GG is several years into answering the question: can you grow chestnuts in northern Wisconsin? When we started the project, I thought our biggest strike against us was our minimum winter temperatures. But the only time we have had significant tree die-off is the when we fall-planted two year old seedlings and didn’t apply wood mulch at the base to protect the roots. About half of those trees died. Otherwise, the seedlings we’ve been planting appear pretty hardy. Now, although GG is located on Washington Island in northern Wisconsin, we are surrounded by the Green Bay and Lake Michigan, which both serve as major thermal reserves, keeping our springs cool and our falls and sometimes winters warmer. So while Washington Island is as north as growing zone 4 on the mainland of WI, we are actually growing zone 5 due to our lake-influenced climate.
Lately, I have begun to think that our primary disadvantage in the chestnut orchard is our low number of growing degree days (GDD). GDD are heat units, basically, with the idea that plants have a required number of heat units to develop and mature. And while Washington Island has warmer minimum temperatures in the winter than mainland Wisconsin at our latitude (45 degrees north), we have a lower number GDD compared to the same area, meaning that a given seedling might be able to mature nuts in Wasusau, WI but not Washington Island, WI due to the cooler summer.
Therefore, we have spent the last three years exploring for trees located in the midwest and northeast that ripen nuts early relative to other chestnuts in the same area, with the hope that those trees do not have as high of GDD requirements to ripen seeds/nuts.
So what are we planting? Stay tuned for the next post!