Warm December weather dominates in both the north eastern part of the US as well as large parts of Europe. At both sides of the ocean this warm weather makes plants equally confused.
Many plants are blooming in New York’s botanical gardens and Boston parks. It’s unlikely that most perennial plants will suffer irreparable damage. However, Belgian fruit farmers fear that an untimely frost on the unhardened fruit trees might have serious consequences for both the tree vigour and fruit yields (see movie below).
Plants can withstand frost, however, the continuous warm weather in Belgium has left many trees not acclimated to true winter conditions. A sudden return to normal, freezing, winter conditions could cause frost damage to tissues otherwise protected by a tree’s natural anti-freeze, e.g. sugars in living tissue.
With no real frost days in Belgium the effect of this mild winter might even extend into next year’s spring. Many trees need a certain amount of chilling days, or days which are sufficiently cold / freezing, to trigger a proper leaf-out response next spring. High spring temperatures should move the development of leaves towards earlier start dates. However, a lack of chilling days has shown to delay this expected response to warmer spring temperatures. Warm winter temperatures therefore not only pose an immediate risk, due to sudden freezing of tissue, but have delayed consequences which extend into the next growing season.
(Header image: early leafing Sambucus nigra)