What is the largest-sized branch anyone has ever used for a cutting?

I am curious if a 4 inch diameter branch could be used. Does anyone know? Typically, I see twigs used for cuttings, and sometimes 1-inch branches. Thanks!

Depends on the plant and the technique you are using. When I plant willows and cottonwood as livestakes I like it when they are 3 to 4 inches across so I can easily hammer them into the ground with a rubber or wood mallet. Of course if the ground is soft then I like smaller ones fine.

If you are taking hardwood cuttings and putting them in a propagation bed then it seems like the smaller sized ones work better. At least based on what I see people doing.

My understanding is that some species only root well if the cuttings are only a year or so old. The larger cuttings would like be too old to root for these species.

But I have also heard of people making fence posts out of green wood and getting sproutes. So all in all I think it depends on the specific species you are wanting to propagate.

Here all willows, poplars, and russian olives are planted as cuttings at least 5 or 6 feet tall. There are a lot of hungry goats, donkeys, dzos etc roaming around, so we need to protect the bark up to about 4 or 5 feet and then still have some above to grow. So the cuttings are often 3 or 4 inches in diameter. These three particular types of trees are unusually eager to grow from cuttings though. I have no idea about other genuses.

Years ago we had our sons cut some black locust and set posts for a fence...they all sprouted nicely
I remember that they were a good size...maybe 10-12 inches in diameter. ..haha, my guy says 6-8 inches...he's pretty sure it was black locust although at the time we had both.  

I've since heard to set them in upside down to prevent that.  Of course, seasoning would have kept them from sprouting also.

Unless it is an easy rooting species anything larger than one inch should be air layered  instead of created like a standard cutting.

I have some tree limbs that are currently wrapped in air layer that are 5 inches in diameter, they are white oak and I need the head clearance so rather than just cutting the branches I decided to make new trees instead of fire wood.

Redhawk

I once put in a fence and rented a post hole digger. I drilled 84 holes in one day trying to get my monies worth out of the rental. I filled the holes with what ever I was clearing. One of the posts was a Wild Black Cherry about 5 inches in diameter and 10 or 12 feet tall. That cherry grew and it then looked like I had used a cherry tree to hang my fence on. I used a variety of trees, maples, oaks, a couple sassafras and even crab apples. The only one out of the 84 to grow was the cherry.

I don't remember the majority of the posts, but I do remember cutting the cherry and dropping it immediately into the hole.

My mother talked about going with my grandfather and his pointing at a row of large cottonwoods something like a half mile or a mile of them.  Apparently as a teenager he had SPLIT all of those to make make fence posts and then built the fence and all of the posts grew into trees.  If a split log can grow into a tree guessing there is very little limit if the conditions are correct.