No, it’s not necessary to remove all the leaves from your lawn—in fact, leaving some behind can be beneficial. While it's important to clear thick layers of leaves that can smother your grass, leaving a light scattering of leaves can help feed your soil while also providing safe winter habitat for pollinators like bumble bees. Leftover leaves will eventually break down, enriching the soil and promoting healthy lawn growth.

Generally, it is not necessary to remove old mulch before applying a new layer. As organic mulch breaks down, it enriches the soil with nutrients. However, you should remove the old layer if it shows signs of fungus or disease, which can be common in moist areas, or if the total depth is already too thick. Avoid letting the total mulch depth exceed 3 inches, as this can harm plant roots. If you do remove old, disease-free mulch, it can be added to a compost pile.

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. 

According to the College of Agriculture and Life Sciences, there are over 10,000 kinds of mushrooms, and some are harmful to both humans and animals. However, not all mushrooms are harmful—some feed on thatch and wood, which provides nutrients for grass and plants. 

But unless you’re a mushroom expert (mycologist), it can be hard to tell poisonous mushrooms from non-poisonous. So if you have kids or pets (or both), removing them is the safest route to take.