Deer: Beauties...or Beasts?
Robert T. Stelloh
Reprinted from the June 1993 issue of The Azalean
Deer are a beautiful sight wandering along the forest edge, stopping now and then to nibble some plant delicacy. However, when you realize the plant delicacy is one you've planted and had high hopes for, your focus shifts away from the beauty of the deer and more to such questions as: "Why do we seem to have more and more deer around here?", and "My garden isn't a deer restaurant - why can't they just eat the wild plants and leave mine alone?", and "What can I do to stop them?"
Deer have been the focus of research by wildlife biologists for the past 20 years, and there are good answers to those questions. The U.S. has a population of about 25 million white-tailed deer (Odocoileus virginianus), about as many as there were at the time of the Pilgrims, and up from only a half million at the turn of the century1. The mule deer (Odocoileus hemionis) is also quite abundant in the western states.
There are good reasons why the deer population has been increasing at a rapid rate, particularly over the past few decades. It has a lot to do with their preferences and adaptability, and our changing land use. While we've been cutting down the forests, we've also removed their natural enemies and actually increased their most desirable feeding habitat, and their population growth is now primarily limited by the availability of food. Deer prefer to browse at the edges of the woods, and our patchwork development of suburban areas, while decreasing the amount of deep woods, is increasing the amount of woodland edges as well as providing them more yards and gardens with an appetizing variety of trees, shrubs and flowers. Increased agricultural crop yields due to the use of fertilizers are also giving the deer a better food supply. At the same time, we have killed or driven off most of the bobcats, mountain lions, wolves and bears, their natural predators. Only hunters remain, and hunting is becoming less fashionable and more dangerous in suburban areas. Finally, the generally mild winters since 1978 have been helpful to them1.
So it isn't your imagination - there really are more deer! In New York the deer population has doubled since 1970, and it has tripled in Maryland and quadrupled in Indiana since 1980, for example. The result of this is an ever-increasing interaction with humans, primarily in the form of automobile accidents and plant damage. Pennsylvania alone reports about 40,000 white-tail highway deaths per year, and nationwide there are over 500,000 deer-related accidents each year. While the deer usually die in such accidents, humans occasionally do also. In 1989, 131 people died as the result of hitting an animal with their car or truck, thousands suffered serious injury, and there were millions of dollars of vehicle damage1.
Another growing problem is Lyme disease, first discovered in 1976 in Lyme, Connecticut, and now the most common tick-borne disease (1400 cases reported in 1986)2. Lyme disease is caused by the deer tick, which includes both the white-tailed deer and the white-footed mouse in its life cycle. "Adult ticks feed and mate on the deer and then drop off to lay eggs. The eggs hatch into tiny deer-tick larvae, which contract the disease by feeding on the mouse, the primary carrier of the Lyme-disease spirochete. The larvae eventually molt into infected "nymphs," an adolescent stage that poses the chief threat to humans. Nymphs are active in late spring and summer, when people tend to be outdoors more...Those most at risk are people who can see deer from their houses."2. Untreated, Lyme disease is very serious and results in cardiac problems, arthritis, and neurological problems.
Since deer prefer the quiet of the woods to the bustle of civilization, they tend to forage only at the forest edge during the spring and summer3. In the fall, young trees and large shrubs suffer physical damage as bucks rub the "velvet" off their new antlers, and practice their rutting activities4. Then, in the winter as their natural food supplies dwindle, deer begin to brave the open areas and work their way into our gardens, looking for more evergreen leaves and deciduous buds. As they browse in a nursery bed of very small or not-yet-well-rooted plants, they can also kill the plant by plucking it out of the ground5.
The seasonal differences in deer activity and its effect on your garden can change from year to year, in a somewhat predictable manner. Severe winters with heavy snowfall will force the deer into your garden earlier, and they'll stay longer and eat more. Similarly, low acorn and native berry production will have the same effects. Collectively, the number of deer and how hungry they are is described in terms of "deer pressure": low deer pressure would describe a few well fed deer, while high deer pressure would describe a large number of hungry deer. Some deterrents will work well for low deer pressure, while stronger measures are needed against high deer pressure.
There are two factors to consider in keeping deer away from your plants - they're creatures of habit, and they have specific food preferences. Thus, the best method of avoiding deer damage is to keep them out of the habit of eating your plants, and the best method of doing that is to not have the plants they prefer. Among a number of ornamentals tested, Euonymus fortunei (groundcover) was their most favorite food, followed closely by various Taxus (yew) species, by Thuja occidentalis (White Cedar, or American Arborvitae), some evergreen Rhododendron species, and some Ilex species. Some of their least favorites are pines, spruce, dogwoods, and mountain laurel. See Table 1 for a more complete list of plants and their relative rankings3.
Table 1: Taste-Tested A list of ornamentals white-tailed deer favor most (97) and least (0) during winter foraging activities. Species Ranking Euonymus fortunei 97 Taxus baccata 84 Taxus cuspidata 80 Taxus x media 77 Taxus brevifolia 77 Thuja occidentalis 68 Rhododendron spp. (evergreen) 47 Hex crenata 40 Ilex x meservae 38 Viburnum carlesii 26 Juniperus Virginian 22 Rhododendron x laetevirens 20 Pyracantha coccinea 18 Rhododendron maximum 17 Rhododendron 'Exbury Hybrids' 17 Ligustrum spp. 16 Rhododendron carolinianum* 16 Mai us domestica 14 Cotoneaster spp. 13 Euonymus alata 10 Juniperus chinensis 9 Eleagnus angustifolia 8 Acer palmatum 7 Rhododendron spp. (deciduous) 7 Enkianthus campanulatus 7 Tsuga canadensis 6 Pinus nigra 6 Ilex glabra 5 Prunus serrulata 5 Betula papyrifera 4 Tsuga caroliniana 3 Chamaecyparis pisifera 3 Philadelphus spp. 3 Viburnum tomentosum 2 Magnolia spp. 2 Ilex cornuta 2 Spiraea spp. 2 Betula pendula 1 Leucothoe fontanesiana 1 Kalmia latifolia 1 Rhododendron spp. (evergreen hybrid) 1 Syringa vulgaris 0 Pinus strobus 0 Cornus sericea 0 Picea pungens 0 Pieris japonica 0 Amelanchier spp. 0 Forsythia spp. 0 Cornus kousa 0 Pseudotsuga menziesii 0 Buxus sempervirens 0 Ilex opaca 0 Abies fraseri 0 Cornus florida 0 Cryptomeria japonica 0 Hibiscus syriacus 0 Picea abies 0 Picea glauca 0 Pinus mugo 0 Pinus sylvestris 0 Pyrus communis 0 Source: Conover, M.R., and C.S. Kania. 1988. "Browsing Preference of White-Tailed Deer for Different Ornamental Species." Wildlife Society Bulletin 16:175-179.
Once you have a deer problem in your garden, there are three primary methods of solving it - getting rid of the deer, fencing the garden, or protecting individual plants. Shooting the deer is usually not possible because of nearby homes, it usually causes a public outcry because of the "Bambi" effect, and it isn't even very effective since it merely makes room for more deer. Some states have attempted to trap deer and release them elsewhere, which is expensive, and we're running out of "elsewhere".1 Birth-control techniques are being developed, but have not been effective thus far. So, getting rid of the deer is not a viable approach for most home plant enthusiasts.
In areas of low deer pressure, you can discourage deer from eating specific plants by applying a deer repellent: something with an offensive taste, odor, or both. Table 2 lists a number of repellents in order of increasing cost3. It's important to note that repellents don't stop the deer from eating a plant, but rather make that plant less desirable6. The human hair and soap must be above the snowline and about 3 feet apart to be effective. Hair can be put into mesh bags and tied to the plants. Bar soap can be left in the wrapper, pierced, and tied to the plants7. Magic Circle™ is applied by soaking cloth strips or pieces of twine in it and laying them on the ground. The other products are sprays, which can in general be mixed with an anti-transpirant to prolong their effectiveness.
Table 2: Control Tools
Repellents for low-to-moderate deer populations. (Costs do not include labor)
Repellent Reported Cost/Acre
Reported Browsing Reduction (percent) Human hair 10.00a 34b Soap 60.00d 38d Magic Circle™ 16.00c-30.00a 18a,b Hinder™ 12.00b-41.00c 43b Miller Hot Sauce™ 11.00a-91.00c* 15b Thiram™ 46.00c - 225.00a 43b Big Game Repellent™ 180.00d-400.00a 46b a. Conover, M.R. 1984. "Effectiveness of Repellents in Reducing Deer Damage in Nurseries." Wildlife Society Bulletin. 12:399-404.
b. Conover, M.R. 1986. "Finding New Ways to Reduce Deer Damage to Crops." Frontiers of Plant Science. 38:2.
c. Craven, S., and S. Hygnstrom. 1987. "Controlling Deer Damage in Wisconsin." University of Wisconsin Cooperative Extension Service Bulletin G3083.
d. Swihart, R.K., and M.R. Conover. 1990. "Reducing Deer Damage to Yews and Apple Trees: Testing Big Game Repellent, Ro-pel and Soap as Repellents." Wildlife Society Bulletin. 18:156-162.
* Incorporates the cost of Vapor Gard.
When repellents don't reduce the deer damage to an acceptable level, or you're not willing to take the risk because of the value of the plants, you can resort to a fence. There are a variety of fences which have been tested for their effectiveness against deer, as listed in Table 3 in order of increasing cost3. In general, the more it costs, the more effective it is. Any fence is a long term investment, any of the fences listed in the table is quite effective, and the primary negatives are the cost of the fence, the visual impact it has on your garden and the space it takes up.
Table 3: Locked Out
A variety offence designs for low-to-high deer populations.
(Costs do not include labor or electrical chargers.)
Type of Fence Deer Pressure Reported Cost/Linear Foot*
Cost for 1 Acre**
Poultry wire low-to-high -- -- Baited electric low-to-moderate 0.10 83.20 Offset moderate 0.35 291.20 The Penn State Vertical Electric moderate-to-high 0.50 - 1.50 416.00 - 1248.00 Slanted seven-wire high 1.50 - 2.00 1248.00 - 1664.00 Woven wire high 2.00 - 4.00 1664.00 - 3328.00 * Craven, S., and S. Hygnstrom. 1987. "Controlling Deer Damage in Wisconsin." University of Wisconsin Cooperative Extension Service Bulletin G3083.
** The cost per linear foot times the 832' feet needed to surround one acre, for ease of comparison with the repellent costs.
Poultry fencing (chicken wire) can be used to protect a few individual plants, by simply enclosing each plant with a 6' high cage of wire fencing supported by some stakes. It's a lot of work for more than a few plants.
The baited fence is a single-strand electric fence, 30" above the ground, with strips of metal foil covered with peanut butter attached to the wire at 3' intervals. It is designed to attract the deer, shock them, and thus teach them not to go into the fenced area. The peanut butter must be renewed every two weeks for maximum effect. One school of thought suggests the fence can be turned off after a few months.
An offset fence is a three-strand set of two electric fences designed to confuse the deer. The first fence has strands at 15" and 43" above the ground; the second fence is 38" inside the first fence with one strand 30" above the ground.
The slanted seven-wire fence is a larger and more effective version. It is a single electric fence at a 30° angle to the ground, with the first strand 10" above the ground, and each of the other strands at 12" intervals. Overall, this makes a fence which is 5' high by 8' wide.
The Penn State vertical electric deer fence is a single five-strand fence, with the first strand at 10" above the ground, and each of the other strands 12" above the previous one for a total height of about 60".
Finally, the woven-wire fence presents a significant physical barrier. It consists of two tiers of 4' woven wire, one above the other and tied together at their common seam, and topped by two strands of wire for a total height of 9 or 10 feet.
Bambi has turned into a suburban "rat with antlers"8, and is rapidly becoming another variable gardeners will have to learn to live with until more effective control measures come out of the current and future research.
Author's note 10/20/93:
Two other fencing variations have been brought to my attention since this article was written. One is a horizontal fence of chicken wire, which the deer avoid walking on, possibly out of fear of getting their feet entangled9. The other is a relatively new product devised and tested by a retired horticulturist in Pennsylvania, which is polypropylene plastic mesh fencing to be attached to existing trees and supplemental posts at up to 30' intervals. Available in black or green, 7.5' or 8' heights, and 2" x 3" or 2" x 1.5" mesh sizes from Benner's Gardens, 1-800-753-4660, this material is said to be effective and virtually invisible, as well as being long-lived (5 to 10 years) and relatively easy to install. For comparison with Table 3, the cost of this material is about $0.50 per foot or $416.00 per acre.
1 Horton, Tom. 1991. "Deer on Your Doorstep." New York Times Magazine. April 28, 1991
2 "Watch out for the tick attack." 1988. Consumer Reports 54:6.
3 Mclvor, D. E. and Conover, M. R. 1991. "Uninvited Guests." American Nurseryman. September 15,1991: 46-54.
4 Personal observation. They seem to prefer 1" to 2" diameter trunks as offering the proper amount of resilience for practice rutting, and perhaps for their ability to get the trunk in between the different branches of their antlers (a 12" diameter tree wouldn't work well for either of those purposes, for example). The results are they have either destroyed or severely wounded our young oaks, magnolias and other ornamental trees by breaking off branches and scraping bark off the trunks. A note on dogwood borers (Volume 6, Number 2 (1991) of Plants & Garden News, Brooklyn Botanic Garden) discusses Valley Forge National Historical Park in Pennsylvania using spiral plastic tree guards on dogwoods to reduce the antler-rubbing damage, with the negative side-effect of softening the bark and increasing the incidence of dogwood borers. The suggested ways to avoid the borers were to make sure the guards are loose, and to only use the guards in late fall and winter.
5 Stelloh, Robert T. 1992. "Using Velcro® for Plant Ties". The Azalean. June 1992.
6 It's somewhat like putting sugar on your french-fries by mistake. If you're not hungry, you'll probably skip them, or get some more and use salt this time. If you are hungry, you'll get over the unexpected taste and eat them anyway.
7 We've tried soap, with apparently some success. Our favorite was Irish Spring, although some studies indicate all deodorant soaps have similar effectiveness. We've noted that something either gnaws or scratches the soap if it's out of the wrapper, and we've also noted that you better tie it quite loosely or future growth can strangle the plant at the tie. We've also tried a repellent fence of string, with 2" by 15" strips of bed sheet at 3' intervals, with the strips dipped periodically in diesel fuel, and we think it helped, but it sure was ugly and smelly. We've seen lion dung from the zoo in mesh bags being used at a conifer nursery, and we've recently heard of throwing "used" kitty litter around the base of plants. Unfortunately, it's hard to know what the deer would have done without someone taking such measures.
8 James, Richard L., Executive Director, Schuylkill Center, Philadelphia, Pennsylvania, as quoted in The New York Times Magazine article, note 1 above.
9 Lay, David, Northern Neck Nursery. 1993. Personal communication. David says it really works, rusty old chicken wire works just as well as new wire, it's easy to install since you just lay it on the ground, and it's invisible for all practical purposes.
Editor's Note:* R. carolinianum now known as R. minus var. minus Carolinianum Group.