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Cohan, all of our troughs have the same wall thickness, so I can't really comment on that. However, I do think there is a minimum trough/soil volume or mass that is probably important to minimize temperature fluctuations and the effect it has on the plants' root systems. (Of course, there will still be those temperature fluctuations, but somehow plants can take it.) I suspect a smallish pot, thin-walled (I presume, and so not adding much mass), especially if partially filled with something other than soil (styrofoam) might be crossing the limit. (Very tough plants sometimes survive here in smallish pots, unprotected, over the winter... not a sure bet, though.)My husband made all of our troughs, starting from an example/pattern that he knew worked (from another local trough-grower). The last trough-building spree was in 2006 (resulting in 16 troughs total), and he used the same rough pattern again. The dimensions are: Square troughs: 22 cm high, 45 cm square (outside dimension), 5 cm thick walls Rectangular troughs: 22 cm high, 38 cm x 76 cm (outside dimension), 5 cm thick wallsSo, they do work. I admit I do fail to overwinter some plants in them but other plants have been very long-lived (e.g. 12 years now)... some of the fatalities may be due to plants that are simply not hardy here (I experiment a lot), or bad choices of plants for the conditions leading to inability to winter over, somehow (). They get no protection over the winter; some of the snow from the driveway (which is usually not much, and melts quickly) gets chucked on top of them (since most of the troughs line the driveway), and that's it. Something I am sort of experimenting with is whether setting the troughs up on blocks (also made of hypertufa) affects hardiness of the plants within... I'm wondering if that is pushing the limits, or not.
Our troughs are moveable... though made of hypertufa (less heavy than other cement mixes or stone), they are still very heavy, however.Perhaps your problem was, at least in part, drainage? The troughs have drainage holes in the bottom (covered with screen), and are filled with a very fast-draining grit mix.
This is my first trough finished today following Ian's instructions in Bulblog 1, 2008. What is advisable: to plant it now or to wait until next year?