Amending soil & killing weeds - Ask Extension
Not much has been done to the soil (1.25 acres) or grass around my house for 2 years. Poa and stilt grass need to be addressed. We have clay soil. Sh...
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Amending soil & killing weeds #927080
Asked March 30, 2026, 2:06 PM EDT
Not much has been done to the soil (1.25 acres) or grass around my house for 2 years. Poa and stilt grass need to be addressed. We have clay soil. Should I take soil samples, amend the soil, and kill the weeds OR amend the soil and then kill the weeds. What if I divide the soil amendment in half applying half in the spring, and half in the fall? Thank you for your assistance.
Baltimore County Maryland
Expert Response
Hi,
Please click on this link to read about lawn maintenance. You will note that a soil test can help inform you of the amendments that are needed for your lawn. Our article on soil testing describes the process and lists soil testing laboratories.
Click on the links to read about Annual bluegrass, Poa annua, and Japanese stiltgrass, Microstegium vimineum. Both are advantageous weeds in that they tend to thrive when the lawn is unhealthy and sparse. They can be eliminated over time by the use of pre-emergents. Because there is a residual seed bank in the soil, it will take several years of applications to eliminate each grass. That said, Poa is a winter grass, with the seed germinating late August/September, while Stiltgrass is a summer grass, with the seed germinating in the late spring. Therefore, you would need to have two pre-emergent applications per year over several years. Pre-emergents would not be indicated at all if your yard needs over-seeding, as seed germination would be at the same time for the grass and the weeds.
That said, you now have to prioritize whether you want to focus on improving the lawn or eliminating the poa or stiltgrass!
Thank you for your question.
Barbara
Please click on this link to read about lawn maintenance. You will note that a soil test can help inform you of the amendments that are needed for your lawn. Our article on soil testing describes the process and lists soil testing laboratories.
Click on the links to read about Annual bluegrass, Poa annua, and Japanese stiltgrass, Microstegium vimineum. Both are advantageous weeds in that they tend to thrive when the lawn is unhealthy and sparse. They can be eliminated over time by the use of pre-emergents. Because there is a residual seed bank in the soil, it will take several years of applications to eliminate each grass. That said, Poa is a winter grass, with the seed germinating late August/September, while Stiltgrass is a summer grass, with the seed germinating in the late spring. Therefore, you would need to have two pre-emergent applications per year over several years. Pre-emergents would not be indicated at all if your yard needs over-seeding, as seed germination would be at the same time for the grass and the weeds.
That said, you now have to prioritize whether you want to focus on improving the lawn or eliminating the poa or stiltgrass!
Thank you for your question.
Barbara
