Ann wrote:
Leythos expounded:

I have two large (8' dia, 5' tall) lilac bushes that have flowered since
the year we put them in, they are larger than the area supports and
we've never pruned them.

I don't know if I can uproot them, split the root ball and then make two
(or more) viable plants out of them.

Any one do this or know if it will work without killing them?

Thanks.

Well, you can take suckers from the base and put them where you want,
they'll grow fairly quickly. Why not prune the main plant to fit the
space? Lilacs tolerate pruning very well.

That is true. The bush can also be split into sections with a spade
while in the ground (perhaps into quarters), then the parent plant
will be minimally disturbed. Lilac should be pruned of old wood every
year for a healthier plant and better flowering. If lilac is not
flowering well it can benefit from root pruning.

http://www.arcamax.com/gardening/s-156685-111528