Winter desiccation injury is a common, unfortunate problem for landscape evergreens like Arborvitae and Juniper. Below are some questions and answers about managing desiccation injury with anti-desiccant sprays:
Q: What is winter desiccation injury and how is it caused?
A: Desiccation injury may occur when water is transpired or "lost" through plant tissue more quickly than it can be absorbed though the roots. This is caused by long dry periods of cold and thaw along with winter winds. Anti-desiccant sprays add a protective waxy coating to the leaves of broadleaf evergreens to help slow the process of transpiration.
The following types of landscape plants are most often susceptible to desiccation and hence are most commonly sprayed with an anti-desiccant:
- Broadleaf evergreens such as azalea, boxwood, holly and rhododendron.
- Conifers such as arborvitae, cedar, cypress, juniper and pine.
- Tender stems such as rose canes and hydrangea stems.
Q: Can anti-desiccants cause plant injury?
Applying anti-desiccants to sensitive plants too early in the season can result in damage. As temperatures begin to drop in late-Fall, plants send water from foliage into roots. If an anti-dessicant is applied before this shift occurs, a higher level of water will be retained in the foliage and this water can cause cellular damage/destruction with the ensuing freezing and expansion. Thus, if anti-desiccants are going to be used, they should be applied late-fall or early-winter, per label directions.
Q: Is plant injury caused by anti-desiccants common?
A: Anecdotally, anti-desiccants are quite variable in terms of their performance, to the point where use with any real regularity may not be justifiable. Though this may not be the case with every one of the myriad of plants that we use in the urban environment, it doesn't mean that practitioners may not find it a useful tool in certain situations, either. If you have looked at pricing and feel that it may be worth your while to make an anti-desiccant application, but you are concerned about plant injury, being conservative and applying first to a small portion of the plant may be the best way to proceed.
Here are some tips for using anti-desiccants more safely:
- Always follow the label instructions carefully!
- Pick an appropriate time to spray: Anti-desiccants are best applied when temperatures are around 40-50 degrees F, with no rainfall in the immediate forecast. Foliage needs to be dry when applied, and the spray needs time to dry afterward.
- Don't spray too early: Wait until December to spray conifers, because these plants must be completely dormant (which involves moving water down to the roots) before applying, or else the spray will trap water in the leaves that will freeze and cause cellular rupturing.
- Spray thoroughly: Plants lose water from both the upper side and under side of the leaves. Be sure to spray the entire plant!
- Caution: Don't spray waxy, blue conifers such as blue spruce – they already have a natural coating that you don't want to damage.
Q: Are there other ways to protect sensitive plants from desiccation, apart from anti-desiccants?
A: Burlap or other similar materials may be used to reduce or prevent winter injury caused by exposure. The burlap is used as a physical wind break to protect the tree or shrub from the harsh winter winds. The burlap is attached to posts or stakes that are driven into the ground. Three stakes are used and driven into the ground in a 'V' shape. The bottom of the V should face into the prevailing exposure direction. The plant should be in the open part of the V. Enough distance should be provided between the shrub or tree and burlap to eliminate the possibility of rubbing in windy conditions. Though not the most aesthetically pleasing, it will protect small shrubs and trees from the harsh conditions that would otherwise result in winter injury. Watering plants well in fall is also recommended, so that plants go into the winter with an adequate water supply.
Winter injury of landscape conifers is a reality that we deal with here in the Northeast. Keeping plants adequately watered throughout the fall and placing a protective barrier of burlap over or around plants to protect them from winter winds and sun will help to reduce the incidence of winter injury. However, the limiting factors may be where the plants are located (i.e. their exposure) and what sort of a winter Mother Nature deals us.
Written by: Susan B. Scheufele, Russ Norton and Rick Harper