She asks for someone to plow the fields but then I have to put away pumpkins again. I've done it 3 times now and there is still no option to go get the head mole-guy. I haven't done the harp thing there is that possibly what keeps resetting it?
The sidequest becomes available only after you complete the fire sanctuary. Once this is done, Guld will be waiting on top of one of the rock pillars as you dive underground at the base of Eldin volcano. If Guld is not there, then that means you haven't completed enough of the story yet. Guld will mention something about it being too hot to find treasure when the sidequest is available.
Here is the entrance to the location by Eldin Volcano you must dive to find Guld, in case it was hard to understand what I was talking about:
UPDATE: Also, I think you have to complete all the jobs that Pumm, the owner of the Lumpy Pumpkin, has for you.
This particular quest is only available in a later part of the game. When ready, Kina will have a "..." bubble over her head and thank you for carrying pumpkins for her before asking for your help again. If you haven't had that chat with her yet, the quest is not yet unlocked.
It only becomes available when...
If you haven't passed that point in the game yet, then you just have to keep playing!