dual-pot method for darlingtonia

sowley(6)July 15, 2005

This spring I began an experiment using a dual pot method to raise darlingtonia (cobra lilies) outside without extra care. Since I have had success, I thought that I would post here about it.

The method consists of a small, glazed pot, containing the plant and growing medium, which is placed in the bottom of a much larger, unglazed pot, the space between them filled in with sand or perlite, and the top of the large pot half-covered with a white cotton cloth. A wire mesh around the inner pot, extending to the lip of the large pot, allows the perlite fill to extend to the top of the large pot. The large pot is then buried almost completely in the ground.

Heat exhange and moisture level are controlled passively by the system, via evaporation. We have had a very hot (90's) and dry summer, but the cobra has sent up several new leaves and is doing very well. It is feeding itself in the usual way.

This method is not lovely, but it is zero care and allows cultivation of the plant in a hostile environment. When winter comes, I will simply cover the pot all the way until March.

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Congrats on your success! In the wild these are often subjected to temperatures into the 90+F range in the summer months, but the ground water moving through the substrate is cool to cold. It is the same habitat that the rare California Ladyslipper, Cypripedium californicum, grows in. So the real trick is to keep the roots cool, not so much the plant itself.

I'm trying out a similar method this summer with Cypripedium orchids here in hot, balmy Kyushu. My setup is less elaborate than yours. I use two unglazed pots, a bit oversized, one sitting directly in the other. The plant is in the top pot of course, and the other pot is sitting in a reservoir of water (a deep dish). The water level in the dish is kept up to where the inner pot is always in contact with it. Evaporative cooling from both pots seems to keep temps about 10F below ambient (which often exceeds the high 80's). In theory, this method should work better in drier air since the rate of evaporation will increase in drier air. Most Cyps can't tolerate soil temps above 75F over the long haul. So far, things look good for most of my plants, but the blinding heat of August has yet to hit. I'm praying! PF

    Bookmark   July 15, 2005 at 4:58PM
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Sowley, how in the world do you keep the soil temp below 70F in 90 degree weather?


    Bookmark   July 15, 2005 at 6:03PM
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I think the trick is that it carries over night temperatures well. Heat is pumped out efficiently enough to get to dusk without harming the plant. Evaporation takes place continuously, so the pot probably gets down to 60F every night.

This method (one very like it, anyway) is used in Africa and keeps internal temperature at around 60-65F with the external pot completely exposed to desert conditions. Mine has the advantage of being mostly buried, and the contrast between surface soil temp and the medium in the inner pot (measured with a finger) is quite striking.

I was inspired to try it when I read a UN article on the practice as a cheap refrigeration method for so-called underdeveloped areas.

There is very little soil in the internal pot, by the way. I wanted to encourage air absorption, even if that meant a risk of drying. If the plant gets off to a good start in the spring, I will count the experiment an unqualified success.


    Bookmark   July 18, 2005 at 2:08PM
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akheadbanger(z?? OH)

Have you tried putting In the Sand, water? that might do it if you live in a Warmer place? Or maybe im not catching summin, if you could get a picture of the set up that would be great im more visual than uhhmmm reading, i have some seeds, so it might work out great. And i bet for even more pots buy a large pot at lowes and do that. and put a couple pots in! and please a picture would be nice!

    Bookmark   July 18, 2005 at 10:37PM
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That is a great idea. It's kinda like the setup for Drosophyllum, except its used to keep the plant cooler. If you plant your plant in a pot, then place it in a bigger pot and burry it so it looks like it's just one big pot this would definately keep the plant cooler. The outter pot would absorb most of the heat, and keep the inner pot cool. The question is though what would be the best substrate for the outer pot? I'm thinking 100% sand, 100% LFS, or a mix of the two would keep things cool.

    Bookmark   July 18, 2005 at 10:51PM
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akheadbanger(z?? OH)

Maybe the bottom half Sand and the top half of the larger pot LFS? or 1/3 LFS and 2/3 sand?

    Bookmark   July 19, 2005 at 1:28AM
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Another interesting point is that you can cool the plant indirectly--that is, if you cool the apparatus around the inner pot (say with hose water) it does not get into the inner pot, and cannot poison the plant with minerals or chlorine. No more keeping frozen rain water for emergencies.

akheadbanger--that's right, wet sand. I used perlite, but sand would be better. The wire or screen "chimney" allows you to place the smaller pot deep in the sand (actually on the bottom of the big pot) without it getting buried.

This setup *may* work without burying the big pot, but I haven't tried it yet--I like to hedge my bets a bit.

    Bookmark   July 19, 2005 at 3:14PM
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Would using an oversized white polystyrene container sitting in water be sufficient for someone who's temperature doesn't get quite as warm during the day? Or would it still pay to put ice on top on hot days?

    Bookmark   February 29, 2008 at 9:30PM
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