Hi, 

You can mow the leaves that have fallen onto grass areas into mulch anytime but if you purpose was to provide habitat for overwintering beneficial insects, this would not be done at all. If you mow the leaves this spring it could be killing the insects that have overwintered there.

Next year you could mow the leaves in the grass to provide nutrients for the lawn, but leave the leaves and dried flowers stalks in garden beds. Leaf litter usually starts breaking down fairly quickly in the spring and flower stakes can break through it. Let the leaves break down slowly in the bed will provide organic matter while also sheltering any insects and providing early season food source for leaf chewing insects (which then further break them down). 

There isn't a set time frame of when yo can start doing garden clean up but typically you want to wait until the days are long and nights are warm enough to give insects time to wake up and emerge. Typically this is more into early or mid-May. If you are getting the 'itch' to start working in the garden as we approach spring, you can mow leaves in the grass, and take large sections of leaves and gently spread them out or move them into a backyard or spot in the garden that neighbors may not judge for being left to be more natural. If you feel the need to start cutting down dried flower stalks, you can pile them in a back garden corner to give any insect time to come out of them before heading to the compost pile. 

There are a few blog posts that provide some extra information: 

https://marylandgrows.umd.edu/2021/12/22/qa-winter-gardening-tasks/

https://marylandgrows.umd.edu/2023/12/15/ground-beetles-how-to-support-these-garden-helpers-during-the-winter/

https://marylandgrows.umd.edu/tag/landscaping/

Hopefully this helps answer some questions. Let us know if you have others!

Emily