They supposedly prefer neutral to slightly alkaline soil.....the lime would help with that. But I'm not sure it is really necessary. Lilacs flourish in the naturally slightly to moderately acidic soils of the PNW without any liming.

Unless you have very acidic soil (pH of 6 or less), I wouldn't bother.

driving the country .... i see HUGE!!! lilacs around century old abandoned farmsteads ...

no water.. no fert.. no lime.. no nothing..

sometimes they are bigger than the old farmhouse ...

if you suspect a problem with your soil.. have a soil test done.. then use the lime .. IF IT IS NEEDED ...

all that said.. is there anything wrong with your lilac ..

ken

Ken. Well I didn't think there was anything wrong until my neighbor suggested that I should put lime around them ...there blooming beautifully so I think I shall follow your advice and leave them be...