Hardiness Zones Explained
Answered by: Inge Poot
Question from: Valentina Congiu
Posted on: October 8, 1999

I’m writing from Italy and I’d like to buy some ginger. But, I saw that in the review of Q&A section of your web page that Mr Richter talks about different growing zones (9,11,4....); what does it mean? There are growing zones following the type of soil and the climate, sure, but I don’t know which number correspond to the climate. Could you explain this?

The zone numbers refer to the average minimum winter temperature that a plant can survive. You must remember that if the plant grows in an other than optimal soil, it will not be able to survive as cold a winter as it might be rated for. In other cases, such as the Himalayan species the minimum temperature they can survive might be much lower than what occurs in the area it is grown in, but if the freezing period is interupted by a thaw, the plant will immediately come out of dormancy and on the resumption of freezing temperatures, die. The rating must therefore be considered a guide only.

The hardiness zone system used on the Richters website is the one developed by the United States Department of Agriculture for the North American continent. It there are at least two others in use in North America. The USDA is not necessarily the best system, but it is the one in widest use – by far. How the USDA zones translate to zones used in other areas is unclear to us. On the basis of temperature only (and, again, temperature is NOT a sufficient determinant of hardiness!) here are definitions of the USDA zones:

Zone 1 means that plants rated for it can survive average minimum temperatures of minus 46 degrees Celsius or minus 50 degrees Fahrenheit.

Zone 2: minus 46 to minus 40 degrees Celsius or minus 50 t0 minus 40 degrees Fahrenheit.

Zone 3: minus 40 to minus 35 degrees Celsius or minus 40 to minus 30 degrees Fahrenheit.

Zone 4: minus 35 to minus 29 degrees Celsius or minus 30 to minus 20 degrees Fahrenheit.

Zone 5: minus 29 to minus 23 degrees Celsius or minus 20 to minus 10 degrees Fahrenheit.

Zone 6: minus 23 to minus 18 degrees Celsius or minus 10 to 0 degrees Fahrenheit.

Zone 7: minus 18 to minus 12 degrees Celsius or 0 to 10 degrees Fahrenheit.

Zone 8: minus 12 to minus 7 degrees Celsius or 10 to 20 degrees Fahrenheit.

Zone 9: minus 7 to minus 1 degrees Celsius or 20 to 30 degrees Fahrenheit.

Zone 10: minus 1 to 4 degrees Celsius or 30 to 40 degrees Fahrenheit.

I presume zone 11 would be 4 to 10 degrees Celsius or 40 to 50 degrees Fahrenheit.

All the rest is tropical.

Do you believe it’s possible to grow ginger in Sardinia?

If your minimum winter temperature is above minus 7 degrees Celsius, then ginger should survive outside, since it is rated to survive in zones 9 to the tropics.

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