Reducing soil temperatures when using a black, plastic training pot

[Emanon]

Does anyone have any recommendations for the best way to insulate or otherwise modify black, plastic training pots for the purpose of lowering the temperature of the soil?
I live in zone 10b and the temperature in summer regularly rises above 100 degrees Fahrenheit/ 38 degrees Celsius. When this happens, I inevitably start to worry about my "full-sun" trees that I have in black, plastic training pots. I usually just cover my pots with aluminum foil but I've found the foil hard to maintain (keep clean, whole and thus effective).

I attached an article that I found on the topic, "A Solution to Heat Stressed Roots in Bonsai Pots," in Bonsai: The Journal of the American Bonsai Society, vol. 43, number 3, at 20-21 (2009), where the author uses an aluminum foil bubble/foam core insulation product. I'm thinking though that I should mostly, or solely, be concerned with blocking radiant heat and less concerned with neutralizing heat transferred via conduction. I basically just want a product (I think) that is the best and/or most efficient at blocking/reflecting sunlight. I shouldn't be concerned with a product's R-value and how good it is at "insulating" my pot. The bubble or foam core just seems to be of little benefit/wholly irrelevant to a containerized plant. And, with these types of products, the foil seems flimsier, more wrinkled and thus harder to keep clean than a thicker aluminum "radiant barrier" product.

I don't know why exactly but I have read that when installing radiant barrier insulation in an attic, it is best to leave an inch of air space between the foil and the roof (i.e. let it droop). If I apply a radiant barrier insulation then, I was thinking it might be best to have the foil come straight down from the pot's lip and attach it to my bench, instead of crumpling it tight against the pot's walls. Has anyone tried that? Also would perforated or not be better?

I was also looking at aluminum foil tapes that can be applied with less wrinkles than just aluminum foil, making it easier to keep it free from dust and mineral buildup (and thus more reflective). But if I did, I have no idea what the difference is or would be between the various foil tapes (rubber, acrylic, or silicone solvent?) (regular vs. HVAC tape vs. a SCIF tape).

Finally, my neighbor has this Insuladd product that can be mixed in with paint. I was thinking of asking him for a few cups and then adding it to some left over white, marine topside paint that already provides UV protection. Has anyone tried Insuladd or a product like it? It's obviously too late to repot any of my trees so I would be applying it with the tree in situ. Would the paint fumes maybe hurt my trees?

In sum lol, does anyone have any thoughts re the best option: aluminum foil, aluminum foil tape, radiant barrier/reflective foil insulation, bubble foil insulation, an Insuladd type product, or something else?

And, just for "fun" I included below the first two pages of an article discussing container heat and its effect on roots. The second page includes a table showing the differing temperatures that are predicted to be fatal to different species. In my experience I've definitely found the roots of certain species of trees to be much more sensitive to temperature than others. In particular, my giant sequoias (Sequoiadendron giganteum) (hardy in zone 6). If you got this far, thanks for reading!

 

[bonsaichile]

How about watering mid-day? We get regularly in the upper 90s here in denver during July, and that's what I do

 

[Shibui]

Summer temp get well above 100 here but I don't seem to have much problem with root damage from heat. Maybe I'm just not looking hard enough.

There are some construction products that would probably work better than foil. You already mentioned under roof barrier - sarking. The stuff over here is thick, relatively stiff and reinforced so should be far stronger than foil. You could make cylinders for the pots and just drop one over each pot to sit on the bench. Cylinders this size should be robust enough to be self supporting. Just replace them when they start to look tatty. There's a foil tape that is used to join sarking sheets that should also work to tape the cylinders together. Not sure how weather proof the adhesive is though.

There's another roof barrier product called aircell which is foil with a thin insulation layer in the centre. That should be even more robust and will add a layer of extra protection and would also suit your needs. As above, cylinders sized to suit the pots could be easily placed and removed. If wind causes a problem a little more tape to hold the cylinders to the rim of the pot should be enough to hold them in place.

 

[Captain.Bonsai]

I’m in 9b and regularly get hot streaks of 100+ during the summer. I have found great success with a combination of 2 simple things:

1. Cedar mulch - or any shredded decorative mulch commonly found at nurseries. They come in large 50ish pound bags and cost around $15 I believe. Surround each pot on the bench with mulch, or place each pot in a bigger pot and fill the bigger pot with mulch around the smaller pot. I haven’t found the need to cover the tree’s substrate. I just use a liberal amount of mulch mounded around each pot, only as high as the top edge of the pot. When I water the plants I also water the mulch which stays damp and provides an insulating heat barrier all day.

2. Shade cloth. I use fiberglass pet screen designed for replacing window or sliding door screens. The company I use is Adfors, they’re on amazon. I reached out and they sent me data sheets on their products; the pet screen blocks 55% light. You can find other shade cloth densities, but I like this better than 30% stuff I’ve found at nurseries. Build a frame and drape the cloth so that the canopies and pots are shaded.

With both of those measures in place I get zero leaf scorch during the summer.

Good luck.

 

[Emanon]

Summer temp get well above 100 here but I don't seem to have much problem with root damage from heat. Maybe I'm just not looking hard enough.

There are some construction products that would probably work better than foil. You already mentioned under roof barrier - sarking. The stuff over here is thick, relatively stiff and reinforced so should be far stronger than foil. You could make cylinders for the pots and just drop one over each pot to sit on the bench. Cylinders this size should be robust enough to be self supporting. Just replace them when they start to look tatty. There's a foil tape that is used to join sarking sheets that should also work to tape the cylinders together. Not sure how weather proof the adhesive is though.

There's another roof barrier product called aircell which is foil with a thin insulation layer in the centre. That should be even more robust and will add a layer of extra protection and would also suit your needs. As above, cylinders sized to suit the pots could be easily placed and removed. If wind causes a problem a little more tape to hold the cylinders to the rim of the pot should be enough to hold them in place.

Thanks! I knew someone on here would know a lot more about things like this than me! I hadn't thought about making cylinders but it makes sense -- efficient and practical. And that was my hope...that a reinforced roof barrier product of some sort would be far stronger than the foil I've been using.

With regard to root damage... I think it's not just death or damage that you can see that's the concern. Like for example on the second page of that article that I attached in my initial posting, the author paraphrases another paper where the authors explained that "Protein synthesis decreased and/or protein degradation increased in excised Illicium parviflorum Michx. [random plant] roots exposed for 15-min to temperatures above 35 C..." I know nothing about plant biology but it seems from this paper and others that I've seen that a number of detrimental things happen to plants as root temperatures increase beyond a certain reasonably (not exceptionally) hot point. In fact, that article I posted goes on after those two pages to only discuss "indirect injury" and 35 degrees Celsius/95 Fahrenheit seems to be the threshold beyond which injury starts occuring. When introducing "indirect injury" the authors write "Research has documented impacts on photosynthesis, carbon partitioning, respiration, water relations, hormone synthesis/response, nutrient uptake and utilization, and root diseases." The trees that I've made some effort to protect against heat just seem to do so much better.

 

[Potsofgreen]

Does anyone have any recommendations for the best way to insulate or otherwise modify black, plastic training pots for the purpose of lowering the temperature of the soil?
I live in zone 10b and the temperature in summer regularly rises above 100 degrees Fahrenheit/ 38 degrees Celsius. When this happens, I inevitably start to worry about my "full-sun" trees that I have in black, plastic training pots. I usually just cover my pots with aluminum foil but I've found the foil hard to maintain (keep clean, whole and thus effective).

I attached an article that I found on the topic, "A Solution to Heat Stressed Roots in Bonsai Pots," in Bonsai: The Journal of the American Bonsai Society, vol. 43, number 3, at 20-21 (2009), where the author uses an aluminum foil bubble/foam core insulation product. I'm thinking though that I should mostly, or solely, be concerned with blocking radiant heat and less concerned with neutralizing heat transferred via conduction. I basically just want a product (I think) that is the best and/or most efficient at blocking/reflecting sunlight. I shouldn't be concerned with a product's R-value and how good it is at "insulating" my pot. The bubble or foam core just seems to be of little benefit/wholly irrelevant to a containerized plant. And, with these types of products, the foil seems flimsier, more wrinkled and thus harder to keep clean than a thicker aluminum "radiant barrier" product.

I don't know why exactly but I have read that when installing radiant barrier insulation in an attic, it is best to leave an inch of air space between the foil and the roof (i.e. let it droop). If I apply a radiant barrier insulation then, I was thinking it might be best to have the foil come straight down from the pot's lip and attach it to my bench, instead of crumpling it tight against the pot's walls. Has anyone tried that? Also would perforated or not be better?

I was also looking at aluminum foil tapes that can be applied with less wrinkles than just aluminum foil, making it easier to keep it free from dust and mineral buildup (and thus more reflective). But if I did, I have no idea what the difference is or would be between the various foil tapes (rubber, acrylic, or silicone solvent?) (regular vs. HVAC tape vs. a SCIF tape).

Finally, my neighbor has this Insuladd product that can be mixed in with paint. I was thinking of asking him for a few cups and then adding it to some left over white, marine topside paint that already provides UV protection. Has anyone tried Insuladd or a product like it? It's obviously too late to repot any of my trees so I would be applying it with the tree in situ. Would the paint fumes maybe hurt my trees?

In sum lol, does anyone have any thoughts re the best option: aluminum foil, aluminum foil tape, radiant barrier/reflective foil insulation, bubble foil insulation, an Insuladd type product, or something else?

And, just for "fun" I included below the first two pages of an article discussing container heat and its effect on roots. The second page includes a table showing the differing temperatures that are predicted to be fatal to different species. In my experience I've definitely found the roots of certain species of trees to be much more sensitive to temperature than others. In particular, my giant sequoias (Sequoiadendron giganteum) (hardy in zone 6). If you got this far, thanks for reading!

I live in 10b too! So Cal 909 and I actually work in the construction industry! The 1 inch gap is the space required for the radiant barrier to have full effect, but radiant barrier comes pre installed on osb sheathing so no air gap? There talking about the space after the radiant barrier in the case of roofing it means having a inch gap between the radiant barrier on the plywood and the insulation or framing in the attic, not a 1 inch gap between the radiant barrier and roofing

as for soil temps Im slowly switching to using 4 gallon square white buckets(offer up) and a pumice top layer for trees I’m growing out, reflects most of the heat and is a cheap alternative...as for trees in bonsai pots i already waterd my shohin elm twice a day when it hit 90 last week

 

[Wires_Guy_wires]

I got the cheapest spray paint, and painted them white. I used carboard to protect the trees from the spray.
It's easy, fast, and it cost me exactly 1.99.

 

[Potawatomi13]

I got the cheapest spray paint, and painted them white. I used carboard to protect the trees from the spray.
It's easy, fast, and it cost me exactly 1.99.

Elegant, simple and cheap.

 

[sorce]

seem to have much problem with root damage from heat

Reckon Newbs tend to have much less foliage on their trees!

White t-shirts.

Sorce

 

[BuckeyeOne]

I've found myself leaning towards more terracotta pots.
Although I'm in 6a, the summers can bring 90f days for periods of 1-2 weeks in a row.
The terracotta pots retain moisture and tend to remain cool for a period after watering. I'll water twice a day during the heat.

 

[HorseloverFat]

I’m in 5a.... so, “Heat damage?” Hehehe

Buuuuuuut....

I got the cheapest spray paint, and painted them white. I used carboard to protect the trees from the spray.
It's easy, fast, and it cost me exactly 1.99.

THIS seems a wonderful solution!

 

[River's Edge]

Purchase the lighter color nursery pots! Tan, light green! they are all throughout the industry! Leave the black ones for us Northerners

 

[Lazylightningny]

I'd be interested to see a side by side test of inner soil temperatures in a white vs. black pot. Are we just assuming that the temperatures are higher because the pot is black?

 

[HorseloverFat]

I'd be interested to see a side by side test of inner soil temperatures in a white vs. black pot. Are we just assuming that the temperatures are higher because the pot is black?

I’d also be interested... you’d think that the composition of materials used to construct the pot would ALSO greatly matter.. maybe, in some cases, enough to negate color entirely... but truthfully I have no idea..

Gotta start running tests! ....yes!

 

[Lazylightningny]

I'd be interested to see a side by side test of inner soil temperatures in a white vs. black pot. Are we just assuming that the temperatures are higher because the pot is black?

Edit: never mind. If I had bothered to read the article the OP attached, I would have seen the results. There was a huge difference in temps at the sides of the pot.

 

[HorseloverFat]

Edit: never mind. If I had bothered to read the article the OP attached, I would have seen the results. There was a huge difference in temps at the sides of the pot.

Crap!.... me too.

 

[Emanon]

I got the cheapest spray paint, and painted them white. I used carboard to protect the trees from the spray.
It's easy, fast, and it cost me exactly 1.99.

Thanks. Painting was my first thought too. I have a white marine topcoat already -- that provides UV protection and should be good on plastic -- and that I'll never use again. So that's free. And then I had planned on asking my neighbor for a cup or so of some Insuladd that I know he has leftover from doing his house with it. So free again. I just know that it wouldn't be good for a human to sit and breathe paint fumes all day, so I made the assumption that it probably isn't good for a tree either. It's good to hear that nothing happened to your trees. I guess the difference is that the trees will be outside all day and not in an enclosed space. If I do it, I should aim to do it, I think (maybe?), on a day with at least a breeze. Alternatively, I found a thick (7mm) aluminum foil tape for about $5 USD, which would be easy to appy evenly and there'd be no issue with fumes...

 

[Emanon]

My bad! I meant the tape I was looking at is 7 mil (0.18 mm). Huge difference lol. Still not bad for the price.

 

[penumbra]

A flat white paint reflects more than aluminum, silver or gloss paint. I don't completely understand the mechanics of it but its true.

My wife slapped some latex house paint on a black plastic nursery pot when she painted the house. I thought it would peel off quickly but it looked good for 3 years. I replaced it with a ceramic pot so it may have lasted longer. I was surprised.

 

[AZbonsai]

Burlap people. You can buy it from your nursery or go to your local coffee shop that roasts their own coffee and they will sell you the bag. Cool looking bags at a reasonable price. They are durable and provide a bit of evaporative cooling after being wet down.