A few days ago there was a thread that started me thinking to measure the pot temperature:
http://figs4funforum.websitetoolbox.com/post/OT-Lowes-Haul-Today-6471924

After trying with an average thermometer, I decided that this must be done more scientifically.
So what I will try to do is the following.
I have ordered this kit with 4 sensors:
http://store.qkits.com/moreinfo.cfm/VK011

This will allow me to collect 4 sets of continuous data sampling every 5 min, for example. I was thinking about these locations:
1- terracotta pot
1- black nursery pot
1- directly in the soil
1- in the shade under a tree (ambient temp)

I am going to run this for 24 hours and see how the temperatures compare to each other.

What do you think?
Any suggestions?

Anybody has an experience using the DS18S20 sensors? Its specs are pretty good:

• Measures temperatures from –55°C to +125°C (–67°F to +257°F)
• ±0.5°C accuracy from –10°C to +85°C

be interested to see results

Greg,

Yes, of course I will share the results. That's the plan!

I wish you would try one of these fabric pots too. I think they're really neat.

Sophie,

That's an idea! But the board can accommodate 4 sensors only. So I have to come with a strategy here. Maybe 1 day like what I mentioned above and 1 day with a fabric pot instead of whatever I decide is a clear outlier  after the first test.

Yes if you can compare same size containers on same surface next to each other with same potting mix and similar moisture content.

 That's a great project!   When I read the previous post about black pots getting hot I checked mine and YEOW! I was shocked how very hot.  I'm very interested in your results of temps inside the pots.    I was thinking to painting some pots white but ran accross these white sleeves to slip over black pots.  i ordered some in different sizes. They didnt come yet.  but easier than painting.
Soni

http://www.amazon.com/ViagrowTM-gallon-Grow-Bag-pack/dp/B00BAZT1N6/ref=sr_1_5?ie=UTF8&qid=1376681634&sr=8-5&keywords=white+grow+bags

Martin,

Since you started talking the details here, that was my version 1:

Case 1, use the dry sand from Home Depot. It is cheap, clean and homogeneous.
2 gal pots for terracotta, plastic and now fabric.
Bury the sensors at the 6 inch depth in the soil and pots, 3 inch from the pot's side.
I have a spot on my concrete patio large enough to put the pots next to each other so the difference is minimal.
Start at 4 or 5 am when the temp is approximately the same. Run for 24 hours at least.

Case 2.  The same as the Case 1 but put the pots on the grass. Dry sand.

Case 3. The same as the Case 1 but add 2 cups of water. On concrete.

Case 4. The same as the Case 1 but saturate the sand with 1 gal of water. On concrete.

Obviously, one can come up with many more scenarios but this should keep me busy for a while.
Also, it is possible that the Cases will be modified as I proceed.

I would think it matters against the hot California sun and hot air that most of us don't have. Also, should try under some leaves/semi-shade.

Greenfig you might want to check the wind speeds. On a calm day I would suspect the pots would retain more heat than if it was very windy. I'm sure there are other variables that could affect the temps in the pots.

Tony, That is the only thing that would be hard to measure. My yard has a 5 ft fence around it + many trees so almost no wind at the ground level. I also don't have a wind sensor, need to get one that works with a USB or serial connection. The question is very valid though, I should try to incorporate the wind too.

Greenfig,
Good luck with your tests.
From past experience growing vegetables in containers, any container temperature above 100 deg F is bad for plant growth. Attached are a few documented tests.
This Kansas State Thesis has several pictures descriptions and tables of test procedures and results.
 
[QUOTE]After four months (June-October), plant variables were measured. Roots were separated into three sections: core (10.2 cm diam.), north, and south, rinsed of all media, dried and weighed. In the bean study, media temperatures at the sun-facing side averaged lowest in gloss and flat white (~36 oC) and greatest in the black control (50.3 oC). Accordingly, total root biomass at the sun-facing side was reduced by 63 to 71% in black compared to flat and gloss white containers. In heat-sensitive maples, media temperatures at the sun-facing side averaged up to 7.7 oC greater in black, black shade and green than in other treatments; temperatures in black shade may have been lower if shade cloth had covered the sun-facing sides of containers in addition to only the media surface. Media temperatures in the core averaged 3.5 to 3.8 oC greater in black than in flat and gloss white, resulting in up to 2.5 times greater below ground biomass and up to 2.3 times greater above ground biomass in flat and gloss white than in black pots...

At temperatures over 30 oC, root growth slows considerably (Johnson and Ingram, 1984). For many woody species root growth will stop completely at temperatures above 39 oC (Mathers, 2003). The roots of some woody species (e.g., Ilex crenata ‘Helleri’) die when exposed to temperatures of 51 oC for merely thirty minutes (Martin et al., 1989). Studies have revealed that temperatures inside nursery containers can rise much higher than 51oC, and commonly surpass 54 oC in the southern states (Ingram et al., 1989; Martin et al., 1989) (Mathers, 2000).
[/QUOTE]
Note:
30 deg C = 86 deg F
39 deg C = 102 deg F
51 deg C = 124 deg F

Good luck with your experiment.

I have my own theories on plastic pots and temperature. I believe in small black plastic pots( 1-5 gallon )the bulk of the roots push through the soil and congregate around the black plastic. If the pots aren't shaded then the black plastic cooks the roots touching the plastic severely stunting the growth of the plant.

As a side note, I use fabric pots on all small plants now.

My experiences mirror Jason's. I grew a tree in a five gallon, white bucket while in Houston. When I removed the tree from the bucket, there were roots extending beyond the growing mix on half, but no more than 2/3 of the distance on the other. All of the cuttings I rooted this year are in 1 and 2 gallon Root Pouch (fabric) containers and sitting on a table under partial shade. Yesterday while tending to them, I noticed a significant difference in the temperature and weight ( moisture level) of the trees on the south side of the table than those just one row in. The table they sit has a steel mesh top so air circulates under the containers, but that does not seem to dissipate enough heat from those containers on the south side. I think it would be interesting to measure how much of an effect watering at different times has on the overall temperature and peak temperatures in the containers. To my mind, the ability to control temperature by daily watering is the biggest advantage of a fast growing mix (especially in the south). I'm curious how accurate it is. ~james

Pete, Jason, and James,

Thank you for your feedback. It seems quite a few people grow the figs in pots and I am glad that my data might be interesting to the fig community!

I am happy to say that I received the board with one sensor (the other 3 sensors have been shipped separately).
I am testing it now and it works great! It reports the temp in C and F from 1 sec to 99 min (selectable).
I set it to 5 min for now just to play with the device.

It is happening!!

Please see the board in the photo attached. The sensor is a black chip attached to the blue terminals at the bottom. I have a 100 ft cable, the sensors will be soldered to the cable when they arrive.
The data sample in on the screen. It doesn't log the time so I have to record the start time but that is not a big deal.

greenfig, great idea. i'm looking forward to seeing the results.

but, where do i find out best temps for container soil for figs?

Susie,

At the moment, I don't have an answer for you. That would require some basic research with googling.
I am sure somebody here knows what would be the best temp for the container figs.

My initial goal was to find/measure the temperature ranges for different container types after I discovered how hot was my terra-cotta pot with an unhappy kumquat in it.

i get it, green. i would have thot a terra cotta pot with the ability to breath would always be cooler than plastic. i really need to see your results.

The science community has stated above 85F and the plant starts suffering due to roots loosing efficiency.

thanks james. now i'll be able to put green's research into context.

green, please don't forget to post results.

[QUOTE=james]The science community has stated above 85F and the plant starts suffering due to roots loosing efficiency.[/QUOTE]

And this amazes me because terracotta has been holding thriving plants long before plastic nursery pots were invented! I mean look at Europe. They've been using clay pottery for ages with no ill effects.

I'm sorry, Sophie. I should have said "when temps in the root zone approach 85F the roots' efficiency start to decline." Having said that, terra cotta does keep the root zone cooler than black plastic.

Any probe style thermometer (cooking or oral) can be used to get a quick check of the soil temperature, you would be surprised at how hot the roots get in most containers.

Soil temperatures to keep in mind:
50 deg F to 80 deg F   = Normal root growth.
85 deg F to 100 deg F = Slow or no root growth.
110 deg F and over     = Root die back

Very interesting experiment.  Will be good to know your results of the variation between pots.  

My unheated pool temp currently reads 95 degrees at 9pm at night, so my fig pot temp must be well above 85 in the day and night.  I've got plenty of growth and figs.   For instance, my desert king that I started this winter is already my tallest fig grown in a pot.  It's over 7 feet already even after pinching.   

Hi all,

I have the first results to report!
I was surprised how HOT was the medium inside!! Please see the plot and the photos.

The fabric was the hottest, black plastic was next and the terra-cotta was the coolest but the was no direct sun almost all day!! Tomorrow might be a different day.
Inground soil was quite cool so there is a huge benefit to bury the pots!

The setup:
- 4 sensors were soldered to 15 ft long cables and waterproofed with epoxy;
- the black cable markings correspond to 5,10,15,20 cm, the depth indicators;
- used 3 x 2 gal pots, black fabric, red terracotta, and black nursery plastic;
- one sensor is in the inground soil, a loan with grass;
- data collection: every 5 min for 24 hours, from 10 pm to 10 pm approx.;
- dry silica sand from Home Depot was used as a medium;
- the sensor depth at all 4 locations was 10 cm (4 inches);
- the pot orientation was West-East on the South side of my house;
- the day turned out to be very cloudy (the first like this during the entire summer!!);
- the direct sun exposure is approx. 10 am -5:30 pm, but it was on and off often;
- absolutely no wind;
- the measurements are in C, the C-F table is on the plot.

Next:
a) tomorrow is supposed to be a sunny day, I want to see how bad it would get with the dry sand.
b) add 1/2 gal of water to each pot and measure the difference.
c) replace the sand with some real fig soil, measure the temp.

Enjoy! I appreciate your feedback

Greenfig, Nice experiment that you have going here. It will be interesting to see the temps on a sunny hot day! Tks for sharing your info.

Sure, Mark. Now I am more curious than before to try with the real soil. I think the results will be different because the soil density and heat capacity are different.

Greenfig,
Thanks for posting the results.
I'll be watching for updates and future experiments.

You know something that might need to be compared is the soil temp inground compared to the containers.

green, now that you have the equipment, may i suggest another test? i think it would be very interesting to measure the temps in two identical pots, one on pavement, one on soil. i have been warned about placing pots on pavement.

[QUOTE=cobb4861]You know something that might need to be compared is the soil temp inground compared to the containers.[/QUOTE]

Cobb4861,

On the plot, the purple line is the temp in the inground soil, in my loan with grass, for a comparison.
I am sorry if that was not clear, I will try to explain better.

[QUOTE=susieqz]green, now that you have the equipment, may i suggest another test? i think it would be very interesting to measure the temps in two identical pots, one on pavement, one on soil. i have been warned about placing pots on pavement.[/QUOTE]

Susie,

Yes, that is coming! I am interested to know how substantial is the difference too.
The pavement radiates the heat a lot and long after the sun is down.

Just read back thru and saw that. Your doing a great job!

Hi,

Here is the results of the Test 2. It is very similar to the Test 1, the only difference is the weather. It was very sunny all day, very hot with max temp at 36C or 97F :(
Today was a perfect day to bake my imaginary figs..

To remind the setup: 3 pots are on the concrete on the South side of my house filled with the dry sand.
The data collection is every 5 min from the sensors buried 10 cm in the center of the pots. The control sensor is in the ground at 10 cm depth.

Max temp for the fabric pot: 51C or 124F
Max temp for the terra-cotta pot: 46C or 115F
Max temp for the plastic pot: 50C or 122F
Max temp for the unground sensor: 30C or 86F

The best performing pot is terra-cotta, the worst: fabric.

Now I feed sorry for my real figs that are about 5 feet away. They are not growing fast enough and now I know why!
I am surprised they are not dead. It is the time to save them. 

Please see the figure attached.

Tomorrow I will add the 1/2 gal of water to the sand and that will be all for the sand. I need to buy a bag of soil to try the soil on the concrete and on the grass.

Wow, the forecast today is 37C or 98.6F and those high temps are going to be around all September.

Hi again,

Please see my final report on the temp testing in the silica sand.
I joined all 3 test (today's and the previous ones) on one plot.
The Test 3 was with the water saturated sand that I added last night, the pots were still on concrete.

The results are very interesting for me.

Some points:
The atmospheric temperature was higher than yesterday (see the green line for the soil temp) but the pot temps were much lower! My explanation is that the water evaporation cools the media down, by a lot!  And in different ways for different pots.

The largest impact was on the fabric pot. Its highest temp today was 35C vs. 52C yesterday! Wow! That is 13 degrees!

The terra-cotta dropped 6 degrees (40C today).

The plastic dropped only 4 degrees (46.5C today).

So, if you want to keep your figs happier in the hot climate, water them well! 

It seems there is a huge benefit in growing the figs in fabric. They provide enough oxygen and cooler when watered.

The black plastic pots need to be shielded from the sun, the plants will just cook there.

I will try on the grass and with the real soil next.

Enjoy!

P.S. Two figures attached are the same but one is larger if you want to see more details. It is better to do this in a separate window. Or as snagplus is saying:
TO ENLARGE THESE PICS, MOUSE OVER, RIGHT CLICK, OPEN IN NEW TAB OR WINDOW

Thanks for the sharing.This place takes a step further with your analysis
probably thats why the japanese di it like in the picture with fabric supported by plastic pots like the ones used for chicken live stock.

Thanks, Eli! Interesting idea, and a cheap one, fabric in plastic crates.

Found it on ken love website http://www.hawaiifruit.net/

http://www.hawaiifruit.net/figstation/index.html 
I think we should do the same experiment and compare the state among different pots.

Good experiments require a good preparation :) I discovered that it was a little challenging to find different 3 pots of similar shape and size in my area (without going far and order online paying extras). But hay, it is all fun now since I know how to do it :) Even more, yesterday I found a way how to get 5 min interval data from my local weather station about a kilometer away so now I can compare the soil temps with the ambient air temp. Care for an extra line on the plots?

probably a direct relation?

Almost direct, you will see a delay at night since the air temp cools down quicker.

Great information. Keep up the good work!

Thanks! 
It is hot like hell today.
I didn't have time to get the soil and just put the pots with sand on the grass and watered them.
I will post the wet-sand-on-grass results tonight. Stay tuned!

Ok, here is the last sand measurement plot!
I joined all 4 days in one figure.
The today's numbers were collected on the loan grass and, as you have already probably known, you figs are the happiest there!

Looking at the green line of the soil temps you can tell that today was as hot as yesterday, which allows you to directly compare today's grass with yesterday's concrete temps.
The difference is huge and the temps for the terracotta and fabric pots are very close to the soil temp.
The plastic pot temp sucks big time. Although it is still lower than on the concrete, it is much worse than anything else.

My thoughts: People always go around blaming one pot or another but at the end it seems the cheapest one wins (i.e. a black nursery ).
I think the pot selection should depend on your climate. I don't think mine in LA would be suitable in the same way in Maine, for example. The temp, precipitation, and humidity are totally different. As you can see from the plots, the watering and the pot placement location make a huge difference too. As far as the soil selection goes, I will try to test it during the next few days after I buy some soil.

As before, as snagplus was saying:
TO ENLARGE THESE PICS, MOUSE OVER, RIGHT CLICK, OPEN IN NEW TAB OR WINDOW

Greenfig, Thanks for your hard work with this experiment! Your results were quite surprising and I learned a lot too! :D

GreenFig, Keep the data coming! Really good comparative information for one and all. Tks

Greenfig,
Thanks for the experiment and the updated data.
One benefit of the black pots on concrete that may not be evident...
The tree is automatically pruned by the heat, the root growth is decreased, decreasing the vegetative growth. This helps keeps the trees smaller for those who are growing in containers ; )

If your still doing more tests, I'd like to see the black nursery pot on grass but shielded with reflective material (aluminum, or white paint, etc).  Thanks for the great info!

Nice experiment! It was very educational.