The recent cold snap has me wondering if my plants survived. Many factors will determine the survival of plants. The cold is only one of them, but it is the main one on the mind at this time.

Plants have been rated for cold hardiness. Riley County currently is in Zone 6A, according to the U.S. Department of Agriculture’s Plant Hardiness Zone map. This map indicates that on average our area gets to -5 to -10 degrees. Last Tuesday, one area temperature reading was -18.4 degrees.

Two researchers at the Arnold Arboretum in Boston developed the first geographical hardiness zone systems. Alfred Rehder published his in 1927 and Donald Wyman published the second in 1938. Updated versions have frequently occurred since those early ones.

In 2012, the USDA updated its plant hardiness map based on 1976 to 2005 weather data. It did this to include a longer period of data to smooth out year-to-year weather fluctuations. After this winter, perhaps it will be revised again.

The USDA system is based entirely on average annual extreme minimum temperature in an area. It is limited in its ability to describe the climatic conditions a gardener may have to account for in a particular area for plant health. There are many other factors that determine whether or not a given plant can survive in a given zone.

Besides how low the temperature gets, humidity, precipitation, rainy-dry cycles and high air temperatures affect plant survival.

Site considerations must also be taken into account, such as soil type, soil drainage, water retention, water table, tilt toward or away from the sun, natural or manmade protection from excessive sun, snow, frost, wind, etc. The annual extreme minimum temperature is a useful indicator, but ultimately only one factor among many for plant growth and survival.

Only this coming growing season will determine which plants survived.

I suspect less fruit loads and some loss vigor of perennials. Annuals that come from seed each spring will not be affected. Just like the power grid, a diverse source is beneficial.

You can find out more by going to Riley County’s K-State Research and Extension website at www.riley.ksu.edu.

You may contact Gregg Eyestone at the Riley County office of K-State Research and Extension by calling 537-6350, stopping by 110 Courthouse Plaza in Manhattan or e-mailing geyeston@ksu.edu.

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