I have several sawtooths that are about 8 years old. They have been producing acorns for about 3 years but they are only about the size of a pea. Not sure why the acorns won't/don't get any bigger but they have been like this for 3 years. I put triple 10 around them late last fall but didn't put a whole lot of it. Any idea what I can add to soil make them produce bigger acorns?