Data from Weather Underground
In the center of the state, weekly average temperatures were in the 50s-60s in October, decreasing to mid 30s-40s in November. Then it became quite cold with average temperatures decreasing to 23 degrees in the week of December 11th. After that, the average temperatures hovered around the 30s in January, increasing to the upper 30s in mid-February, which was again followed by colder temperatures in March. What interested me more was what huge fluctuations in maximum and minimum temperatures did to our cover crops. The differences between minimum and maximum temperatures were sometimes more than 50F in the same week. For example, in the week of December 11th, the minimum temperature was 4F, while the maximum was 39F. In the week of February 19th, the minimum was 31F and the maximum 73F. In the week starting March 19th, the minimum was 17F, while the maximum was 71F. These temperature fluctuations could potentially cause havoc when cover crops start to wake up from dormancy and then get hit with significant freezing temperatures.
After this temperature roller coaster it seems spring has really begun now. Accuweather and the National Weather Service do not call for significant frost anymore. So it is time to check to see what the cover crops look like. Winter killed cover crops like oats and radish are dead by now although we hear of some oats surviving in southern Pennsylvania. Winter-hardy cover crops are just starting to regrow, being still in a semi-dormant state, so it may be too early to tell if they will definitely make it. From my own observations and from extension agronomy educators around the state, however, it seems that cover crops have come through the winter surprisingly well. Most annual ryegrass varieties at our Rock Springs Agronomy Research Farm looked excellent. These plots are established at the end of September, but are heavily fertilized which helps improve winter survival by stimulating growth and storage of reserves in the late fall. We did observe a few gaps in stands of some varieties but they were relatively minor. One variety completely winterkilled but this was the exception. Rye, triticale, and wheat showed a few dead tips but the growing point seemed to be unaffected. Hairy vetch had completely winterkilled in a mixture with radish that grew very aggressively in the fall - in this case we attribute winterkill to the fall competition because the same hairy vetch planted next to it looked like it survived the winter just fine. Some reports have come in from Huntingdon County of fall slug damage in radish, crimson clover, and small grain cover crops planted after wheat. This resulted in poor stands this spring. Triticale also exhibited fall slug damage, but despite that stands looked good this spring. Reports from the southeast tell us the cover crops triticale, crimson clover, and ryegrass are looking good. This despite some tops burning off during the last cold snap in March. This was attributed to a lack of snow cover so snow mold was no problem, and no excessively cold nights. A farmer in Forest County reported good survival of hairy vetch and rye, despite late planting of the rye cover crop (hairy vetch was established in August). Our reports suggest the survival of winter-hardy cover crops looks very good in Pennsylvania this spring. The huge temperature fluctuations do not seem to have done lasting harm to our cover crops.