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.
 

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.

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