Mature lilac bushes that are large and overgrown are more challenging to remove than small lilac bushes. Large lilac bushes have deeper roots that are more widespread, making it harder to dig them up and remove them. If you don’t dig under and around the primary roots, then you run the risk of the lilac bush growing back. So, it is a time-consuming process if done correctly. 

While you don’t need to put anything down before mulch, you can apply a pre-emergent herbicide to prevent weed growth. As long as you remove weeds before you spread mulch, you should be in the clear. But a herbicide is something that you can put down before mulch as an extra layer of protection.

If you have a large area of brush and vegetation to clear, forestry mulching may be the best option. This method works well for relatively flat areas that don’t have many large rocks or mature trees to clear. Forestry mulching is a relatively quick process that improves soil health, reduces fire risk, and leaves behind usable mulch.

It’s possible to over-mulch leaves. If the leaf mulch is thick enough that it’s blocking and smothering the grass, that’s a problem. Ideally, you should still be able to see the grass when you’re done mulching to ensure its ability to continue growing. The solution is to make another pass at the top layer of leaf mulch to collect some of the top layer.