Q. Hi Peter. I enjoy your column very much. My frustrations with being surrounded by neighbors with invasive tree roots, noxious ivy and raspberry runners is only surmounted by the larger question: what to do with all of the rocks that are displaced when planting? Though I agree in principle with the idea of not bringing in “foreign” soil, as a fellow Lakewood resident, you must realize that for every bucket of soil there are three bushels of big round rocks. We do sift, and have been rather creative about using as many rocks as possible, but we are running out of room. Do you have any suggestions for how to find out about some solutions for this problem? Who might need this type of fill, or where can they be dumped? I really hate to go out to prepare any more planting areas because I know there will be another mountain of rocks sitting there and I just don’t know what to do with them anymore. Thanks for listening. Judy Cross – Lakewood, WA
A. Although my yard does have plenty of “gravel” I have not run into that many big round rocks. The deposits in my part of town tend toward the medium to small. Because of the glacial origin of our soil there can be quite a bit of variation even within town limits. Also as I have mentioned in previous columns in addition to the glacial history of your yard’s soil you also have the more recent history of its development when your home was built and the potential redistribution of topsoil. So you may dealing with a very shallow topsoil profile and having to dig into areas of soil with lot’s of what my Dad would euphemistically call “potatoes”. The best thing to do in this situation is to set up raised beds in your new garden areas. They can be as simple as wooden timbers, bricks or cinderblocks or as elaborate as low curved retaining walls. This allows you to use some of the native soil but not have to dig too deeply and be greeted by bushels of big rock. Six to twelve inches of depth is best for a raised bed. So you may be wondering what you should fill the bed with if you don’t wish to bring in topsoil. I prefer to only add organic matter and mix it with the existing soil. Products like Cedar Grove Compost (http://www.cedar-grove.com) are great for making raised beds. Just be sure to mix some of the existing soil into the compost to make sure there are soil minerals available to the plants. If you really have no existing topsoil to work with then use either their Vegetable Garden Mix which is equal parts screened sandy loam, Cedar Grove compost screened to 7/16″ and sand or their Two-Way Topsoil 50% Cedar Grove Compost screened to 7/16″ and 50% sand. Tagro (http://www.tagro.com/) also has some products that would work as well. If you have enough of your own soil use Tagro’s potting soil mix which contains no sand. It is 20 percent Tacoma biosolids, 20 percent high-quality maple sawdust and 60 percent clean, aged bark. If you do not have enough existing soil to use Tagro mix which contains 50 percent biosolids, 25 percent sawdust and 25 percent screened sand.