If they're in the same soil it apparently won't need lime either. I suspect you just had to wait for it to get big enough to bloom or overcome some other issue.

I've never gotten that lime thing either. Most plants, lilacs included, tolerate a range of soil pH and our soils tend not to be overly acidic so that lilacs are outside their 6.0 to 7.0 pH comfort zone. I have several lilacs in my garden, one of the few plants that were in place when I moved in many years ago. My soil runs right around 6.3 and the lilacs bloom heavily. In fact, one 50 year old lilac tree is underplanted with rhodies and all plants are thriving.

I agree that age/maturity is most likely a factor in producing flower buds.

Maturity, yes, but also sun all day.

Don't be surprised if it blooms white for a few years. I had some Sensation lilacs at my nursery that bloomed white in 2 gal. pots. I did some research and apparantly that happens when they are young.

I'm thinking they'll be properly colored because the buds are opening and they look pretty dark, alot darker than my old traditional is.

Congrats on the upcoming blooms...that's exciting. Since it's already begun blooming before you added any lime, that indicates it probably was something else, as everyone has mentioned. My last (and now current since I just planted some small lilacs) garden had a lilac that needed to grow taller than the nearby fence before it started blooming. Sometimes they just need to be mature enough, and tall enough to get plenty of sunshine, to bloom.

Keep us posted on how it develops. I've got one large inherited no-name one (the last from a lilac hedge that lined the entire large farm that became my neighborhood here in the city), plus I planted 'President Lincoln' and 'Lavender Lady' both of which probably won't bloom for awhile, though the no-name is loaded with buds.

In any case, congrats and send in some pics if you can.
Take care,
Grant