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Three years ago I planted these ,,Syringa'' Lilac. Out of the 4 ,I have 2 left. They are 3' and 4' tall, healthy but narrow. One had over the last 2 years each summer only 3 flowers, the other one none and that one is growing healthy. So I can not tell at this point if it is a ,,LUDWIG SPAETH'', or a ,,MONGE'', or a,,PRESIDENT GREVY'', or a ,,MADAME LEMOINE''. My question is do they need to be pruned, when is the right time and how much pruning down? Hope to hear from you! You might already know me, it is me Edelweiß.

You got a nice answer from luis about your hydrangea. Lilacs are similar in that they set the buds for next year's blooms in late summer. If you prune it now, you will be cutting off next year's flowers. If you need to prune it, it should be done immediately after it blooms. But it should need little pruning, just cut off any dead wood, any branches that are crossing and rubbing on each other, and maybe some branches that are growing in towards the center, to be sure light and air can still get to the center.

But one thing about lilac that is different from hydrangea: If you don't prune it, you do definitely want to deadhead it, that is cut off the spent blooms as soon as they are done, before they set seed. Just cut the flower spike off at the base, without taking more of the branch. If you don't remove the flowers before they set seed, it will tend not to flower much the next year. Lilacs basically only bloom well every other year, if left alone. This is an evolutionary adaptation. Lilac seeds are big and heavy and don't have a travel mechanism. So they don't go very far. The every other year bloom thing cuts down on the competition between this year's seedlings and last year's.

But what luis told you about fertilizing applies to lilacs too. Giving them high Nitrogen fertilizer will tend to produce lush growth at the expense of flowering. Giving them high N fert late in the season can lead to injury as it puts out new tender growth just before frost, when it should be working on preparing for winter.

If your plant is tall and narrow, it may be that it isn't getting enough sun?

Thank you for your informative reply about my lilacs. It is so amazing for me what one can learn in this forum. Talking to you makes it a little more personal. I will be checking, but will be slower for a while, because I will be painting with my oldest son my house. By ghosh there are a lot of rooms. Take care, Edelweiß!