The people at my awesome natural planted store told me I really needed a fertilizer or my plants would slowly die if they were just tied to driftwood or if gravel was the only substrate I had.
I seriously just squirt some of this stuff occasionally in the tanks and my plants don't die. I do not have a real planted tank yet, just floating and tied plants. So if I can do it, you can do it. :) I don't even really pay enough attention to how much I should use.