My interest in plant hardiness(ability
of a plant to over winter) began the summer before I decided
to open a nursery in Truckee Having studied botany in Michigan,
I assumed that many of the ornamental plants I knew would grow
here. As I walked and drove around Truckee in the summer of 1975,
I was surprised not to see certain plants such as holly, boxwood
and hydrangea that are common in Michigan. I became acquainted
with longtime Truckee gardeners such as Roxie Archie, Barbara
Small, the Quilicis and members of the Tinkerbelles Garden Club.
I found that they had tried growing these and other species and
couldn’t winter them over successfully in the long term.
Like most California gardeners, I owned a Sunset western Garden
Book came to the conclusion that Truckee was in the very coldest
part of Sunset’s Zone 1.
Sunset’s climate zone
rating system is based on many factors including latitude, elevation,wind
patterns,snowfall and temperatures. In most of the U.S.,a different
plant zoning system developed by the U.S.Department of Agriculture
(USDA) is used. In this system,zones are classified by average
minimum annual temperature.
During the summer of 1975,
I did considerable research on local temperatures and snow depths.
I obtained records from the Truckee Airport and began comparing
them to the maximum and minimum temperatures at my home in Prosser
Heights. I also compared temperatures with friends in different
Truckee locations and found tremendous variation even in the
same subdivisions especially in minimum night time temperatures.
The next summer I began landscaping
in different locations around Truckee and started evaluating
success and failure of various plants. That constant evaluation
continues to this day.
Over the years I have relied
primarily on the USDA zoning system in rating plant hardiness
Virtually all plants rated as surviving in USDA Zone 3 live in
all locations in Truckee. Many to most plants rated as surviving
in Zone 4a live in the warmer parts of Truckee with adequate
snow cover. There are a few Zone 5 plants that live here in protected
locations. As mentioned earlier, USDA zoning is based on average
minimal annual temperature. If we used this criterion, Truckee
would be rated Zone 6! I t became clear that that something other
than cold winter temperatures was affecting the ability of plants
to survive here.
There are a number of factors
which affect survivability in mountainous areas. At the top of
the list is low night time temperature in May,June and early
July. Before the weather station at Bodie became official, Truckee
was often the coldest spot in the nation during these months.
Weather data collected at Boca and Sagehen Field Station indicate
even lower temperatures than at the Truckee Airport or Truckee
Ranger Station. The Truckee area has one of the shortest frost
free periods in the continental U.S. There is a 90% chance of
having at least 12 frost free days in late July and early August
and only a 50% chance of having 36 days frost free. There are
years where there have been only 10 frost free days out of 365!
Freezing temperatures are very harmful to new bud and shoot growth.
When new growth is frozen,most plants will have the energy to
force a second set of new shoots. However, if this happens several
times in a season, a marginal plant will often die.
Desiccation is another factor
affecting adaptability. This is the evaporation of moisture in
plant tissues faster than it can be replaced. Many native plants
in harsh climates grow close to the ground where they are covered
with snow and protected from wind. Snow insulates roots and snow
melt at ground level provides moisture. Wind and sun speed up
moisture loss as well as does low humidity.
Culture affects adaptability.
More or less water than a plant is adapted to will affect its
survival. Planting in soil which is inadequate and fertilizing
too much or too little can lessen a plant’s chance of survival.
Recently, Sunset
has published a Northeastern Garden Book which will be very
helpful to local gardeners. In this book, plants listed as
growing in zones 44 and 45(mountains of Vermont and northeastern
plains) are very comparable to those we would suggest for Truckee.
This book will be helpful to gardeners in Jackson Hole, Wyoming,
Bridgeport and Mammoth Lakes, California which all have similar
climatic conditions to ours. The editors of the latest edition
of Sunset Western Garden Book used some of Eric Larusson’s
suggestions in plant zoning but the publication still falls
short of being useful in selecting plants hardy in Truckee.
