Why do you think they grow for up to two years before dying off ? What are you growing? How do you plant them?Are you digging out a large planting hole and filling it with compost or are you planting in a hole big enough to take your plant in the contaminated soil?

Oh dear - deisel contamination should really be sorted out by a specialist company that deals with contamination - they may also have info as to how long your problem may persist if you do not have treatment carried out.

I wouldn't expect anything to survive for any length of time in soil contaminated by diesel. The big question is how the contamination occurred and can you get who ever contaminated to sort out.

i would be tempted to try and replace as much of the soil as possible, not an easy job but if you want to grow plants there that survive, you will have to.