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permaculture - Re: [permaculture] Creating frost-free microclimates

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  • From: jedd <jedd@progsoc.org>
  • To: permaculture <permaculture@lists.ibiblio.org>
  • Subject: Re: [permaculture] Creating frost-free microclimates
  • Date: Sun, 7 Oct 2007 12:34:30 +1000

On Fri, 5 Oct 2007, Richard Archer wrote:
> I'm developing a site that tends to be frosty through winter and
> into mid-spring. Overnight low temps get down to -6 C. Daytime
> maximums in Winter range from about 4 C to 14 C.

I get down to -4, maybe -5 - but in winter at least get higher
temps - usually up around 20C. (Where are you, btw? I'm around
the top end of the hunter.nsw.au)

Warmer day time temperatures make it easier to use a pebble/stone
mulch for its thermal inertia. Another frost-protection method you
didn't mention is covering the young plant (once it gets to a certain
height its new growth is typically better protected) with a tripod of
timber and growing winter vines over the thing.

Or even using an artificial covering -- I usually bubble wrap my
passionfruit, for example, from May through September. This is
easy to do as its growing on a trellis, so the framework to attach to
is easy. For standalone plants you need something special - 4x steel
posts with 2" polypipe loops over the plant and shadecloth over the
top, for example. The same structure is reusable in subsequent
years, or alternate for summer protection of other plants.

> - Sun traps - a parabolic planting facing sunwards and to hopefully
> retain sufficient heat from the day to prevent frost at night.
> Can also use water to reflect more heat into an area.

You definitely need something to accumulate and release the heat
with this approach, and rocks are typically the best option. You
may need a backup plan in the event of several days of 4C max, as
you just won't get the necessary heat input to keep you going
through the nights.

> And in a non-permaculture approach... has anyone had experience
> with overhead sprinklers automatically triggered with a frost
> sensor?

I haven't tried this, as I don't have sufficient water pressure (I'm
on gravity feed only) to do sprinklers, and I'd be worried that all
my plants would die in one night if the power or sensor went out.

I can recommend getting a couple of temperature dataloggers that
you can put about the property. These will log temperatures at
various intervals (mine are usually set to 5 or 30 minute) and run for
months at a time, then get plugged into a USB port on your poota,
with the data coming in as a CSV. They're accurate up to 0.5C,
but are particularly useful for working out temperature differences
between two or more sites. These are definitely planning devices,
rather than reactive / triggering devices. The only ones I know of
are from Jaycar and cost about $120 each.

In the Designers' Manual, Bill talks of frost amelioration by digging
holes. I never quite got how this worked, and have been meaning
to try it out - or better yet find someone who's done it and can
comment on its efficiency. Page 120 / Figure 5.13 for those with
the tome at hand.

Jedd.




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