White cardboard soil sunblock. Good or bad?

[Mike Corazzi]

If you made a white cardboard cutout in this shape to slip over the soil, would it be good or bad
as a soil cover (loose) to inhibit heat during the 190 degree days?

 

[Doogliebop]

If you made a white cardboard cutout in this shape to slip over the soil, would it be good or bad
as a soil cover (loose) to inhibit heat during the 190 degree days?



View attachment 484685

I'm constantly thinking of ways to keep pots from baking in the South Louisiana heat. The best I can conjure up is to buy a pack of white throw-a-way rags from the hardware store to drape over the pot/roots.

As for your question, it seem plausible. Although it would need to have something attaching the two corners that are closest to keep it from falling/blowing off.

 

[Clicio]

If you made a white cardboard cutout in this shape to slip over the soil, would it be good or bad
as a soil cover (loose) to inhibit heat during the 190 degree days?



View attachment 484685

I have used white moist towels around the pots in the summer here.
It works fine to keep the pots from heating up too much.
Most of my trees are usually in full shape in the summer, so the ramification plus the leaves shade the soil.

 

[Mike Corazzi]

I'm constantly thinking of ways to keep pots from baking in the South Louisiana heat. The best I can conjure up is to buy a pack of white throw-a-way rags from the hardware store to drape over the pot/roots.

As for your question, it seem plausible. Although it would need to have something attaching the two corners that are closest to keep it from falling/blowing off.

Small rock. Also put a few holes in the cardboard.

Serendipity says a priority mail box would maybe work nicely.

 

[ShadyStump]

I keep thinking that it could trap heat in the space between the the cardboard and the soil surface.
I was about to say you might perforate it, then your last post popped up. LoL
Some sort of spacer between the cardboard and the pot would allow airflow so heat and steam doesn't get trapped.

 

[Eckhoffw]

Or….. moist white towels

May be a pain caring for those cutouts each watering.

 

[rockm]

I understand trying to come up with ways to shield pots from heat, but this solution only goes halfway. The issue with pots in the sun is NOT really because the soil surface heats up in the sun, but because the SIDES of the pot are exposed to more sunlight. As noted, trees actually shade the surface for the most part. However, the sides of pots are left exposed to sun, particularly in the afternoon as the sun's angle changes. That exposure heats the root mass more deeply than surface exposure, since the sides expose the depth of the pot to the sun.

It's hard to beat simply draping white towels over the soil surface/around the trunk, then having them drape down the sides of the pot. Also, towels "breathe" allowing air exchange/evaporation--evaporation is a cooling process. Covering the soil might create a pressure cooker of sorts, preventing evaporation and allowing heat build up in the pot, not to mention making watering on hot days a lot more difficult.

 

[Diggumsmack2]

I use aluminum foil, it's shapeable (depending on the thickness), it reflects visible light and heat & it doesn't need wetting maintenance.

 

[rockm]

I use aluminum foil, it's shapeable (depending on the thickness), it reflects visible light and heat & it doesn't need wetting maintenance.

Towels don't need "wetting maintenance." I don't wet mine down unless temps are forecast into the upper 90's. As I said evaporation is a cooling process. Wetting down the towels can provide additional, relatively long-lasting cooling effects. Foil doesn't do that and um, it's not used to cook baked potatoes for nothing. It also traps heat pretty efficiently...just sayin.

 

[Shibui]

Some pretty way out ideas here. My question is do you really need to do anything? Reality is quite different from what many of us presume.
Summer daytime temps here get well over 40C (100F) but in 40 years growing bonsai I have not noticed steam, cooked roots or anything of that sort. I have seen trees suffer from sunburnt trunks, burnt leaves and trees even die but only from dehydration.
I am quite comfortable with ceramic pots and black plastic nursery pots in summer sun.

 

[rockm]

Some pretty way out ideas here. My question is do you really need to do anything? Reality is quite different from what many of us presume.
Summer daytime temps here get well over 40C (100F) but in 40 years growing bonsai I have not noticed steam, cooked roots or anything of that sort. I have seen trees suffer from sunburnt trunks, burnt leaves and trees even die but only from dehydration.
I am quite comfortable with ceramic pots and black plastic nursery pots in summer sun.

Not talking about "way out" ideas about steam, or cooked roots, but heat plays a significant role in root health. It can be critical for some temperate zone species. Larch, for instance, seems to have issues with heated roots in the summer--temps over 70 consistently for a month can cause them to decline and die over a period of years or even a single summer. Saw it happen a couple of times before I gave up trying to keep larch here. We're not in their natural range. Why would trying to minimize the impact there with shading the pot be a bad thing?

Mirai says temperatures over 105 F (easily achieved in full sun, exposed pot in summer) can compromise Ponderosa pine's vascular tissue. There are a few Ponderosa growers who say looser soil mixes allow hot water vapor in the soil, which can kill or damage roots and cause slowing or partial death of branches etc.

I've seen my native trees slow down significantly in the summer. I grow Southern U.S. trees that are native to some pretty hot natural habitats. They keep growing in summer a bit if I shade pots in the hottest parts of the summer.

So, when it gets above 90, yeah, I shade the pots, like Mike Hagedorn. Can't hurt, can provide an extra margin of safety and growth for the tree. What's the downside?

 

[Mike Corazzi]

Towels don't need "wetting maintenance." I don't wet mine down unless temps are forecast into the upper 90's. As I said evaporation is a cooling process. Wetting down the towels can provide additional, relatively long-lasting cooling effects. Foil doesn't do that and um, it's not used to cook baked potatoes for nothing. It also traps heat pretty efficiently...just sayin.

One way to test anything silver colored is to touch your car after it's been in the sun.
The paint is usually far cooler than the chrome.

 

[Diggumsmack2]

One way to test anything silver colored is to touch your car after it's been in the sun.
The paint is usually far cooler than the chrome.

What make car are we talking about?

 

[hemmy]

There was an ABS Journal article (2019?) on this topic (American Bonsai Journal Volume 53, number 3).

As I recall, it tested interior substrate temps in sun/shade with various coverings. As previously mentioned, evaporative cooling is VERY important and should be not be impeded on the substrate surface. They concluded that white cloth (T-shirt material) on the top and sides kept the interior temps the coolest.

 

[Colorado]

Not talking about "way out" ideas about steam, or cooked roots, but heat plays a significant role in root health. It can be critical for some temperate zone species. Larch, for instance, seems to have issues with heated roots in the summer--temps over 70 consistently for a month can cause them to decline and die over a period of years or even a single summer. Saw it happen a couple of times before I gave up trying to keep larch here. We're not in their natural range. Why would trying to minimize the impact there with shading the pot be a bad thing?

Mirai says temperatures over 105 F (easily achieved in full sun, exposed pot in summer) can compromise Ponderosa pine's vascular tissue. There are a few Ponderosa growers who say looser soil mixes allow hot water vapor in the soil, which can kill or damage roots and cause slowing or partial death of branches etc.

I've seen my native trees slow down significantly in the summer. I grow Southern U.S. trees that are native to some pretty hot natural habitats. They keep growing in summer a bit if I shade pots in the hottest parts of the summer.

So, when it gets above 90, yeah, I shade the pots, like Mike Hagedorn. Can't hurt, can provide an extra margin of safety and growth for the tree. What's the downside?

The downside is that it’s a pain in the ass and it looks…well….not great.

 

[Clicio]

The downside is that it’s a pain in the ass and it looks…well….not great.

I guess dead trees don't look so great too..

 

[James W.]

What works well for me is to set the pots down in some mulch. Most of mine are setting on the ground, the few that are on a shelf are sitting inside a larger pot filled with mulch. I think it looks better than white towels.
Better to wrap the white cardboard around the pot than to cover the soil?

 

[AJL]

Maybe better to consider building a shade house or frame to keep your most heat-sensitive species under in summer?

 

[Emanon]

Some pretty way out ideas here. My question is do you really need to do anything? Reality is quite different from what many of us presume.
Summer daytime temps here get well over 40C (100F) but in 40 years growing bonsai I have not noticed steam, cooked roots or anything of that sort. I have seen trees suffer from sunburnt trunks, burnt leaves and trees even die but only from dehydration.
I am quite comfortable with ceramic pots and black plastic nursery pots in summer sun.

I attached below the first couple pages on an article I found before posting a question on this forum re how to treat the outside of black, plastic pots in defense of high heat. Here's that thread. (That thread has a bunch of good suggestions from members of the forum on how to fix the "problem", if you think it's a problem...) The authors of the attached article though, explain what happens to roots at what temperatures (in their opinion). It was published in a journal called HortScience and here's a direct link to the full article, including free PDF download. I'm sure other articles have been published since, but it looks like there is some basis for concluding that high enough heat affects growth negatively.

 

[rockm]

I attached below the first couple pages on an article I found before posting a question on this forum re how to treat the outside of black, plastic pots in defense of high heat. Here's that thread. (That thread has a bunch of good suggestions from members of the forum on how to fix the "problem", if you think it's a problem...) The authors of the attached article though, explain what happens to roots at what temperatures (in their opinion). It was published in a journal called HortScience and here's a direct link to the full article, including free PDF download. I'm sure other articles have been published since, but it looks like there is some basis for concluding that high enough heat affects growth negatively.

A lot of work in that article... I am too lazy and cheap for such a solution. I just use old dog towels thrown over the pot every morning after watering. Removed after the sun goes down.