Hardiness A Much Misused Word

When we consider the selection of plants, the question of hardiness immediately arises. Some hold the opinion that one particular plant is hardy, others disagree and claim that another is better suited. Therefore, we should first settle the question of what hardiness is and what we understand by the use of that word.

Much confusion stems from the broad meaning of the word and also from what is meant by hardiness in America, in Europe and in Asia where most of our plants come front. Most earlier garden books were based on European experience; others were copied from European sources, and since many plants are of European origin, the term “hardy” meant and means that the plant is hardy for Europe, England, the western and central continent.

There the Winter is of a maritime climate, while in the northern United States the climate is continental, indicating great differences in climate and geography. Before we can understand the variations, these great differences must be analyzed.

I compare the climate of the central and eastern United States with that of Europe in such a way as to call the climate in the northeastern United States a combination between Spanish Summers and northern Russian Winters. Similar to the central and eastern United States is the climate of eastern Asia. Generally, we can say that eastern Asia is like eastern North America, and Europe, which really is only the western extremity of Asia, is like the west coast of North America.

The multitude of plants which we have from China, Japan and Manchuria is the best illustration of this. Equally well, grow the eastern native American azaleas together with the eastern Asiatic species, and we all know how well the firs, cypresses and cherries thrive.

Topography of Eastern Europe

In topography eastern Europe is similar to the North American continent, as the mountains run north-south (the Ural, Rocky mountains and the Appalachian system), while central and western Europe is markedly different. The mountain ranges arc crossing east-west, blocking the cold currents from the north, the warm ones from the south. Besides, the whole climate is modified by the surrounding sea, controlled by the warm Gulf Stream, creating in general a maritime climate, moist and moderate, with few variations. The prevailing winds being westerly on the northern hemisphere are always moist, neither extremely hot nor cold; the easterly winds on the other hand, carry little moisture, arising, as far as Europe is concerned, in the prairies of Russia.

In North America those same prevailing westerlies, if from the southwest, are tropical, hot and humid. When from the west, they are dry, hot in the Summer and cold in the Winter. When coming from the northwest, these winds are very dry and result in the extremes of temperature we know so well. The easterly winds in the coastal regions are moist and cool. The mountains run from north-south, without blocking any of these air currents. Instead, the currents are enforced so that changes occur suddenly. As a result, Winters compare to those of eastern Asia.

Therefore, what is considered “hardy” in the gardens of Europe is an entirely different “hardiness” in the northeastern United States. A perennial may go through the slowly varying Winter in Europe, with its fogs and moisture, whether covered with snow or not. That same plant has to undergo a greater climatic variation here, often without a snow cover, including exposure to a penetrating, dry, cold northwester wind, against which the sealing of the buds is insufficient, and drying out the freezing weather, accompanied often by sudden thawings under an intense clear sun.

Hardy in England Not In US

Evergreen plants, which are considered hardy in England, are not hardy in more southern latitudes in America because they miss the moist moderate Winter and the slow changes from Fall to Winter and Winter to Spring. We might name only ivy, rhododendron hybrids, cherry laurel, boxwood, holly, apricots, walnut and European grapes. Only where the climate is similar, either in our more southern states, coastal regions or the west coast, is the climate favorable to their growth. Therefore, the word “hardy”‘ does not mean much if applied so broadly without the naming of the district or the zone the plant is planted in.

On the other hand, native northern United States plants, resistant to the climatic changes of the zone, are found not to be resistant in the same manner to the moderate European climate, with the result that die-back, loss of needles or bud injury occur.

This is due to the moist, cool weeks of the European Autumn, while on our continent the native plants mature during dry, warm days. In Europe, American plants do not find the chance to mature well enough in such a climate. The following Winter finds the wood and the buds unprepared for even a mild Winter. Examples are hemlock, which loses its needles in windy places in northern Germany, red and pin oaks, which will not thrive too well in such latitudes, and the tulip tree, which suffers in the buds. Naturally, the breeding and selecting of plants should include the possibility of growing the plant in wider areas, extending its limit further north, and, in fact, accelerating its northward advance, which has been continuing since the glacial age, when the plants, driven south, began to return northward. Also the resistance against the great fluctuations, desiccation and stronger solar radiation should be kept in mind in order that the next generation will survive Winters in a more northern climate.

Unfavorable conditions demand a certain necessity for mulching, covering and shading. Mulch will keep the roots in a definite, more permanent, less fluctuating condition. Covering with boughs will shade the branches from the sun and winds in the late Winter (we must remember that New York is in the same latitude as Madrid, Spain).

Planting in shadier locations than their native habitat demands will also prevent damage because there is less radiation, less fluctuation, less desiccation and less premature development in the Spring, thus preventing damage by late frosts. In such a place a retarded plant will survive better. It is often wise not to set a plant, just to have it, in a place where it will never flower. It is wiser to place it in a sheltered spot, perhaps less prominent, where it will flower well. Such a plant can be hardy when treated right, tender when mistreated.

We should take more care in using the word “hardy”, elucidating the meaning of the word in regard to zones, localities, sun and shade, and other immediate environmental conditions.

H. Rohrbach

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