There is no one definitive answer to the question of how deep to till your garden. The depth at which you till will depend on a variety of factors, including the type of soil you have, what you’re growing, and how much work you want to put into it.
In general, though, most people recommend tilling a garden bed at least 8 inches deep. This will loosen up the soil and allow for better drainage and air circulation. If your soil is particularly dense or clay-like, you may need to go even deeper. And if you’re growing vegetables or other crops that require rich soil, be sure to mix in some organic matter (such as compost) before tilling.
Of course, there’s no harm in going too deep – just be prepared for a bit more work involved in keeping your garden bed well-maintained!