During our first growing season, and after having read the same kinds of “How to grow hops” literature that is commonly available, we believed that good winter protection was necessary to protect our hop crowns from the cold temps which can occur in our Blue Ridge Mountains. We regularly get into the teens and single digits, and occasionally slightly below zero near the end of winter.
Our choice for protection that first season was to mound the dirt up around the sides of the crown with a center cap of grass clippings over the top center of the crown. This gave them the look of little volcanoes throughout the yard. The results the following spring were less than satisfactory.
The heavy covering kept the crowns cold longer. It further prevented moisture from evaporating and running away from the crowns. All of this promoted the growth of mold and possibly other diseases under the cap of grass clippings over a few crowns. Dormancy break was severely retarded in some varieties and several crowns throughout the yard showed beginning signs of rot or decay.
The second winter season, we decided to test the resilience of hops to cold weather. So while we trialed a new type of mulching product on the yard, we took 200 plants, comprising 18 different varieties, that had been started during the growing season and were in 6” pots, and placed them out in the open on the ground with only a couple handfuls of dirt on top, just to cover the crowns. Several still had buds exposed to the air.
Our winter ended up being one of the coldest on record in nearly 100 years for this area. The pots remained frozen solid for at least two months straight with no thawing at all. Between February 21st and March 10th, 142 (71.4%) of the 200 pots had started sending shoots up through the dirt. Several of the exposed buds even began elongating and greening up. By April 15th, (87%) of the 200 pots had begun sending up shoots. The pots that did not make it through the winter appeared to not have a strong root system to begin with or were small and could not store enough sugar reserves for the winter.
These results seem to indicate that hop plants are very resilient to the cold and that winter cold protection may not be as important as previously thought. Our tests and observations indicate that a light soil application is the only thing necessary to protect healthy and well-rooted hop plants in the mid-Atlantic region. If soil erosion is a concern, than a suitable form of mulch can be lightly applied. Please see our studies on various mulches to get an idea on what may and may not work.
Finally, a side note. We spoke with several upper mid-west growers from around the Great Lakes region about covering hops in the winter. Considering the extreme cold weather that region receives, we assumed that winter protection was mandatory. The respondents told us that they do not cover their hops at all, with one saying that a light covering of plain soil is the most they do. Furthermore, many pictures of the Pacific northwestern hop yards in the winter do not show any mulching of hop crowns.