T-Sum Growing Degrees Update
The T-Sum (temperature summing) is calculated by summing the daily average temperature (adding the daily
maximum and minimum temperature in degrees F and dividing by 2), and then subtract 32 degrees (base
temperature for T-Sum). If the average is less than 0, discard the number; if the number is positive, it is
accumulated, from January 1st as a growing degree-day (gdd). One web site you can track the thermal time is at:
http://uspest.org/OR/, which is the direct web site to all weather stations on this system. Use “simple average” and
32 degrees base temperature to plug into the calculator. This T-Sum 360 F or T-Sum 720 F system for calculating
gdd’s is only to be used for timing nitrogen fertilizer applications on grass pasture and hay fields. If you want
earlier pasture production, then when 360 F gdd’s is accumulated, that is the best time to apply 50-60 lb/ac N. If
you are applying high rates (100-150 lb/ac) of nitrogen to grass hay fields, than apply around 720 gdd’s. This
strategy is based on C.O. field research (2 site years at Powell Butte and 2 site years at Madras).
Table 1. T-Sum dates for the present year(s) for 180, 360, 540, 720, and 900 accumulated T-Sum growing-degree
days (GDD’s) from January 1st for selected Oregon locations. (Fertilize at 360 gdd’s for pasture, if you want earlier
forage, and around 720 gdd’s for grass hay.) (GDD’s using 32 degrees F base temperature as of March 1, 2015)
Fertilize
Fertilize
Pasture
Grass Hay
Location/Elevation Year
180 GDD’s
540 GDD’s
900 GDD’s
360 GDD’s
720 GDD’s
Madras
2008
Feb 16
Mar 10
Apr 6
Apr 25
May 6
(2440’)
2009
Feb 6
Mar 20
Apr 8
Apr 20
May 3
2010
Jan 21
Feb 16
Mar 12
Mar 30
Apr 17
2011
Jan 27
Feb 28
Mar 19
Apr 4
Apr 23
2012
Jan 31
Mar 8
Mar 27
Apr 12
Apr 22
2013
Feb 16
Mar14
Mar 31
Apr 12
Apr. 27
2014
Feb 17
Mar. 9
Apr 26
Apr 8
Apr 19
2015
Jan 26
Feb 11
493
Prineville 4 NW
(2840’)
2008
2009
2010
2011
2012
2013
2014
2015
Feb 23
Feb 3
Jan 23
Feb 3
Jan 29
Feb 11
Feb. 14
Jan 24
Mar 14
Mar 15
Feb17
Mar 8
Mar 8
Mar. 13
Mar 5
Feb 8
Apr 14
Apr 7
Mar 15
Mar 29
Mar 31
Mar. 30
Mar 28
Feb 25
May 3
Apr 20
Apr 4
Apr 17
Apr 15
Apr. 11
Apr. 11
568
May 14
Apr 30
Apr 19
May 4
Apr 25
Apr. 28
Apr 24
Redmond
(3077’)
2008
2009
2010
2011
2012
2013
2014
2015
Feb 24
Feb 4
Jan 24
Feb 4
Feb 16
Feb 28
Feb. 11
Jan 27
Mar 18
Mar 20
Feb 25
Mar 10
Mar 16
Mar. 12
Mar. 5
Feb 13
Apr 22
Apr 10
Mar 21
Apr 1
Apr 10
Apr. 6
Apr 3
444
May 5
Apr 25
Apr 15
Apr 28
Apr 22
Apr. 10
Apr 15
May 16
May 9
Apr 26
May 12
Apr 30
May 5
Apr 29
Powell Butte
(3180’)
2008
2009
2010
2011
2012
2013
2014
2015
Feb 20
Feb 3
Jan 20
Jan 27
Jan 29
Feb 4
Feb 11
Jan 25
Mar 10
Mar 15
Feb 16
Mar 2
Mar 8
Mar 12
Mar 5
Feb 8
Apr 13
Apr 7
Mar 15
Mar 28
Mar 28
Mar. 30
Mar 23
234
May 2
Apr 21
Apr 6
Apr 16
Apr 16
Apr. 10
Apr 8
May 14
May 6
Apr 26
May 5
Apr 24
Apr 27
Apr 20
Bend (Agrimet)
2008
Feb 24
Mar 18
Apr 14
May 3
May 14
(3650’)
2009
2010
2011
2012
2013
2014
2015
Feb 4
Jan 29
Jan 27
Feb 8
Feb 4
Feb 11
Jan 25
Mar 19
Feb 28
Mar 3
Mar 10
Mar 11
Mar. 5
Feb 10
Apr 9
Mar 24
Mar 31
Apr 3
Mar 28
Mar 19
503
Apr 21
Apr 16
Apr 19
Apr 20
Apr 9
Apr 7
May 3
Apr 29
May 6
Apr 27
Apr 25
Apr 17
Paulina (3688’)
2008
2009
2010
2011
2012
2013
2014
2015
Mar 18
Feb 25
Feb 13
Mar 9
Mar 8
Mar 13
Feb 27
Feb 2
Apr 22
Mar 31
Mar 17
Apr 2
Mar 29
Apr 1
Mar 15
Feb 15
May 6
Apr 23
Apr 15
Apr 27
Apr 16
Apr 18
Apr 3
485
May 16
May 3
Apr 27
May 12
Apr 24
May 2
Apr 15
May 24
May 15
May 13
May 22
May 5
May 10
Apr 30
Christmas Valley
(4360’)
2008
2009
2010
2011
2012
2013
2014
2015
Mar 12
Mar 1
Feb 12
Feb 14
Mar 11
Mar 14
Feb 24
Feb 6
Apr 24
Apr 8
Mar 28
Apr 1
Apr 9
Apr 4
Mar 16
310
May 8
Apr 23
Apr 23
May 4
Apr 23
Apr 27
Apr 9
May 17
May 12
May 13
May 18
May 6
May 8
Apr 24
May 27
May 21
May 25
Jun 3
May 16
May 15
May 9
Fort Rock (raws)
(4430’)
2008
2009
2010
2011
2012
2013
2014
2015
Mar 13
Feb 25
Feb 11
Feb 13
Mar 9
Mar 13
Feb 18
Feb 4
Apr 24
Apr 5
Mar 16
Apr 1
Apr 9
Apr 1
Mar 13
355
May 8
Apr 21
Apr 16
May 2
Apr 22
Apr 22
Apr 4
May 17
May 8
May 3
May 15
May 5
May 4
Apr 13
May 26
May 18
May 17
Jun 1
May 14
May 11
Apr 30
Seneca (4665’)
2008
2009
2010
2011
2012
2013
2014
2015
Apr 30
Apr 10
Mar 28
Apr 11
Mar 29
Apr 3
Mar 9
Feb 18
May 7
May 2
Apr 23
May 9
Apr 20
Apr 26
Apr 8
205
May 17
May 17
May 14
May 23
Apr 30
May 8
Apr 22
May 27
May 25
May 26
Jun 6
May 14
May 15
May 5
Jun 11
Jun 2
Jun 6
Jun 15
May 23
May 24
May 16
Mylen Bohle