In my experience, old lilacs age in different shapes. You say there are plenty of suckers, but are there many large old single twisty stems? The best way,IMO, is to take out several of these old stems/trunks each year. It only hurts for a few minutes! I put on wood ash during the winter and a good organic mix of 4 pt seed meal/1 pt rock phosphate/ 1/2 pt greensand or granite dust during the spring.

I have restored old lilacs by taking out the old thick branches, only remove one third of the largest branches as close to the ground as possible after it flowers this year and then fertilize it heavily. Next year take another third of the old largest branches. By year three, you should have a nice amount of blooms and a good looking bush, much shorter than the old one but healthier. Final year take the last of the old thick branches and you should have a nice looking lilac.

Thank you for the responses! There are numerous large branches, a few of which I will prune out as recommended each year. There is a carpet of Also, thanks for reminding me about wood ash as fertilizer. I've only ever used lime as fertilizer for lilacs. Will definitely consider your 'spring mix', marthacr.

Off topic: I mowed yesterday & used the bagger; have a nice pile of clippings started. Also, discovered a sad peony tucked under the forsythia. I'll try and liberate it after it blooms. Found a nicely located patch of bittersweet, too.

Hello Maureen;
The bittersweet is not good news, it is really invasive and hard to contain. I spent years trying to remove it at my last home.
The peonies sounds wonderful. Good luck.
diene