Good afternoon, my reader. Hardiness zones are a climatic and agronomic term. It involves the division of the territory of a country or a large region into regions, united according to the principle of the minimum annual temperature. The knowledge of which zone, according to long-term observations, the area belongs to, makes it possible to determine which crops can be grown in it: each plant has a frost resistance limit.
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It should be remembered that zoning is always conditional: in any of the frost resistance zones there may be areas where the microclimate differs significantly from the average values.
How do USDA hardiness zones work?
The term itself is associated with the US Department of Agriculture, which first began to process statistics on the average annual temperature and the suitability of an area for growing different crops. Based on the data collected, the United States was divided into regions aggregated by the "average absolute minimum." It is defined like this:
- monitoring the temperature for a number of years;
- the most severe colds are noted;
- the sum of the values of negative temperatures is added up and then divided by the number of years that the observation lasted.
It is important not to confuse the average absolute minimum with just the absolute minimum: record frosts during the observation period may be colder than the average.
Since there are no distinct boundaries of climatic zones in the United States, it was the division into zones of the USDA that turned out to be the most convenient. There are 12 zones in total - from ZM-11, where the average absolute minimum is + 10 ° C, to ZM-0 - the Arctic zone, where the average minimum is –51 ° C.
Does this work in Russia?
Geographically, Russia is much more diverse than the United States, and the meteorological observation system is based on different principles. Nevertheless, there is some data:
- Moscow - ZM-5;
- Nizhny Novgorod - ZM-4;
- Novosibirsk - ZM-3;
- Vladivostok - ZM-5;
- Krasnodar - ZM-7.
However, all this is purely indicative: within one settlement, data from two meteorological stations can give values for two different zones. And even in areas with a difficult microclimate, such as the North and North-West Caucasus, zones can even lie in spots, "jumping" within a radius of several tens of kilometers from ZM-5 to ZM-7.
Indicator Plants
In general, zoning is used to determine which plants will winter in a frost-free zone. Here are just a few examples:
- ZM-4 - two-bladed ginkgo, pointed yew, privet;
- ZM-5 - common pecan, holly crenate;
- ZM-6 - boxwood, Atlas cedar, berry yew;
- ZM-7 - Chilean araucaria, evergreen sequoia.
- ZM-8 - Japanese medlar, myrtle, laurel viburnum.
We remind you that the higher the zone number, the warmer it is. In addition, the zone does not take into account the snow cover: those plants that die in the fresh air often winter under the snow.
Does it make sense to use zones?
The point of all frost resistance zoning is to determine where and which plants will take root exactly. Without this, the gardener and arborist will have to work blindly.
However, there are several problems:
- Small amount of data. If in the United States the average absolute minimum has been determined for decades, then we are still only collecting data: previously, the method was not used and the indicator was not calculated.
- New zoned varieties and hybrids are constantly being bred, and the old ones adapt to the climate. In order not to go far for an example: the walnut, which previously grew no north of Belgorod, has advanced almost to the Moscow region over the past 30 years.
- The climate is changing and the data is out of date.
Nevertheless, the idea of zoning by frost resistance of plants based on observations of the average absolute minimum is very productive and in the future it will be good to help gardeners.
Do you know how USDA hardiness zones work?
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