Desiccation is injury incurred by plants when water is transpired through leaves faster than it can be uptaken by roots. This is usually caused by extended periods of cold, dry weather, winter winds and/or instances of freezing and thawing. Antidesiccant treatments apply a waxy coating to the leaves of broadleaved evergreens which helps stem water loss through transpiration. Landscape plants which commonly suffer from desiccation and therefore may benefit from antidesiccant treatments include; broadleaved evergreens such as azaleas, rhododendrons, boxwoods and hollies; conifers like arborvitae, cedar, cypress, juniper and pine; as well as tender stems such as rose canes and hydrangea stems.
This winter has been less than ideal for applying antidesiccants, what with several feet of snow on the ground and on plants for what seems like months, this has made getting second rounds of treatments out where needed very difficult. So the question becomes, is it still beneficial to treat at this time? Yes. The ground is and will remain frozen for some time, making water lost through leaves irreplaceable through roots. And as the days length increases extended exposure increases the chance for desiccation to occur .
If plants are covered with snow, treatments should be applied to exposed portions. Snow will provide somewhat of a natural protective barrier against moisture loss. Plants entirely buried in snow obviously cannot be treated, once the snow melts the state of their health needs to be reassessed.
Antidesiccants can only be applied while the ground remains frozen. Late season treatments can be applied at a reduced rate so as to keep residues from the product from hindering plant growth during spring and summer. When soil begins to thaw, it is too late for treatment. If you have concerns about your landscape plants during this brutal winter, call your arborist as soon as possible, even in the snow they can at least make a preliminary evaluation and advise as to the most beneficial approach.