How long have you been using your current ERP system? Maybe it's a decade-old SAP install. Maybe it's an Oracle environment held together by customizations and institutional knowledge. Either way, a mature ERP is expensive to maintain, difficult to integrate with modern tools, and increasingly a bottleneck forAI and automation initiatives the Board is asking about.
There are three paths forward. Each has tradeoffs, and anyone who tells you otherwise is selling something.
Below is a decision framework for comparing the three main ERP modernization paths: Leave-and-layer, strangler fig, and full replacement.
Keep the old system. Build modern capabilities on top of it.
This is the lowest-risk, fastest-to-value approach. The legacy ERP remains as the system of record, but modern tools are layered over it. This includes AI-powered automation, better reporting interfaces, workflow engines, and analytics platforms that are all connected through APIs and middleware.
Why companies choose this: It's pragmatic. The core ERP still works. The book still close and the audits still pass. What's broken is the experience (clunky interfaces, manual workarounds, no real-time visibility). The leave-and-layer approach fixes immediate issues without betting the business on a massive transformation.
The catch: It doesn’t really solve the problem. It just defers it. It achieve quicker wins versus other approaches, but the old system's problems are still underneath. Building on top of an existing foundation has limitations. The legacy data model, performance constraints, and technical debt just get hidden. Over time, the layers can become their own form of complexity.
Best for: Organizations where the ERP is stable and functional but outdated in terms of user experience and capability. Also, it’s a potential first move while figuring out a longer-term strategy.
Replace the legacy system one piece at a time until there's nothing left to replace.
Named after the vine that slowly grows around a host tree and eventually replaces it, this approach targets individual ERP functions (accounts payable, procurement, reporting) and migrates them to modern tools one by one. The old system keeps running, handling less and less, until all functions are fully migrated.
Why companies choose this: It spreads risk and cost over time. Each migration is a manageable project with its own business case. Organizations gain incremental value along the way instead of waiting years for a single go-live. If something goes wrong with one piece, the problem stays more contained.
The catch: This approach requires sustained executive commitment over a long timeline. In practice, many organizations stall halfway. They migrate the easy stuff, declare victory, and leave the hard parts running on legacy indefinitely. They’re stuck maintaining two systems with integration complexity in between.
Best for: Companies with strong transformation leadership and the patience to see a multi-year migration through to completion. Not for the faint of heart or the short of attention span.
Rip it out. Start fresh. Go live on a single date.
This is decommissioning the legacy ERP entirely and cutting over to a new platform. It's the cleanest end state and the approach vendors love to sell.
Why companies choose this: Sometimes the old system is truly end-of-life. Vendor support has ended, technology is obsolete, or customizations have created something so fragile that layering or “strangling” isn't realistic. A full replacement is the only option that offers a completely clean data model and modern architecture from day one.
The catch: It’s a big undertaking with shifting timelines and budgets. The entire organization will change how they work. It requires a lot of planning, change management, employee training, data cleanup, process improvements, and more. A vendor might hand over a neat, linear plan, but real transformations are never that easy.
Best for: Organizations where the legacy system is outdated, too costly to maintain, restricts growth, or no longer meets major requirements. Leadership must be prepared to commit the resources, time, and organizational energy required.
The choice between these three paths isn't permanent. Layer where it makes sense, replace if needed, and only start fresh when the ERP is truly beyond repair. Assess each function and match the right strategy to the right problem. Perhaps the AP process, the GL, and procurement workflows are all in different states of health. Treating them all the same is like prescribing the same medicine to every patient at the hospital. Pick a starting point, prove it works, and build from there. Progress beats perfection every time.
At Trenegy, we have an unbiased approach to helping organizations navigate ERP modernization and the change that comes with it. To chat more about this, email info@trenegy.com.
Trenegy is a non-traditional consulting firm based in Houston, Texas.
