Dem Pots Are Hot

[RazinCane]

Do those of you that container grow, do anything about the heat black nursery pots absorb in warm weather, to keep from cooking the root mass? I've potted a few dozen boos in March and have given them full sun the last 2 months and they are done shooting for the most part and have about leafed out. Now that temps are in the 80's the pots are uncomfortably hot to the touch and I've moved them to a shade area for the summer to help beat the heat. Was just wondering how others deal with the heat. Thanks.

[needmore]

I keep mine in full sun all summer so that the plants are ready to be planted in full sun should that be the case. I try to water them of an evening so that they are moist starting the next day. In weather like we're having now that means watering at least every other day, if not every day that it does not rain. This is where up-potting can be helpful if done with awareness, when over-potted the soil will stay moist longer which is also what can cause problems with some species and smaller sizes of plants. The deck plants get even hotter and needmore water...

[tomgun]

I have them out in the sometimes over 100 degree sun here in California. I never noticed a problem other than I better not forget to water.

[RazinCane]

I noticed the heat when I touched the pots, if you place your hand on the side of the pot in that kind of heat I think you'll notice your hand is blistering. Actually it's not the air temp as much as the direct sun hitting the sides of the black pots that is the cause of the excess heat. I've thought of designing a nursery pot sombrero out of cardboard to shade the sides.

[foxd]

I wonder why they don't make white plastic pots for nurseries?

[RazinCane]

Maybe it's not an issue and I'm just over thinking it. It just would seem anytime a pot is too hot to touch it wouldn't be an optimal situation for the plant inside it. Maybe I'll try sticking a meat thermometer down the inside edge of the pot to see just how hot it is, sounds like a project.

[Alan_L]

Maybe I'll try sticking a meat thermometer down the inside edge of the pot to see just how hot it is...

At first I was going to make fun of this, but then thought about it, and that's a good idea! I've got a wireless meat thermometer for the grill so I can monitor the pot temp all day long.

Pots on the driveway get especially hot. Now I'll be able to find out how much hotter they do get.

[needmore]

I suppose the white ones would be more costly, although I've seen white but not blow mold white. I have read estimates of the black pots reaching 140F+ so let us know what your soil temps hit.

[va_highlander]

I wonder why they don't make white plastic pots for nurseries?

At a guess, I'd say because of UV stabilization. White would not last very long, when exposed to sunlight.

Also, if I'm rememberin' my heat-mass transfer aright, the difference between black and a lighter color is significant, but not as great as one might think, especially when compared to variaton due to intensity of insolation, surface reflectivity, &c.

All from memory, so ummv.

[movenosound]

I've seen a few different sizes of white nursery pots, though they were specifically the square variety. I have always thought that the problem with white nursery pots was that they are not fully opaque, or, if that was the wrong word for what I am trying to say, they let some light reach the interior of the pot, in other words the soil and roots and whatnot. This then leads to screwed up root growth and algae and all kinds of nonsense. But, I have used them, with great results, but never with a plant that was going to spend all day outside in full sunlight. I like your empirical approach, with the temps and whatnot.

[firemountain]

I have been potting several bamboo species since last year, so I am still a novice. What I do is actually line my pots with pinkboard. They are cut to fit and then lined with tar paper. This will help keep the sun from overbaking the roots in the hottest part of the summer. I have my Ph. Nigra and Fargesia Scabrida plants in large containers by using this method, and have had great success.

[David]

I've grown bamboo in pots, and have noticed that the only problem with hot pots is the rate of evaporation, and the need for frequent watering.

You could always paint the pot white with a latex paint like Gripper, or wrap some aluminum foil around the outside or you could just water every day.

I really don't think it's a problem, but it would be fun to see the difference in temps using the various ideas that have been mentioned, and if they have any effect on the growth rates.

[RazinCane]

Some may not consider the heat absorbed in the summer by black nursery pots to be a problem or concern but if 140F + is a possibility and simply gluing a cardboard sleeve to the outside of the pot can lower the pot temp down to air temp thereby reducing the temps in the pots 40-50F, that would substantially reduce evaporation, requiring less watering and less leaching of nitrogen and less stress on the plants. Moving them in the shade June, July and August accomplishes the same thing. By June my plants have shot and leafed and are recovering from the energy expended during shooting season and the shade is a welcome relief from the oppressive heat of summer. Moving plants from sun to shade and back again is one of major benefits of container growing and one I utilize to great benefit to the plants and myself, as anyone that has watered in full sun in July can attest.

[va_highlander]

...simply gluing a cardboard sleeve to the outside of the pot can lower the pot temp down to air temp...

Not quite down to "air temp", I am guessing. There will still be conductive heat transfer from the cardboard to the pot.

In point of fact, just leaving the cardboard loose, with a gap between the sleeve and the pot, should provide superior results.

[Alan_L]

An easier and weatherproof solution would be to just nest the pot in a second pot of the same size. I realize that's a waste of a pot and can be expensive with the larger pots, but it's simple enough.

I'm going to try this in my temperature experiments. I hope to do some tests this weekend, as it's going to be cloudless, or so they say.