Apply a repellent when you suspect deer are around the garden, even if you haven't seen damage yet. In spring and summer, spray first when new growth emerges and again when plants show 6 inches of new growth. Be particularly watchful in July and August when plants have little new, succulent growth for deer to browse and the does are still feeding their young.
Continue to inspect your garden, and spray into the fall and winter. To ensure that the spray dries quickly, apply when the temperatures are above 40°F and the weather is sunny and calm. Even then, deer change feeding habits only after repeated exposures to repellents.
McAninch has tested several products over many years, including Deer Away (a formulation of putrescent eggs), Hinder (a soap-based product), and other new products. Animal-urine repellents are most effective if the particular predator frequents the area. ″Fear of predators is primarily a learned behavior,″ says McAninch. If you don't have any coyotes in your area, coyote-urine products won't evoke a lasting fear response in local deer.
In addition to animal urines, one promising new product is Tree Guard. The active ingredient in Tree Guard is bitrex (denatonium benzoate), a bitter compound that tastes terrible to deer. Over the winter of 1996, it performed best in one test of seven repellents under heavy deer-feeding pressure. ″It was only one test, however. Tree Guard should receive more consideration and testing to see if it can be added to the arsenal of effective deer repellents,″ McAninch says. Consider these deer repellent tips for your home, school or community garden.