
For whatever reason if you've let that lawn get too tall then you have some work to do to get that lawn back into shape. Don't worry about cutting it twice to do that though. It's ok to cut it at the same height you've been cutting unless you are dry weather which of course isn't the case now. When you do cut the grass you will have a lot of clippings to pick up and you do want to pick those clippings up because they will smother parts of the grass and kill it. However what do you do with those clippings once you've got them off the lawn? you can put those clippings around the trees you have in the lawn. You can put in a nice thick 8 inch mulch. This will do a wonderful job of weed suppression and it will making mowing easier and you won't harm the tree or shrub by mowing under it.
If you don't like the way that pile of grass looks under your tree you can put a thin layer of bark mulch on top and still have a thick mulch without the expense. Don't use your clippings though if you used a weed and feed fertilizer earlier this spring. You could kill your tree. When you put down your mulch. Don't bury any limbs. It's ok for them to be on top of the mulch though.
whenever you put down any kind of mulch you want to stay back from the trunk just a little bit because that bark isn't used to being underground and it will make it easier for decay and insects to come in. So hold back just a little bit. Make sure to leave the mulch three or four inches away from the tree. Putting grass on the garden is a great idea as well. That grass is just too valuable to throw away.