I have the same situation in my yard. Silver Maple and Norway Maple both have tremendous mats of fine surface roots. There is really NOTHING you can do about it long-term. The root system is SO vigorous, its sort of like some type of underground kudzu.

My opinion is the only way to garden under these trees is in containers. Even then, you need to move them around every few months during the growing season so that roots don't infiltrate the pots.

I have done hostas in containers before, and they will overwinter pretty well in Zone 6.

If you raise the soil, the tree roots will just grow up into the new soil. I have 3 huge norway maples in my yard. The only way I can plant under them is to start with small plants, and dig around until I can find soil (and not roots). My hostas are at about the drip line of the trees, but directly under the trees, I have lamiastrum, some sedums, epimedium, pachysandra, and a few others that like dry shade.

I basically use a mattock (grubbing hoe) and cut out a hole through the roots. This allows me to plant a reasonably large root-ball and let it get started. So far as I have seen, this has absolutely no bad effects on the tree as a small loss of roots is un-noticed..

George

The hosta experts over on the hosta form would say you are fighting a losing battle. The hosta will lose the water wars that will ensue. But if you are determined, I have found it easiest to sneak a small division in root heavy areas. Then sit back and BE PATIENT. The hosta, if hardy will find its way and grow. I do this under ever greens and it has been working well.

We understand from many of our other hostaholic friends that Maples are horrific. Our problem is Red Pine, which also has that thick fine mat of surface feeder roots - probably why the CCC planted so many of them in this sandy dry soil. (Oddly, Jack Pine trees don't have this problem). Now, after having had these tree roots actually strangle several hostas to death, here's what we do, and it works.

We dig as big a hole as we can, fooeee on any tree roots we cut. Important part: line this hole with COMMERCIAL GRADE weed barrier cloth. This is the stuff that's like a thin fibreglass cloth, NOT the cheaper plastic like stuff. Be sure there's no breaks, and if overlapping, be very generous with the overlap. We hand remove the tree root masses, heavily amend the remaining sandy soil with rotten leaves and such and plant the hosta. Be sure, as well, to leave enough of the weed barrier cloth to stick above the soil level around the hole. This we hide with pine straw mulch, as it's readily available. We've done this for years and thereby know it works. Should the hosta rootball begin to be crowded in this nest in a few years, merely take a pike and poke holes into the bottom of the barrier cloth, assuming you dug your original hole deeper than the layer of the pesky surface roots from the trees. By this time the hosta is healthy and established and will extend roots out of these new bottom holes. If you have hostas already being strangled, hurry, dig them out, rip the tree feeder roots away from the hosta crown and roots, then replant as explained above. 9 out of 10 will recover and then thrive. If you've waited too long, you may want to pot the strangled one up for a season or two before re-planting in the ground. We have many hundreds of hostas growing here in our Red Pine grove and none in the lined holes have problems, yay!