Deer will eat just about any plant if they are hungry enough, but certain plants are in more danger than others. Petunias (Petunia spp.) are not deer's favorite plants, but they are occasionally or frequently damaged if deer visit the yard.
Petunias are typically grown as a flowering annual, though these plants are actually tender perennials hardy in U.S. Department of Agriculture plant hardiness zones 10 through 11. Certain sources describe petunias as tolerant of deer, but most agree that hungry deer will readily eat these plants.
Deer prefer plants with young, succulent growth, and petunias fit that description nicely as they grow and flower from midspring until frost. If you have problems with deer and you're growing petunias, you'll need to provide some protection to minimize damage to the plants.
One of the simplest ways to minimize the amount of damage to petunias is planting them near the house. If that doesn't work, planting behind deer-proof fence is a reliable solution. For more exposed locations, you can use repellents to help keep deer away.
Deer-proof fencing is considered the most reliable way to keep deer out of plants. Straight fences must be 8 feet high to prevent deer from jumping over them, or you can use a fence that is 6 feet high and slants outward at a 45-degree angle. Deer fences come in a variety of materials, including woven wire and polypropylen mesh. Mesh barriers are less sturdy than wire but blend in with the landscape and are easy to work with. If you want to try electric fencing, use one strand 30 inches off the ground marked with flagging tape or polytape so the deer can see the fence before they run into it.
Commercial deer repellent solutions are available, but there is also a nontoxic homemade repellent that is highly effective. Beat whole eggs, then mix them with water at a ratio of 1 part eggs to 4 parts water and pour this mixture into a sprayer. To keep the egg mixture from clogging the sprayer nozzle, remove the white membrane attached to the egg yolks before beating eggs. Once on the plants, this egg mixture is weather-resistant, but you have to reapply it every 30 days.