January Weed of the Month: What's in my Soil?
Protect your garden from unwanted pests
January 15, 2021
A shocking number of weed seedlings popped up the first spring of my new garden. If you're planning a garden or landscaping project, consider how the materials you use could bring in invasive species – weeds, seeds, and unwanted pests.
Compost can be a huge help to your garden, but the material can also introduce weeds. Most weeds and weed seeds will be killed by the hot composting process – if hot enough for long enough. But not all composting processes or products are the same. If you're purchasing compost, look for the US Composting Council's Certified Compost seal ensuring that it has been tested for quality. The Minnesota Composting Council has additional information on their website.
If you have a backyard compost pile or visit a small compost operation, it's more likely that the compost isn't tested and may not be mixed well enough or get hot enough to kill weed seeds. It's best to keep plants that have gone to seed out of your compost pile and avoid adding plants that spread by runners or plant fragments. When you're unsure if the soil or compost may introduce unwanted weeds, you can test out a small batch by watering it and watching for seedlings to come up.
Soil and mulch can be trickier since they're not heated. Consider buying from nearby sources to reduce the potential for spreading other unwanted pests. Some pests, like gypsy moth egg masses (Lymantria dispar) or jumping worms (Amynthas species), could be identified by a visual inspection. Mulch pieces smaller than one inch typically wont harbor emerald ash borer, another concerning pest in Minnesota.
Plant nurseries selling transplants have rules they must follow and are inspected by the Minnesota Department of Agriculture (MDA). When sharing transplants with friends be sure you know what you're getting and do your research so you don't swap invasive plants. And to be sure you're not trading unwanted pests like jumping worms or seeds mixed into the pots, wash the soil from the roots and share as bare-root plants.
Visit the Midwest Invasive Plant Network website for information on avoiding invasive garden plants.
To learn more about the gypsy moth, visit the Minnesota Department of Agriculture website.
For more information on jumping worms, the Minnesota Department of Natural Resources has information.
To learn more about composting, visit the U.S. Composting Council website.
The MDA has information on removal and disposal of noxious weeds.