all the top dressing is going to do ... is feed the trees roots... making it even more aggressive than it already is ...

3 inches sounds a bit deep on top dressing ... plus you dont tell us what kind you are thinking about ... there are a lot of hosta that will not handle being buried 3 inches too deep ... but again.. it might matter what you bury them with

ken

I would dig up the favorites, put compost and bone meal
in a wider,deeper hole and replant a division (maybe half) if the hosta is big.
Where there were really dense roots,under a maple,I buried a very large pot, screen on the bottom, filled with good earth & compost, then planted my hosta...that woked really well, trouble is, it's not easy to dig a large enough hole...this is when strong husbands come in handy!
Heather

Within a year the Maple feeder roots will go through the screen. They go down to about 16". If they can lift thousands of pounds of concrete sidewalks and driveways, a screen is no big deal. Only treated spin out fabric will deter the Maple or any other kind of tree roots.