If you’ve been researching Black Locust decking, you may have encountered a claim that goes something like this: “Black Locust used to be harvested as old growth, and that wood was superior. Today’s Black Locust is new growth and can’t match it.”
It sounds like a reasonable concern. It references real concepts — old growth timber, wood density, ring growth. And it’s being circulated by at least one high-profile tropical hardwood retailer as a reason to choose their products over Black Locust.
There’s just one problem. It’s scientifically incoherent. And when you understand why, the argument doesn’t just fall apart — it actually inverts, and becomes one of the strongest arguments for Black Locust over tropical hardwoods.
Here’s the full picture.
What Is “Old Growth,” Actually?
Old growth forest is a specific ecological classification. It refers to forest that has reached an advanced stage of development, typically defined as trees that are at or beyond half their maximum natural lifespan — generally 120 years or older for most commercially harvested species.
Old growth trees, by definition, are slow-growing species that take a very long time to reach that age. Douglas Fir, for example, can live 500–1,000 years. Western Red Cedar can live 1,000+ years. Old growth stands of these species took centuries to develop and are irreplaceable on any human timescale.
For softwood species like Cedar, Redwood, and Cypress, there is a meaningful distinction between old growth and new growth. The heartwood of old growth specimens — the dense, resin-rich inner core — is more rot-resistant than the sapwood-heavy, faster-grown newer timber. This is a real and documented difference.
But here’s the critical point: this distinction does not apply to Black Locust. And the reason why tells you everything you need to know about what makes Black Locust extraordinary.
Black Locust Doesn’t Live Long Enough to Be Old Growth
According to the USDA, Black Locust grows quickly — at 2–3 feet annually when young — and lives for about 50–75 years. The USFS Fire Effects Information System confirms a typical lifespan of 60 years, with a maximum of approximately 100 years. Multiple independent sources confirm: Black Locust is short-lived and rarely reaches 100 years of age.
Old growth is generally defined as trees 120 years or older. Black Locust cannot be old growth because it doesn’t live long enough to qualify. The species tops out right around the threshold where old growth classification begins. There is no old growth Black Locust to harvest. There never was, at commercial scale. The claim is based on a category that simply doesn’t apply to this species.
When a retailer tells you that “old growth Black Locust” was superior, they are either confused about basic forest science, or they are deliberately invoking a concept they know doesn’t apply in order to cast doubt on a competitor’s product.
Why Black Locust Doesn’t Need to Be Old Growth
This is where the story gets genuinely interesting — and where the contrast with tropical hardwoods becomes stark.
For softwoods, old growth matters because rot resistance develops slowly. Cedar and Redwood need centuries to accumulate the resins and extractives in their heartwood that make them durable. Young-growth softwood has a high proportion of sapwood, which is far less durable. That’s the legitimate basis for the old growth vs. new growth distinction.
Black Locust works completely differently. Its rot resistance comes from flavonoids — primarily robinetin — that develop in the heartwood early in the tree’s life. On sites with ideal growing conditions, it takes just 10–20 years to produce poles with fully developed rot-resistant heartwood. By the time a Black Locust tree reaches 20–30 years of age — the typical commercial harvest window — its durability properties are fully expressed.
This is not a gap or a weakness. It is one of the defining characteristics of the species. Black Locust achieves in two decades what takes other species centuries. The USDA Wood Handbook places it in the highest decay resistance class — “very resistant” — based on this fully developed wood, harvested at exactly the age the industry harvests it.
There is no superior, older version of Black Locust waiting to be found. What you get at 20–30 years is what the species produces at its best.
Now Compare That to Ipe
While Black Locust is achieving peak performance at 20–30 years, consider what’s happening with Ipe. According to WWF and Mongabay research, Ipe trees grow extremely slowly, needing between 80 and 100 years to reach maturity. Per the Wood Database citing CITES proposal data, mature Ipe trees occur only once per 300,000 to 1,000,000 square feet — or 3 to 10 hectares — of forest area. When a mature Ipe tree is cut, that forest patch loses a tree that took a century to grow and cannot be replaced on any practical commercial timescale.
This is why Ipe was added to CITES Appendix II in 2025. The species cannot regenerate fast enough to keep pace with demand. Every Ipe deck ever built consumed a century of forest growth. There is no sustainable harvest model for a species with this growth profile under commercial pressure.
Contrast that with Black Locust:
- Reaches harvestable size in 20–30 years
- Average lifespan of about 60 years — meaning it can be harvested, and a new tree can reach maturity, within a single human lifetime
- Grows aggressively as a pioneer species, colonizing disturbed land without requiring planting
- Fixes nitrogen in the soil, actively improving the land it grows on
- Can be coppiced — cut at the base and regrown from the same root system — producing multiple harvest cycles from a single planting
The sustainability contrast isn’t subtle. It’s a species that takes a century to replace versus one that replaces itself faster than most people’s mortgages.
The Selective Application of the Old Growth Argument
It’s worth asking: why does the old growth argument get applied to Black Locust but not to the tropical hardwoods being sold as alternatives?
Every species has old growth and new growth variants. If you buy Garapa, Massaranduba, or Tigerwood, you are almost certainly getting new-growth timber — because old-growth tropical forest is exactly what CITES and conservation organizations are trying to protect. The very act of selling commercially available tropical hardwood implies new growth harvesting.
Apply the same logic consistently: if new growth is inferior, why should customers buy new-growth Tigerwood? The argument, applied fairly, undermines the alternative being recommended just as much as Black Locust.
The selective application of the “new growth” argument — used only against Black Locust, never against the tropical hardwood being offered as a replacement — reveals its true purpose. It’s not a scientific concern. It’s a sales tactic.
The Bottom Line
“Old growth Black Locust” is not a real category. The species doesn’t live long enough to produce old growth timber. Its rot resistance and durability develop early in its lifecycle and are fully expressed in commercially harvested wood. The USDA’s highest decay resistance classification applies to Black Locust as it is grown, harvested, and sold today.
The argument that commercially available Black Locust is inferior “new growth” is scientifically baseless. And the comparison it implies — between Black Locust and slow-growing tropical hardwoods — actually makes the strongest possible case for Black Locust’s sustainability credentials, not against them.
A species that achieves peak durability in 20–30 years, regenerates within a human lifetime, improves the soil it grows on, and requires no chemical treatment is not a compromise. It’s the answer to everything wrong with tropical hardwood sourcing. See how Black Locust compares to the alternatives →
