The Pros and Cons of Black Locust for Decking: A Sustainable and Durable Choice

When considering materials for your deck, durability, sustainability, cost, and aesthetics typically play a crucial role in the decision-making process. Among the many options available, Black Locust (Robinia Pseudoacacia) stands out as an exceptional choice. Known for its natural rot resistance and impressive strength, Black Locust offers an eco-friendly alternative to traditional decking materials like pressure-treated wood, synthetic decking, or tropical hardwoods. However, there are plenty of misconceptions, promoted by manufacturers of petroleum-based composite decking and tropical hardwood decking.  Let’s take a closer look at the pros and cons of using Black Locust for decking, to help you make an informed decision.

Pros of Black Locust for Decking

Exceptional Strength

Black Locust is one of the strongest and hardest woods in North America, ranking in the top 3 of all strength categories by the USDA. Based on the Janka hardness rating, Black Locust is about 30% harder than White Oak, one of the higher-end flooring options in the USA.  Please see table Table 5–3a of the USDA Wood Handbook for more details.

Natural Rot and Pest Resistance

Unlike many other decking materials that require chemical and heat treatments to resist rot and insect damage, Black Locust naturally contains high levels of flavonoids and other compounds that deter decay and pests. Coupled with the grain/cell structure and hardness, Black Locust is rated as the most rot-resistant wood in North America by the USDA. Please see table Table 14–1 of the USDA Wood Handbook for more details. This makes it an excellent choice for outdoor applications for all climates.

Sustainability and Eco-Friendliness

As an abundant and fast-growing tree, Black Locust is a natural and sustainable choice compared to other decking options. The tree has a short lifespan, rarely reaching 120 years old, which is what most consider to be the threshold for “Old Growth.” Old Growth does not correlate with sustainability; in fact, because Black Locust regrows so quickly, it is inherently renewable and abundant.

Low Maintenance Requirements

Black Locust wood has a very dense grain pattern, which makes it naturally weather-resistant, requiring minimal maintenance.  If left in its natural state with no stain or oils, it will weather to a silvery-gray patina over time, which creates a classic weathered look. If a richer wood tone is preferred, periodic applications of finishes can help maintain its original golden hue. Additionally, unlike many of the tropical hardwoods, Black Locust can be painted or stained to the color of your choice.

The Natural Appeal of Real Wood

Real wood adds warmth and natural beauty to residential and commercial construction. Discerning homeowners appreciate the feeling of real wood on their bare feet. Unlike composites, real wood does not overheat and is safe and comfortable to walk on barefoot.  And the unique and distinctive grain patterns of Black Locust create a beautiful visual appeal. 

 

Cons of Black Locust for Decking

While black locust has many advantages, there are a few challenges to consider:

Higher Initial Cost

Black locust is more expensive upfront compared to traditional softwood options like pressure-treated pine or cedar. However, its long lifespan and minimal maintenance requirements make it a cost-effective choice in the long run. Not to mention its natural beauty compared to softwoods, pressure-treated wood and composite products. Over time, the durability and resilience of black locust offset the initial cost, providing excellent value for money.

Short Board Lengths

Because the Black Locust tree grows quickly and does not grow as tall as many other decking sources, it is harder to yield long lengths of black locust for decking. This means that 12’ is typically the longest length for decking boards.  Most homeowners and landscape architects are fine with this as this showcases the natural wood and variation, just like indoor flooring. 

With that said, advances in milling techniques are creating new ways to provide longer length boards in mass quantity.  In fact, Robi Decking is preparing to launch a new line of finger-jointed long-length black locust decking boards later in 2025. Stay Tuned!

Workability Challenges

Due to its extreme hardness and density, black locust is not always as easy to cut, drill, and fasten compared to softer woods. (Note that this is common with hardwoods, and Black Locust is easier to work with than tropicals, which also produce toxic sawdust). Using high-quality carbide-tipped tools and pre-drilling holes for fasteners gets around these challenges easily though. And remember this strength is what ensures a sturdy, long-lasting deck that will not easily dent or warp, making the extra effort worthwhile.

Final Thoughts: Why Black Locust is a Top Choice

Despite a few considerations, black locust is an outstanding decking material for those seeking durability, sustainability, and natural beauty. Its remarkable resistance to rot and pests, coupled with its low maintenance and eco-friendly qualities, make it a superior alternative to chemically treated or tropical hardwoods. While the initial cost may be higher, the long-term benefits far outweigh the upfront investment, making black locust a worthwhile choice for a deck that will stand the test of time.