How to Stop Deer from Eating Your Plants and Trees with Soap
To stop deer from eating your plants and trees with bar soap, purchase a strongly scented soap that contains tallow or sodium tallowate. Try to avoid soaps that contain soil-affecting ingredients like salt, boron, and chlorine bleach. Next, sprinkle grated shavings of the soap around seedlings. For bigger plants, cut the soap into 1-inch chunks, skewer them, and place the skewers near the plants. Cut the bars in half and hang them near the biggest trees and shrubs.
Determine how much bar soap you need. Deer can eat to within about 3 feet (0.91 m) from soap. Calculate the circumference of a circular border around your trees and plants that is at least 3 feet (0.91 m) away from them. Use 1 bar of soap per 3 feet (0.91 m) around this border. For example, if you have an 100 foot (30 m) border, 100 / 3 is 33, which is roughly the amount of soap bars you need—each spaced 3 feet (0.91 m) from each other. You can also use 1 bar of soap for every 10 feet (3.0 m) if you don't have lots of deer activity near your home. Calculate how much liquid soap you need. If you're going to apply liquid soap, you need to apply approximately 0.068 ounces (2 mL) to the stem of each plant and tree. Count the number of trees and plants within the area you need to protect and multiply the number by 0.068 (ounces) or 2 (mL) to get the amount of liquid soap required. If you count 25 trees and plants total, you need 1.7 ounces (50.28 mL) of liquid soap. Purchase bar or liquid soap that contains tallow. This is derived from animal fatty acids and is the repellent. Go to your local grocery or drugstore and find the personal hygiene section. Locate bar soap or liquid soap and make sure the ingredients list contains tallow (also known as sodium tallowate). Depending on the extent of your deer problem, you may want to purchase bulk packages to save money. Always select the strongest scent possible to increase the soap's deterrent effect. Don't use soaps that contain coconut oils—they might attract deer. Avoid soaps that contain soil-affecting ingredients. Most soaps have ingredients that can either damage soil or alter its pH of and destabilize the environment for plants. Try to avoid soaps with salt and sodium compounds, boron, chlorine bleach, and alkaline compounds. Don't worry if some of these ingredients are present—just do your best to avoid as many as possible. Shave bar soap and sprinkle it around seedlings that have yet to appear. For young seedlings, shavings are best. Use a long-grain grater to shave the soap into small shavings. Hold the grater at a 45-degree angle to a flat surface and drag the soap across it. Afterward, sprinkle the pieces evenly in a circle about 2 to 3 feet (0.61 to 0.91 m) from the soil that harbors your seedlings. Press the soap firmly but carefully down the grater and take care not to cut your hands. Create soap cubes and skewer them near budding smaller plants. Cut each bar of soap into pieces about ⁄ 2 to 1 inch (1.3 to 2.5 cm) around. Insert a skewer into the tip and place each one just above budding plants. Replace the skewers about once a month or anytime they are destroyed by rain. These skewers are also great for dehydrating bugs and aphids in the nearby soil. Don't use more than 1 soap skewer per plant. Cut your soap bars in half and hang them in your garden to protect larger trees and plants. Use a paring knife to cut your bars of soap in half. Afterward, wrap them in cheesecloth or burlap and use a stapler to fasten them to stakes in your garden. Be sure to space each piece of soap evenly across your perimeter. If you're using 33 bars of a soap for a 100 metre (330 ft) long perimeter, space each bar out by about 3 metres (9.8 ft). Hang each bar of soap at least 7.8 inches (20 cm) from the central stems of the plants. Don't hang your soap bars directly on shrubs, as they will attract rodents when they drip down the stem. Spray liquid soap around your plants and trees if you have a big garden. For a high volume of trees and plants, use a spray bottle or backpack sprayer. Apply the soap in a circle around each plant and tree from a distance of 3 feet (0.91 m). For medium-sized gardens, use a spray bottle to apply the soap. If your garden is on the larger side, pour your liquid soap into a backpack sprayer for application. Conduct reapplication every 63 days to mimic repellent spray programs. Note that liquid soap can sometimes increase damage from other animal species. Always keep an eye out for damage and switch to bars if this appears to be the case. 
Determine how much bar soap you need. Calculate how much liquid soap you need. Purchase bar or liquid soap that contains tallow. Avoid soaps that contain soil-affecting ingredients. Shave bar soap and sprinkle it around seedlings that have yet to appear. Create soap cubes and skewer them near budding smaller plants. Cut your soap bars in half and hang them in your garden to protect larger trees and plants. Spray liquid soap around your plants and trees if you have a big garden. 