Think of Unicorn Magic like a switch that you can turn on and off.
Earth Pony is always on. Have you ever played a video game and had the "passive healing" effect? Like all characters could be healed bit by bit, automatically, just by being within the certain presence of a character? Like an ability that was just part of the character and maybe it went away if they fainted, but they caused an effect?
Like just their presence was causing the magic?
Passive abilities are very important, and in fact in video gaming circles are highly sought after because usually the more powerful an ability is, the more you have to do to flip the "on" switch.
Since we don't have video game mechanics to see what passive powers earth ponies might have, it can be easy to ignore.
But don't pass over passive.

I think a lot of it may be passive - like "blessing the land" just by living on it. But there are also more active applications - like sprouting plants quickly or shaping and enhancing their growth.

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Indeed!