Deer-Resistant Plants: Truth or Fiction?

[From the October 2013 issue of the UC IPM Retail Nursery & Garden Center News]

Is there such a thing as a deer-proof plant?

Perhaps…but there are a variety of reasons deer may choose to ignore or consume specific plant spe­cies at a particular time and place.

Certain plants native to California (and elsewhere) have evolved natural defenses against being eaten by brows­ing mammals; some are toxic, some are distasteful, and some have thorns. However, in recent decades, we've modified California's suburban and semi-rural environments in ways that have provided deer with lots of food resources, including both landscape and garden plantings that are highly-palatable and are green and lush during our state's normal dry season (Fig. 2). Furthermore, we have given deer extra protection through hunting restrictions, and historically we've con­trolled natural enemies of deer (such as mountain lions and coyotes) in and around human habitation. So, in many areas, deer densities in the recent past have reached an all-time high.

The plants most resistant to deer browsing are those that contain toxins of some type, such as oleander, which is poisonous to most mammals. Other plants may be poisonous only at cer­tain stages of growth, and they will be seasonally deer-resistant. Many plants that may listed or labeled as “deer-resistant” will simply be low in terms of palatability or preference, but when food is scarce and/or deer are numer­ous, they will nonetheless be eaten.

Late summer and fall, before the first rains occur, is usually the time of year when deer find food resources in short supply. Some gardeners have observed that fawns seem to “sample” just about everything. During years of drought, deer seem to eat almost everything, including plants that have not been damaged in previous seasons. If deer damage to landscapes occurs only for a short period during the late summer or fall, it is possible that application of commercial deer repellents can lower the palatability to deer of valuable plantings; this is most likely to succeed if treated plants are already low in terms of deer palat­ability and when deer have other food choices. Comparative tests of deer repellents generally show that those containing “putrescent whole egg sol­ids” as an active ingredient are among the most effective, but when deer are starving, even the best repellents may not succeed.

Your store may carry your own list of deer-resistant plants. If not, consult your local UC Cooperative Exten­sion office or UC Master Gardeners, or refer to gardening publications for suitable deer-resistant plants for your area. Two highly acclaimed books, Deer in My Garden, Volumes 1 & 2, were written by Nevada County-based Master Gardener Carolyn Singer based on her experience in the Sierra Nevada foothill environment. But realize that not all plants on such lists are going to be deer-resistant in every situation and what works for one region of California may not survive deer pressure in a different region. Talk to neighbors about what plants or methods have worked for them in the recent past.

Recognizing that deer damage differs according to location, time of year, plant age, weather, and deer numbers, it may be prudent to try a “trial-and-error” approach before investing in new plantings. You might choose a few plants you're considering, but leave them in their pots and place them in the area where you want to plant. Watch them for a few days to see if deer begin feeding on them. Be flexible about your choices. For valu­able perennial shrubs and trees, it may be necessary to provide a protective barrier, such as a wire mesh cylinder or a tree tube, until the plant reaches an age or height when it will be less susceptible to deer damage.

To find out more about managing deer, see the UC IPM Pest Note: Deer.

 

This article was originally published in the October 2013 issue of the UC IPM Retail Nursery & Garden Center IPM News. See this and other articles at http://www.ipm.ucdavis.edu/RETAIL/retail-newsletter.html.