Zone
« Reply #10 on: August 08, 2012, 11:28 AM »
I've only put up a screen when we had those days of>100F earlier this summer.  The pots were scorching hot and the soil was very warm; my reasoning being most roots don't like it that hot.  I keep the soil moist, but the temp of the soil/substrate still gets very warm.  I don't have factual evidence of any benefits, but figured it wouldn't hurt.
 

0soyoung

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Re: Sun Screen for the Root Zone
« Reply #11 on: August 08, 2012, 12:23 PM »
I've only put up a screen when we had those days of>100F earlier this summer.  The pots were scorching hot and the soil was very warm; my reasoning being most roots don't like it that hot.  I keep the soil moist, but the temp of the soil/substrate still gets very warm.  I don't have factual evidence of any benefits, but figured it wouldn't hurt.

Roots only grow at temperatures in the range of 40F to 95F - see the Warnell School of Forestry for example. Roots of most temperate species die at temperatures above104F (Google 'supraoptimal root temperature'). The science has been done for years now. Ya'll just need a simple 'meat thermometer' probe, say, to measure your soil temperatures.
« Last Edit: August 08, 2012, 12:28 PM by 0soyoung »
 

Chrisl

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Re: Sun Screen for the Root Zone
« Reply #12 on: August 08, 2012, 12:30 PM »
Good idea Osoyoung.  I didn't know the upper range of root growth can be as high as 95F.  I was thinking in the mid 80s.  Thanks for the info!
 

rockm

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Re: Sun Screen for the Root Zone
« Reply #13 on: August 08, 2012, 02:22 PM »
I think the tolerances mentioned could have a lot of leeway. Ponderosas and some other pines (like pitch pine) grow in places where their roots are hemmed in by solid rock. Such rock bowls are pretty harsh environments, with shallow root zones and wildly fluctuating temperatures, as well as moisture levels.

I'd think (and I have no research to bear this out) that ponderosas are quite capable of handling both very high and very low temperatures. I haven't provided much cover for the Pondy I got from Andy Smith. It sits in full sun all summer. I water it two or three times a day, as it is in an extremely porous mix of dry stall and pumice in a six inch deep pot that's about 20" x 12" or so. I've only covered the pot with a wet white towel two or three times when temperatures approach 107.

It hasn't shown any signs of stress and is putting out pretty massive growth.
 

davestree

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Re: Sun Screen for the Root Zone
« Reply #14 on: August 09, 2012, 10:38 AM »
Ponderosas are one thing but just about everything else doesn't like too much heat.  Some of the trees I have in full sun, like black pine, I make sure to shade the pot.  Especially the smaller pots.  During the recent heat wave many of my trees were on the ground in the grass where they stayed much cooler and put on growth.