Soil Temperature Estimate Map

The morel community often talks about the “Rule of 100” for estimating good environmental conditions for morel-fruiting. The rule of 100 states that morels are likely to start fruiting once the Low + High temp equals 100F. Another way to say this is when the average daily temperature is 50F.

For example once the daily highs are 60F and lows 40F –> 60 + 40 = 100F

Of course, this doesn’t account for a brief warming in February followed by more snow or freezing temps. This also doesn’t account for warm periods in an area still covered by snow.

I think a better indicator of the start of morel fruiting in any region is using soil temperature. This past week I added a Soil Temp layer to my recently published morel map. This estimates the soil temperature across all of Washington and Oregon, and provides a simple way to visualize areas that are still too cold to likely be producing. Today on Feb 20th, it’s still too cold everywhere.

So, when are we going to start seeing morels in Oregon and Washington? Morels can start to show up in low elevation areas as early as March. The first ones of the year will likely be in urban areas growing on woodchips, likely close to a southern-facing wall where temps are likely to be warmer than the surrounding areas.