Dr. Leonard Perry, Horticulturist in Residence, King’s Garden
Horticulture Professor Emeritus, University of Vermont
Deer have become one of the most serious problems in gardens and landscapes, including the King’s Garden. If you’ve been there near closing time, you may have seen the staff putting up the single strand electric wire fence around the beds outside the walled garden. Obviously with the King’s Garden, those plants inside the walled garden are not touched by deer. “Out of sight, out of mind” applies there. 
At the 6th Annual King’s Garden Symposium, Dr. Perry covered many types of repellents and fencing methods. One of the repellents mentioned was the Deer Chaser, developed by fellow symposium speaker Dr. Lee Reich. This uses a motion sensor to activate a radio and light, using both sound and visual deterrents.
Knowing how to control deer successfully means knowing something about them and their behavior. This is important in order to use repellents effectively, and to know when fences may be the only or best answer. Here are some highlights from my presentation on Deer Control in Landscapes and Gardens at the 6th annual King’s Garden Symposium. Check out more articles on deer control specifics that were covered at the talk, online (pss.uvm.edu/ppp/articleA.html).
Before you start investing in deer deterrents, you should first assess whether they have any chance of working. Deer feeding is a function of alternative food sources. If there are woods nearby, perhaps these will provide enough alternate food if your landscape becomes less inviting.
Deer feeding is primarily a function of population pressure. Too many deer, and too little food, and they will eat most anything. In this worst case, fencing may be your only effective control. To determine your control strategy for deer, first examine the current deer damage and pressure. Understanding deer behavior, with many tips for control, are outlined in the book Deerproofing Your Yard and Garden, by Rhonda Massingham Hart.
If there are fewer than five deer per square mile, with only occasional browsing and buds
nipped in the spring, try repellents or more long-term landscaping choices. If there are 
about five to ten deer per square mile, with damage through the summer including loitering and feeding during daytime, you may try the same techniques first. If these don’t work, you may need to resort to controlled dogs and fencing. Finally, if there are more than ten deer per square mile, with most plants being damaged and stripped to the ground, start with fencing and dogs but work toward cooperative community controls.
Deer are “neophobic” (afraid of anything new), so one tactic is to use several deterrents and to rotate them frequently. This is because deer learn quickly. Deer also have a main goal of not getting eaten. Once they determine that something will not attack or go after them, and this only may take a few days, a particular control technique becomes ineffective. Keep deterrents mysterious or frightening to deer.
With low population pressure in my own landscape, I have successfully used motion-activated lighting for control. Yet when I fail to move this (it is mounted on a portable stand) every few days, the deer learn it is stationary and no threat. Then there is the story of a neighbor with a chained dog. Once the deer learned the dog was on a chain, and the length of the chain, they began feeding just outside the dog’s range in spite of its frantic barking.
Keep in mind that deer in wild country or rural areas will be more scared of humans than suburban deer who get used to having them around. Perhaps this is based partly on hunting each fall in rural areas.
As with control of most four-legged garden creatures, deer are creatures of habit. As with humans, it is easier to prevent habits before they even become habits. The best controls often begin before there is a problem. Start using deterrents in spring before deer visit your landscape or find your choice plants, and hopefully they’ll pass it by. You might consider this as educating your deer.
Remember though that deer are adaptable. If they do taste and like your plants, in spite of your deterrents, they may just stick around. As author Hart says, “once they adapt to your garden, they adopt it.” If deer adopt your garden, you’ll need to try other deterrents and strategies. Just as people have different tastes, likes and dislikes, so do deer. This perhaps explains in part why deterrents vary so widely in effectiveness from one location to another, as well as “resistant plants”. You’ll have to experiment and determine the best controls for your own landscape or garden.
When it comes to finding food and not becoming food themselves, deer are smart and clever. But as author Hart points out, even on your worst day you are smarter than deer. Remember you can be successful by using such knowledge of deer behavior with your controls.