Vol. 44 MAY, 1916 No. 5

What is Hardiness?

PROF.  N. E. HANSEN, HORTICULTURIST, BROOKINGS, S.D.

By the term hardiness is understood the capacity to resist against any special condition of environment.  So in speaking of hardiness of the plant it may mean hardiness as to either cold, heat, drouth, fungus or insect trouble.  In the present discussion hardiness against cold will be considered mainly, since that is the most difficult problem we have to meet in this horticultural field.  It would be of great advantage could we determine by examination of the plant its power to resist cold.  If we could determine by the looks of a new apple tree its power of resistance to our test winters, it would save us many thousands of dollars and much vexation of spirit.  Some years ago the Iowa State Horticultural Society made a determined and praiseworthy effort to determine hardiness by some characteristic of the plant, especially in apple trees.  A chemical test of the sap of hardy and tender varieties was made.  The palisade cells of the leaf, and the cellular structure of the wood, were examined under high powers of the microscope to determine some means by which a tender variety could be distinguished from a hardy one, but no general rule or conclusion could be formulated.  In a general way nurserymen and orchardists say that a variety that ripens its wood well in the fall shows it by the twigs being sturdy and not easily bent, while twigs that are not well ripened indicate lack of hardiness.

The winter of 1884-85 was preceded by a late, wet autumn that kept trees of all varieties growing very late, so that winter came before the wood was ripened.  In all the literature on this subject, I have been unable to find any method by which a hardy variety could be distinguished from a tender one of the same species, or, in other words, there is no correlation between morphology and hardiness.

Although we do not know what determines hardiness, we may still go ahead with our experimental work.  We do not really know what electricity is, but inventors in that line have enough of a theory on this subject so that they are able to work very successfully with this gigantic force of nature.  We know there is a difference in hardiness between the red cedar of Tennessee and the red cedar of Minnesota, and that it is safest for us to plant the tree as it is found at the north.  The same applies to many other trees that are found native over a wide area.  At Moscow, Russia, the box elder as first imported was from St. Louis, and it winter-killed.  Afterwards they got the box elder from Manitoba, and it proved perfectly hardy.  Although botanically both are the same, yet there is a difference in hardiness.

My way of securing hardiness is to work with plants that are already hardy.  I like to work with native plums in my plant breeding experiments because there need be no concern about their hardiness.  We know they are hardy, or they would not be here after thousands of years of natural selection in this climate.