[Market-farming] Growing Degree Days

Dave or Kathy Campbell dkcampbell at southslope.net
Fri Jan 3 19:11:12 EST 2014


Yep, I use degree days to anticipate blooms of plants my bees forage on,
emergence of weeds and insect pests (for IPM) and so on.  You must note
carefully when blooms, insects, and weeds first show, as well as when they
hit full stride.  Do this over several years so as to build up a durable
profile of when things happen.  This can make you a LITTLE more independent
of the calendar, because you are using this year's weather instead of an
arbitrary calendar date.

You do have to keep a good weather log (daily highs and lows in temperature)
to correlate with the events you are timing.  Get a good high-low
thermometer; a lot of cheap high-lows don't even show the same "now" temp on
both sides of the scale.  Each morning I write down yesterday's low & high
in my daybook.  (I also keep a good record of rainfall-bees don't forage on
bad days, so that a week of bad weather in the spring will mean no honey
flow six weeks in the future!)  Anyway, each Sunday morning I transfer the
week's data into my "GROWDAYS" program.

GROWDAYS takes the average between high and low and adds that to a cumulate
"growday" sum.  Of course, a freeze will kill plants, so you start the sum
over whenever it freezes.  Furthermore, different plants start growing at
different temperatures-for corn, say, this is about 55 deg, or maybe 40 deg
for dandelions.  So you choose a start temp to use for a base: if the day's
average is below that base, you add nothing to the growdays cumulative.  In
my case, I'm interested in dandelions, because my bees use their pollen to
start spring buildup, so I use a base of 40 deg.  I've fixed GROWDAYS to use
whatever base temp I want, tho.

Got all that?  You can google PHENOLOGY on the web to learn more; many state
agriculture departments have information about this, and programs to
calculate it.

My GROWDAYS program is in Excel.  I'm happy to share it with those who want.
Because my own copy has over a decade of my own weather on it, I'll need to
strip all that out before distributing it; so, there might be a delay before
I get around to sending you it.  Email me separately to not clog up this
bulletin board.  Actually, though, if it turns out a whole bunch of folks
want it, maybe I could just post it here.  Is that allowed/possible?

 

==Dave Campbell   / Adelyn's Organic Garden  / Tiffin IA /  USDA Zone 5a

 

From: market-farming-bounces at lists.ibiblio.org
[mailto:market-farming-bounces at lists.ibiblio.org] On Behalf Of Buck Family
Sent: Friday, January 03, 2014 12:52 PM
To: market-farming at lists.ibiblio.org
Subject: [Market-farming] Growing Degree Days

 

Hi folks,

 

My understanding is that some ag businesses (corn, soybeans, small grains)
use growing degree days to help time activities like planting, etc.  I'm
wondering if anyone uses this type of information for timing vegetable
growing activities like direct seeding, transplanting and harvesting.  Have
any of you tried this?

 

Regards,

Roy

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