One of the great mysteries of landscaping in Minnesota is knowing all of the elements involved which cause so-called “winter burn” on our garden coniferous evergreens. We do know exposure to the winter sun especially in mid to late winter, the location and genus of the “victim” are all contributing factors.
We also noted that the winter of 2008-2009 was one of the worst winters for winter burn. We noted that some yews in full sun facing south or southwest in full exposure, in front of a stucco structure showed not a millimeter of any winterburn. We also observed many Taunton spreader yews allegedly resistant to winter burn in full shade covered with brownout byApril first.
We concluded that there are a variety of factors which cause winter injury to susceptible evergreen conifers, not least of which is late summer watering and plant exposure to winter wind.
With autumn soon upon us, we will be confronted with “to water? or not to water? from mid October into November until snowfall.
I never had winterburn on any evergreen for 35 years on my grounds until the winter of 2007-2008. I owned about 25 yews displayed one place or another in my landscape. My irrigation system is usually turned off around October 24th. I was alarmed for yews when well grown and groomed are elegant shrubs or trees. Most are located under some canopy of deciduous tree, just shady enough, I felt, to warrant confidence my plants were safe from winterburn…as they appeared to be for 33 years.
Last autumn as an experiment, I decided to stop irrigating the garden three weeks earlier, thinking I had allowed these yews to go into winter without sufficiently acclimating to the harsher temperatures and the winter environment in general. I lost nearly 200 years of yew plant growth on my property, including a tree 25 feet tall. Many lost were located in deep shade.
There have been some professional studies regarding winter burn on conifers in general, but information from them has been contradictory. Some encourage watering regularly until snowfall. Others recommend easing off on watering gradually in order “to toughen” the plants up.
On one point studies recommend…do not, as a rule, fertilize coniferous evergreens after August 1. Encouraging new growth on the plants delays “hardening” them off for the cold season.