Willamette Weather or Why the Walnut Crop Failed in 2010

Many of our local crops from tomatoes to walnuts did not do well this year. And you can blame it on the weather. Why the weather? Crops of all sorts depend upon the weather for the warmth, coolness, dryness, or wetness required at different stages of their life cycles. Walnuts, for instance, need some but not too much rain during the pollination period around April through May. Look at the average annual precipitation for the Eugene area in the following figure.

Notice that the curve is fairly smooth except for February being slightly less than it should be. This is due to the length of February being the shortest month by 5 to 10 percent. If you add around 0.5 inch to February, it becomes a smooth curve. This is what plants expect in terms of rainfall. This is what they are genetically tuned to thrive with. However, the 2010 water year was different. The general weather patterns were shifting from an El Niño to a La Niña event without the usual neutral year. In Oregon, this often messes up the springtime and early summer weather patterns away from average toward wetter and cooler. Now take a look at the rainfall I recorded for 2010 versus annual in the following image.

Notice that the largest anomaly from average was during March through June. Walnut pollination season precisely. Hence, no commercial walnut crop. Here is why I care: I love to eat walnuts throughout the year, but especially in the winter and spring. I also enjoy baking my award-winning walnut sourdough bread. But no walnuts to be had at my local Herrick Farms, so this year I am paying double the price for imported walnuts from California! The wet June also explains why my wife's tomatoes were a pulpy disaster. Strangely though, the Cherry Bomb chile peppers and the tomatillos were great. So was the excellent cabbage that had a great mustardy tang to it.

While the distribution of rain over the year was quite odd, the total amount for the year was not very different from average. You can see this in the following picture which shows cumulative rainfall during an average year (in Eugene about 50 inches; at my house maybe 55 inches) versus the 2010 season (about 58 inches as measured at my home).

The good news from all this is that the odds are extremely good that this spring and summer will not resemble last year's. Thank goodness for that. But there is a price to pay: we are likely to have a colder, wetter start of the 2011 rain year, but hopefully later a perfect year for walnuts.