Maureen of Chicago wrote: "Recently we put in a school garden. I was planting a Knock Out rose in an area with thin, dry soil that contained gravel and dry cement from the building's construction. I began to amend the soil with peat moss and top soil, but was told by a horticulturist to stop as the rose could take care of itself even in that soil.
"I am a bit confused; I know that there is the "$5 plant in a $10 hole" theory, and also that many prairie native plants will indeed do just fine in a thin soil. But I am afraid the rose might not make it this winter.
"Would you please give me your opinion?" -- Maureen, Chicago
Knock Out roses are pretty tough and hardy for roses, Maureen, but they are not made of steel. Like any roses, they need decent soil, and the soil you are planting in sounds positively indecent.
The cement alone would be a problem; it is very alkaline and roses prefer an acid. But they also need plenty of organic matter.
I don't think peat moss and topsoil are the answer, though. What is sold as "topsoil" is often of very poor quality, with little or no organic content or nutrients. Peat moss does help make the soil a little more acid, but it also has few nutrients and doesn't do much for soil structure.
I would mix the topsoil with plenty of compost -- plant material that has been digested by microorganisms and insects to make its nutrients available to the plants' roots. It's best to dig 3 or 4 inches of compost into the whole bed when you start a new one. But if you are just planting one plant, dig a wide hole and mix a couple of good shovelfuls into the soil. Water the plant well and mulch.
Don't forget to water your rose and give it some slow-release fertilizer every couple of months during the growing season. Knock Out roses need relatively little care but they don't entirely take care of themselves.
Where do you get compost? You often can buy it bagged. Your volunteers may have home compost piles. If you have the money, you can get a truckload delivered from some garden centers.
But for next year, a compost pile also would be an excellent school project. It's full of science and math and things to look at under a microscope. Kids can compost their lunch leftovers. The leaves that are about to fall would be superb material to start with.
Here is a University of Illinois Extension Web site that will teach you all the basics. And here is one that gets more into the science of composting. Or take a field trip to the Garfield Park Conservatory's Demonstration Garden. And here's one about the science of composting. This one is for Chicago composters and talks about rodent-proofing bins. And then there are my own voluminous posts on the subject.
This post is part of The Chicago Gardener, a blog of the Chicago Tribune.
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