Black Locust as a Utility Pole

Thoughts on whether to dry a Black Locust pole before burying the end, and related issues. March 28, 2010

I have a customer that asked a question while discussing details of a project we're currently working on. He would like to place a 6" x 108" locust post in the yard to place an area light on. He asked me if he should get it dried in a kiln to make it less likely to rot at ground level. Would it matter if it's outside in the northeast?

Forum Responses
(Sawing and Drying Forum)
From contributor O:
Someone else may need to correct me but I believe that locust, while not quite as eternal as hedge, is right up near the top as a first class fence post. It would be a waste of time and money drying. It will rot off at ground level or not depending how it is installed. Water must not collect at ground level. The best practice is to dig a hole. Cement the bottom of the post in a footer below the frost zone and to a depth relevant to how high it will be standing above ground and then backfill the top 1/3 or 1/2 of the hole with crushed stone to allow drainage. In the long run you need to keep weeds and dead leaves from accumulating around the post and providing a place for damp.

From contributor N:
I don't think I would waste my money on drying it. Locust has been used for fence post for years, and I would say that most posts were cut and then put right in the ground. I see fences here in Kentucky that have been up for years, and still have many, many years of life left, that were made of locust. Now, most of that locust is black locust, I don't know how many species there are of locust, and if one is any better than the other.

From Gene Wengert, forum technical advisor:
Black locust is an excellent choice. However, the outer sapwood (whitish in color) will be subject to fairly rapid decay and deterioration, so oftentimes the sapwood is removed (mechanically such as with a draw knife or similar) before the pole is put into use. Drying is not necessary. As the poles dry in use, the screws holding the light fixture may need to be tighten in a month or two and maybe again in 6 months.

The best construction technique is to use a concrete footer that extends several inches above the ground and then fasten the bottom of the pole to this footer using a metal bracket made to do this (commercially available). For a tall pole, side braces may be needed. Next best is to put the pole in contact with the soil, using concrete if a firm anchor is needed. For a fence post, if it super critical to have long life with no failures, the pressure treated southern pine is the best species choice. Otherwise, heartwood from a rot resistant species like black locust or osage orange is a fine choice.

From contributor O:
Gene, your best suggestion just leaves you a post supported at one point on the end and immediately requires guy wires for the 108 inch post in question, or the wind will take it over very soon. The sort of anchoring system you suggest (all concrete underground) is usable where multiply post are used (say a deck) and provision for cross bracing can be made. A concrete and drained embedment using a wood suitable for fence post would have a considerable lifetime, and would avoid the obvious inconvenience, hazards and downright ugliness of above ground bracing.

From Gene Wengert, forum technical advisor:
You are correct and that is why I indicated that side bracing would be needed.

From contributor D:
Black locust has a long life. Honey locust, while respectable, doesn't last as long. I advise people to strip the bark, stack and let them dry for one year before setting them. When time doesn't allow drying then remove the bark and alligator char the bottom of the post so that all areas that contact the ground and up to 3" above grade are charred. This will discourage both rot and insects. When you strip the bark and both dry and char the post you can expect it to last very long indeed. Concreting it is dandy but unnecessary in clay soil when you properly tamp the backfill. That is unless the light is very large/heavy.

From Gene Wengert, forum technical advisor:
You might be interested that when the Western U.S. was surveyed, there often was a lack of trees or other landmarks to use as permanent markers for the survey. Therefore, the surveyors would have non-native wood stakes that they would char in the fire and then bury at a spot that needed to be marked for the future. Even after 100 years these pieces of charred wood were able to be located and the wood was identified on order to provide positive ID of the survey markers. They only used heartwood; sapwood is so prone to decay that they avoided it. In short, charring does indeed work, but it certainly weakens the wood greatly, so might not be appropriate for fence posts or light posts.

From contributor M:
We always stack and let them dry for a year before using post. The bark will fall off and the post will turn black. A green locust that has had the bark and sapwood removed can be used, but the seasoned post will outlast it by many years. As a side note, cross-arm pins used in the telephone industry to support glass insulators were heart black locust.