I grow lilacs also. I have good bloom. These are the possible problems I can think of.

*lilacs need full sun to flower best.

*they prefer neutral to slightly alkaline soil. They do poorly in acid soil. It is usually possible to make acid soil alkaline enough to work for lilacs. A good local nursery will be able to help with this if it is your problem.

*lilacs like well-drained soil. If your soil is very clayish you may need to water less or find a way to improve drainage.

*flowering plants generally need adequate phosphorous to bloom well. My soil is phosphorous poor and I amend it with phosphorous from a rock powder I buy via mail order because I live in a small city and it is not available locally (even though it is mined in this state - go figure.) I have astonishingly good flowering on all of our plants, lilacs, irises, roses, asters, everything. I tend to credit the rock phosphorous for the good results.

If my thoughts don't seem to apply to your situation, perhaps you could get more useful advice from a local extension agency or nursery (forget big box stores, they don't claim to offer advice). I hope you get those lilacs up and running properly by next bloom season.

Make sure your fertilizer is not high in nitrogen. Too much nitrogen and the lilacs will grow nice leaves at the expense of the flowers

Hi, thank you for your help. Would a 5-10-5 fertilizer be good to put on the lilacs next spring or would I need something with a higher phosphorous amount? A local farm store sells a triple phosphorous fertilizer and that's all that is in it. Thanks again for your help.

If you could get your soil tested that would be ideal. I would try to find a phosphorous rock powder. The reason is because the man-made phosphorous fertilizers tend to be somewhat toxic to soil microorganisms. Research is showing that it is highly desirable to have these microorganisms. They work with the N (Nitrogen) P (Phosphorous) K (Potassium - don't know why potassium is "K", but it is.) NPK has long been recognized as desirable, but in the last 10 years research has discovered that microorganisms help plants to absorb NPK and fight pathogens that can inhibit plants. In other words, ongoing research has increased our understanding of how soil works for plants.

If you can't find rock phosphorous (made by grinding rock that is high in the mineral phosphorous), and I know I have to get it by mail, buy the straight phosphorous and follow the instructions for how much to add. The rock is not toxic except at levels you would not use. A quart around a 6 foot tall plant would be good. Too much of the man made phosphorous fertilizer would inhibit growth. Just follow the instructions. As I said in my first post, the results of rock phosphorous powder are terrific in terms of good bloom. One good thing about rock phosphorous powder is that it is recycled by the plant. Leaves contain phosphorous. When they drop in the fall they will break down at the base of the plant and the phosphorous will be taken up again. It is not something you would need to replace every year. It is likely you would not need to do it more than every 5 or 10 years.

I live in an area of Montana that has phosphorous poor soils and my roses, for example are just covered with blossoms. Like them, the lilacs also bloom very heavily. If you test your soil just one time you will know if this is your issue. We have very high potassium so I never use potassium. It is a mineral also and is recycled like phosphorous. Nitrogen is organic, not mineral, and does dissipate. However, generally, shrubs don't need nitrogen unless they are obviously yellowing (which also happens with VERY severe phosphorous deficiency. Generally, adding nitrogen promotes leaf growth and can reduce flowering as leaf growth takes the plants attention. A NPK fertilizer mix is probably not what you need.

Again, a single soil test may be helpful in determining if you are deficient in anything critical.

One last thing, it does take two years in the ground for lilacs to bloom. Very young plants are busy rooting and don't bloom. Lilacs should bloom AFTER two SUMMERS in the ground.

Bone meal, widely available in garden centers, is good as an organic phosphorous soil supplement.

- Steve