Black Temporary Nursery Pots - Insulate or Lost Cause

[Firstflush]

I have a few plants that should absolutely be taking off that I’m trying to grow out. All pre bonsai material, but some really cool stuff. I think the daily heating and cooling of the black nursery pots are having an affect.

I was thinking on using strips of car windshield reflecting cover to keep the heat down on the plastic.

Any theories on this? Should I build some wood boxes? Cheap temporary pink terracotta?
I was pondering mulching the top of the soil but I don’t think that will keep the plastic temps down.

 

[Kanorin]

Wrap the sides with aluminum foil?

 

[Firstflush]

Duct tape is reflective too.

 

[Clicio]

I think the daily heating and cooling of the black nursery pots are having an affect.
I was pondering mulching the top of the soil but I don’t think that will keep the plastic temps down.

Well, summer here is a bigger problem than in southern USA, and we keep seedlings, saplings and bonsai in training in black plastic pots with no issues, as long as the pot is the right size for the plants and they are repotted at the right time into a bigger pot.
But... Terracota pots are a good option as they keep their inner walls cooler and moister than plastic ones.

 

[Forsoothe!]

Rocks are useful in moderating temperatures. Rock gardens imitate mountainsides facing east, west or south. The clear, thin air intensifies the rays of the sun, and the angle of the mountain surface tipped up and ~aimed~ at the sun makes the surface absorb the heat in the sunlight, help keep the surface cooler during daytime, and the heat absorbed by the rock of the mountainside is re-radiated back out overnight which is usually really cool when the sun goes down. The rocks are cool by sunrise and the cycle of absorbing heat starts again.

Another important moderator of temperature is shade and the passage of air. Air gains/loses temperature really fast, and an object shaded by something with an air gap between the object to be cooled and the object projecting the shade can remain remarkably cooler. Mulching your plants under loose rocks would help keep temps down.

 

[sorce]

White tees, sheets.

It definitely has an effect.

I've measured something like a 80 F difference from black pot side to inside near trunk soil temp.

That kinda difference will get US sick!

Sorce

 

[Leo in N E Illinois]

Wrap your pots with something reflective, anything reflective, don't wait. White cotton rags, old TShirts are fine.

Or just set plastic pot inside taller, deeper, wider Terra cotta pot. Leave the space between terra cotta and plastic empty. The terracotta will shade the plastic. Keeping it at ambient temperature. When you water, the terracotta will wick moisture and cool the plastic nicely.

 

[AZbonsai]

It is a little hot here.

I cover my black pots with burlap. You should do the same.

 

[Firstflush]

Trying this....

 

[AZbonsai]

Well, summer here is a bigger problem than in southern USA,

How about the south west?

 

[Brent]

Here's great article by Andy Walsh:

Root Heat in Bonsai and Nursery Containers

I just double pot everything that gets direct sunlight. Put one gallon potted tree inside a 2 gallon empty pot for example. It shades the inside pot and creates an insulating air layer. It's cheap and very easy to do. It has other benefits too: It can be used to prevent blowover from wind. Simply having a wider base helps, but in our windy area I put a stake through the outside pot to give it even more stability. In our windiest areas, I stretch a wire along a row and attach the the stakes (vineyard pencil rod) to the wire. Almost impossible to blow over.

I have discovered that if you use 40% shadecloth for sun protection, the pots won't heat up above the ambient temperature.

Used pots can be had cheap or free from nurseries. If you have to buy them, blow molds (the thin pots with all the ridges) are very inexpensive.

Brent
EvergreenGardenworks.com

 

[jason biggs]

@AZbonsai how can you only be zone 9 and get to 47 degrees?
we are zone 11a and never really see 40 degrees??
Man that must be HAWT !!!!

 

[Clicio]

How about the south west?

In fact you are right, I was thinking Georgia and Florida. Things can get very hot in the southwest.

 

[Clicio]

It is a little hot here.

If it means 48°C it is much hotter than anywhere in Brazil. I am amazed.

 

[AZbonsai]

If it means 48°C it is much hotter than anywhere in Brazil. I am amazed.

Yes, 47.2 C according to my converter. Today may be our third day of record breaking heat.

 

[AZbonsai]

122 F (50 C) is hottest I have been through. Closed down the airport because the planes had never been tested at those temperatures. I was mowing lawns working my way through ASU.

 

[Kadebe]

Here's great article by Andy Walsh:

Root Heat in Bonsai and Nursery Containers

I just double pot everything that gets direct sunlight. Put one gallon potted tree inside a 2 gallon empty pot for example. It shades the inside pot and creates an insulating air layer. It's cheap and very easy to do. It has other benefits too: It can be used to prevent blowover from wind. Simply having a wider base helps, but in our windy area I put a stake through the outside pot to give it even more stability. In our windiest areas, I stretch a wire along a row and attach the the stakes (vineyard pencil rod) to the wire. Almost impossible to blow over.

I have discovered that if you use 40% shadecloth for sun protection, the pots won't heat up above the ambient temperature.

Used pots can be had cheap or free from nurseries. If you have to buy them, blow molds (the thin pots with all the ridges) are very inexpensive.

Brent
EvergreenGardenworks.com

How about wooden grow boxes? Does the soil temperature get as high as nursery pots? Somebody already did an experiment on these?
edit typo

 

[Clicio]

From seed, BRT, always in black plastic pots, dappled sun.

 

[Leo in N E Illinois]

Somewhere around 130 to 135 F, most life simply expires. Exception being mainly the "hot springs, thermal vent, microbes".
That is 54 C to 57 C.

Black plastic in 117 F and direct sunlight only has to heat up 20 degrees above ambient and it will kill roots.

 

[Forsoothe!]

As long as there is plenty of moisture in a pot so transpiration is not interfered with, the roots can take any temperature the canopy can take. If the roots get too dry, then the canopy cannot cool itself with (one of the functions of) transpiration. Full sun plants will take higher temps than shade tolerant plants. Any individual plant acclimated to more shade will be less tolerant of hot roots. Transpiration = growth and high transpiration = high growth, just as low transpiration = low growth. Are there upper and lower limits? Sure. What are they? They are species-dependent and probably pretty predictable based upon the plant's natural range mean temps.