Question
I planted a gallon lilac 3 or possibly 4 years ago. The tree/shrub is at least 6 feet high and has never bloomed. It is planted on the west side of our property--and on the other side of the fence is a lilac that blooms each season and the neighbors never do a thing to it. My lilac is a Montaigne Lilac(syringa vulgaris Montaigne). Should I use one of the bloom fertilizers?

Answer
Tina,
Usually when a lilac doesn't bloom it is from pruning at the wrong time of year. I do not think this is the case here.
Is the lilac recieving at least 6 hours of sunlight a day? This is required for the buds to set and open.
If you have been fertilizing it, were you using a fertilizer high in nitrogen? The high nitrogen content will stop flower production in favor of leaf growth.
I would recommend using a fertilizer with a higher potassium content, such as a 5-10-5. This will encourage blooming. You may not see any results this year, since lilacs set their buds on the previous years growth.
Good luck.
Ed Gulliksen