Second Brain is more about productivity and efficiency.
A Digital Garden is more about exploration, growth, and learning in public.
Second Brain
Definition
The Second Brain is - as coined by Tiago Forte - "an external, centralized, digital repository for the things you learn and the resources from which they come".
It is a method of externalizing your thoughts, ideas, and information into a digital system. It is a framework designed for Personal Knowledge Management. This system can be a note-taking app, a project management tool, or any other digital tool that allows you to store and organize in formation. The goal is to free up mental space by storing information that resonates with you externally, and to create a system that helps you to recall and use that information effectively when Getting Things Done or doing Alignment (TODO publish).
Digital Garden
Definition
Digital Garden is a unique approach to cultivating and nurturing our thoughts and ideas in a (public) digital place. It's like a personal Wiki site for Personal Knowledge Management.
The essence of digital gardening lies in the act of nurturing and connecting your thoughts and ideas (see Linking your thinking), letting them grow over time, and pruning them when necessary.
It's less structured than a Second Brain and more organic. And unlike traditional blogging, which is often a performative act, digital gardening is more akin to a captain's log, a space for exploration, real-time editing, evolving thinking, and Learning in Public.
While both concepts involve the use of digital tools for knowledge management, they are not exactly subsets of each other. They can be used independently or together, depending on your needs and preferences. For example, you could use a digital second brain to capture and organize your thoughts privately, and then share some of those thoughts in a digital garden for others to see and learn from.