I can't say there is a hard and fast rule. I do know they may be" too tall" to eat the leader buds but still not big enough in diameter to stand up to a buck in rut rubbing his antlers on your tree and tearing it to shreds. This happened to a neighbor and me on separate occasions when the neighborhood buck made his fall rounds. I now cage my trees in cylinders made of conrete reinforcing wire ( got the idea from St. Lawrence Nurseries). I used steel stake like used in bracing conrete forms and wired the cage to the stakes. Should provide quite a barrier when Big Buck comes around this year. The cages will likely stay up for at least five more years.
Location: Helena, MT zone 4
posted 6 years ago
I forgot to mention using the "bone sauce" advocated by Sepp Holzer. I've made some this last month and it wasn't hard at all. The video here on permies.com or YouTube was a good explanation that I found easy to follow. Holzer has had great luck keeping the equivalent of mule/white tailed deer (roe deer) and elk (red deer) off of his trees in Austria. Now that my trees are all treated for the next many years, again my concern is keeping the bucks from tearing them up with their antlers. Reproduction does strange things to us all, ya know? We were visited a few weeks ago, and he/she didn't even try the caged ones. With them staked down, they are not likely worth the effort.
Deer eat buds like cattle eat grass: it is their preferred food!
I suppose that if there were other trees to eat and you sprayed your baby tree with something smelly like urine it might help, but, if it is winter and the deer is hungry enough it will eat whatever it can.