I have a Silver Leaf Maple Tree in my front yard that is 7 yrs. Old and is approx. 16 - 18 ft. tall. However the first 2 or 3 limbs on the bottoms are no more than 3 to 3.5 ft. long, and the rest of them are not that long. It is tall and skinny. I think it has a flat root system, right? The soil in our front yard is very hard clay, and I was wondering if that's keeping it from growing wider? What can I do to the soil to help it grow better? Thank you...