Hardiness Zones

WHAT DOES IT MEAN?

HARDINESS (From 'ORNAMENTAL CONIFERS' Editor Julie Grace.)

It is obviously not enough to quote such vague expressions as "hardy" or "near hardy" as they have no international bearing whatever and can be used only in a strictly local sense. For this reason we have used the United States system which is now fairly widely recognised and is set out below related to both Celsius and Fahrenheit temperature scales. It should be remembered that if a conifer is rated as hardy in, say Zone 4, it is not necessarily at its happiest in those conditions but nevertheless will survive and make growth in those conditions. On the other hand, it is often possible to plant (for example) a Zone 6 plant in a Zone 5 area provided it is located in shelter and not fully exposed to the elements. One must always be prepared to loose such plants however, during exceptional cold snaps, there being many examples on record of mature trees some thirty or so years of age thriving happily in such conditions until an extra period of cold puts an end to their gamble with the elements.

Given below is the relation of Zones to actual minimum temperatures. One can use this system in two ways. Firstly, knowing your average coldest winter temperature, you can arrive at the zone number for your area. You will then be able to plant any conifer rated at that number or lower. For example, if you are Zone 5 you will be limited to growing only plants hardy in Zones 5 down to 1. It may be however, that you know of Zone 6 plants growing happily in your particular area through your winters, in spite of the scale rating you as 5. This is sometimes the case where the factor of low humidity or dry winters interfere or even air currents on a sloping site and in such cases you can safely assume, that you are able to plant Zone 6 plants as well. At best the Zone system is a rough guide and observation and trials for your area are in the end your best indicator.

HARDINESS CHART

Approximate Average Minimum Temperatures for each Zone

Where there is no frost danger, the term hardiness is reference to the amount of wind or salt wind a plant can withstand. This is particularly so in coastal Taranaki and inland on the ridges where the trees are exposed to severe wind