MadSci Network: Agricultural Sciences

Re: In a residential garden, with an installed sprinkler system, at what time...

Date: Thu Jan 27 01:37:22 2000
Posted By: Steven Seefeldt, Staff, Crop protection/weed science, AgResearch
Area of science: Agricultural Sciences
ID: 945192223.Ag

These are difficult questions to answer, but I will make an attempt.  
1.  Is it wise?  If you set the timer and it freezes hard before it comes 
on, then you may get some damage to your equipment.  In winter, aren't you 
supposed to drain the lines etc. to prevent the expansion-contraction 
damage of freezing and thawing water?  I the frozen north, one would do 
this (or for those of us in the Southern Hemisphere - the frozen south).
I imagine you are in a fairly warm area where really hard freezes are 
non-existant.  I will address the rest of this letter as if that was the 
case.  Therefore - if a freeze is expected, I would recommend running the 
sprinkler the whole time.  The warmer water running though the system will 
protect it.
2.  Impossible to answer!  No one can predict the time when freezing 
begins.  If it is near 0 C (32F) when the sun goes down start it, especialy 
if there are no clouds.  To go from 0 C not freezing to 0 C frozen takes a 
loss of 80 calories per gram of water (called the latent heat of fusion).  
To go from 1 C to 0 C only takes a loss of 1 calorie per gram.  So one can 
be at 0 C for a long time and not see any ice.  Watch a big thermometer put 
in a freezing room.  It gets to 0 C fast enough, and then it takes its own 
sweet time getting to -1 C.  Anyway its all a wild guess on the time of 
actual freezing, so turn it on early.
3.  Keep it on till the sun is up or it warms up.

I assume we are talking about protecting spray equipment and not plants.  
So maybe this is the time to go on and on about the earth's resources ... 
and the wise use of fresh water.  If it's winter, drain the lines.  If you 
only have one or two nights of frost a year turn it on low early and turn 
if off when it's warm.  Hope the message gets to you before a frost.  We 
are in mid-summer here in New Zealand.

Cheers, Steve

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