Individual species in cover crop mixtures will respond differently to below freezing temperature. Learn about their characteristics here.
Diakon Radish: Intercourse,PA (planted 9/1/15)
After a seasonable fall, the first hard frost hit on October 18th here in Central Pennsylvania. The temperature declined below freezing, and on our research farm it hit a low of 23F. This did our summer cover crops in. If you planted mixtures of warm- and cool-season cover crops, you will notice that the summer annuals are now dead. Some of the mixtures I evaluated on Friday showed that, sorghum, sudangrass, all the millets, mungbean, soybeans, cowpea, sunnhemp, had all winterkilled. Oats and all the brassicas are still alive – most typically don’t die until the mercury decreases below 17F. So the different varieties of forage radish, turnips, swede, and kale are still alive and putting on more growth in these days until roughly the end of December in this part of the state. At that time they typically are killed by low temperatures. Other covers, such as cereal rye, wheat, barley, annual ryegrass, hairy vetch, crimson clover, Austrian pea, and rape, are typically winterhardy as long as they have enough growth but are not too rank. We have noticed a lot of winterkill if annual ryegrass get taller than 8”, or when legumes such as Austrian pea, hairy vetch, or crimson clover show some flowers in the fall. If your annual ryegrass is already 8” tall it is recommended to mow it back to 4” or so to guarantee winter survival.