Re-use weedy dirt
I have an area along the side of my house that is weed patch. I clean it out every year and the weeds grow back. I am planning on taking out the top few inches and replacing it with gravel for maintenance and drainage reasons. I want to reuse the soil in a mound in another part of my garden. Is there a way I can do this with out transferring the weeds? I am thinking about layering or covering with a tarp for a season.
Multnomah County Oregon
Thank you for asking about your weedy patch. The weed seeds will transfer with the soil, but you may still reuse it. Soil has a "seed bank", and each time it is stirred it up, a new batch of seeds sprout as they get enough light and warmth to grow. Seeds can remain viable in this "bank" for many years. So rather than trying to kill them all, your goal is to stop them from being able to sprout.
The layering is a good idea, often called "lasagne gardening". Covering with the tarp isn't as reliable as a permanent mulch layer, as there are likley seeds surviving even after a year under a tarp. The seeds deep in the layers remain, so limit turning the soil once you establish a weed-free area. In the area you gravel, plan how to deal with the newly uncovered seeds, and how you'll weed the gravel, as seeds blowing in will sprout in a gravel bed.
Here are articles from the Oregon State Extension Service that will be helpful to you:
"Turn weedy, boring curb strip into low maintenance flower bed" http://extension.oregonstate.edu/gardening/node/667 and "How long do weed seeds survive in the soil" http://extension.oregonstate.edu/gardening/how-long-do-weed-seeds-survive-soil
This article, too, though how much sun your area receives needs to be considered for solarization to be useful: "Harness the sun to kill weeds, plant diseases and pests" http://extension.oregonstate.edu/gardening/harness-sun-kill-weeds-plant-diseases-and-pests
Please ask follow-up questions as you continue with this project, or any others in your garden.