[permaculture] Creating frost-free microclimates

jedd jedd at progsoc.org
Sat Oct 6 22:34:30 EDT 2007


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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