What type of gardening are you trying to do (vegetable, landscape, etc)?

Adding soil to cover roots (especially if more than an inch or so) is frequently detrimental to the health of the tree. Adding dirt on top can suffocate the roots, and trees will often attempt to compensate by growing new roots into the dirt you added and putting you back to where you started with roots in your way.

Cutting roots is also not healthy for the trees. If you remove large roots, the tree could become unstable. Removing a few smaller roots is not as likely to have an immediate impact on the tree, but can still lead to problems. Possible problems with root removal include lack of tree stability, reduction in ability to get enough water and nutrients, and introduction of wounds which can allow disease to enter the tree.

Diana how close to these trees are you trying to plant?

I would avoid any general pruning of the roots of your big trees if it can be avoided. Every year I probably end up cutting a couple inch round roots of my ash trees in my flower beds typically near the drip line of the trees.

trees are super competitors... anything you add ... like nice fresh soil .... or fertilizer .. etc .. they will come and take.. period ...

you will never beat a tree ...

if you cut one root ... the tree .. being super competitive.. will replace it with 3 to 6 new ones ....

dig hole.. insert plant.. refill with the native soil .. and broadcast any fertilizer and all water...

if you dig this nice little hole.. amend the soil .. and only water the plant in that hole.. WHERE DO YOU THINK the tree will grow roots ...

trust me.. i learned that lesson the hard way ...

good luck

ken

Thank you for responding.
I was just about to put more top soil dn and now I definetly won't. I have a lawn, various shrubs, a 10X20 garden in the center of the lawn, and many trees. Both trees and shrubs are very rooty. I am trying to plant flowers underneath or nearby. Sometimes I am about a foot away. Even in an area where I am not planting there are roots showing. The soil isn't very good which is why I put dn the top soil. In the planting areas I have ammended the soil as much as possible, the roots are very close to the surface.
I don't think it's good for the trees and shrubs to be that exposed.
Thanks for any help.

Diana, you've been given good advice. Tree roots grow where they find suitable conditions. Shallow roots are not a problem for the tree, just the gardener;^)

Ken is exactly right. When you dig out a small space to install your perennial plant, the nearby tree roots soon find all that nice prepped soil and very quickly infiltrate it with new feeder roots. It's just what trees do.

Your best option, if you want to keep the trees around-and I hope you do-is to explore the plant world for those types which are able to survive under these conditions. Just to give you one example from my yard, which may not translate to your location: Hostas, those tough stalwarts of shade gardens, have no chance for a long life under my giant silver maple. They start out okay, but then get SMALLER each subsequent season as they are utterly out-competed by the maple roots. Meanwhile, right nearby, is a large old patch of lily of the valley. These, with no help from me, come up and do their thing year after year, and are even spreading.

That's just one example out of a great many, but you get my idea.

+oM