Soil Temperatures 93-104?!?

Backwardsvg

Shohin
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Not sure if this is important or not but has anyone ever checked their soil temperatures? We are getting abnormally hot temps here and so I thought it would be interesting to see what my soil temps are. I had a range depending on the media, size of pot, color etc but it was anywhere from 93-104 degrees F. That seems incredibly hot to me! To be fair I stuck the probe in the ground near the trees and it was 93! Now I am sure it depends how deep you go etc. but that has to affect the roots right? I have black plastic training pots / nursery pots so I am wanting to get feed back. Maybe spraying the pots white? moving more out of the sun? I have moss on some but not sure what to do or to do anything!

Also I have my trees in a place that gets full sun from 5 AM - 8 PM. I may be trying to find a new place depending on the answer here haha. Thanks!

Read this a bit and seems like above 81 is the best for root growth?
 

rockm

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Not sure if this is important or not but has anyone ever checked their soil temperatures? We are getting abnormally hot temps here and so I thought it would be interesting to see what my soil temps are. I had a range depending on the media, size of pot, color etc but it was anywhere from 93-104 degrees F. That seems incredibly hot to me! To be fair I stuck the probe in the ground near the trees and it was 93! Now I am sure it depends how deep you go etc. but that has to affect the roots right? I have black plastic training pots / nursery pots so I am wanting to get feed back. Maybe spraying the pots white? moving more out of the sun? I have moss on some but not sure what to do or to do anything!

Also I have my trees in a place that gets full sun from 5 AM - 8 PM. I may be trying to find a new place depending on the answer here haha. Thanks!

Read this a bit and seems like above 81 is the best for root growth?
It is VERY important, but we in the more Southerly part of the U.S. take this as a given. Soil temps above 90 can cause all kinds of problems, including death. Soil temps over 100 can kill roots pretty quickly.

To protect against this, many bonsaiists in the South keep their trees in afternoon shade, or shade the pots. Beginning in late April,when air temps start to push 90, I put white tshirts or towels (wetting them can cool even more with evaporation) over the pots exposed to the after noon sun. It is important to put them on before the sun hits them and take them off after the sun goes down to help keep the pot at its coolest. I keep the towels etc. on when temps are forecast to rise above 85 or so. Surface temps on objects can greatly exceed the air temp by as much as 20 degrees or even more. Sun rays are most intense from April to June as the angle of exposure steepens. After the summer solstice, it starts to decline. In other words April to June has the strongest sun and can heat things more quickly
 

GGB

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I do what RockM said above and it keeps the trees very happy. I only started doing it last summer, when temps are predicted to hit 90 or above, my trees look so much better since doing this. You could probably even do it at lower temps than 90 but it becomes a chore if your collection isn't tiny
 

Backwardsvg

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Dang good to know maybe I will find a place that is a bit more shady. I guess I sacrifice the sun a bit for the soil not getting so darn hot.

I am interested that in 5b I am getting that hot. I thought I wouldn’t have that issue unless I was closer to the mason
 

sorce

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I'm relieved to realize that was probably why I got some stuff on hurt....
Paying too much attention to growing food to even consider those 100's on the trees.

White tees.

Sorce
 

rootpuma

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it's been triple digits in south Texas. I put up a shade canopy like you see at the beach or kids ball parks...water every single night and they are kicking along just fine.
 

WNC Bonsai

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Nigel just did a video on this and showed that placing aluminum foil over the soil surface can reflect a lot of the sunlight and keep soil temps lower. Down here though I keep most in the shade after about 1PM. The only trees that remain in full sun after that are a couple of pines and my blue spruce. On those I have a layer of long fiber sphagnum which acts as a sort of mulch and since it is moist the evaporation from it helps keep things cooler. Fortunately, we have not seen 90 here yet but it has gotten kind if close a couple of times.

 

rockm

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Nigel just did a video on this and showed that placing aluminum foil over the soil surface can reflect a lot of the sunlight and keep soil temps lower. Down here though I keep most in the shade after about 1PM. The only trees that remain in full sun after that are a couple of pines and my blue spruce. On those I have a layer of long fiber sphagnum which acts as a sort of mulch and since it is moist the evaporation from it helps keep things cooler. Fortunately, we have not seen 90 here yet but it has gotten kind if close a couple of times.

Um, can't get past the hair--and using aluminum foil... Foil isn't a great thing to use because it prevents evaporation (which is a coolant). White cloth (preferably cotton) is more effective. The hair thing is easily solved with a comb and/or a trip to the barber, or maybe a weed-wacker... 😁

Oh, and the long fibered sphagnum moss is good too, but it doesn't cover the sides of the pot, which heat up the root mass as much or more than the sun on the surface
 
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Leo in N E Illinois

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Dang good to know maybe I will find a place that is a bit more shady. I guess I sacrifice the sun a bit for the soil not getting so darn hot.

I am interested that in 5b I am getting that hot. I thought I wouldn’t have that issue unless I was closer to the mason


We never used to get very warm. In the past 3 out of 5 years would have zero days of temps over 90 F. Climate change is real. We are seeing the changes in out back yards. We are having more frequent hot days.

I have used pieces of cardboard, lean them around to shade the pots, but keep the leaves of the trees in the sun. In "the wild" grasses shade the roots and trunks of trees. You can also group trees close enough together that the sun does not get between the pots - this is what nurserymen do in greenhouses. Then only the outer row of pots get heated by direct sun. You can have an outer row of empty pots surrounding your trees. The empty pots might look tacky, but they will shade the pots in the middle with trees.

I also have used cache pot system for plastic pots. Set the plastic pot inside a taller, larger diameter, empty clay pot. The clay pot shades the plastic pot. The one half inch or so empty air space between the interior of the empty cachepot and the plastic pot with the tree serves as insolation from the heat of the sun striking the outside of the clay pot. This works when pots are of nesting sizes. Bonsai display pots rarely are of nesting sizes. I regularly use this for my orchids, where they are in standard 3 inch rounds and the cache pots are 4 inch rounds. That way, leafs in the sun, roots in the shade. Works on windowsills or outside.

With the cachepot, the clay will wick moisture, clay (terra cotta) set on shallow trays with a little water, the clay will wick water up and release humidity and evaporatively cool the root zone a little while the tray underneath has some moisture. Not a big effect, but a minor effect that can be taken advantage of.
 
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WNC Bonsai

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His measurements really aren’t all that meaningful since he failed to also include temp measurements of a control pot left uncovered, so we don’t really know whether the foil did anything useful or how much. I am making measurements today comparing an uncovered pot to one where the soil has a layer of moist sphagnum. Results to come in a few hours but I can tell you it does make a significant difference so far.
 

WNC Bonsai

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Here’s the results, but first some explanation. I watered about 9:30am then made the first measurements at 10am and repeated hourly. The pots were about the same size, 16-18” brown clay ovals. Both have essentially the same soil mix, pumice, Permatil, pine bark, 40:40:20. One is bare soil and the other has a cover layer of NZ long fiber sphagnum. Air temps dropped around 2pm as a result of scattered clouds moving in. You can clearly see though that the sphagnum cover had a cooling effect probably due to evaporation as well as insulation from the direct sun. I only had the two pots so for a real scientific study you would want to do this with at least 3-5 replicates of each and make multiple measurements at various depths and locations in the pot. These temps are an average of two measurements one on each side of the tree. OK enough talk here are the results.D3C12B90-7FB8-4529-9650-C7956D3B1099.png
 
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rockm

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Here’s the results, but first some explanation. I watered about 9:30am then made the first measurements at 10am and repeated hourly. The pots were about the same size, 16-18” brown clay ovals. Both have essentially the same soil mix, pumice, Permatil, pine bark, 40:40:20. One is bare soil and the other has a cover layer of NZ long fiber sphagnum. Air temps dropped around 2pm as a result of scattered clouds moving in. You can clearly see though that the sphagnum cover had a cooling effect probably due to evaporation as well as insulation from the direct sun. I only had the two pots so for a real scientific study you would want to do this with at least 3-5 replicates of each and make multiple measurements at various depths and locations in the pot. These temps are an average of two measurements one on each side of the tree. OK enough talk here are the results.View attachment 444557
A measurement of the actual clay sides of the pot might also be warranted. The outer root mass is in direct contact with the interior walls of the pot. I've measured temps on the rims of my bonsai in full sun at 120 F on some hot July and Aug. days. One of the reasons I began covering them waaay back when.
 

Catagonia

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I live near Sacramento CA where we get essentially no cloud cover and temps routinely over 100 from early June through September. I noticed a few weeks ago that my ceramic pots were almost painfully hot to the touch in the afternoon sun. I’ve moved most of my potted plants (bonsai and otherwise) into a morning-sun-only spot or a dappled-light-only spot and they seem happier. It’s funny how all my container plants are developing an annual migration pattern.
 

Mike Corazzi

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SACRAMENTO ?????

You can't have bonsai in SACRAMENTO !!! Not without salt and grease for the frying. :rolleyes:

It rains here every day. Sometimes 2-3 times a day. Coors, the rain comes from a wand sprinkler that I have to run to "COOL" before starting the "rain."

Sometimes I also use ripped up old sheet squares that can stay damp to cover the bottom of the tree. Those get "rained" on, too.
So far. so good. ;)
 
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