Growing black locust vs osage orange for fence posts

My wife and I own a piece of land that we are planning to build on in 12-15 years. After the house is built, I'd like to put in a split rail fence around the back yard. In the meantime, I thought I'd grow the fence posts. Not in place, but to cut down and process. Any input on choosing between black locust and osage orange? It's in Eastern Pennsylvania, clay soil. I'm wondering how the two compare regarding:
-rot resistance
-difficulty in splitting and making the holes for the rails
-speed of growth, specifically diameter of trunk
-anything else you can think of?

Alex

Hi Alex,

I can't address all your questions, as I am growing black locusts for posts in situ, rather than for split-rail. (I recently toured a farm during my PDC and they were doing the same, using old dead trees in place for nice easy electric fence posts.)

Here is a one-pager of my observations from a couple years ago, going over planting tips at 1y.o up to 3.5 years of age.

https://permies.com/t/165139/a/161714/Trees-Black-Locust.png

Now that the trees are 5 years old...

1)Their diameters range from bicep size to a large thigh size -see attached for the biggest as of January '23.  
2) About 15-20ft tall, or two stories.
3) Significant (fractal-like) fairly symmetric branching started about waist height.  This makes them look less appealing for saw-logs, as the central leader trunk is short.  
4) They are strong enough that I often sleep between them in a hammock.
5) Thorns about 1" long max, and painful!
6) Significant suckering: Another row of trees (parallel to the first) about 8ft away is naturally forming in my no-mow pollinator strip / shelterbelt.

Other's results will vary!  Our Black Locust spacing is 10 ft, linear pattern.  Maintenance is brush hog'n along either side, and occasionally pruning with loppers or mini Stihl electric chainsaw.

Fun Fact: A benefit of Osage Orange is that you can graft Seedless Che onto it!

red cedar would also work well. maybe see if your state has a seedling sales program through dept of forestry.

Mulberry grows faster than Osage and slower than locust, but the wood is reported to be nearly as durable, and the tree itself has no thorns.

If I had a large parcel of land to fence in I would plant shipmast locust in two parallel lines, and pile brush in between.

I planted hundreds of osage orange trees in zone 4b in April 2020.  They were about 6" tall when I planted them.  Now the biggest are about 10" tall.  I figure they are growing between 1" and 2" a year, so at this rate, I shouldn't be dead more than 150 years by time they would make good fence posts.  On the other hand, I have black locust I have planted that grew several feet a year.  That makes it a pretty easy choice where I am.  Add to that the fact that black locust seem to grow much straighter than osage orange, so for fence, they would work much better.  That has been my experience here, in this zone.  Somewhere warmer, I have a feeling I would have had very different results.

Dad cut a bunch of hedge posts when I was too young to help more that by stacking the lighter brush. (I'm 48 now.) He sold one of the properties, but of the ones he used here, there's one I think my sons will have to replace in the next twentyish years.

The trees never grew on my property, nor did black locust. I got some black locust seeds in a trade. Germination wasn't good. One survived long enough to put in the ground. I think it's three or four years old now.

I picked up a bag of hedge apples last fall and soaked 'em a while, them bashed 'em up and spread in an air-prune box. I haven't counted the survivors, but there's a bunch.

What does my limited experience mean for you? Only that hedge (Osage) may be easier to propagate. Then again, I don't know how my locust seed were collected or stored. Or how old they were. Your mileage may vary.

Osage Orange seedlings