If you are bad at tuning by ear, then you should practice it every day. It's great ear training. When I was a kid, we didn't have tuners. By ear was the only way to tune. If I was practicing at home then I tuned to the A440 of my quartz metronome. When I was playing with my band I tuned to the keyboard or guitar.
Pro tip: The "harmonics method" is slightly inaccurate, due to our tuning system called "equal temperment." If you tune by harmonics starting from the lowest string, then your highest strings will be slightly out of tune (and vice versa). This tuning anomaly will be more pronounced if you have 5, 6, or more strings.
The most accurate way to tune by ear is to match your E string to a reference E, your A string to a reference A, your D string to a reference D, and your G string to a reference G.
The second most accurate way (assuming your bass is set up with good "intonation") is to tune your E to a reference E pitch. Then fret the E string at the 5th fret to make the note A. Match your open A string to this pitch. Then fret your A string at the 5th fret to make D, and tune your open D string to that. Finally, fret the D string at the 5th fret to make G, and tune your open G string to that pitch.
The harmonics method is the third choice for accuracy, but it is often our first choice in actual practice. It is easy to hear the "beats" if we are slightly out of tune. As we get closer to in tune, the beats get slower, and then when we are perfectly in tune, the beats stop. It's a really practical way of tuning by ear, especially in a noisy environment.
If I am playing with a guitarist who uses a capo or an "open" tuning (like DADGAD) then I always check my tuning by ear against theirs (even if my digital tuner says I am "in tune.")