I am looking for anyone who can help me undertand my Indian Magic Crabapple tree. It was planted in 2002 into clay soil with some bonemeal & good garden soil taken from another bed & this was mixed to create a good mix of soil.

The tree I believe was 2 years old at the time & was bought in a pot. It was not root bound & seemed to have a good root system though not thick by any means. The tree looks healthy all the time & even produces apples every year. The problem is its size because in 5 years it has only grown say 1 1/2 feet taller. I have tried the extra nitrogen fertilizing even at the cost of fruit but I get the fruit but not the size. It is suppose to be 16X16 when fully grown according to the label. I can not figure out why this tree remains so short. If anyone has an Indian Magic tree please let me know if this is normal for the tree. The tree is planted about 30' from my neighbors Black Walnut tree & I know Black Walnuts can cause problems. The tree is so healthy though I don't think the Black Walnut is slowing it down. Thank you MaMoo