What's New at Oregon Viticulture

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20 April 2026

We have observed this significant day (4/20) by making a few changes in the code of the Windows version of GDDCALC. This is in line with the tighter approach to code safety that newer versions of the C compiler insist upon.

24 February 2026

A newly refactored version of GDDCALC (Linux version only) is now up on this website. The two search displays in particular have been rewritten using GTK best practices, which involve placing visual components inside invisible grids. This will enable displays that have a constant appearance across various Linux distributions.

29 December 2025

After lying fallow since last April (the ssl cert had expired) the Linux version of OregonViticulture has been retooled a little. We now have a functioning ssl cert (so you can access the site via https) and have rewritten the 3 tests that a user can use to see whether the solar calculations are working correctly. This is meant primarily for those who download the software to run on their own computer. We hope software changes have improved the user experience. Using the Gtk toolkit to build the user interface, as we did, sometimes produces different and sometimes awkward effects on different computers and under different versions of the Linux desktop.

4 February 2024

The Windows version of GDDCALC is contained in two zip files. For some time (weeks? months?) the download page of this website contained a code error that prevented users from downloading those files. A user brought this to our attention and we have fixed the problem. You can now download those files here.

16 January 2024

We have updated some visuals in the Linux/OpenBSD version of GDDCALC. The text boxes (where you observe or type in various parameters) are prettier (why not?) and their labels have been reworked slightly. Otherwise the software is unchanged. For what it is worth, we are currently looking at local weather statistics to see whether growth properties have been materially affected by the warming temperatures of global climate change. That is a moving target and may or may not be significant in Western Oregon.

10 April 2022

When GDDCALC was first released 15 years ago, laptop screens were much smaller than they are now. Because GDDCALC was meant to be available in the field with a portable computer it was developed on a MacBook with a 1280 x 800 maximum screen resolution. Almost all laptops now have screens that are larger and with better resolution. Accordingly we have updated GDDCALC by making its display larger and easier to read. You can download the newer version here.

1 April 2022

A slightly nicer update of the Linux version of GDDCALC has been placed on this website. You can find it here.

19 March 2022

The Linux version of this software is now available. Go here to download a description and installation instructions. Note that the Linux version runs equally well in openBSD (and probably also in FreeBSD, though we haven't tried it there).

1 March 2022

Recent changes in some browsers have impacted the way in which these browsers treat downloadable zip files. Since the downloads page of this site offers zipped software for download, we have had to modify the page. If you tried to download our files in the recent past and failed, please be advised that the problem has been corrected. Our GDDCALC app and its source code can now be downloaded from any reasonable browser (Firefox, Brave, Vivaldi, etc.)

22 February 2022

A new, simpler version of GDDCALC for Windows has arrived and can be downloaded here. It differs from previous versions in two ways. (1) The method for specifying persistant descriptors has been reworked and is much simpler. (2) You can no longer record results. This procedure was unwieldy and confusing, has been removed entirly. A pencil and paper will suffice.

16 February 2022

Two things: (1) The Linux version of this software will very soon be available. Look for it in the downloads page of this website. And (2) a newer, simpler version of the Windows version will also be available there.

3 July 2021

The Microsoft Windows version of GDDCALC has been updated and runs well under Windows 10. The Macintosh version has been withdrawn and work has begun on a Linux version. You can go here to download the Windows version of GDDCALC.

31 May 2021

As you can see below, it has been many years since this website was active. We plan to get it going again. This will include a rewrite of the downloadable software, and we will also update the GDD estimates for global warming. Note that we also have a secure (https) connection, something that was rare for non-commercial sites in 2007. So stay tuned.

19 November 2007

Both the Windows and Macintosh versions of GDDCALC have now been validated for sites in southwestern Oregon. In other words, you can use the program to calculate GDD for all Oregon sites west of the Cascades and north of the California border which also meet the maximum elevation criterion (500 meters). The program is also valid for sites in southwestern Washington.

In addition to assimilating data from southwestern Oregon, we have removed a bug associated with the year 2000. (Yes! A Y2K issue, but not the one you think.)

This newest version of GDDCALC is Version 0.8 and is the version you will get when you download it from this website.

28 August 2007

The Windows version of GDDCALC has been upgraded from Version 0.7 to Version 0.71. Certain issues around the placement of text have been resolved in the newer version.

13 July 2007

The Macintosh (actually, OSX) version of GDDCALC is now available from the downloads page.

11 July 2007

Minor changes to the software have resulted in an upgrade from Version 0.61 to Version 0.62. These are the versions now offered here. A Macintosh version of the software will be put up in a week or so.

13 June 2007 - Global Warming Issues

Recently there has been a great deal of discussion about the effect of global warming on harvest times in the Oregon wine country. In an attempt to get beyond anacdotal evidence we decided to look carefully at temperature data from 21 stations in and about the Willamette Valley. Most cover a period of 46 years, from 1961 through 2006. We divided the data into two groups, the first 23 years of that period and the second 23 years. At each station we applied Student's t test (p. 185, Burrington and May, 1953) to see whether the mean values of GDD in each 23-year period were different at the 0.05% significance level.

The somewhat surprising result is that at most stations and during most months there is no reason to believe (at the 0.05% level) that the earlier and later GDD values are from different populations. The principal exceptions are during midsummer at some stations (July, August, September) where temperatures have indeed been higher in recent years. At several locations midwinter temperatures (October through February) have actually been lower recently, but not significantly so.

Specifically, in July eleven of the 21 stations show a statistically significant warming trend. In August nine stations display a warming trend. In September four stations have been warmer in recent years. It appears that our subjective impression that recent summers have been warmer is correct.

Because mid Summer and early Fall are critical in viticulture, and we have found a warming trend at some (though not all) Willamette Valley stations during this critical period, we have decided to revise our model by giving greater weight to recent years in the equations that connect insolation to growing degree days. As a result GDDCALC now produces a slightly higher value for GDD during the growing season. The version of GDDCALC that implements this change has been designated 0.61 and is the version now available on our downloads page.

27 April 2007

The website is now well under way. The Windows version of GDDCALC is now available here - both the executable and the source code. The executable is known to work under Windows 2000 and some earlier versions of Windows, but nothing is promised with regard to later versions (XP and Vista). If the executable does not do well with your version of the Microsoft operating system we invite you to download the source code and recompile or redesign it - this is Open Source software.

At the present time GDDCALC is validated for the Willamette Valley and environs, and southwest Washington. It will reject queries for sites outside that region. Our plan is to gradually expand the region for which GDDCALC is valid. Stay tuned. We will announce progress here, on this page. When GDDCALC is modified you will be able to download new versions. The present version is designated 0.6.

You can email us at this address. As with any open source project, we appreciate and encourage bug reports.