i luv this data. to start with, i'm burying my pots 1/2 way down.

many thanks green.

Good stuff.. did I miss where you published soil vs sand?

Greg,

No, you didn't miss anything yet. I didn't want to just post short one-sentence updates. 
What new (unpublished) I have now is the soil temps in the same pots as the sand above +
the temps in 3 plastic black nursery pots covered by different things.

My thoughts were to test what people use most and what is easily available to buy. So, I got a white plastic pot, a white outside - black inside plastic growers bag, and foil.

Please see the temps for the soil in the 3 diff pots compared to the sand tamp attached.
It seems that as soon as you keep your pots watered, the light sand medium is as warm as the darker soil.

Energy loss thought the evaporation takes care of the heat added by the sun?

Tonight I should have the results for 3 black plastic covered by a white grower's bag and inserted in a white plastic pot.
Please see the photos attached.

Next: comparing the black nursery with a white grower's bag with a white plastic pot (what is used as a cover now).

Thanks for your interest!!

I'm confused, do you mean that the black plastic pot wins the prize of crappiest root environment? Because it is the farthest from ground soil growing conditions always, based off of these results.
By the way, great work once again. Very useful information.

I wonder also how much the last test would vary with all three pots the same inside and out, except

one directly on grass
a small sheet of weed block material under one
a small sheet of plastic under one
a paver stone or piece flagstone or similar under one
and ground control as always
(I realize this would require one more probe than you have so it would require more than one run, or just using the old info from the pot directly on grass loam)

Reason being, if a person wants to not have the roots grow into the ground(some don't) then what is the best option for a root block that allows heat to be moderated by the earth.

Here are the measuring results in the 3 black 2 gal nursery pots filled with dark potting soil and located on the loan grass..
1 is exposed fully
1 is covered by a white plastic grower's bag
1 is inserted in a white bucket

The protection of the plastic pots helps a little but they still are not as good as the terra-cotta or fabric but became much better!


For tomorrow I should have 1 exposed, 1 covered by foil, 1 covered by a brown paper bag.

Thanks for looking!

Hi again,

I realize that you already probably have the data fatigue but I would like to finish posting the results of the measurements just in case they will be useful.
Only one more test left after this.

Today are the results of the temps in the 3 black 2 gal nursery pots in the following setting:
1. covered by a paper bag
2. bare black pot
3. wrapped in a foil 

+ the inground soil temp.

All 3 pots are filled with some dark potting soil that I use for figs. The soil was moist as if the figs grow there.

A big surprise: the paper bag cover is BETTER than the foil! By a little but still better.
The bare black pot suck big time, as expected.

Tomorrow: white growers bag, bare, white square plastic pot: like in the Sep03 photo but without the place pot inside.

Thanks for watching!

TO ENLARGE THE PIC, MOUSE OVER, RIGHT CLICK, OPEN IN NEW TAB OR WINDOW

So, here is my last test.

You will find the results of the temp measurements in the 2 gal
1) white plastic grower's bag
2) white square plastic pot
3) black nursery pot
4) inground soil 

As you can see from the green line displaying the temp in the ground, today was as hot as yesterday, the black pot temps are also the same.

Surprisingly, the white grower's bag is not as good as the black covered in foil or a paper bag. This is good news since we have a lot of those black pots!
In the hot climate covering them with almost anything helps a lot and may prevent roots from cooking.

Happy figging, everyone! I hope the test results help at least one person :)
If you have any questions, please ask.

TO ENLARGE THE PIC, MOUSE OVER, RIGHT CLICK, OPEN IN NEW TAB OR WINDOW

WOW Igor,
I've kept up with your results and I am a little scared for my figs in black plastic pots. Looks like I'm going to be busy covering them today. Your analysis of temps is invalueable and I thank you.

What would be the results if tests were done on actual growing plants. I took a look at mine yesterday and found most pots to be in the shade throughout most of the day. The shade from their own foilage or the plants adjacent to them. True, before they become large enough they are exposed to direct sun but seem to grow quite nicely under the sun of Northwest Florida.

Jake

Jake,
I posted a link earlier in this Topic  to a Kansas State Thesis that documents growing plants in different colored pots and the resulting differences in root mass and  above ground mass. attached is a picture of one of the included diagrams.

great info,  confirms most of what I had suspected. I have painted my black pots white with a noticable difference in soil temp as measured by my fingers  ;o)

Jake,
There is no denying that the plants will grow, The argument is being made to grow them in white or light colored containers. There has been much documented about the increase in plant size and root mass when soil temperatures are moderated, its accepted in the nursery industry, one national wholesale nursery has already changed their pots to white exteriors, cost is usually the limiting factor (black pots are cheaper). And as the document stated there was an increase in root mass and top growth with lowered soil temperatures, it was an over 200% increase for both.

BTW, try a side by side comparison next season, you will absolutely see the difference.

maybe nurseries preffer to keep plants size down?

My thanks greenfig, this has been very educational.  Plus, a timely subject..!  

We’ve had somewhat of an unusual hot spell here and I been wondering if it was affecting my babies.  They are in direct sun and of course, I had just moved them up to 3 gal plastic before this heat wave hit……urgh.  I have been going a little heavy on water to keep cool, think now maybe I’ll pile some loose straw where direct sun hits for protection.   Think too, I’ll put a soil thermometer on my list.  Thanks again for sharing.

Thank you all for your input!
I am glad that you find the results interesting/valuable.

Pete, the Kansas State results can be considered now a subset of ours since we tested more pot combinations :)
it is nice they almost match what we have also found.

On a serious note, I have learned a few things about the black pot gardening.
I was especially surprised by the amount of cooling done via the water evaporation.

Some noticeable improvements can be done through:

1. placing a pot in a shade or shielding the pot with paper, wood, fabric, etc.
2. location, location, location... The cement floor is bad, the grass loan is better, half burying is best.
3. choosing a non-plastic pot (terra-cotta, fabric)
4. regular watering, the water evaporation is a huge energy draw for the soil
5. pot color, the light is better

But again, you have to adjust the results to your climate needs. In the south you want to keep the pots cool, in the north you might want to keep them on the sun since it is not as hot.

Greenfig,
Thanks again for formulating your experiments and posting the results.

The conclusion for potted figs may be that you can use the Sun to "Solar Prune" the fig trees. The heat automatically prunes the roots at the perimeter of the pots, which also reduces the top growth. This actually reinforces Belleclaires method of growing potted figs : )

Getting into that time of the summer again and I thought I would revive an old post by greenfig. Trying a couple alternatives using the auto sun reflective shields and bungees. The shields are only $1 at the dollar stores and the same for the bungees. Was able to wrap the pots, however only wrapped the west facing side of the Sips to deal with the mid day heat.

I believe that loamy soil in pots heats like a soup bowl and thus the plants suffered. the plants stayed hot even through the night and couldnt cool down.

The only plants which did well even in full sun were in good aerated potting mix.

I remember after reading this thread and several other similar ones I ran out and bought Reflectix from HD.

 

Made little 'space jackets' for cuttings in the 1 gal. black nursery pots.  I no longer use those pots but it did work well at the time.  

I have about half a house worth of plywood cut into squares of various sizes that shield my pots. I use one large one as the main blocker and a smaller one to help out if I don't move them quickly enough as the sun moves. It doesn't look great but works well. It was 115F a few days ago and my figs looked great all day. I was getting rid of a couple of Janice cuttings that were not doing well compared to the others the soil was very hot and the root growth was very poor. Does anyone have experience with Janice in scorching heat.

Bumping this important topic again,
This year i will use single use alluminium pans to cover one side of my pots as the sides abut other pots.

Does anyone have any experience using them?? They should be good for several seasons??
They are with much thicker than foil.
Each one costs 0.15 cents.

My kids bought me a laser measuring gun. Was not expensive and works pretty good. I went out to the green house on Christmas day and checked temps on surfaces (it only measures surface temps) Most of the soils temps. were in the mid- 70's which I think is good. I've included a link.   https://www.amazon.com/gp/product/B00DMI632G/ref=oh_aui_detailpage_o01_s01?ie=UTF8&psc=1

Noel thanks, your lucky with 72..
Here I get 107f in black pots. Maybe ill start cooking steaks on these black pots :)