Jellyman & harvestman are onto it. I've been killing black walnuts on my farm for the last two years. Not a lot of them but perhaps two dozen...alongwith hackberrys, box alders,and ashes. If there is a misshapen BW near where I want to put an apple....the BW dies. I have used both methods mentioned....girdling & boring (and a third, 'hack & squirt' ... opening up the bark with a hatchet and squirting in a herbicide.) I've only used 41% Round-Up undiluted. It will kill the tree within a month. For me I use a 3/8" drill bit and drilled holes, one on each side.....downward angle for about 2 1/2 to 3"...then filled the hole with the 41%RU. Crossbow & Garlon are effective also, however, I have not used them. I've done this in July and it kills the tree. Girdling will kill the tree, but slower...it may take a year to die. I think given your sense of diplomacy with the neighbors the drill method would suit you just fine. There are lengthy discussions on killing big trees in the 'Habitat' forums on the website for QDMA. Quality Deer Management Association www.QDMA.com

Elizabeth, others who can explain this better may post, but meanwhile PLEASE read about what soil solarization does beside kill the grass. It will also destroy all the beneficials in your soil. Ditto re restraint using plastic. Newspaper/cardboard topped with mulch will most definitely do the job. HTH, Rosie

Grasses and "weeds" do uptake soil nutrients but whether it would be enough to adversly affect fruit trees is highly debatable. Some orchards around here have "clean" soil with no grass or "weeds" evident, but most have grass growing in the orchard along with the trees and that grass is mulch mowed right back into the turf where the grass clippings can supply some nutrients to the soil. Heavily mulching around the tree trunk to aid in suppressing grass growth there can help make mowing easier, but constantly spraying plant killers to control growth would not be an acceptable organic proactice.

How come nobody has answered this yet?! While it may seem harmless to add only 3-4" of soil, it really is a bad idea. For one, you don't want any roots to grow upwards. Second of all, flowers planted in the root zone are going to compete with the tree for water and nutrients. And they're going to lose. So don't bother. Keep a nice open soil area for the trees, as stress free as you can make it with no nearby digging. So to answer your question, yes you should definitely be concerned with harming the trees and to limit that harm you should build your planters somewhere else. I challenge you to find one professionally designed landscape that includes flowers in the root zone of trees. You're not going to find it.