Double-potting

Welcome aboard Hamish, Hi Everyone, I like your experiments Hamish, its a
fun & interesting contribution, for myself, I live on top of part of the
great dividing range in Australia west of Brisbane & North of Toowoomba in
a vast dry vine forest, hoop pine & eucalypt area. Its an unimaginably dry
place in my garden because I am on a small sharp razor back peak with
extremely little soil & lots of rocky base ground, with heat wave spikes at
times, much more evident every year now with what I call global dryness
fluctuation, especially now when early Spring daily westerly winds coming
from the vast dry plains behind the mountain ridges in the distance & the
end of cool winter days. Its dry enough that my bulbs that survive have to
deal with farm dam water or ground water running low at times & species
that are not usually dormant species, do become dormant here over a few
seasons of conditioning. Eucharus lily a non dormant spp fall into semi
dormancy some recently re-emerge & I thought they must have died last year.
Even Crinum bulbuspermum another non dormant spp, fall into complete below
ground dormancy here every year with out fail, with every leaf becoming
dry. Eventually spring rain or even as late as next summer rain months
later brings new growth & flower spikes at random. I doubt this is common
elsewhere in wetter or cooler climates. Probably because other growers are
more sensible :) Your experiments have given me some great ideas to retain
some moisture in my favourites for next dry season.

If your still experimenting, you may have fun with a floating system,
suspending your pot above water in Styrofoam pontoons. I have seen small
vegetable farms that have this sort of floating pontoon idea in the Cook
Islands, they send roots down, but bulbs may not. It may be too moist but
if u sit a clay pot in water now, it may be similar. Some bulbs wont root
down to water but some will. This may produce a very regular cooler
temperature for you, dependant on the size & depth of water combined with
volume of surface cover foam. Thought you might think its a fun experiment.

Usually we remove some of the previous message but my browser is having
a coronary so ill leave it in for others to see.
Happy growing
Steven Australia

On 17 August 2015 at 20:13, Hamish Brown <Hamish.Brown@plantandfood.co.nz>
wrote:

I have also been curious about how best to keep my alpines cool. Are
friend told me double potting was the way to go but to make it work
properly the requirements are quite specific.

* The outside pot has to be terracotta

* The inside pot should fit snugly (using the same size terracotta
works best)

* The outside pot has to be sitting in a basin of water kept as
full as possible without saturating the bottom of the inner pot

Not being satisfied with unsubstantiated recommendations I ran an
experiment in my driveway where I had 4 replicates of a range of different
pot treatments

* Green plastic with a dark stone mulch

* Green plastic with a white stone mulch

* Plastic covered in aluminium foil with a dark stone mulch

* Plastic covered in aluminium foil with a white stone mulch

* Terracotta

* Terracotta plunged in sand

* Double terracotta

I place a thermopile in each pot and logged temperature at 15 min
intervals over a one month period. I can't remember all the results off
the top of my head (I will write them up properly soon) but the interesting
bits where this:

* On a cloudy day all pots had a temperature similar to air
temperature

* On a sunny day all pots where hotter than the air

o The green plastic with dark stone mulch was up to 10 degrees hotter

o Adding a white stone mulch cooled the pots by 2 degrees

o Adding aluminium foil to the outside of pots (reflecting the suns
radiation) made pots a further 2 degrees cooler

o Double terracotta pots were by far the best system for keeping pots
cool. Provide the outer pot was kept moist they got no hotter that air
temperature.
Double terracotta is also good because the inner pot stays clean so it is
ready to go if you want to take it to a show. The down side of double
terracotta is the cost. Wrapping pots in foil and giving them a light
coloured surface mulch is a cheaper alternative to reduce heating of the
roots

Hope this information is useful

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--
Steven : )
Esk Queensland Australia
Summer Zone 5 Winter Zone 10