Harvest Moon Magical Melody - Acquiring and Unlocking Fertilizer
If you're like me and you google things when you're stuck you'll probably realize there isn't really much information out there about how to find the only item required to unlock Fertilizer, Limestone. The information you can find too is all conflicting, I was quite annoyed honestly. Well, hopefully this will put an end to all that! To be honest despite what you may have read getting Fertilizer isn't all that hard. It shouldn't take any more than 5 or 6 ingame days, depending on what your current stamina meter is of course!
To get started what you will want to do is head over to the mine and start going down floors. Not too many though, Limestone has kind of a sweet spot I have come to realize. It can commonly be found between floors 10 and 50 or so. Also, Limestone doesn't come from the fancy rocks down here or whacking the dirt it comes from the plain common looking rocks. Sure, you can get it from whacking one of the crystals but I have found that it's much more common from the every day ordinary rocks.
Ultimately your goal is to collect 10 Limestone's and ship them. If at any point you need to check your progress when collecting the Limestone to see how many you've shipped bring up the menu and cycle through until you get to the Shipped Items tab. Go down a few categories until you reach the one with the picture of the gem. Click on this and go down the list until you see Limestone, it'll be right in here!
Once you ship 10 Limestone you'll get mail from Liz and she'll tell you that the store is now stocking Fertilizer. When you head over to the shop you'll see it in their list for 150G a bag. Not too shabby considering how much it raises the value of your crops! Honestly I think it's a total waste to grow crops without it once you have access to it. It greatly benefits all crops except grass raising their value.