What tree in the NE will rot the slowest?

Probably Juniperus virginiana.

Dave

Northern white cedar. Highly rot resistant woods from other regions include Western red cedar, Southern cypress, & Redwood.

But if you made an edging out of a wood that does rat within a few years, the types of fungus that interact where the wood touches the soil are healthful for the garden, & ultra-essential for some kinds of plants like vacciniums or dogwoods; plus it provides habitat for edible or just mushrooms & decorative turkeytails which don't do as well on rot-resistant cedar. If the edging is easy enough to make, it can be replaced about every four or five years, whenever the previous edging has just about turned to good soil amendment. I have made edging out of fat birch limbs & quite enjoyed watching them rot away, & the plantlife loved it.

-paghat the ratgirl

If you can get it, osage orange is probably unbeatable. It grows wild around here although not in great numbers. It is not what I'd call an beautiful tree but the wood has properties that are quite outstanding.

While not specifically native to the NY area, black locust or Robinia pseudoacacia is an extremely durable wood with well known properties for long term contact with soil. It is used extensively for fence posts. It is native to large parts of the eastern seaboard to the Appalachian Mts and into parts of the midwest and is very commonly grown throughout all other areas of the country.

Locust -- Should be fairly common in Central NY. We've got loads of 'em in the eastern part of the state.

Check with a rural Agway or feed store to see where some farmer has a stand of them he uses for fence posts.

Jim

Eastern recedar (Juniperus virginiana) - the red heartwood will last more or less indefinitely. And the darned things are everywhere up your way - look in old farm fields let go in the 1920-1940's