It must be too warm where you have put it. Do you have a cold place like a shed or garage where you could put it? Or some way of stopping the pot freezing. If it were in the ground it could be left out all winter. Lilac is very hardy. BTW Lilac buds are always green during the winter, they don't have brown scales covering them like some trees. But they shouldn't be unfurling yet.

you are trying to kill it.. with too much love..

throw it outside.. and let it take winter.. like its supposed to ...you can barely kill the things ... even better is you heal it in mother earth ...

be nice to know what zone you are in ...

keep in mind.. whats cold to you.. is usually irrelevant to a zone appropriate plant ... the link seems to indicate Ls are z4 to many as low as z2 ... though we dont know what type yours is ...

ken

https://www.google.com/search?q=%3Blilac+zone&ie=utf-8&oe=utf-8#q=lilac+zone

Thank you Floral and Ken for your most helpful comments. You're right! I should never have brought it indoors. Cannot plant it outside as it isn't my property....

However, I can put it in my basement garage which is dark and cold but not freezing). How much and how often should I water it? I understand when plants are dormant during winter they don't require much water but still need some water.

The Lilac was not specifically identified. Label just said "Syringa" (so I would assume that means "Syringa vulgaris" or common lilac).

I believe we are in the Z4 Zone (Lots of rain and average winters.....typical Northwestern weather in this corner of Montana .

I am pretty sure they are hardy in your zone (correct me if I am wrong). You will have to keep it where it is for now, and winter them outside next year.

If kept where it is now all Winter it is unlikely there will be a 'next winter.' The lilac needs to be cooled down gently until it is in a temperature similar to outside. Just prevent the soil in the container from freezing. The soil need only be just moist.