Have not heard of peppermint oil as a deer repellant,but there sure are a bundle of other products out there. Is there any reason you want to use peppermint oil?

Well that would certainly give the deer minty fresh breath...: ) sorry-I don't know about the peppermint oil-that sounds like it would be very expensive if you have alot of plants. If you would consider other repellant ideas, I make a simple one from water and eggs. I can make several gallons from just one egg. I mix it in a 2 gallon jug and let it sit just a couple days-the longer it sits the more concentrated it is. The mixture smells....well.. rotten, until it dries then I just reapply after each rainfall...we're having a drought so I haven't done that in weeks but just to make sure I still apply it. I have intact hostas and hydrangeas,two of the most sought after salad greens for deer and I live on the border of the Cuyahoga Valley National Park if that tells you anything.We get deer.
My neighbor has daylilies that are chomped to the stem but mine just 20 feet away are intact. Need I say more? It's cheap;it works.

~Babs

Thank you for the suggestion Babs! I live in Medina 🙂.... I'm so upset because the deer jumped my friends and munched on my tomato plants and flowers. I have been here for 16 years and that has never happened....ugh. I usually use liquid fence but I'm going to try your recipe as well. I appreciate it

Having problem with deer eating my sweet potatoe vines. I heard peppermint was a good deer deterrent.I I mixed 1/2 t of peppermint, 1/4 t of dawn, detergent as a carrying agent, in a spray bottle full of water. Applied it to the vines. In the morning I noticed the deer still ate the leaves, even more so! They more than they had been!