What are frost-resistance zones?

Looking through foreign gardening sites, I often find the indication of frost-resistance zones in the annotations to plant conditions. You can reproach me for inattention, but on the Russian Internet-resources, seeds and magazines I have not seen anything like that – and it would be so convenient, considering our huge territory! I decided to dig deeper…

The division into frost-resistance zones is widely used in at least three countries – Canada, the USA and Great Britain. The scale from 0 to 12 covers the range of minimum winter temperatures from -53.9 to +12.8 °C. In the last couple of decades, this scale has also been used in Western Europe.

However, this is hardly applicable to the territory of Russia: according to the division principle adopted in Western Europe, Moscow, St. Petersburg, Astrakhan and Murmansk would have to be attributed to one zone. This does not correlate well with reality.

Frost resistance zones in Russia

However, for Russia, frost-resistance zones are not a strange concept either. The first attempts to develop a scale for our country were made as far back as 1915. Especially popular are Kolesnikov A.I.’s version that divided USSR into 60 zones and Galaktinov I.I., Wu A.V. and Stelmakhovich M.L.’s map with 76 zones on the territory of former RSFSR.

In contrast to Western studies, domestic studies took into account a much larger set of seasonal and monthly temperatures, annual precipitation, evaporation, growing and frost-free periods, and other data.

Disadvantages of dividing into frost-resistance zones

Any gardener with experience will tell you that relying on the temperature scale alone in choosing a crop for a plot is not wise.

  • The climate map, for obvious reasons, does not have strict boundaries between zones. In addition, if the U.S. territory is visually easy to perceive and looks like a relatively evenly distributed spectrum (except that the mountains in the west change this picture a little), the situation for the UK is somewhat different – the map is not so clear.

U.S. and U.K. hardiness zones

  • Winter temperature prediction based on statistical data alone does not always give the right answer: frost-resistance zones cover quite large areas, but there are areas with milder or harsher microclimates in these areas. So sometimes the data from such multi-year studies may not be enough – the wind map, humidity, topography should be additionally taken into account.
  • The issue also touches on the ecological problem – in recent years, global warming has had a very serious impact on the climate of the entire planet. The data of the past decades are losing their relevance, and scientists have fewer baseline values to calculate the “arithmetic mean” more accurately. The scale of frost-resistance zones of the mid-20th century is slightly outdated, and it is better to be guided by more modern climate maps.

In addition, not all plants can be applied to this scale – for example, some species of bamboo can tolerate frost down to -30 °C, but may die from a sharp difference in temperature. And breeding does not stand still – specialists in this field do not tire of working on the development of more resistant varieties, significantly blurring the boundaries of the climate map for many crops.

Otherwise, it is a very useful, though not self-sufficient, tool for the gardener or farmer. Commercial organizations are actively guided by it, taking into account the margin of error and additional data.

The maps and table are from Wikipedia.