I would leave it till Autum, because lilac usually flower in spring, Although some may say take a chance ,as long as you prepare the ground beforehand ,and dont disturb the roots.
I think you may lose the flowers if you move them, or at least put them back as the plant will be trying to establish itself rather than produce flowers. I don't think you will kill it as long as your make sure the new site is as suitable or even better than the old one. Lilac's like the sunshine and prefer humus rich well drained soil that is neutral to alkaline. Make sure you take up a good amount of soil with the rootball.
Posts
I think you may lose the flowers if you move them, or at least put them back as the plant will be trying to establish itself rather than produce flowers. I don't think you will kill it as long as your make sure the new site is as suitable or even better than the old one. Lilac's like the sunshine and prefer humus rich well drained soil that is neutral to alkaline. Make sure you take up a good amount of soil with the rootball.
When you do move it (and I too would leave it until autumn) take as large a rootball as possible - most lilac is grafted and is prone to suckering.
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.