Garden Q&A: How to control stiltgrass

For The Baltimore Sun

My front lawn has been overtaken by Japanese stiltgrass. It’s making serious inroads in my backyard, and this year it exploded in my woods. I much prefer the moss and clover that used to grow in my yard! Other than mowing stiltgrass before it flowers and drops seed, and waiting for spring to apply crabgrass pre-emergent weedkiller to the lawn, what can be done to eliminate this invasive species? And what about the woods?

We have been swamped with desperate questions about stiltgrass, which is having a banner year in the moist soil. Sadly, constantly mowing a lawn causes stiltgrass to grow at a lower height but still set seed. A more successful control strategy is to mow tall plants as they “flower” (starting about mid-August) and cut off the flowering culm (stalk of seeds) before seed matures. You’re too late for this as a lawn strategy, which requires letting the lawn go unmowed late July, early August. However, you can use this strategy for large patches in a woods or natural area. For large areas, weed-whack the plants to ground level (bare earth), shortly before it produces mature seed but too late for it to regrow before the first frost. Because stiltgrass is an annual and has shallow roots, hand pulling is effective, too. We feel your pain.

How many soil samples should you take from a lawn at one time? Front, back, and both sides for a total of four? Or can you mix them all together and send just one sample?

The goal is to get a good representation of your soil. If the soil around your home is basically the same on all sides, then you do not need to send separate samples for each side of the house to the soil testing laboratory. However, if the soil is significantly different in one area — for example, all the top soil was bulldozed away at one time or a load of off-site soil was dumped in one area — then that area should have its own test done. It could be very different than the rest of the property. In general though, we recommend taking multiple slices of soil (as you'll see in the video on our website) from all around a testing area. Mix them in a bucket and take 1 cup of soil to send away for testing. That is your representative sample. Search “soil testing” on the HGIC website for a video showing how to collect a soil sample and information on what to test for and where to send it. Soil testing is a good investment, and this is a great time of year to get it done to prepare for annual fall fertilization and lawn renovations.

University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Maryland’s Gardening Experts” to send questions and photos.

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