Left out in the elements, milk rots, and its sourness clouds deer’s sense of smell. Without the ability to sniff out predators, deer will abandon areas with the scent of milk.
A homemade spray can be made with any milk (whole, 2%, skim, or buttermilk) and is most effective if the milk has been left out of the refrigerator for at least 24 hours.
If the milk has curdled or is too thick, place it in a blender, add water, pulse for a minute, then strain the mixture before pouring it into a spray bottle.
Liberally spray the entire plant, including stems, leaves, fruits, and vegetables. Saturating crops with milk spray will not negatively affect their growth.
Don't spray after rain or if dew is present. You want the plant to be completely dry so the milk adheres better, and then it can last about ten days, even if it rains a bit.
You can increase the potency of the milk spray by adding a beaten egg to the mixture. The stench of rotten eggs and milk baking in the sun will drive away even the hungriest deer.