Hi bluegrassmom, allow me to ask you something that might help you succed next time. Are you planting every new tree in the exact same spot that the others that died? I will be back on that depending on your answer. Other than that here it goes my 2 cents:
1) dig a big hole (3 feet or more) and 2 feet in depth.
2) Mix in as many bags as you can afford of one not too expensive garden soil
3) make a big mound with the result
4) plant your JM in the top of the mound so that at least half of the root ball is above the original soil level. Mulch generously
Your JM should be alright there
